(slide size ÷ image size) = (slide distance ÷ image distance)
(1 ÷ focal length) = (1 ÷ image distance) + (1 ÷ slide distance)
slide size = (image size × focal length) ÷ (image distance - focal length)
image size = slide size × (( image distance ÷ focal length) - 1 )
image distance = focal length × (( image size ÷ slide size) + 1 )
focal length = ( slide size × image distance ) ÷ ( image size + slide size )
Refer to ANSI/ISO 11314 - "PHOTOGRAPHY-PROJECTORS-IMAGE SIZE/PROJECTION DISTANCE CALCULATIONS" for more infomation.
We also created MathML version of these formulae.
JTK Dev Home > Projection Calc > Proj. Calc Math