Combating Keystoning - Equation Derivation

Diagram explaining the abbreviations (8KB)

From:

2KB

we have

2KB

and

2KB

i.e. the throw distances for the top and bottom of the image are known. Given this information and the beam angle we can calculate the width of the image at top and bottom:

1KB

1KB

The ratio of the bottom width to the top width gives us the fractional increase in image size over its full height; subtracting this from 1 and multiplying by 100 gives the percentage change in the size of the top:

4KB