D = f*H/h
where
D = distance from lens to object
(d = distance from lens to 35mm film)
f = focal length
H = height of object
h = height of object's image on 35mm film
I've seen some form of this equation in several places including these two threads:
How do I calculate the distance of an object in a photo?
Is the formula for object image size given focal length, etc. independent of sensor size?
The problem I'm having is with f. From the magnification for a thin lens:
M = D/d = H/h = f/(f-D)
I can't figure out how to arrive at
D = f*H/h
Any help? Thanks.