I'd like to make a recessed lensboard but you've likely figured that out. What I'm wondering is how deep I can go without risk of vignetting.

The extreme case would be for a 90mm on a 5x7. I can't find anything on angle of view for 5x7s but assuming it's similar to 18mm on 35mm then I found 93degrees. Does that sound right?

The lensboard is 5" across but between everything I figure about 4" of recessed area.

From my high school math I get the following.

tan angle = opp/adj

angle is half the 93degrees so 46.5 degrees.

opp is the depth of the recessed board and for the moment unknown

adj is half the width. So 2"

That works out to 2" deep and no vignetting far more then my 1" need. OTOH it's only measuring from the middle of the lens. If I use 1" for the adj then I get just over 1".

Am I on the right track? Any obvious screw ups? I know the lens itself will be forward of the recessed 1" so I think I'll have a built in safety factor.

BTW I apologize to all the math teachers that told me I'd use this stuff some day.