What kinds of digital SLRs are available?

What kinds of digital SLRs are available?

There are three kinds of digital SLR systems being made as of September 2005:

1. big lenses, big sensor
2. big lenses, small sensor
3. small lenses, small sensor

We will discuss each in turn.

Big lenses, big sensor. Canon and Kodak have taken the most obvious approach to the challenge of transitioning from film to digital: build a digital sensor exactly the same size as one frame of 35mm film. The result is a chunk of silicon 24x36mm in size, which is vast compared to the sensor in a point-and-shoot digicam. The benefit of this vast sensor is reduced noise, which looks like grain, in low light/high-ISO situations. The drawback of a vast sensor is that manufacturing a flawless piece of silicon this big is very expensive. The only consumer-priced camera in this category is the 13-megapixel Canon EOS-5D ($2950; check amazon.com for the latest price). If you have a strong back and an unlimited budget, the 16-megapixel Canon EOS-1Ds Mark II ($7000; available at amazon), is a great choice. It is probably the best digital camera made and produces image quality that rivals medium format film (e.g., 6x6cm Hasselblad). The only other full-frame digital SLRs made were the discontinued Kodak DCS Pro SLR/n and SLR/c bodies. The Kodaks were cheaper than the Canon but not quite as functional and the fact that they were discontinued is a good illustration of why you want to buy a digital SLR from a market leader. I own a 5D and have written a full review of the Canon EOS 5D.

Big lenses, small sensor. In order to keep the cost of the body within a range of $700-1500 and allow photographers to use their old 35mm system lenses most digital SLRs fall into this category. The front of the body has the same lens mount as an old film SLR. The back of the body has a sensor that is smaller than the 24x36mm standard frame of an old film SLR. The result is a camera that looks the same as the old film camera but multiplies the magnification of all the lenses. Having a smaller sensor is like cutting the center out of a drugstore proof print. You don't capture all the information on the left and right and top and bottom of the frame. It is as though you took the picture with a telephoto lens. The viewfinder has been adjusted so that what you see optically is what is captured in the digital file. If you're coming from the film world you will need to do a mental adjustment. A 50mm normal perspective lens on a big lens/small sensor camera behaves like an 80mm telephoto lens on a film camera. A 20mm ultra wide-angle lens behaves like a 30-32mm slightly wide angle lens on a film camera. Nearly all the popular digital SLRs fall into this category and their various merits will be discussed below.

Small lenses, small sensor. The biggest problem with the "big lens, small sensor" situation is that photographers are forced to cart around lenses that are much larger, heavier, and, theoretically, more expensive, than they need to be. A big heavy Canon telephoto lens is big and heavy mostly because it is built to cast an image circle large enough to cover a 24x36mm frame but the Canon EOS 30D body's sensor is only 15x22mm in size. Any engineer would look at this "big lens, small sensor" situation and say "Why not come up with a standard reasonable sensor size and then make lenses that are just large enough to cover that sensor with an image?" That's precisely what the Four Thirds consortium did. Olympus and Kodak seem to be the originators of the standard but Fuji, Panasonic, Sanyo, and Sigma have signed on as well according to www.four-thirds.org. This seemed like a great idea at the time (2002) but four years later only three Four Thirds system bodies have been built, all by Olympus, and only a handful of lenses, all from Olympus and Sigma.

If you have a a robust checking account and/or a lot of Canon EOS film camera lenses an unlimited budget the "full-frame" Canon EOS-5D (big lenses/big sensor; medium weight; $2900) is the obvious choice. If you don't need state-of-the-art performance and value compactness above all, the Olympus E System is a reasonable choice (see my review of the Olympus E1 for more detail; the current best buy is a complete starter kit with the E-500 for $790 from amazon). More than 90 percent of photographers, however, will find that the engineering compromise of "big lenses/small sensor" fits their budget and needs. This has led to the introduction of lenses that have the big lens mount for a 35mm film camera but optically cover only the small sensor of a mid-range digital SLR. These are sold as "digital-only lenses" or "digital camera lenses" but in fact they won't work on a full-frame digital SLR--the corners of the image would be black. Canon denotes these lenses as "EF-S", Nikon as "DX".