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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.
It is 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 full
frame DSLR or 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, which means they don't have
a large enough image circle to cover a full frame digital sensor. These 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 smaller digital sensors 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 DSLRs 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 DSLR), 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 Rebels and the Canon 20D and
later models. 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
Updated June 29, 2012
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