All of this is good news for wildlife photographers or any one else using long lenses since all of their telephoto lenses "act" like they are longer due
to the field of view crop. It is like having an instant teleconverter but without any loss of image quality or loss of light. And you don't have to spend megabucks for a bigger, longer, and heavier lens.
bad news for photographers when they use wide angle lenses because the field of view crop throws away much of the image. A 28mm wide angle lens on a digital SLR with a 1.6X FOV crop has the same field of view as a 45mm
lens on a 35mm film camera. The wide angle lens now acts like a normal lens. Manufacturers are coming out with a variety of wider angle lenses for use on digital cameras. Some of these are "digital only" lenses.
Digital lenses are being produced for digital cameras with a field of view crop. As you can see from Illustration A, the image circle doesn't have to be nearly as big to cover the digital sensor so these digital lenses
can be much smaller in size. "Digital only" lenses are optical lenses like any other lens, they just have a smaller image circle.
There are two reasons "digital only" lenses won't work on film SLRs. One is that the
image circle won't cover the 35mm film format. The second is you could damage the lens and/or the camera.
The newer digital SLRs have a smaller mirror so some of the new digital lenses protrude farther into the mirror
box. If you could mount some of these lenses on a film camera body (or even an older model digital SLR), you would risk damage from the larger mirror striking the back of the lens. To prevent this from happening, these
lenses are designed so they won't mount on the cameras they could damage. In some cases, there are do-it-yourself modifications to get some of the newer lenses to fit on some older digital cameras. The most
notable example is to saw off part of the rear mount of a Canon EF-S 10-22mm lens so it will fit on a Canon 10D body. You do this at your own risk.
Why would someone
do this? Because the digital only EF-S 10-22mm lens won't mount on a Canon 10D, it is only for the Canon Digital Rebel and the Canon 20D. Canon 10D owners want the truly wide angle of view that this lens provides (the
equivalent of 16-35mm in 35mm terms). Since the mirror barely clears the back of the lens, some 10D owners modify the lens to fit. As I said, you do this at your own risk.
If you have or will soon get a digital SLR with a FOV crop, enjoy the larger images from your telephotos lenses which have all grown longer. And save your money for one of the new
wider angle lenses so you can once again have a truly wide angle field of view.
April 10, 2005