The Blogger

Digital Camera vs Analog Camera

2009-02-03T14:26:00.002+07:00

Banyak orang yang masih rancu antara kamera digital dan kamera analog. Sebagian dari mereka menyebut kamera digital sebagai kamera otomatis dan kamera analog sebagai manual. Dalam hal ini saya akan mencoba menjelaskan perbedaan antara kamera digital dan kamera analog sehingga pengertian masyarakat umum dapat lebih benar. Semoga dapat cukup membantu bagi anda-anda yang masih awam dalam dunia fotografi.

Kamera Analog

Sebelum era digital orang sudah mengenal berbagai macam jenis dan merk dari kamera analog. Sebutan analog berbeda dengan otomatis dalam ruang lingkup kamera. Analog dalam kamera mengacu pada sistem kerja mekanik dari suatu kamera. Sistem kerja kamera analog yang banyak digunakan oleh masyarakat umum adalah menggunakan film seluloid 35mm sebagai sarana untuk menangkap cahaya(dalam hal ini biasa disebut gambar). Walau kamera analog banyak jenisnya tapi prinsipnya sama, yaitu menerima data gambar melalui proses kimiawi suatu media. Sebenarnya media penerima gambar tidak hanya film seluloid 35mm. Tapi dalam hal ini saya tidak akan membahas lebih lanjut karena topik pembahasan kali ini adalah perbedaan kamera digital dan kamera analog.

Film pada kamera analog berfungsi ganda sebagai penerima gambar sekaligus sebagai penyimpan data gambar yang dihasilkan. Pada media film berlaku 1 gambar yang kita perolah akan disimpan dalam 1 media film. Umumnya produsen menyediakan 1 roll film yang berisi sejumlah film dengan tujuan agar para konsumen tidak perlu selalu mengganti film yang sudah terpakai.

Sedangkan pengertian otomatis adalah kemampuan suatu kamera dalam menyediakan fungsi-fungsi otomatis dalam hal pengaturan cahaya yang masuk sehingga gambar yang dihasilkan dapat memiliki komposisi pencahayaan yang tepat. Berbeda dengan fungsi manual dimana kita harus mengatur sendiri sebarapa banyak cahaya yang masuk agar dapat menghasilkan gambar yang sesuai dengan harapan kita.

Kamera Digital

Pada kamera digital sistem penerimaan cahaya untuk menghasilkan suatu gambar dengan menggunakan sensor yang digunakan untuk menggantikan media film pada kamera analog. Sensor yang berada dibelakang lensa setelah menerima cahaya akan mengirimkan data mentah digital ke prosesor suatu kamera. Prosesor kamera tersebut berfungsi untuk mengolah data mentah digital menjadi data digital gambar yang lebih baik. Setelah pemrosessan, data gambar yang masih dalam bentuk digital akan disimpan dalam mendia penyimpanan berupa memori yang tedapat dalam kamera digital.

Sensor yang banyak dipakai oleh produsen berupa semikonduktor dengan nama CCD(charged-couple device semiconductor) dan CMOS(complementary metal-oxide semiconductor). Kualitas maupun ukuran dari sensor ini salah satu dari faktor penting yang mempengaruhi kualitas dari gambar yang akan dihasilkan.

Media penyimpanan data digital gambar pada kamera digital terpisah dengan media penangkap cahaya. Media penyimpanannya biasa disebut memori memiliki berbagai macam jenis bergantung dari produsen pembuat kamera. Yang umum digunakan adalah tipe-tipe Compact Flash(CF), Secure Digital(SD), Multi Media Card (MMC), Memory Stick (MS) dan (XD).

Kamera Digital versus Kamera Analog
Dewasa ini kamera digital sudah sangat umum digunakan oleh masyarkat. Banyak keuntungan yang didapatkan dengan menggunakan kamera digital. Faktor utama adalah masalah kepraktisan. Dengan kamera digital waktu yang digunakan untuk mendapatkan hasil foto jadi lebih singkat. Kita tidak perlu lagi menunggu untuk mencuci film dan mencetaknya karena hasil foto yang kita ambil dapat langsung kita lihat saat itu juga.

Faktor kedua adalah biaya. Dengan kamera digital kita tidak perlu mengeluarkan uang untuk biaya pembelian film dan cuci cetak suatu foto. Hasil dapat disimpan langsung ke komputer tanpa proses scanning.

Dengan uraian diatas semoga dapat membantu pemahaman tentang kamera digital dan kamera analog bagi masyarakat umum.

Diambil dari sentradigital.com

Color Temperature - Wikipedia

2008-11-15T12:27:00.002+07:00

Color temperature: "Because it is the standard against which other light sources are compared, the color temperature of the thermal radiation from an ideal black body radiator is defined as equal to its surface temperature in kelvin, or alternatively in mired (micro-reciprocal degrees kelvin).[1] For source other than ideal black bodies, the color temperature of the thermal radiation emitted from it may differ from its actual surface temperature. In an incandescent light bulb the light is of thermal origin and is very close to that of an ideal black-body radiator.

However, many other light sources, such as fluorescent lamps, emit light primarily by processes other than raising the temperature of a body. This means the emitted radiation does not follow the form of a black-body spectrum. These sources are assigned what is known as a correlated color temperature (CCT). CCT is the color temperature of a black body radiator which to human color perception most closely matches the light from the lamp. Because such an approximation is not required for incandescent light, the CCT for an incandescent light is simply its unadjusted temperature, derived from the comparison to a black body radiator."

Controlling the photographic exposure and rendering

2008-11-07T13:37:00.000+07:00

Camera controls are inter-related. The total amount of light reaching the film plane (the "exposure") changes with the duration of exposure, aperture of the lens, and, the effective focal length of the lens (which in variable focal length lenses, can change as the lens is zoomed). Changing any of these controls can alter the exposure. Many cameras may be set to adjust most or all of these controls automatically. This automatic functionality is useful for occasional photographers in many situations.

The duration of an exposure is referred to as shutter speed, often even in cameras that don't have a physical shutter, and is typically measured in fractions of a second. Aperture is expressed by an f-number or f-stop (derived from focal ratio), which is proportional to the ratio of the focal length to the diameter of the aperture. If the f-number is decreased by a factor of , the aperture diameter is increased by the same factor, and its area is increased by a factor of 2. The f-stops that might be found on a typical lens include 2.8, 4, 5.6, 8, 11, 16, 22, 32, where going up "one stop" (using lower f-stop numbers) doubles the amount of light reaching the film, and stopping down one stop halves the amount of light.

Exposures can be achieved through various combinations of shutter speed and aperture. For example, f/8 at 8 ms (=1/125th of a second) and f/5.6 at 4 ms (=1/250th of a second) yield the same amount of light. The chosen combination has an impact on the final result. In addition to the subject or camera movement that might vary depending on the shutter speed, the aperture (and focal length of the lens) determine the depth of field, which refers to the range of distances from the lens that will be in focus. For example, using a long lens and a large aperture (f/2.8, for example), a subject's eyes might be in sharp focus, but not the tip of the nose. With a smaller aperture (f/22), or a shorter lens, both the subject's eyes and nose can be in focus. With very small apertures, such as pinholes, a wide range of distance can be brought into focus.

Image capture is only part of the image forming process. Regardless of material, some process must be employed to render the latent image captured by the camera into the final photographic work. This process consists of two steps, development and printing.

During the printing process, modifications can be made to the print by several controls. Many of these controls are similar to controls during image capture, while some are exclusive to the printing process. Most controls have equivalent digital concepts, but some create different effects. For example, dodging and burning controls are different between digital and film processes. Other printing modifications include:

Chemicals and process used during film development
Duration of exposure – equivalent to shutter speed
Printing aperture – equivalent to aperture, but has no effect on depth of field
Contrast
Dodging – reduces exposure of certain print areas, resulting in lighter areas
Burning – increases exposure of certain areas, resulting in darker areas
Paper texture – glossy, matte, etc
Paper type – resin-coated (RC) or fiber-based (FB)
Paper size
Toners – used to add warm or cold tones to black and white prints

Wikipedia

Photographic cameras

2008-11-07T13:29:00.001+07:00

The camera or camera obscura is the image-forming device, and photographic film or a silicon electronic image sensor is the sensing medium. The respective recording medium can be the film itself, or a digital electronic or magnetic memory.

Photographers control the camera and lens to "expose" the light recording material (such as film) to the required amount of light to form a "latent image" (on film) or "raw file" (in digital cameras) which, after appropriate processing, is converted to a usable image. Digital cameras replace film with an electronic image sensor based on light-sensitive electronics such as charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) technology. The resulting digital image is stored electronically, but can be reproduced on paper or film.

The movie camera is a type of photographic camera which takes a rapid sequence of photographs on strips of film. In contrast to a still camera, which captures a single snapshot at a time, the movie camera takes a series of images, each called a "frame". This is accomplished through an intermittent mechanism. The frames are later played back in a movie projector at a specific speed, called the "frame rate" (number of frames per second). While viewing, a person's eyes and brain merge the separate pictures together to create the illusion of motion.

In all but certain specialized cameras, the process of obtaining a usable exposure must involve the use, manually or automatically, of a few controls to ensure the photograph is clear, sharp and well illuminated. The controls usually include but are not limited to the following:

Focus - the adjustment to place the sharpest focus where it is desired on the subject.
Aperture – adjustment of the iris, measured as f-number, which controls the amount of light passing through the lens. Aperture also has an effect on focus and depth of field, namely, the smaller the opening [aperture], the less light but the greater the depth of field--that is, the greater the range within which objects appear to be sharply focused. The current focal length divided by the f-number gives the actual aperture size in millimeters.
Shutter speed – adjustment of the speed (often expressed either as fractions of seconds or as an angle, with mechanical shutters) of the shutter to control the amount of time during which the imaging medium is exposed to light for each exposure. Shutter speed may be used to control the amount of light striking the image plane; 'faster' shutter speeds (that is, those of shorter duration) decrease both the amount of light and the amount of image blurring from motion of the subject and/or camera.
White balance – on digital cameras, electronic compensation for the color temperature associated with a given set of lighting conditions, ensuring that white light is registered as such on the imaging chip and therefore that the colors in the frame will appear natural. On mechanical, film-based cameras, this function is served by the operator's choice of film stock. In addition to using white balance to register natural coloration of the image, photographers may employ white balance to aesthetic end, for example white balancing to a blue object in order to obtain a warm color temperature.
Metering – measurement of exposure so that highlights and shadows are exposed according to the photographer's wishes. Many modern cameras meter and set exposure automatically. Before automatic exposure, correct exposure was accomplished with the use of a separate light metering device or by the photographer's knowledge and experience of gauging correct settings. To translate the amount of light into a usable aperture and shutter speed, the meter needs to adjust for the sensitivity of the film or sensor to light. This is done by setting the "film speed" or ISO sensitivity into the meter.
ISO speed – traditionally used to "tell the camera" the film speed of the selected film on film cameras, ISO speeds are employed on modern digital cameras as an indication of the system's gain from light to numerical output and to control the automatic exposure system. A correct combination of ISO speed, aperture, and shutter speed leads to an image that is neither too dark nor too light.
Auto-focus point – on some cameras, the selection of a point in the imaging frame upon which the auto-focus system will attempt to focus. Many Single-lens reflex cameras (SLR) feature multiple auto-focus points in the viewfinder.

