> One other thing to keep in mind is that lenses aren’t especially cheap, and in this case you’d rather have too wide of a lens rather than something too tight,

> One other thing to keep in mind is that lenses aren’t especially cheap, and in this case you’d rather have too wide of a lens rather than something too tight, so people might go for the 16mm instead of the 20mm. If that's the issue then you can shoot the image with the 16mm and then crop to get exactly the same image (other than resolution) as you would have shot with the 20mm lens. For example, here[0] I have an image shot with a Samyang 14mm rectilinear lens, distortion-corrected and exported to JPG with UFraw. I then loaded that image into Hugin, set the input crop factor to 1 (full frame), and re-exported with a 84x61.9 degree field of view based on some online FOV tables[2] for a 20mm lens in a full-frame camera. As you can see, the resulting image[1] is what you would expect from a 20mm rectilinear lens. Hugin can also translate from a fisheye lens to rectilinear if that is the type of lens you happened to have on hand. The trade-off is that you're losing some resolution, but you would usually be downscaling from the raw image anyway for the online listings. [0] https://imgur.com/d0SumPb https://imgur.com/d0SumPb [1] https://imgur.com/gbz6mys https://imgur.com/gbz6mys [2] https://www.nikonians.org/reviews/fov-tables https://www.nikonians.org/reviews/fov-tables