Quote Originally Posted by David A. Goldfarb
. . . put a ruler in the scene at the subject position or estimate the width of the subject field and compare it to the width of the film, so if I'm shooting a macro scene that's about 4.5" wide with a 2-1/4" square (6x6cm) camera, then my magnification ratio is 1:2.
Isn't the width of the image on the film the significant value rather than the width of the film itself?[/i]