Many other elements of the imaging device itself may have a pronounced effect on the quality and/or aesthetic effect of a given photograph; among them are:

Focal length and type of lens (telephoto or "long" lens, macro, wide angle, fisheye, or zoom)
Filters placed between the subject and the light recording material, either in front of or behind the lens
Inherent sensitivity of the medium to light intensity and color/wavelengths.
The nature of the light recording material, for example its resolution as measured in pixels or grains of silver halide.

Wikipedia

Changing Your Camera's Mind

2008-11-04T16:35:00.000+07:00

Testing Your Camera

Thanks to digital, you can easily test the latitude of your camera and find out exactly how it will render tones. Follow this process to find out at exactly which point your camera begins to lose detail in the highlights and shadows. With this knowledge you will know what you're camera will do to a scene before you trip the shutter.

Find any colorless, single-toned subject; a white wall works well. You're going to take a series of photographs of it at several different exposures. Switch into manual mode, meter the wall, and photograph it just at the settings your camera recommends. That's you're middle gray exposure. Now take exposures as you lower the shutter speed by each setting (1/3 or 1/2 stop) up to 3 stops overexposed. Repeat the process in the other direction from your middle gray down to 3 stops underexposed.

You've just created a gray chart that will tell you at what point your camera renders pure whites and blacks. Looking at the histograms of these images will tell you how your camera treats various exposures.

First look for which exposure shows your highlights (whites) beginning to clip on the right side of the scale. It's usually between 2-3 stops overexposed, depending on your camera. If my whites begin to clip at 3 stops over, then whenever I'm using that camera I would never want my whites to be more than 3 stops higher that my meter's middle gray reading. Knowing this tells me how to meter my highlights, and they are the most important tones to control in exposure.

Another thing to notice from the test is how your shadows react differently than your highlights. Look at your histograms in the underexposed frames. It takes the shadow frames reach a true black, as opposed to the highlights which race to the clipping point. Highlights lose detail quickly. With some cameras the highlights begin to lose detail only two stops over middle gray, while the shadows retain detail as much as 3.5 stops under.

Knowing your camera's limits will help you push things to the edge without falling off.

Exposure Compensation

There are times when it's a good idea to photograph in an auto-exposure mode. I'm thinking of situations where the lighting is changing quickly and you're trying to capture moments. In such situations you don't always have time to check your exposure. If you have to shoot in auto-exposure mode, learn to use your camera's exposure compensation setting.

Exposure compensation lets you tell your camera to under or overexpose by an amount you set. For example, if you are taking pictures on a family ski outing, the bright snow is going to throw off your meter. You can compensate for this by setting your exposure compensation to +1.5 stops, which will cause your camera to overexpose by that amount and keep the snow white. (Of course, make some test frames before you take my word for it! I don't want to be responsible for destroying the memories of your family ski trip.)

If you're photographing someone in front of a black wall, you can compensate by setting your exposure compensation to -1 or more stops, so that it underexposes. By making a few exposures and checking them on your LCD screen, you can narrow in on the exact setting for your situation.

WARNING!!! Don't forget to turn off exposure compensation when you no longer need it. As long as it's active, every photograph you take will be over or underexposed to the level you set. Most cameras have an indicator to remind you that exposure compensation is set, but I guarantee that you will forget that it's on from time to time.

www.zibtips.com

Histogram

2008-11-04T16:20:00.003+07:00

The Scientific Meter

Learning about the histogram is a little daunting at first. But stick with me here. The histogram is a feature well worth spending a few minutes to grasp. Being able to read the information in a histogram will make you a master of exposure.

The histogram is simply a graph that displays the tones in your photograph. The graph runs from dark to light in 255 steps. The dark areas (shadows) are graphed on the left and lighter areas (highlights) to the right. The far left of the scale is perfect black and the far right is perfect white.

If you over or underexpose your photograph, pixel data will run off the chart to the right or left. This is called clipping. And it is bad. In a good exposure, all of your graphed pixel data will stay on the chart. Information that goes off the scale to the left or right is basically lost data (pixels to the right will be recorded as pure white and those to the left as pure black). So try to keep it all on the chart.

photography and histograms On your camera's LCD screen, the histogram can be checked to ensure your exposure settings were right for the given photograph. When I start to photograph in any lighting situation I'll select my shutter speed and aperture settings and make a test exposure. Then I look at the histogram of the test on my camera's LCD screen. The histogram gives me a perfect indication of where my exposure is. If my highlights or shadows are clipping, I can make a quick adjustment to perfect the exposure. Then, until the light changes, I don't have to think about exposure. I know it's dead-on.

The Typical Histogram

The typical histogram will have a bell curve in the middle (the midtones), as most tones in photographs are average tones. On the left side of the graph, the shadows should drop off without hitting the edge of the graph, as should the highlights on the right. Anything going off the edge of the graph is tone information clipped off the scale, usually caused by an incorrect exposure setting. Again, a proper exposure generally keeps all of the graph visible in the scale, avoiding clipping.

Right and Wrong

Above is an example of the histogram of an overexposed photograph. Notice how the highlights at the right of the graph scale up and off the chart. And the shadows at left trail off too far from the edge (meaning I don't have any black in my photograph).

Below is an example of the histogram of an underexposed photograph. It's the same problem, only reversed. While this photograph doesn't have much in terms of highlights, underexposing means we've lost a lot of shadow detail.

Now look again at the histogram on the flower photograph at the top of this tip. You'll see how the tones in that correctly exposed histogram are smooth and mostly fall within the edges of the graph.

On the Computer

Most digital imaging software will display histograms, and slider controls usually appear below the histogram for adjusting the tones in the image. If you move the shadows slider, everything to the left of it will register as completely black. If you move the highlights slider, everything to the right of it will register as completely white. The midtones slider will affect the overall brightness.

In the days of the darkroom, one of the first lessons to learn was how to get a true black in your print. It wasn't intuitive, and many photographers will remember being sent back into the darkroom to try again until they successfully completed the lesson. With the histogram, you can instantly achieve that true black, as well as a true white. And the graph of the histogram gives you mathematical proof.

Protect Your Highlights

If you have to lean one way or the other in exposure, always protect your highlights. Don't let them fly off the right side of the histogram. You're better off slightly underexposing if you have to. Detail in overexposed highlights is lost and basically unrecoverable. Your shadows are much more flexible and can be lightened to recover lost detail.

www.zibtips.com

Getting Exposures in Photography Right

2008-11-04T16:16:00.000+07:00

Photo Exposure - Highlights and Shadows

Your camera's meter is smart enough to get you a good exposure for most average scenes. But it isn't smart enough to know what it's looking at, and it can easily be thrown off by bright or dark subjects. And since your meter is trying to average your photograph into an 18% gray tone, it's going to underexpose bright scenes and overexpose dark scenes. To take your photography and exposures to the next level you need to know when to override the advice your meter is giving you.

I'm going to explain how to expose for highlights and shadows. Of course, if you're using a handheld incident meter, you can move along. This tip addresses reflective meters like the one in your camera.

This concept was a breakthrough for me when I was starting out in photography. It might take you some thinking to grasp this, but it's worth it. The most important thing is this:

With bright subjects, you need to add light to the meter's recommendation. With dark subjects, you need to subtract light from the meter's recommendation. That's how you achieve a correct exposure.

Exposure - Light Subjects

Your meter wants everything to be gray, even when you point a camera meter at a white subject. To make the white turn into gray, the meter will suggest underexposing. Think about when you exit a dark movie theater and find yourself in the bright outdoors. Your instinct is to squint to keep things dark until your eyes adjust to the bright light.

But you don't want a squinty, dim photo. You want your white object to appear white. Otherwise the photo will lack the proper contrast and appear flat or dull.

So instead of squinting, you need to override your meter and adjust your camera in the other direction. You actually need to let in more light than your meter suggests so that the white object will appear white. That's the secret. More light in your exposure equals brighter tones.

I'll talk about calibrating your camera later on, but most whites fall around two stops over the 18% gray that your meter suggests. So you can meter a white and open approximately two stops (again, test your camera to be sure) to achieve a good white that still has a minimum of detail.

Exposure - Dark Subjects

Dark subjects work on the same principle as light subjects, but in reverse. In order to stay dark, they need less light, less exposure. So if you're metering off a black object, you'll need to close down to a smaller aperture or else raise your shutter speed.

A good black will fall around two and a half stops under the 18% gray that your meter suggests. Again, test your camera to be sure.

Conclusion

So to re-cap, with bright subjects you need to overexpose from your meter's reading. Bright objects need more light so they can remain bright. And in the opposite direction, dark subjects need to be underexposed from your meter reading. Dark objects need less light so they can remain dark.

Once you are able to visualize that principle of light, you're on your way to understanding exposure and having great exposures in your photography

www.zibtips.com

How Meters Work

2008-11-04T15:59:00.002+07:00

Exposure

The correct exposure is essential to the quality of your image.

Some people follow the philosophy "Fix it in the computer." But that should be the last resort. Fixing a photo on the computer is not the magical answer that it has been made out to be. In fact, every tonal adjustment you make to your photo on the computer, making it lighter or darker, etc., reduces the amount of pixel data in your photo. So as you're "saving" your image, you're actually degrading it, throwing away data. Best to get it right in camera.

Meters

The meter in your camera measures the light in your scene telling you or your camera what shutter speed and aperture settings will provide the proper exposure.

It's important to know how the meter sees and what it is trying to do. A meter takes in all of the tones in the scene (light and dark) and averages those tones to compute an exposure setting. The meter is finding an average, aiming for an 18% gray tone. And that's great for most scenes, where light and dark tones average into gray, such as the photo below.

Types of Metering

Advances in camera metering systems over the years have been impressive. Still, it's important to know what your meter is thinking and how various meters see the light.

Most cameras will read the light in the scene by measuring the brightness of light reflected through the lens. For more accurate light readings, handheld meters can tell you how bright the ambient light is in any environment. Here is a quick breakdown of typical modern metering options:

Matrix or Evaluative Metering — This type of metering breaks the scene up into multiple segments which are analyzed for brightness and then compared to a pre-programmed database of thousands of typical photographic scenes. All of this happens instantaneously. Matrix/Evaluative metering modes are very accurate and useful especially in situations where you're using an auto-exposure mode or when the light is changing frequently. While not perfect, they come close in most situations.

