Monday, June 25, 2007
D-SLRs: Entry-Level, Midrange, Pro
What’s the difference?
D-SLRs have much larger image sensors than today's typical compact digital cameras. Larger sensors gather light more effectively, resulting in better image quality, especially at higher ISO settings. But all else isn't equal: D-SLRs generally have better image-processing engines and A/D converters, too. Some compact models feature larger-than-usual sensors and improved high-ISO quality, but if image quality is a primary concern, D-SLRs provide more of it than any compact digital camera.
D-SLRs use one of four basic sensor sizes. Most use the "APS-C" size, so-called because it's around the size of an Advanced Photo System C-format image. Four Thirds System D-SLRs (those from Leica, Olympus and Panasonic) use an even smaller sensor, although still much larger than the typical compact digital camera sensor. Canon's EOS-1D Mark III (like its predecessors) uses an "APS-H" sensor, slightly larger than the APS-C. And Canon's EOS-1Ds Mark II and EOS 5D use "full-frame" sensors, which are the same size as a full 35mm film frame.
Just how "wide" a given lens is depends on the size of the imaging element, be it a film frame or a digital sensor. Smaller sensors see less of the image formed by the lens, thus narrowing the angle of view. As a result, on D-SLRs with smaller-than-full-frame sensors, a given lens will "see" a smaller area of the scene, producing a telephoto effect. Used on an APS-C D-SLR, a 100mm lens will frame like a 150mm lens on a 35mm SLR (1.5x crop factor). Used on an APS-H D-SLR, a 100mm lens will frame like a 130mm lens on a 35mm SLR (1.3x crop factor). Used on a Four Thirds System D-SLR, a 100mm lens will frame like a 200mm lens on a 35mm SLR (2x crop factor). On a full-frame D-SLR, of course, a 100mm lens will frame just as it does on a 35mm SLR-this being the primary advantage of the full-frame sensor for several years. All D-SLR manufacturers now offer very short focal-length lenses for their smaller-sensor cameras, though, so all D-SLR users can do true wide-angle photography.
Not surprisingly, larger image sensors are more expensive, and thus found on the more costly cameras. The entry-level and midrange D-SLRs use APS-C and Four Thirds System sensors.
Most D-SLRs come with rechargeable batteries good for 500-2,000 shots between charges. Few compact digital cameras can match that, due in part to their always-on live-view LCD monitors, and in part to less-robust rechargeable batteries.
On the other hand, most compacts can be run on readily available AA batteries, while few D-SLRs can. A few entry-level D-SLRs do run on AA batteries; I've taken more than 1,600 shots on one with a set of lithium AAs.
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