Is length in a photograph proportional to angular distance in the photographed scene?
Example: I take a picture with the horizon vertically centered. In the picture, I know that the point 1 inch above the center corresponds to 10 degrees above the horizon. Does that mean the point 2 inches above corresponds to 20 degrees above the horizon?
If not, what is the correct formula?
I'm primarily interested in the answer for 35 and 50mm photographic lenses, but a general formula (based on lens parameters) would be good too.
Astrophotography makes me think that angular distance in reality isn't proportional to linear distance in a photograph, but I wasn't sure.