I've come across this old 35mm film camera that has a light meter in the body (but not through the lens). Since the meter is set for 50mm, I've had to do some guesswork with other focal lengths. I've found a formula of: New_F-Stop = Old_F-Stop x ((50mm ± Other_Lens_Length)/50mm) but this really limits what I can use. Does anybody know of software or a better formula? Thanks.