This question already has an answer here:
i am sure there is a simple answer, but i have seem to have forgen it. How do you calculate the relative apparent size of the subject
i have seen a formula with the field of view and tangent, but i am looking at a simple way to estimate on the fly what lens to use to make the subject 3X larger or smaller than where it is at, with a 50mm for instance.
i seem to remember halfing and doubling focal lenght, but that doesn't seem to work, 400mm is a lot more magnified than X3 (50 to 100 to 200 to 400mm)
Since "super zooms" like 24-240mm are 10X optical zooms, is it based on the starting 24mm lenght, which gives 10 increments, the relative X2 magnification would be 24-48-72-96-120-144-168-192-216-240mm
but that logic seems to break with other applications...
i though of angle of view, but 10° increments of fov, gives only 7 steps from 24 to 240mm (84-74-64-54-44-34-24-14° but 14° diagonal angle of view is 130mm and the next logical step 4° is 500mm
any simple way to estimates?