# Projection Calculator Math

## Basic Formula

(slide size ÷ image size) = (slide distance ÷ image distance)

(1 ÷ focal length) = (1 ÷ image distance) + (1 ÷ slide distance)

## Derived Formula

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.

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