Spot Metering — Spot meters read the brightness of a single spot in the middle of the frame, allowing you to take a precise reading of a small area. Spot metering is very handy when you're shooting in manual modes and have the time for extreme precision.

Incident Metering — Handheld meters provide highly accurate light measurements by metering the ambient light in a scene. That is, they tell you exactly what settings to use on your camera by telling you exactly how bright it is. There are drawbacks to using a handheld meter, including the cost of the meter. And for an accurate reading, the meter has to be in the same light as your subject. This can be problematic in a situation like a concert, where access to the stage is often controlled.

Latitude

Correct exposure settings are essential for serious photography. While your eyes are capable of seeing detail over a wide latitude, film and digital cameras have a much tighter latitude. If you expose for the sunlight, things in the shade will appear dark. If you expose for the shade, everything in the sunlight will be too bright. There are techniques to balance the light in such situations, such as using fill-flash.

But it bears repeating: Setting the correct exposure is essential to the quality of your image.

www.zibtips.com

How to Take Better Night Photos

2008-10-28T16:12:00.001+07:00

Do you like to take photos at night? I know I do. There's something magical about them - pictures of the moonlight sky and dazzling neon lights convey a special something that daytime photos can't.

When I started out taking digital photos at night, boy, did I have problems! The issue is that many digital cameras do not perform very well under low-light conditions. To take good night photos, there are some tricks you need to remember - so here are a few of them.

Tip 1: Use Long Exposures

The key to successful night photography lies in a long exposure. We’re talking about exposures measured in seconds. When a long exposure is used, more light is allowed into the camera, allowing the details in your night photo to be captured.

The problem with using long exposures is that you may shake the camera, resulting in poor pictures. The way around this is to use a tripod. I prefer to install a tripod with a shutter-release cable to ensure that I don’t jolt the camera at all.

Tip 2: Take Control Shots

One problem with digital cameras is that there are always some pixels on the image sensor which are bad. When taking day photos, these defects are not discernible. However, they are pretty obvious in night photos. How do we correct these? Here’s a simple way – take a control shot, then use image editing to subtract out those bad pixels.

This is how it works. The next time you’re out to take night photos, go ahead and snap a picture of Scene A, as you normally would. Then, when it’s convenient, take a photo of the exact same Scene A again, but with the lens cap on.

Now you will have two images, one night shot and one control shot (with the hot pixels). Load them up in say, Paint Shop Pro. Switch to the control shot and select Edit and Copy from the menu. Next, switch to the night shot and paste the copied image as a new layer. Then, select the new layer and change the Blend Mode to Difference and click OK. You’ll get the correct night shot with the hot spots subtracted out.

Tip 3: Try to Capture Motion

With a long exposure, you have many creative options when it comes to photography. This includes capturing motion. For example, have you ever wondered how those professional photographers shoot pictures of trails of car lights as they zoom down the highway at night? It’s all due to long exposures. Try to keep this in mind the next time you’re taking a night photo – you don’t have to restrict yourself to still images.

Tip 4: Play with the Aperture

In addition to shutter speed (which determines exposure time), you can play around with the aperture size of your digital camera. There are two scenarios here. If you set a long exposure, try to use a small aperture to avoid overexposing any stationary lights. in the picture. On the other hand, if you set a short exposure, try using a larger aperture to avoid any motion in your shot.

Tip 5: How to Use the Flash

As a general rule, I turn the flash off when taking night photos. There are some exceptions though – one specific example I can think of is trying to shoot a subject in the foreground, with motion trails of car lights in the background. In this case, bring along an external flash unit and shine it on your subject manually. Set a long exposure, then have your subject wait until the picture is taken.

Tip 6: When to Take Night Photos

When’s the best time to take night photos? I usually like to take them during dusk when colors and details are easier to capture. I’d recommend that you do some research on the evening before the photo shoot. Decide on the location, then come back the next day to take the photo at dusk.

sentradigital.com

The History of Photography

2008-10-28T14:33:00.003+07:00

Fotografi identik dengan pembicaraan mengenai cahaya. Refleksi obyek dengan penghantar cahaya yang ditimpakan di sebuah bidang, itulah inti fotografi. Akhir abad ke-5 SM, seseorang bernama MoTi menemukan gejala fotografi berupa sebuah refleksi gambar terbalik pada sebuah tembok ruangan gelap. Saat ditelusuri, ternyata sumber refleksi dari gambar terbalik tersebut berasal dari sebuah lobang bertutup kaca yang ada di sisi tembok lainnya.

Generasi berikutnya, seorang Arab yang bernama Ibn Al-Haitham pada abad ke-10 Masehi menemukan fenomena yang sama pada tenda miliknya yang bolong. Hanya sebatas itu informasi yang masih bisa kita gali seputar sejarah awal fotografi karena keterbatasan catatan sejarah. Bisa dimaklumi, di masa lalu informasi tertulis adalah sesuatu yang amat jarang.

Fotografi dalam makna yang sebenarnya terus berkembang. Pada tahun 1839 adalah tahun awal fotografi. Di Prancis, fotografi pada saat itu disebut kemajuan teknologi. Gambar dua dimensi pun sudah dapat dibuat permanen.

Istilah Photography dicipta pada tahun 1839. Ketika teknologi senifoto terus berkembang bersama dengan kemajuan manusia, ilmu sangat penting bagi menjamin mutu kerja seorang senifoto yang kemudian disebut fotografer (Photographer). Pada tahun itu, di Perancis dinyatakan secara resmi bahwa fotografi adalah sebuah terobosan teknologi. Saat itu, rekaman dua dimensi seperti yang dilihat mata sudah bisa dibuat permanen.

Penemu fotografi dengan pelat logam, Louis Jacques Mande Daguerre, sebenarnya ingin mematenkan temuannya itu. Tapi, Pemerintah Perancis, dengan dilandasi berbagai pemikiran politik, berpikir bahwa temuan itu sebaiknya dibagikan ke seluruh dunia secara cuma-cuma.

Seorang peneliti Perancis lain, Joseph Nicephore Niepce, pada tahun 1826 sudah menghasilkan sebuah foto yang kemudian dikenal sebagai foto pertama dalam sejarah manusia. Foto yang berjudul View from Window at Gras itu kini disimpan di University of Texas di Austin, AS. Niepce membuat foto dengan melapisi pelat logam dengan sebuah senyawa buatannya. Pelat logam itu lalu disinari dalam kamera obscura sampai beberapa jam sampai tercipta imaji. Metode Niepce ini sulit diterima orang karena lama penyinaran dengan kamera obscura bisa sampai tiga hari.

Kamera mulai diperkenalkan ketika para pelukis menghadapi masalah untuk merekam gambar (potrait) sekitar abad 17 dan 18. Justru itu mereka telah mencipta kamera Abscura untuk kemudahan merakam gambar.

Tahun 1900 seorang Jurugambar telah mencipta kamera Mammoth. Kamera ini amat besar ukurannya dimana beratnya 1,400 pound. Lens seberat 500 pound. Sewaktu mengubah atau memindahkannya tenaga manusia sebanyaki 15 orang diperlukan!. Kamera ini menggunakan filem sebesar 4 Â½ x 8 kaki dengan bahan kimia sebanyak 10 gallons digunakan ketika memprosesnya.

Dalam era teknologi, perkembangannya sangat ketara sekali apabila senifoto telah diadu kemajuan teknologi dan wujudnya adalah Kamera Digital yang diramalkan akan mengambil alih peranan senifoto tradisional (analog atau film).

Memasuki peradaban lebih modern, Fotografi Tidak semata heliografi lagi karena cahaya apa pun kemudian bisa dipakai, tidak semata cahaya matahari. Tahun 1901, seorang peneliti bernama Conrad Rontgen menemukan pemanfaatan sinar-X untuk pemotretan tembus pandang. Temuannya ini lalu mendapat Hadiah Nobel dan peralatan yang dipakai kemudian dinamai peralatan rontgen.

Cahaya buatan manusia dalam bentuk lampu sorot dan juga lampu kilat (blits) kemudian juga menggiring fotografi ke beberapa ranah lain. Pada tahun 1940, Dr Harold Edgerton yang dibantu Gjon Mili menemukan lampu yang bisa menyala-mati berkali-kali dalam hitungan sepersekian detik.

Blitz atau Flash atau cahaya bantu buatan manusia ditemukan jauh setelahnya. Penemuan alat bantu foto bersejarah ini juga menggiring fotografi ke beberapa ranah lain. Pada tahun 1940, Dr Harold Edgerton yang dibantu Gjon Mili menemukan lampu yang bisa menyala-mati berkali-kali dalam hitungan sepersekian detik. (berbagai sumber)

sentradigital.com

5 Simple Steps To Better Digital Macro Photography

2008-10-28T14:28:00.002+07:00

If your looking for a quick & simple way to improve your digital macro photography, we're here to help! Rather than going home empty-handed on a dull day, use the diffused qualities of overcast natural light to illuminate close-up subjects.

Macro photography is one photographic genre that benefits from the soft light and low contrast that dull grey weather conditions bring. Employing some simple tried and tested techniques will certainly improve your macro photography substantially. Try the 5 following tips..

1. Search for Subjects

Spend a little time looking for the perfect image, rather than rushing all the time. The obvious shot might be the entire waterfall, but try and look that little bit closer and deeper, and you'll discover there's a new world of subjects all around you without the need to wander elsewhere.

2. Don’t Use a Tripod

Why not take your digital camera off the tripod and explore the shooting opportunities right where you're shooting. Having found something you like, you can then choose to use the tripod to achieve the composition you have in mind. Don't let your creativity be restricted by your equipment!

3. Polarizing Filters

Often there's no need to add a filter - it can lead to longer exposure times, but working with water, glare and contrast can be a problem, even under overcast skies. Try experimenting by making exposures both with and without filters. You'll be surprised at the differences.
4. Shoot Parallel

Make sure that you use adequate depth of field by selecting the smaller apertures. Then ensure that you align your camera parallel to your subject. This prevents out-of-focus areas from ruining your shots!

5. Composition.

Try positioning the subject according to the Rule of Thirds. Experiment with both landscape and portrait format images in order to see what works. Ultimately, the look will be down to a matter of personal choice.

sentradigital.com

How to Vignette Your Digital Photos

2008-10-28T14:20:00.001+07:00

The vignette effect is an attractive and elegant look to give to your digital photos, and is achieved by smoothly blending the photo against a single-colored background.

This effect works best on portrait photos - though there is nothing stopping you from trying it out on any type – and has been used by photographers as far back as the early 1900s.

