Fisheye or not?
Can I use my regular X mm wide angle lens instead of an X mm fisheye?
I get this question quite often. People usually already have an 8 or 10mm wide-angle lens (on crop) or a 12 or 14mm wide-angle lens (on full frame) and, with all the talk about fisheye lenses, wonder if they can just use that to produce full 360×180° panoramas.
The answer is: Of course you can, but you will need to take more images to cover the entire sphere. With both fisheye lenses, you can get away with as little as 4 images to cover everything — with the non-fisheyes you need a bare minimum of 12, but more like 16 shots to have captured everything.
Without wanting to get technical, this has to do with the field of view that both lens types offer (due to the different projections): The fisheye typically shows you much more than the wide angle since, grossly simplified, the fisheye “squeezes” things the more you move away from the center, whereas the wide angle lens tends to “stretch” things. In terms of numbers, both fisheyes give you a 180° field of view around the diagonal. The wide angle lenses in turn only give you 110-120°…
Click on the image here to see a quick visual comparison between the different lenses / images they produce. Pay particular attention to what is included and what is not included in the extreme corners.
Lenses used for the comparison above: Peleng 8mm ƒ/3.5 fisheye and Sigma 10mm ƒ/2.8 fisheye on a 1.5x crop sensor, and a Sigma 12-24mm on full frame sensor (to simulate 8mm/10mm on crop).
PS: A good comparison of what the different fisheye lenses look like on the different sensors sizes, check this page.