Using a fisheye for wide-angle coverage on a DSLR
Updated Mar 19, 2009
Most digital SLRs (DSLR) have an image sensor that is smaller than a 35mm negative. As a result the field of view of the captured image is smaller when compared with the same lens on a 35mm SLR. This discrepancy in lens coverage is commonly referred to as a "cropping factor" in DSLRs and becomes a hinderance when searching for an affordable lens to give a wide field of view. One way to obtain wide-angle coverage on a budget is to use a fisheye lens.
In some cases it's desirable to have a wide field of view without any noticeable distortion - this is where software correction is helpful. Luckily there is a free software solution, PanoTools that can take care of this problem (and many others). PanoTools is extremely powerful. Unfortunately it is fairly cryptic to use. The simplest configuration and the one covered in this writeup is to use the program as a PhotoShop plug-in (This of course requires Adobe PhotoShop).
Note: The values below assume a 16mm fisheye lens on a 1.6x crop factor DSLR.