Wednesday, October 1, 2008
Is Now The Time For Full-Frame D-SLRs?
With more options, state-of-the-art technology and lower prices, D-SLRs are worth a careful look for serious outdoor shooters
With sensors the same size as a full 35mm image frame, full-frame D-SLRs provide the same angle of view as a 35mm SLR with any given lens. This is a big advantage for wide-angle fans, as it doesn’t require special extremely short-focal-length lenses to do wide-angle photography. Because smaller sensors “see” less of the image produced by any lens, cameras employing them require shorter focal lengths to produce a given angle of view (see Figure A, p. 66).
A related full-frame-sensor benefit is less diffraction. When you stop a lens down to increase depth of field, diffraction starts to affect image quality adversely. The smaller the lens opening, the greater the diffraction, and the worse the image quality. Because they produce a given angle of view with a longer lens, full-frame sensors yield less diffraction at any given ƒ-stop: A 24mm lens stopped down to ƒ/22 has an aperture diameter of 24/22 or 1.09mm. The 16mm lens needed to produce the same angle of view with an APS-C sensor has an aperture diameter of just 0.72mm at ƒ/22 (16/22). Of course, the shorter lens produces more depth of field than the longer one, so you don’t have to stop down as much to get the same depth of field. But the super-short focal lengths also tend to produce more distortion and vignetting.
Wide-angle photography isn’t the only advantage of full-frame sensors. You also get better image quality because larger sensors have room for more and/or larger pixels. More pixels mean finer detail, and you can blow up the images bigger. Larger pixels gather light more efficiently than smaller pixels, yielding a wider dynamic range and less noise at any given ISO setting. There are technological tricks camera manufacturers use to maximize image quality even from small pixels on small sensors, but all other things being equal, bigger pixels and more pixels are better.
Full-frame D-SLRs do have a few drawbacks. For one thing, they cost a lot more. Full-frame sensors are much more difficult to produce than smaller sensors, and they use a lot more material (an eight-inch silicon wafer might yield 200 APS-C sensors, but only 20 full-frame ones).
Another drawback is that wildlife photographers don’t get the “free focal-length boost” provided by smaller-sensor cameras. A 300mm telephoto lens on a full-frame D-SLR frames just as it does on a 35mm film SLR. On an APS-C D-SLR, the same 300mm lens frames as a 450mm lens does on a 35mm SLR. On a Four Thirds System D-SLR, a 300mm lens frames as a 600mm lens on a 35mm SLR. A smaller, lighter lens takes you a lot further with a smaller-sensor camera.
A final drawback of the full-frame sensor is that it tends to collect more dust than a smaller sensor, an especially critical factor when you’re frequently changing lenses in the field. Canon’s EOS-1Ds Mark III and Nikon’s D700 counter this by incorporating sensor-dust-removal systems.
We should point out that 35mm “full-frame” sensors aren’t the largest image sensors used in D-SLRs. The “medium-format” D-SLRs (those based on medium-format film cameras rather than 35mm SLRs) use sensors that are much bigger than “full-frame,” generally with a lot more pixels. As we write this, Hasselblad just announced the H3D II/50 medium-format D-SLR with a 49.1x36.8mm 50-megapixel Kodak CCD sensor that’s twice the size of a full-frame 35mm sensor. But that camera costs nearly $40,000—the 35mm-based models are far and away the most popular and the most affordable D-SLRs.
Canon EOS-1Ds Mark III
The current “king” of the 35mm-form-factor D-SLRs, at 21.1 megapixels, Canon’s EOS-1Ds Mark III is a do-it-all camera that can handle everything from epic landscapes to quick wildlife action. Dual parallel-processing DIGIC III image processors optimize image quality and operating speed (the camera can shoot those huge files at up to five per second, in bursts of up to 56 Large/Fine JPEGs or 12 RAW images), and reduce energy consumption (the Mark III can make up to 1,800 shots with a freshly charged battery—very handy when out in the field).
As a landscape camera, the Mark III provides 45% more pixels than any other 35mm-form-factor D-SLR (and 65% more than any other full-frame D-SLR). Its 14-bit A/D conversion can recognize 16,384 tonal or color gradations (vs. 4,096 for 12-bit conversion) for smoother, more detailed images.
The three-inch LCD monitor provides Live-View capability, which makes it easier to shoot low- and high-angle images. You even can send (using provided software) the live image to a laptop monitor and run the camera from there.
You’d expect a 21.1-megapixel full-frame D-SLR to be a great landscape camera, but the EOS-1Ds Mark III is a fine wildlife camera, too, featuring virtually the same AF system as the EOS-1D Mark III action camera. It’s true that you lose the “telephoto” factor of a small-sensor D-SLR when you use a full-frame D-SLR, but with the Mark III’s 21.1-megapixel images, you can crop in on the central portion of the image, increasing the effective focal length, and still have lots of megapixels. Also, the Mark III’s central AF point functions down to ƒ/8, so you can add a teleconverter to get back the “lost” focal length. One of our editors captured some excellent in-flight shots of various birds using our Mark III test camera with a 300mm ƒ/4 lens and a 2x teleconverter, a combination that won’t autofocus at all on the more compact EOS 40D.
Of course, as an EOS-1-series camera, the Mark III features Canon’s most rugged construction, with a magnesium-alloy chassis, external covers and mirror box, excellent dust- and weatherproofing, and a 300,000-cycle shutter. The EOS Integrated Cleaning System (including a grounded low-pass filter over the image sensor that vibrates ultrasonically each time you switch the camera on or off) helps keep the big sensor dust-free.
The Mark III can use all EF Canon lenses, but not EF-S lenses (which were designed specifically for the smaller-sensor cameras). This provides focal lengths from 14mm super-wide-angle and 15mm full-frame fish-eye to 800mm super-telephoto, including zooms from 16-35mm to 100-400mm, true 1:1 macro lenses and three manual-focus tilt-shift lenses.
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