1. First Things First

Before we get started it is a good idea to choose the photo that you want to vignette and create a copy of it to work with; this is a simple safety measure to make sure that you don’t make any permanent changes to the original image that you didn’t intend. Now that you’ve created a copy of your photo go ahead and open it in your preferred image editor – I've used Jasc Paint Shop Pro for this article, but most of the widely used editors can create the same effect using very similar techniques.

2. Cutting Out the Subject

The first step taken to vignette a digital photo is to cut out or select the subject from the rest of the image, and this can be accomplished using the selection tool in your image editor. Most photos using the vignette effect use oval or rectangle shapes, and while these may provide the best results it does not mean that you can’t experiment with others.

First choose a shape that you like and then proceed to set the feathering level – this is what will cause the picture to blend into the background smoothly. A quick rule of thumb is that the larger the photo is, the higher the feather level will be. Start off at around 50 and then experiment to find the number that gives results that you prefer.

Next, it is time to cut out the subject – using the selection tool create your preferred shape at an adequate distance around the subject, and once you are happy with the size proceed to the next step.

3. Removing the Background

Now we need to invert the selection. If you are using Paint Shop Pro then click Selections > Invert on the menu bar; other image editors will have a similar method to invert the selection. What this does is reverse what we just selected - instead of having the subject selected we now have everything other than the subject selected!

The next part is very simple – press the delete key and watch as you are presented with your vignette photo. All that is left to do is to crop the background a little if desired, then your vignette photo is complete!

sentradigital.com

How to Use the Selective Focus Technique

2008-10-28T14:09:00.001+07:00

Have you ever wondered how those professional photographers make their subjects stand out from the surroundings?

For example, a flower may stand out against a blurred background, or a small insect is set against a blurred leaf. Well, its not difficult to achieve this effect.

The trick is to use the selective focus technique - one of the standard techniques used by professional photographers.

With this technique, we can choose one part of the image to be sharp and in focus, while the rest of the image is kept out of focus. It's very useful in macro and close-up photography.

Note that it is in fact possible to achieve the selective focus effect using image editing programs. You can simply select one part of the photo, keep it sharp and then blur the rest. However, personally, I choose to shoot the image with selective focus because the effect always looks more natural.

So how do you achieve selective focus? Here are some tips.

Aperture size

For selective focus, try choosing your widest f-stops (i.e. aperture size), such as f/2.8 or f/4. Couple this with a fast shutter speed to ensure enough light is present in the photo. I also recommend using a neutral-density filter to allow you to use wide f-stops.

Telephoto Settings

A good tip is to zoom in as much as possible, or choose a telephoto lens. I've achieved much better results by using strong telephoto.

Locate Out-Of-Focus Areas

Another trick to achieve the selective focus technique is to search for an element that can be strongly out of focus. For example, if you're shooting an insect, choosing to have out-of-focus leaves surrounding the insect is a good idea.

Angle To Subject

This tip takes a bit of practice, but is very effective at times. Choose an angle to the subject that causes background and foreground elements to be farther from the focused subject. This causes them to be strikingly out of focus.

LCD Review

With the advent of digital photography, you can (and should) check your composition in the LCD to be sure the in-focus and out-of-focus areas are correctly captured.

sentradigital.com

Baby Photography - A Guide To Getting Great Baby Shots

2008-10-28T14:00:00.001+07:00

One of the most important factors in photographing babies is patience and the way you apply child psychology when relating to the baby. Babies over six months may be shy and may not react well to a complete stranger.

This is where child psychology comes in - you must try to play with the baby, or even become a child yourself while taking the photograph. The keys of your car can be very effective. But remember, your job is to take a baby portrait; you must be able to react quickly when the infant responds to your entertainment. Shooting a portrait of a newborn baby can be difficult. At this age the baby will not be active, so it's better to focus on close-up head shots. Try using natural light from a bedroom window to add atmosphere.

Babies over a few months of age will be more alert and will have a lot more movement in them. Shooting fast is a necessity, the infant will tire quickly. The baby will bore quickly and can prove tricky to shoot! If you are serious about baby photography and you tend to shoot from your own studio make sure you have a lot of toys to amuse the infants. A light color background will work best and use both color and black & white.

Parents may be worried about the affect of studio lights on their baby. Remember that strobe lights have no effect on babies and children, so don't worry. If you're photographing somebody else's baby, be sure not to handle a baby without the parents consent, as most parents will be very protective and won't react well to a stranger lifting the infant.

Watch out for the babies hands & fingers. Fingers in the mouth can be attractive to photographers but on most occasions they will obscure the face & spoil your shot! Also on the legal side of things, If you plan to resell the photographs to an agency or site, make sure you ask the parents beforehand, and get a release form signed by the parents.

There is a large market out there for baby pictures but agencies or magazines won't touch them without the parents consent. Here area few tips to remember when shooting pictures of babies. Keep them in mind and you'll certainly notice a marked improvement in your baby images.

Try to work quickly as Babies will tire quickly.
Have items at hand to distract the baby!
Try to use pale and light backgrounds or backdrops.
Take both Color and Black & White shots.
Focus on the Baby's expression and eyes.

sentradigital.com

7 Tips for Shooting Great Digital Photos

2008-10-28T13:58:00.001+07:00

Do you have trouble shooting good digital photos? Perhaps you've been taking digital photos for some time, but never really got the beautiful shots you wanted.

Maybe you somehow messed up the photos you took of important events, like your daughter's birthday or your trip to Paris.

You can imagine the frustration one feels when photos of memorable events turn out ugly

So how do you begin to take good photos? Well, the first thing to remember is this: It's the photographer that takes great photos, not the camera. Think about that for a minute. It's true isn't it? I've seen some people take great photos with a simple point-and-shoot camera, while some take lousy shots with the most expensive SLR.

Fret not! Read these tips on shooting digital photos and apply them the next time you have a chance. Before long, you'll be shooting photos like a pro!

1. Know Your Camera

Does this sound familiar? You buy the latest digital camera out there, come home, rip off the box, then proceed to fiddle with the device. You briefly flick through the hundred page camera manual and then never look at it again. Not a good idea! If you buy a digital camera, you owe it to yourself to understand its ins and outs. Learn how to control exposure, how to use different camera modes and how to use the flash. The knowledge you gain about the camera will be invaluable when you're out in the field taking those special photos.

2. Learn to Control the Flash

One of the most important things you need to know about digital photography is to control the flash. Personally, I hate to rely on the automatic flash that comes with the digital camera. Depending on the situation, you need to switch off or switch on the flash.

For example, when taking outdoor photos, it is sometimes good to turn on the flash to illuminate the subject, especially if he or she is in the shade. On the other hand, you can also choose to turn off the flash when taking indoor shots. Sometimes, using the flash indoors will result in unnatural skin color and harsh glare in your photos.

3. Play with the Macro Mode

Almost all digital camera these days have a macro mode. This setting is ideal for taking close up shots of objects like flowers or insects. On my Canon PowerShot S500, it's represented by a flower symbol. What you do is to pick a subject, turn on macro mode, then get as close to it as your camera will allow. Make sure you allow the camera to focus properly before depressing the shutter button fully.

4. Hold the Camera Level

A basic rule of photography is to hold the camera level. Since most digital cameras come with a LCD, you can use it to properly frame your shots. Next time you're taking a shot, try to look for the horizontal lines and use them as guides. A good example is to make use of the horizon when you're taking a photo of a sunset.

5. Use The Tripod

I recommend this tip to all budding photographers - camera tripods are an essential tool in your photography arsenal. When will you need a tripod? Well, it's useful if you're taking shots under low-light conditions or trying to capture fast moving objects. I like to use a tripod when taking night shots city streets, for example. Always try to look for a tripod that's convenient to carry around. For personal use, you don't need a huge one - just a simple compact one that's easy to pack.

6. Play with the ISO Setting

I find the ISO setting in digital cameras very useful. The ISO setting of a essentially camera controls it's sensitivity to light. If you're taking a photo of a still object, like a flower, then always use a low ISO setting. It allows for a longer shutter speed and produces a cleaner image. If you're shooting a moving object, like a baby playing with a toy, then a higher ISO setting of say 400 would be better. Do take note, however, that a higher ISO setting gives a faster shutter speed and requires less light. This will produce noiser photos.

7. Have Enough Memory Capacity

Just like you must have enough rolls of film when using traditional cameras, make sure you always have enough memory capacity in your digital camera. It's terrible to be on a holiday taking great photos and suddenly realizing you've no memory space left. Here are some general guidelines for digital camera storage.

2 megapixel cameras - get at least a 64MB card

3 megapixel camera - get at least a 128MB card

4 megapixel camera - get at least a 256MB card

5 megapixel camera and above - get at least a 512MB or 1GB card

sentradigital.com

A Guide To Improving Your Digital Landscape Photography

2008-10-28T13:01:00.001+07:00

Digital Landscape Photography is a broad and varied subject matter, with a huge spectrum of possible interest areas and approaches. You may have seen the work of Landscape Photographers solely interested in shooting 'urban' scenes, images of city life, construction or degradation. Or those who enjoy an alternative approach, experimenting with color manipulation, infrared or unusual angled shots. In this guide we'll discuss the most common area of Landscape Photography - the natural world.

Constant evolution of technology within the digital photography market has provided us with the opportunity to go further than ever before with our work. Combining new technology with advanced techniques and more 'know how' means that even the amateur is now capable of producing mind-blowing results. Whether captured on canvas, paper or in as a digital image, landscapes have always been a great artistic theme for photographers. We have and always will be inspired by our surroundings, its colors, shapes, contrasts and impacts. However, producing these results is not easy, even with the digital equipment readily available to us in todays market. It takes technique and more importantly it takes imagination and flair. Lets discuss some of these techniques now..

1. Location Location..

A carefully chosen location is paramount to a good Landscape shot. Think about the purpose of your shot before hand. What is it your trying to achieve? Try to visualize your finished picture. Is it for a particular purpose such as hanging above your fireplace? Or maybe you're trying to capture a beautiful scene such as a mountain range, seascape or moorelands? Location & purpose should come as one.

A great landscape trick is to imagine and assign an emotion to your picture before you take the shot. For example, if you were looking for a shot to hang in the bedroom, think of serenity, peace or calm. If you were looking for a shot for a exhibit, think anger or fury to bring out a striking impact. You'll be amazed how you will naturally change the composition of your shot after thinking of an emotion behind the picture! Give it a try yourself!

2. The Composition..

Keeping it simple and uncluttered is generally a good rule. By removing distractions from your photographs, you will help bring more prominence to your focus subject as the viewers eye will not drift as much. It is also important to include some form of foreground interest into the image too, this may be your main subject or it could simply be part of the background that continues forward.

