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Tuesday, March 10, 2009

Full-Frame D-SLRs

Nature photographers now have six models from which to choose at widely varying prices. These cameras are about more than just a larger image sensor.

Labels: CamerasD-SLRs

This Article Features Photo Zoom

full frameAngle Of View
Because a full-frame sensor by definition is the same size as a full 35mm image frame, any lens used on a full-frame D-SLR will produce the same angle of view it does on a 35mm SLR. This is convenient for 35mm photographers who are transitioning to digital. It’s also handy for wide-angle aficionados. The smaller APS-C sensors used in most D-SLRs crop into the image so that any given lens frames like a lens about 1.5x longer on a 35mm SLR: Put a 28mm lens on an APS-C D-SLR, and it frames like a 42mm lens on a 35mm camera—no longer wide-angle.

Just a few years ago, this was a much bigger deal than it is today because you couldn’t do real wide-angle photography with the affordable (i.e., APS-C) D-SLRs. Now, the camera and lens manufacturers offer affordable very short focal-length wide-angle lenses designed specifically for the smaller sensors, so true wide-angle photography is readily available. But these very short focal-length lenses have a few drawbacks. For one, it’s harder to design and manufacture a distortion- and vignetting-free, really short focal-length lens, so the 18mm focal length needed to provide the view of a 28mm lens on a 35mm SLR with an APS-C D-SLR might not produce the same image quality. For another, shorter focal lengths have smaller aperture diameters for any given ƒ-stop, and smaller aperture diameters lead to diffraction, which reduces image quality. (That’s why the really short lenses used in compact consumer digital cameras rarely stop down beyond ƒ/8.)

Other Factors
With full-frame D-SLRs, you get more than just top image quality and easy wide-angle capability. Full-frame D-SLRs tend to be rugged cameras well suited to the rigors of outdoor photography. Four of the full-frame D-SLRs are all-out pro models designed for hard pro use, and the other two are more rugged than most midrange D-SLR models.

If you work in tough outdoor conditions, these are cameras you can count on. Full-frame sensors require more powerful processors, and those more powerful processors also mean quicker autofocusing and better metering performance. For example, while Nikon’s midlevel D300 offers the same AF and metering features as the D3X, D3 and D700, the full-frame models’ more powerful processors provide quicker AF performance and faster metering calculations. Canon’s EOS-1Ds Mark III employs 45 AF points vs. 9 for Canon’s midrange D-SLRs, plus 60-zone metering (vs. 35-zone), while its dual DIGIC III processors provide faster performance with these more elaborate systems. Likewise, Sony’s A900 employs dual Sony Bionz processors to speed operation vs. a single Bionz unit in the midlevel A700. Canon’s EOS 5D Mark II has the same AF system as its predecessor and essentially the same 35-zone metering system as Canon’s midrange models, but its DIGIC 4 processor improves performance. The Canon, Nikon and Sony midrange D-SLRs offer excellent performance, but the full-frame models are better.


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