Image size calculation
I want to shoot a portrait in which the face fills the frame. I want to use a telephoto lens to get some foreshortening effect. I used the following calculation to see if a lens would give me what I want. The lens is a 250mm which can focus to 9 feet. Is this correct?
F = lens focal length = 250mm = 9.84 inches
G = object size = 12 inches (size of a human head, more or less)
A = distance from lens to object = 108 inches (9 feet)
I = FG/A
I = 9.84 * 12 / 108
i = 1.09 inches
So the resulting image will be 1 inch high, which would fill a 35mm frame but not a 120 frame.
Right? Not right?
co-owner of Photobooth, San Francisco
a Portrait Studio, Camera Shop and Gallery specializing in Tintype, Polaroid, and alternative processes.