Landscape photographers often talk of the 'Rule Of Thirds'. When using the 'Rule of Thirds' you keep the main focus subject off center and away from the middle of the frame. As a result, a photo looks more dynamic, and ultimately more interesting to view. Imagine your image is divided into nine equal parts. Placing your subject where any of these lines intersect or meet, will help in producing a well-balanced, dynamic photo. Yet do remember that your creativity beats any rule hands down! So don't be scared of experimenting with your digital landscape photography composition. Many masterpieces were discovered through experimentation!

3. The Focal Point..

The focal point is closely related to the composition of your image. Simply ensure that your composition has a particular focal point to attract the viewers eye, such as a lighthouse, a boat on the ocean etc. This just makes sure the photo has a dimension and sense of scale. Keeping this technique in mind will also help prevent the image from looking too bland or boring.
You dont have to use something mainstream as your focal point, infact it's more eye-catching and interesting when you choose something completely out of the ordinary. There really is no boundary here, be creative and see what you can come up with. After all, we're looking to achieve impact with our photography. This is what makes good photos striking & memorable!

4. The Time of Day..

The quality and effect of light changes dramatically during the day as the hours pass. As the sun rises, shadows are weaker and pastel colors more apparent in your shots. Atmospheric haze is also at its lowest. As the day progresses the light becomes more contrasting & harsh, with colors fully saturated during the middle of the day. Shooting with the sun behind you, or to one side, will usually work best for maximum color impact. A favorite time to shoot is often in the evening, as the sun sets, the light casts a warm, rich glow which works extremely well for landscape images.

Try placing the main focal images in front of the sun, causing light to break around the edges. The results can be astounding. As the afternoon progresses, the sunlight will create much warmer colours on your subjects or scene. Shooting into the sun as it moves towards the horizon can also create stunning silhouettes. Making a silhouette with a sunset couldn’t be simpler, at this point of day you'll find them everywhere! Once the sun has set the dusk or twilight colors can still glow with warmth. After the sun has disappeared carry on taking pictures using longer exposure times and you'll see the sky takes a dark blue tint which is great for atmospheric scenes.

5. Capturing The Perfect Moment..

There's a lesson to be learned here, a good photographer must have the discipline and self control to take the shot he wants, but also NOT to take the shot he doesn't want! Do not be rail-roaded into taking second rate shots just because factors seem to turn against you. If you cant get the shot you want because it starts to rain, take a walk, explore! Don't see the rain as a set back, see it as an opportunity to capture shots only possible when it's raining!

The last thing to consider is your equipment, which is vital when out shooting Digital Landscape Photography. You DO NOT need extremely expensive kit to take superb shots. There are however some items that are crucial to effective & safe digital Landscape photography. A Camera Bag that is both protective and sturdy is essential if you're walking over rugged areas. The last thing you want is for the strap on your $10 bag to break, and empty your camera equipment over the wet muddy ground!

A tripod is a piece of equipment I would certainly recommend investing in, if you're really interested Digital Landscape Photography. As previously mentioned, it doesn't have to cost the earth! As long as it's stable & fits your camera model correctly you'll be fine. Read more on How To Choose The Correct Tripod. It really will prove invaluable in getting angles & exposures you couldn't achieve by holding the camera by yourself.

Finally a lens cleaning cloth with come in handy on many occasions. Many landscape people interested in digital landscape photography find themselves taking pictures in areas of high moisture or rain where your lens may become foggy. Please don't try to wipe your lens with anything other than a specifically designed lens cleaning cloth! You could scratch the lens surface permanently! You can buy them cheaply from Amazon

"Landscape photography is the supreme test of the photographer - and often the supreme disappointment."
- Ansel Adams -

sentradigital.com

Rediscovering black and white

2008-10-28T12:38:00.002+07:00

Black and white photography...

Black and white photography is very much the cradle of photography: Before colour, there was black and white. Before that, there was paint brushes and paint. Many photographers saw the introduction of colour photography as the death of black and white, but they were wrong: In fact, even today, a lot of photographers work largely — even exclusively — in monochrome. Why? To me, black and white has an amazing quality to it — Seeing something in monochrome allows you to give it a detachment from reality.

Seen at its very simplest, any photograph has four elements: shape, texture, lighting, and colour. Think about a tennis ball: The basic shape is round. The texture is fuzzy and hairy. The colour will often be yellow, and lighting will determine how you perceive it all. The interesting thing is that of all of these qualities, you can’t strip many of them away: You can ignore the shape by getting in close enough to focus on the texture (using macro to capture the small hairs on the tennis ball, for example). You can ignore the texture by getting far enough away that the texture doesn’t matter, or by adding a motion blur (a spinning tennis-ball photographed with a long enough shutter time will have no texture). Without lighting, you wouldn’t be able to see the ball at all.

Colour falls in a completely different category: By stripping it out of your photography, the other qualities of a photograph — especially textures, which often are drowned out by colours — become more apparent. Stripping away colour, then, abstracts yet familiarises a photograph. Going to Kevin’s first photograph is a phenomenal way of illustrating how textures suddenly become vastly more important. The reason why this photo appeals to me is the way the asphalt on the road springs out at you. The lovely contrast in the top-right of the image, combined with the relatively lower contrast in the rest of the photo adds a touch of drama.

To me, this appears to be a photograph commenting on aspects of mental health: The deep black of the trees contrasting against the blown-out highlights on the horizon. The way the photographer takes up a significant part of the photo without really being visible. I don’t know the photographer, and I don’t know how accurate my interpretation might be.

While the general principe of the photo is exciting to me (I loved the angled composition), it does have some serious flaws. I wouldn’t have minded the vastly blown-out horizon so much — it’s one of the charms about black and white photography, that strong contrast and even going outside the dynamic range of your film / imaging sensor / printing paper can look damn hot — but the building and the plants along the road on the left side are a bit peculiarly exposed. The old adage of exposing for the highlights and developing for the shadows (as discussed in an earlier photo critique) would have come in handy here, as it would have allowed you more data to work with, so you can either keep the telegraph poles on the horizon, or so you can edit them out successfully in Photoshop.

If I personally had taken this photo, I would have gone back with a tripod and had a shot at turning it into a High Dynamic Range photograph, just to have some more data to work with to help it along.

Kevin’s second photo had me a little bit baffled. Mostly, I just can’t figure out what’s going on here. Sure, it’s some guy driving a car in the rain, but what intrigues me is the hand. The thing around the wrist — is that a hospital tag? What is the liquid on the driver’s hand? That looks a lit like it could be blood. Is it a doctor, on their way to an emergency? Is the heart-shaped item on the dashboard a radiogram? Is the guy about to be a father? It is a really simple photo, which interestingly enough draws its focus, yet again, from its wild and varied contrast. The sky is completely blown out.

The dashboard is pure darkness. And the hand is the only part of the photo that stands out as being ‘correctly’ exposed. A very fascinating photo that raises a ton of questions. The real question, though: If I hadn’t done a critique of this photo, would I even have looked at it a second time? Probably not: it’s a guy in a car. I would never have noticed the heart, the armband or the blood(?) on his hand. Personally, I think this would have been a better photo if the background had been a lot calmer. A long, open motorway, perhaps, or a forest, or even a hospital in the background… Anything to stop you from looking out of the wind shield, wondering what you’re supposed to be looking at.

Of all the photos Kevin sent to me, this is by far my favourite, and it also rather clearly embodies what I feel black and white photography is about. The photo comes across as an impressionistic piece, in that his toes are in a blur (is it because he’s in a river, and the refractions work as a motion blur? Maybe…). The torn trousers and the fluid motion of the water bring holiday-type-thoughts to my mind. While this photo might have a lot less of a message than, say, the previous photograph, it is a much more appealing photo to me, visually.

This photograph wouldn’t be out of place in a trendy restaurant or an edgy art gallery: It’s obviously not a snapshot of someone’s feet: Deliberation, planning, and exquisite exposure comes together to create a powerful visual image.

In addition, it’s worth noting that this photo doesn’t look as if colour would have added much to it: It’s all about the motion and texture.

On a personal level, I would probably have treated the photograph to a slight re-crop. It’s a personal preference thing, which doesn’t necessarily add much to the photo the way the photographer intended, but I’m very much a ‘get into the action’ kind of guy: In artistic photos, I find you often don’t need the context that is added to a photo. As such, with a bit of re-cropping, I landed at this:

So, why should people still bother with black and white in the digital age? Well, in many ways, black and white photography has become easier than ever. By using the digital darkroom (and especially by using the channel mixer to turn a colour photo into monochrome), you get a lot more influence and control over how your photograph is rendered.

sentradigital.com

Teknik Dasar Fotografi

2008-10-24T15:09:00.003+07:00

Apa itu Fotografi ?
Fotografi adalah seni atau suatu proses penghasilan gambar dan cahaya yang dipantulkan oleh objek masuk ke lensa kemudian diteruskan ke bidang film, sehingga menghasilkan gambar.
Mengenal Kamera dan bagian-bagiannya
Kamera
Ada beberapa jenis kamera seperti:

View finder kamera
View kamera
Twin lens camera (Box)
S.L / Single Lens Refflex
Instamatic camera
Palaraid kamera
Kamera digital

Bagian-bagian kamera

Lensa
Menurut macamnya dikenal lensa normal sudut lebar, lensa dan lensa tele. Lensa normal adalah lensa yang sudut pandangnya serupa mata kita. Jarak antara lensa dengan film normal (50 mm). Sudut lebar adalah lensa yang panjang fokalnya lebih kecil dari normal. Dan lensa tele adalah lensa yang panjang fokalnya lebih besar dari normal.
Gabungan dari ke tiga lensa disebut lensa zoom (zoom lens).
Selain itu masih ada lensa tambahan seperti lensa makro, lensa C.U dan lain-lain

Diafragma
Diafragma adalah sejumlah lempengan-lempengan baja yang dapat diatur, sehingga lubang menjadi besar atau kecil. Bilangan diafragma disebut stop biasanya disingkat F.
contohnya : F4 ,F5, F8 dan seterusnya.
Diafragma bisa diatur dengan merubah angka skala diafragmanya yang terdapat pada gelang yang melingkar pada lensa dengan angka-angka 1,4. 2,8 . 4,5 . 6,8. 1,1. 16.

Kecepatan /rana /shutter speed
Rana adalah sejenis tirai yang dapat dibuka selama waktu tertentu, misalnya 1/60 detik
Fungsi rana atau kecepatan adalah sebagai alat pembuka dan penutup masuknya cahaya kebidang film serta untuk melindungi film dari cahaya.
Rana pada kamera ada dua macam menurut gerakannya: Rana pusat dan Rana celah.
Biasanya angka kecepatan pada kamera tertulis T.B, 1.2, 4, 8, 15, 30, 60, 125, 250, 500, 700, 1000, dan sebagainya. Angka-angka 1.2, 4, 8,15 menunjukkan lamanya waktu membuka kecepatan 1 detik, 1/4 detik, 1/8 detik, 1/15 detik dan seterusnya.
T: time, bila tombol kecepatan ditekan akan membuka dan kalau ditekan lagi akan menutup.
B: Blub, bila tombol kecepatan ditekan akan membuka dan jika dilepas akan menutup.
T dan B : dipergunakan untuk pencahayaan lebih dari 1 detik.

