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Tuesday, July 23, 2013

Top DSLRs For Wildlife

To capture the decisive moment in animal activity and behavior, choose a camera with the AF performance, speed and image quality that are up to the task

Labels: CamerasD-SLRsGear
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Frames Per Second
Birds-in-flight photographers like to shoot at high frame rates to capture exactly the right wing position. Today's highest-rated DSLRs for frames per second (fps) are Canon's EOS-1D X (12 fps at full resolution with AF for each frame) and Nikon's D4 (10 fps at full resolution with AF for each frame). One reason why these cameras have "only" 18 and 16 megapixels is to obtain these frame rates—affordable technology doesn't currently exist to process 36-megapixel images at 10 per second. There are also limits on how quickly a DSLR can raise and lower the mirror.

Mid-range and entry-level full-frame DSLRs are slower: 4-6 fps. In APS-C, Sony's SLT-A77, with a fixed mirror, can do 12 fps with continuous AF—but it has an electronic viewfinder that isn't ideal for birds in flight, but fine for a lot of other wildlife photography (see the "EVF DSLRs For Wildlife" sidebar). Canon's 18-megapixel EOS 7D can do 8 fps, Nikon's 12.3-megapixel D300S and the 16.2-megapixel Pentax K-5 series, 7 fps. Nikon's 24.1-megapixel D7100 can do 7 fps in 15.3-megapixel 1.3X DX crop mode, in which a 300mm lens frames like a 600mm on a full-frame camera.

Besides fps, you also should consider buffer capacity. When you shoot a series of images, the camera stores them in its buffer as it writes them to the memory card. When the buffer fills, either the camera stops shooting until buffer space becomes available or the shooting rate decreases drastically. The higher-end cameras have bigger buffers, allowing you to shoot more frames before filling them. The lower-end cameras have much smaller buffers—in some cases, a few RAW files will fill the buffer. With these, you'll either have to settle for brief bursts or shoot JPEGs. The Nikon D4's buffer can hold 92 12-bit lossless compressed RAW files or 170 Large Fine JPEGs, while the D800's can hold 21 of the former or 56 of the latter, and the D7100's buffer, just 7 12-bit losslessly compressed RAW files or 73 Large Fine JPEGs—another reason why Nikon pro action shooters go with the D4. Bear in mind that the lower-end DSLRs aren't likely to be able to maintain focus on a flying bird for more than a few frames, so longer bursts aren't really needed.

High-ISO Image Quality
Digital cameras deliver their best image quality at lower ISO settings because lower ISO settings call for more exposure (i.e., a longer shutter speed and/or wider aperture), which means more photons hit the sensor. Photon noise (which accounts for much of the noise in normal photos) increases as the square root of the photon count. In simple terms, if 4 photons hit the sensor, you get 2 photons of noise, a 2:1 signal-to-noise ratio. If 100 photons hit the sensor, you get 10 photons of noise, for a 10:1 S/N ratio. If 10,000 photons hit the sensor, you get 100 photons of noise, for a 100:1 photonic S/N ratio. This largely is why higher ISOs are "noisier" than lower ISOs with DSLRs. When you set a higher ISO, the meter calls for a faster shutter speed and/or a smaller aperture, which means less light reaches the sensor and thus the S/N ratio goes down.

More light is better, and bigger sensors can collect more because there's more area there to do it. More light means less noise. There are other sources of image noise, but this is the main reason why full-frame sensors can deliver better image quality than smaller ones, especially at higher ISO settings.

Pixel size also comes into consideration. Higher pixel counts provide the ability to crop into images more and can deliver finer details in fur and feathers, assuming the image is sharply focused and not blurred by camera shake or subject motion—or details lost to noise. But the more pixels you have on a given-size sensor, the smaller they will be. And smaller pixels are less effective at collecting light than larger ones. So, the best high-ISO performance for a given generation of technology is found in full-frame sensors with big pixels (i.e., lower megapixel counts). The all-time (so far) high-ISO champ on DxOMark.com's sensor ratings is the discontinued 12.3-megapixel, full-frame Nikon D3S, with a score of 3253. (The score is the highest ISO setting that meets specified signal-to-noise ratio, dynamic-range and color bit-depth criteria.) But the 36.3-megapixel, full-frame D800 (with much smaller pixels) isn't far behind, with a score of 2853 (the 16.2-megapixel, full-frame D4 scored 2965). And when all of DxOMark.com's image-quality criteria are considered, the D800E and D800 are the two highest-scoring cameras overall. So pixel size matters less than sensor size; the highest-scoring APS-C sensor is the 24-megapixel unit in the Nikon D5200, at ISO 1284—23rd place overall. (You can find good data on dynamic range, color and noise for many DSLRs and other cameras at DxOMark.com.)


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