Fokus (Pengatur Jarak)
Fokus adalah pengaturan lensa yang tepat untuk jarak tertentu.
Untuk menajamkan gambar pada bidang film kita perlu mengatur jarak atau focus pada kamera dengan cara memutarnya lalu melihatnya pada jendela bidik.
Untuk memfocuskan gambar pada kamera ada beberapa macam: kaca buram, gambar geser, gambar rangka, micro prisma.

Skala tajam (ruang tajam)
Ada tiga faktor yang menentukan ruang tajam yaitu:
Lensa, masing-masing lensa menghasilkan ruang tajam yang berbeda.
Jarak pemotretan, makin jauh objek yang kita fokuskan, makin luas ruang tajamnya.
Diafragma, makin kecil lubang diafragma, makin luas ruang tajamnya. Makin besar lubang diafragma, ruang tajamnya semakin sempit.

Film
Film yang dijual dipasaran ada dua macam yaitu: film negatif dan film positif.
Film negatif terbagi dua: film negatif B/W dan negatif color dan film positif pun terbagi dua B/W dan color.
Masing-masing pabrik mengeluarkan standar kepekaan film umpamanya ASA Amerika , JIS jepang dan DIN Jerman.
Film yang ber ASA tinggi berbutir kasar dan film yag ber ASA rendah berbutir halus.
Hal-hal yang penting diperhatikan waktu membeli film baik film negatif atau positif yaitu pada masa kadaluarsa film, bahan prosessing, tempat menjual film kena terik matahari atau terlindung.

Setting Kamera Untuk Melakukan Pemotretan
Siapkan Kamera yang akan dipergunakan
Bersihkan body kamera dari debu menggunakan brower atau kain planel.
Bersihkan lensa kamera dengan lens cleaner (pembersih lensa).
Pasang lensa ke body kamera. Perhatikan titik yang ada di lensa dan yang
dibody kamera harus saling ketemu kemudian putarlah lensa berlawanan arah jarum jam sampai tertedangar bunyi klik.
Pasang batu baterei kamera.
Pasang pegangan lensa seperti filter dan sun cup
Mengisi film
Cabutlah engkol kombinasi penggulung film ke atas sampai punggung kamera terbuka secara otomatis.
Masukkan film ke dalam kamera jepit film dengan baik dan forforator film harus masuk di gigi pembawa film.
Film yang mengandung emulsi menghadap ke lensa kamera.
Kemudian tutup punggung kamera dan tekan sampai terdengar klik.
Untuk mengetes apakah film sudah terpasang baik atau tidak, kokanglah kamera apa bila engkol penggulung film berputar ke arah yang berlawanan dengan arah panah penggulung film, berarti film sudah terpasang dengan benar.
Menyetel kecepatan ASA film dan kecepatan rana
Pastikan ASA yang digunakan dan sesuaikan kecepatan rana dengan kemampuan anda.
Hindari menggunakan kecepatan rendah, karena gambar akan kabur bila anda memotretnya kurang mampu, gunakan kaki tiga bila anda terpaksa menggunakan kecepatan rendah.
Peganglah kamera dengan tangan kiri,
posisi kaki kuda-kuda dan mata mengintip di jendela pengamat.
Memfokuskan lensa,
Intiplah kedalam lubang pengamat dan arahkan kamera, sehingga objek utama tampak ditengah
lingkaran kecil poros mikroprisma.
Cara memfokus gambar patah (split image),
Putarlah gelang fokus sampai bagian atas dan bawah dari split image dalam lingkaran poros mikroprisma bertemu membentuk objek yang utuh.
Cara fokus mikroprisma
Putarlah gelang fokus sampai objek dalam lingkaran poros mikroprisma
tampak terang.
Kalau anda kesulitan dengan cara diatas waktu memfokuskan, gunakannlah seluruh bidang kaca sekeliling lingkaran poros mikroprisma, cara ini biasa digunakan pada pemotretan malam hari.
Atur komposisi sesuai dengan storyboard (rancangan gambar).
LS: long shoot, FS: fokus shoot, MS: medium shoot, CU:clouse up

Membuat tulisan dengan latar belakang pemandangan
Dengan cara mounting
Tulisan langsung dibuat diatas kertas foto atau gambar lain sesuai selera anda.
Membuat tulisan diatas plastik transparan lalu ditumpuk dengan gambar yang anda inginkan.
Lakukanlah pemotretan menggunakan lensa CU atau Macro lens.
Multi Expose
Membuat tulisan dulu diatas kertas hitam pekat usahakan tulisan warnanya kontras.
Lakukan pengambilan gambar tulisan tadi dengan diafragma kamera naik 2 stop dari posisi pencahayaan normal.
Tekan tombol perewin film untuk kamera yang tidak dilengkapi dengan multi expose. Kemudian kamera dikokang kembali.
Lakukan pengambilan gambar diluar sesuai dengan selera anda dengan pencahayaan naik ½ stop dari pencahayaan normal.
Super Infus
Membuat tulisan dahulu diatas kertas putih tulisan hitam.
Potret tulisan tersebut menggunakan film artho/high contras for slide title dan proses film tersebut. Maka akan diperoleh tulisa negatif hitam putih, kemudian klise negatif tersebut di kontek ke film artho dan proses maka akan diperoleh klise positif hitam putih.
Siapkan slide color yang akan dijadikan background.
Sekarang tumpuklah ketiga film tersebut dengan urutan sebagai berikut:

Film negatif high contras /ortho
Film positif high contras / ortho
Film slide color untuk backgroundnya

Lakukan pemotretan film no.2 dan no.3 di atas kotak lampu dan lampunya dalam posisi menyala.
Tekan multi expose kamera kemudian kamera dikokang kembali.
Cabut film no.2 dan no.3 dan lakukan pemotretan ke film no.1.
Kalau ingin tulisannya berwarna pasanglah filter warna di depan lensa kamera anda.
Prinsip-prinsip Komposisi Fotografi
Komposisi adalah cara mengatur/menyusun bagian-bagian dari gambar (misalnya garis-garis, bentuk, ruang bebas, bayangan, warna, tekstur, dan lain-lain) agar gambar lebih menarik dan mudah dimengerti. Beberapa prinsip biasa digunakan untuk meningkatkan efektifitas gambar. “Perlihatkan apa yang ingin Anda perlihatkan”, merupakan salah satu prinsip yang baik.
1.Subjek
Tampilkan suatu subjek utama dalam sebuah gambar. Kesampingkan bagian-bagian lain dan pisahkan hal-hal yang tidak perlu ada dalam foto.

2.Penempatan subjek utama

Bayangkanlah Anda sedang membagi gambar dengan garis bayangan mendatar dan tegak lurus menjadi 3 bagian yang sama besar. Titik temu dari garis-garis tersebut adalah tempat dimana Anda dapat meletakan subjek utama dan elemen-elemen pelengkap.
Jika menggunakan garis mendatar sebagai subjek utama, misalnya garis batas (cakrawala) antara udara dan lahan pertanian, aturlah agar bagian yang satu lebih besar dari bagian lainnya.
Posisi subjek tidak harus selalu berada di tengah-tengah agar komposisi nampak lebih menarik. Dan hindari penempatan subjek pada posisi yang gelap.

3.Titik pandang
Pilihlah posisi kamera yang paling tepat saat mengambil gambar, sehingga hal-hal yang ingin Anda perlihatkan menjadi lebih jelas.

4.Sediakan lebih banyak ruang untuk garis pandang dan garis gerak.
Beri ruang di depan subjek untuk mengesankan subjek Anda sedang bergerak atau melihat sesuatu.

5.Batas antar bagian gambar sebaiknya digunakan untuk mempertegas hal apa yang ingin Anda komunikasikan.
Namun, perhatikan dengan seksama agar objek yang ditonjolkan tersebut tidak membingungkan atau merusak komposisi.

6.Cahaya dan bayangan.
Gunakan pencahayaan yang menyebar agar gambar nampak jelas dan usahakan agar subjek anda menghadap sumber cahaya.
7.Lakukan pengambilan gambar secara bervariasi agar gambar lebih menarik.
Gunakan jarak yang berbeda antara kamera dan subjek dalam setiap pengambilan. Berapa jarak subjek yang sebaiknya tampak dalam gambar

Diambil dari sigitsetiawan.wordpress.com oleh Sigit Setiawan

Teknis Fotografi & Fungsinya

2008-10-24T15:05:00.001+07:00

Fotografi bukan segalanya tentang kamera. Dikatakan bahwa fotografi adalah seni bermain dengan cahaya. Tanpa adanya cahaya, maka mustahil fotografi itu ada. Menghasilkan sebuah gambar yang bagus, harus memiliki visi yang kuat dalam hal ‘melihat’. Memperhatikan cahaya, komposisi dan momen adalah hal-hal yang penting untuk diperhatikan dalam membuat foto yang dapat dikategorikan ‘bagus’.

Namun, sepertinya mustahil dapat menghasilkan foto seperti itu jika tidak mengenal dan memahami dari masing-masing teknis fotografi dasar. Fotografi memang bukan segalanya tentang kamera, namun kamera adalah alat untuk menyalurkan visi kita itu. Maka, sekiranya perlu mengenal dan memahami bagaimana kamera bekerja.

Tugas utama dari kamera adalah mengatur intensitas cahaya yang masuk dan pada akhirnya mengenai film/sensor (selanjutnya saya sebut medium). Apabila, kamera mengizinkan terlalu banyak cahaya yang masuk maka medium akan terbakar (overexposed). Dan sebaliknya. Bagaimana agar cahaya yang masuk itu tidak berlebih dan tidak kurang, atau dengan kata lain ‘pas’. Berikut saya jabarkan satu-satu.

Aperture
Atau yang sering juga disebut dengan difragma atau bukaan lensa adalah berfungsi untuk mengatur seberapa besar lensa akan terbuka. Fungsi ini lebih tepatnya terletak pada lensa. Logikanya, semakin besar bukaannya, maka akan semakin banyak cahaya yang akan masuk. Seperti sebuah kran air. Semakin besar kita buka keran tersebut maka akan semakin banyak air yang akan keluar.

Penulisan Aperture yang benar adalah f/x. Sehingga apabila dikatakan nilai Aperture-nya adalah 5.6, maka penulisan yang benar adalah f/5.6. Jadi jangan bingung apabila ada yang bilang bahwa bukaan lensa 2.8 lebih besar dari bukaan lensa 5.6. Karena kalau secara penulisan matematisnya memang benar khan? (f/2.8>f/5.6) Tapi kebanyakan kita malas untuk bilang f/2.8 atau f/5.6, karena kita orangnya simpel sih…

Efek Samping dari Aperture
Seperti obat batuk yang memiliki efek samping, begitu juga dengan aperture. Efek sampingnya adalah semakin besar bukaan lensa, maka akan semakin kecil daerah fokusnya. Dan sebaliknya. Daerah fokus inilah yang biasa dikenal dengan DOF (Depth of Field).

Shutter Speed
Atau yang biasa disebut juga dengan speed atau kecepatan rana bertugas untuk mengatur berapa lama mirror terbuka lalu menutup kembali untuk membatasi berapa banyak cahaya yang akan masuk. Seperti teori keran, apabila kita membuka keran terlalu lama, maka wadah penampung air tadi akan kelebihan sehingga akan meleber keluar. Kalau dalam kasus fotografi, medium akan terbakar.

Penulisan shutter speed yang benar adalah 1/x. Sehingga apabila dikatakan bahwa sebuah foto menggunkanan speed 60, maka penulisannya yang benar adalah 1/60 detik. Jadi jangan bingung kalau dikatakan bahwa speed 60 lebih cepat dibandingkan 30. karena secara penulisan matematis memang begitu khan?

Efek Samping dari Shutter Speed
Seperti berpacaran yang memiliki efek samping, seperti sulit melirik wanita/pria lain, begitu juga dengan shutter speed. Semakin cepat shutter speed, maka akan gambar akan semakin terlihat diam (freeze). Dan sebaliknya, apabila speed terlalu lamban gambar akan terlihat blur dikarenakan gerakan yang terlalu cepat, sehingga objek terlihat bergerak sangat cepat.

ISO atau ASA
Adalah tingkat sensitifitas medium dalam menerima cahaya. Semakin tinggi nilainya, maka akan semakin tingkat sensitifitasnya. Artinya, apabila kita merubah nilai ISO atau ASA ini menjadi lebih tinggi, sedangkan aperture dan speednya tidak diubah, maka medium akan menerima cahaya lebih banyak. Dan sebaliknya.

Efek Samping ISO atau ASA
ISO adalah tingkat sensitifitas sensor (medium), sedangkan ASA adalah tingkat sensitifitas film (medium), jadi perbedaannya hanya dimediumnya saja. Tapi logikanya sama. Kecuali efek sampingnya. Dimana apabila menggunakan film ASA tinggi, maka gambar akan terlihat grainy (berbentuk titik kecil namun banyak). Sedangkan penggunaan ISO tinggi akan menghasilkan noise (seperti bentuk cacing namun banyak).

Diambil dari arc-en-ciel.do-talk.com

Anatomy of an ARP Poisoning Attack

2008-10-23T08:17:00.008+07:00

Hackers lie. Skillful hackers lie well. And well-rounded hackers can lie both to people and to machines.

Lying to people, known as "social engineering," involves tactics (detailed at length by convicted hacker Kevin Mitnick) such as posing as a company's employee so the company's real employees will blab secrets freely. Lying to machines involves lots of different techniques, and a commonly used one -- ARP Cache Poisoning -- is the focus of this article. ARP poisoning enables local hackers to cause general networking mayhem. Because it's mostly "incurable," every administrator should be aware of how this attack works.

ARP Refresher

In Foundations: What Are NIC, MAC, and ARP?, we explained that Address Resolution Protocol (ARP) is how network devices associate MAC addresses with IP Addresses so that devices on the local network can find each other. ARP is basically a form of networking roll call.

ARP, a very simple protocol, consists of merely four basic message types:

An ARP Request. Computer A asks the network, "Who has this IP address?"
An ARP Reply. Computer B tells Computer A, "I have that IP. My MAC address is [whatever it is]."
A Reverse ARP Request (RARP). Same concept as ARP Request, but Computer A asks, "Who has this MAC address?"
A RARP Reply. Computer B tells Computer A, "I have that MAC. My IP address is [whatever it is]"

All network devices have an ARP table, a short-term memory of all the IP addresses and MAC addresses the device has already matched together. The ARP table ensures that the device doesn't have to repeat ARP Requests for devices it has already communicated with.

Here's an example of a normal ARP communication. Jessica, the receptionist, tells Word to print the latest company contact list. This is her first print job today. Her computer (IP address 192.168.0.16) wants to send the print job to the office's HP LaserJet printer (IP address 192.168.0.45). So Jessica's computer broadcasts an ARP Request to the entire local network asking, "Who has the IP address, 192.168.0.45?" as seen in Diagram 1.

All the devices on the network ignore this ARP Request, except for the HP LaserJet printer. The printer recognizes its own IP in the request and sends an ARP Reply: "Hey, my IP address is 192.168.0.45. Here is my MAC address: 00:90:7F:12:DE:7F," as in Diagram 2.

Now Jessica's computer knows the printer's MAC address. It sends the print job to the correct device, and it also associates the printer's MAC address of 00:90:7F:12:DE:7F with the printer's IP address of 192.168.0.45 in its ARP table.

Hey ARP, Did You Know Gullible Is Not in the Dictionary?

The founders of networking probably simplified the communication process for ARP so that it would function efficiently. Unfortunately, this simplicity also leads to major insecurity. Know why my short description of ARP doesn't mention any sort of authentication method? Because in ARP, there is none.

ARP is very trusting, as in, gullible. When a networked device sends an ARP request, it simply trusts that when the ARP reply comes in, it really does come from the correct device. ARP provides no way to verify that the responding device is really who it says it is. In fact, many operating systems implement ARP so trustingly that devices that have not made an ARP request still accept ARP replies from other devices.

OK, so think like a malicious hacker. You just learned that the ARP protocol has no way of verifying ARP replies. You've learned many devices accept ARP replies before even requesting them. Hmmm. Well, why don't I craft a perfectly valid, yet malicious, ARP reply containing any arbitrary IP and MAC address I choose? Since my victim's computer will blindly accept the ARP entry into its ARP table, I can force my victim's gullible computer into thinking any IP is related to any MAC address I want. Better yet, I can broadcast my faked ARP reply to my victim's entire network and fool all his computers. Muahahahahaa!

Back to reality. Now you probably understand why this common technique is called ARP Cache Poisoning (or just ARP Poisoning): the attacker lies to a device on your network, corrupting or "poisoning" its understanding of where other devices are. This frighteningly simple procedure enables the hacker to cause a variety of networking woes, described next.

All Your ARP Are Belong To Us!

The ability to associate any IP address with any MAC address provides hackers with many attack vectors, including Denial of Service, Man in the Middle, and MAC Flooding.

Denial of Service

A hacker can easily associate an operationally significant IP address to a false MAC address. For instance, a hacker can send an ARP reply associating your network router's IP address with a MAC address that doesn't exist. Your computers believe they know where your default gateway is, but in reality they're sending any packet whose destination is not on the local segment, into the Great Bit Bucket in the Sky. In one move, the hacker has cut off your network from the Internet.

Man in the Middle

A hacker can exploit ARP Cache Poisoning to intercept network traffic between two devices in your network. For instance, let's say the hacker wants to see all the traffic between your computer, 192.168.0.12, and your Internet router, 192.168.0.1. The hacker begins by sending a malicious ARP "reply" (for which there was no previous request) to your router, associating his computer's MAC address with 192.168.0.12 (see Diagram 3).

Now your router thinks the hacker's computer is your computer.

Next, the hacker sends a malicious ARP reply to your computer, associating his MAC Address with 192.168.0.1 (see Diagram 4).

Now your machine thinks the hacker's computer is your router.

Finally, the hacker turns on an operating system feature called IP forwarding. This feature enables the hacker's machine to forward any network traffic it receives from your computer to the router (shown in Diagram 5).

Now, whenever you try to go to the Internet, your computer sends the network traffic to the hacker's machine, which it then forwards to the real router. Since the hacker is still forwarding your traffic to the Internet router, you remain unaware that he is intercepting all your network traffic and perhaps also sniffing your clear text passwords or hijacking your secured Internet sessions.

MAC Flooding

MAC Flooding is an ARP Cache Poisoning technique aimed at network switches. (If you need a reminder about the difference between a hub and a switch, see this sidebar.) When certain switches are overloaded they often drop into a "hub" mode. In "hub" mode, the switch is too busy to enforce its port security features and just broadcasts all network traffic to every computer in your network. By flooding a switch's ARP table with a ton of spoofed ARP replies, a hacker can overload many vendor's switches and then packet sniff your network while the switch is in "hub" mode.

Scared? Good, Now Calm Down!

This is scary stuff. ARP Cache Poisoning is trivial to exploit yet it can result in very significant network compromise. However, before you jump to Defcon-7, notice the major mitigating factor: only local attackers can exploit ARP's insecurities. A hacker would need either physical access to your network, or control of a machine on your local network, in order to deliver an ARP Cache Poisoning attack. ARP's insecurities can't be exploited remotely.

That said, hackers have been known to gain local access to networks. Good network administrators should be aware of ARP Cache Poisoning techniques.

Since ARP Cache Poisoning results from a lack of security in a protocol that is required for TCP/IP networking to function, you can't fix it. But you can help prevent ARP attacks using the following techniques.

For Small Networks

If you manage a small network, you might try using static IP addresses and static ARP tables. Using CLI commands, such as "ipconfig /all" in Windows or "ifconfig" in 'NIX, you can learn the IP address and MAC address of every device in your network. Then using the "arp -s" command, you can add static ARP entries for all your known devices. "Static" means unchanging; this prevents hackers from adding spoofed ARP entries for devices in your network. You can even create a login script that would add these static entries to your PCs as they boot.

However, static ARP entries are hard to maintain; impossible in large networks. That's because every device you add to your network has to be manually added to your ARP script or entered into each machine's ARP table. But if you manage fewer than two dozen devices, this technique might work for you.

For Large Networks

If you manage a large network, research your network switch's "Port Security" features. One "Port Security" feature lets you force your switch to allow only one MAC address for each physical port on the switch. This feature prevents hackers from changing the MAC address of their machine or from trying to map more than one MAC address to their machine. It can often help prevent ARP-based Man-in-the-Middle attacks.

For All Networks

Your best defense is understanding ARP Poisoning and monitoring for it. I'd highly recommend deploying an ARP monitoring tool, such as ARPwatch, to alert you when unusual ARP communication occurs. This kind of vigilance is still the greatest weapon against all kinds of attack -- for, as Robert Louis Stevenson wrote, "The cruelest lies are often told in silence."

by Corey Nachreiner, WatchGuard Network Security Analyst

Mobile Ad-hoc Network

2008-10-17T16:58:00.001+07:00

A mobile ad-hoc network (MANET) is a kind of wireless ad-hoc network, and is a self-configuring network of mobile routers (and associated hosts) connected by wireless links – the union of which form an arbitrary topology. The routers are free to move randomly and organize themselves arbitrarily; thus, the network's wireless topology may change rapidly and unpredictably. Such a network may operate in a standalone fashion, or may be connected to the larger Internet.

Mobile ad-hoc networks became a popular subject for research as laptops and 802.11/Wi-Fi wireless networking became widespread in the mid to late 1990s. Many of the academic papers evaluate protocols and abilities assuming varying degrees of mobility within a bounded space, usually with all nodes within a few hops of each other, and usually with nodes sending data at a constant rate. Different protocols are then evaluated based on the packet drop rate, the overhead introduced by the routing protocol, and other measures.

The Children's Machine One Laptop per Child program has developed a cheap laptop for mass distribution (>1 million at a time) to developing countries for education. The laptops will use IEEE 802.11s based ad hoc wireless mesh networking to develop their own communications network out of the box.

Vehicular Ad Hoc Networks (VANET) are a form of MANETs used for communication among vehicles and between vehicles and roadside equipment.

Intelligent vehicular ad hoc network (InVANET) is a kind of Intelligence in Vehicle(s) which provide multiple autonomic intelligent solutions to make automotive vehicles to behave in intelligent manner during vehicle-to-vehicle collisions, accidents, drunken driving etc. InVANET uses WiFi IEEE 802.11 b/802.11g/802.11p and WiMAX IEEE 802.16 for providing easy, accurate, effective communication between multiple vehicles on dynamic mobility. Effective measures to track the automotive vehicles, media download /upload, conference between vehicles are also preferred. InVANET can also be applied for artillery vehicles during warfare, battlefield, and peace-time operations. Mesh networking in mobile applications have been demonstrated in multiple military scenarios.

Wireless Ad hoc Network

2008-10-17T15:41:00.001+07:00

A wireless ad hoc network is a decentralized wireless network. The network is ad hoc because each node is willing to forward data for other nodes, and so the determination of which nodes forward data is made dynamically based on the network connectivity. This is in contrast to wired networks in which routers perform the task of routing. It is also in contrast to managed (infrastructure) wireless networks, in which a special node known as an access point manages communication among other nodes.

The earliest wireless ad hoc networks were the "packet radio" networks (PRNETs) from the 1970s, sponsored by DARPA after the ALOHAnet project.

Application

The decentralized nature of wireless ad hoc networks makes them suitable for a variety of applications where central nodes can't be relied on, and may improve the scalability of wireless ad hoc networks compared to wireless managed networks, though theoretical[2] and practical[3] limits to the overall capacity of such networks have been identified.

Minimal configuration and quick deployment make ad hoc networks suitable for emergency situations like natural disasters or military conflicts. The presence of a dynamic and adaptive routing protocol will enable ad hoc networks to be formed quickly.

Wireless ad hoc networks can be further classified by their application:

* mobile ad hoc networks (MANETs)
* wireless mesh networks
* wireless sensor networks.

Medium Access Control

In most wireless ad hoc networks the nodes compete to access the shared wireless medium, often resulting in collisions. Using cooperative wireless communications improves immunity to interference by having the destination node combine self-interference and other-node interference to improve decoding of the desired signal.

Access Control List

2008-10-17T15:09:00.001+07:00

In computer security, an access control list (ACL) is a list of permissions attached to an object. The list specifies who or what is allowed to access the object and what operations are allowed to be performed on the object. In a typical ACL, each entry in the list specifies a subject and an operation: for example, the entry (Alice, delete) on the ACL for file XYZ gives Alice permission to delete file XYZ.

ACL-based security models

In an ACL-based security model, when a subject requests to perform an operation on an object, the system first checks the list for an applicable entry in order to decide whether to proceed with the operation. A key issue in the definition of any ACL-based security model is the question of how access control lists are edited. For each object; who can modify the object's ACL and what changes are allowed.

Systems that use ACLs can be classified into two categories: discretionary and mandatory. A system is said to have discretionary access control if the creator or owner of an object can fully control access to the object, including, for example, altering the object's ACL to grant access to anyone else. A system is said to have mandatory access control (also known as "non-discretionary access control" in the security literature) if it enforces system-wide restrictions that override the permissions stated in the ACL.

Traditional ACL systems assign permissions to individual users, which can become cumbersome in a system with a large number of users. In a more recent approach called role-based access control, permissions are assigned to roles, and roles are assigned to users.

File system ACLs

On file systems the process's user identifier (in POSIX, effective UID) is the principal means of control.

The list is a data structure, usually a table, containing entries that specify individual user or group rights to specific system objects, such as a program, a process, or a file. These entries are known as access control entries (ACEs) in the Microsoft Windows, OpenVMS, Linux and Mac OS X operating systems. Each accessible object contains an identifier to its ACL. The privileges or permissions determine specific access rights, such as whether a user can read from, write to, or execute an object. In some implementations an ACE can control whether or not a user, or group of users, may alter the ACL on an object.

The ACL is a concept with several different implementations in various operating systems, although there is a POSIX "standard". (The POSIX security drafts, .1e and .2c, were withdrawn when it became clear their scope was too wide and the work would not complete, but the well-developed parts defining ACLs have been widely implemented and are known as "POSIX ACLs".)

Networking ACLs

In networking, ACL refers to a list of rules detailing service ports or (network) daemon names that are available on a host or other layer 3 device, each with a list of hosts and/or networks permitted to use the service. Both individual servers as well as routers can have network ACLs. Access control lists can generally be configured to control both inbound and outbound traffic, and in this context they are similar to firewalls.

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

Broadcast Address

2008-10-17T13:36:00.001+07:00

In computer networking, a broadcast address is an IP address that allows information to be sent to all machines on a given subnet rather than a specific machine. The exact notation can vary by operating system, but the standard is laid out in RFC 919.

Generally, the broadcast address is found by taking the bit complement of the subnet mask and then OR-ing it bitwise with the IP address.

Example: to broadcast a packet to an entire class B subnet using a private IP address space, the broadcast address would be 172.16.255.255.

This can be found from the subnet mask (255.255.0.0) and the IP address (eg. 172.16.48.196) - the complement of the subnet mask is 0.0.255.255, and 172.16.48.196 | 0.0.255.255 = 172.16.255.255.

A special type of IP address is the limited broadcast address 255.255.255.255. A broadcast involves delivering a message from one sender to many recipients. This broadcast is 'limited' in that it does not reach every node on the Internet, only nodes on the LAN.

IPX

The Novell IPX protocol allows broadcast as well. When the network address is specified as FFFFFFFF, the packet is to be sent to all the networks available. When the target node address is specified as FFFFFFFFFFFF, the packet is intended to be received by all the computers in the network.

Ethernet layer

Broadcast is possible also on the underlying data link layer. Ethernet frames can be addressed to every computer on a given LAN segment if they are addressed to MAC address FF:FF:FF:FF:FF:FF. Ethernet frames that contain IP broadcast packages are usually sent to this address. ARP typically uses segment-wide broadcast for its queries.

IP address spoofing

2008-10-17T13:21:00.002+07:00

iIn computer networking, the term IP (Internet Protocol) address spoofing refers to the creation of IP packets with a forged (spoofed) source IP address with the purpose of concealing the identity of the sender or impersonating another computing system.

How spoofing works

The basic protocol for sending data over the Internet and many other computer networks is the Internet Protocol ("IP"). The header of each IP packet contains, among other things, the numerical source and destination address of the packet. The source address is normally the address that the packet was sent from. By forging the header so it contains a different address, an attacker can make it appear that the packet was sent by a different machine. The machine that receives spoofed packets will send response back to the forged source address, which means that this technique is mainly used when the attacker does not care about response or the attacker has some way of guessing the response.

In certain cases, it might be possible for the attacker to see or redirect the response to his own machine. The most usual case is when the attacker is spoofing an address on the same LAN or WAN.

Uses of spoofing

IP spoofing is most frequently used in denial-of-service attacks. In such attacks, the goal is to flood the victim with overwhelming amounts of traffic, and the attacker does not care about receiving responses to his attack packets. Packets with spoofed addresses are thus suitable for such attacks. They have additional advantages for this purpose - they are more difficult to filter since each spoofed packet appears to come from a different address, and they hide the true source of the attack. Denial of service attacks that use spoofing typically randomly choose addresses from the entire IP address space, though more sophisticated spoofing mechanisms might avoid unroutable addresses or unused portions of the IP address space. The proliferation of large botnets makes spoofing less important in denial of service attacks, but attackers typically have spoofing available as a tool, if they want to use it, so defenses against denial-of-service attacks that rely on the validity of the source IP address in attack packets might have trouble with spoofed packets. Backscatter, a technique used to observe denial-of-service attack activity in the Internet, relies on attackers' use of IP spoofing for its effectiveness.

IP spoofing can also be a method of attack used by network intruders to defeat network security measures, such as authentication based on IP addresses. This method of attack on a remote system can be extremely difficult, as it involves modifying thousands of packets at a time. This type of attack is most effective where trust relationships exist between machines. For example, it is common on some corporate networks to have internal systems trust each other, so that a user can log in without a username or password provided he is connecting from another machine on the internal network (and so must already be logged in). By spoofing a connection from a trusted machine, an attacker may be able to access the target machine without authenticating.

Services vulnerable to IP spoofing

Configuration and services that are vulnerable to IP spoofing :

* RPC (Remote Procedure Call services)
* Any service that uses IP address authentication
* The X Window system
* The R services suite (rlogin, rsh, etc.)

Defense against spoofing

Packet filtering is one defense against IP spoofing attacks. The gateway to a network usually performs ingress filtering, which is blocking of packets from outside the network with a source address inside the network. This prevents an outside attacker spoofing the address of an internal machine. Ideally the gateway would also perform egress filtering on outgoing packets, which is blocking of packets from inside the network with a source address that is not inside. This prevents an attacker within the network performing filtering from launching IP spoofing attacks against external machines.

It is also recommended to design network protocols and services so that they do not rely on the IP source address for authentication.

Upper layers

Some upper layer protocols provide their own defense against IP spoofing. For example, Transmission Control Protocol (TCP) uses sequence numbers negotiated with the remote machine to ensure that arriving packets are part of an established connection. Since the attacker normally can't see any reply packets, he has to guess the sequence number in order to hijack the connection. The poor implementation in many older operating systems and network devices, however, means that TCP sequence numbers can be predicted.

Other definitions

The term spoofing is also sometimes used to refer to header forgery, the insertion of false or misleading information in e-mail or netnews headers. Falsified headers are used to mislead the recipient, or network applications, as to the origin of a message. This is a common technique of spammers and sporgers, who wish to conceal the origin of their messages to avoid being tracked down. Less fraudulently, some netnews users place obviously false email addresses in their headers to avoid spam or other unwanted responses.