Question

A projector lens projects an image from a 6.35 cm wide LCD screen onto a screen 3.25 m wide. If the focal length of the projector lens is 13.8 cm, how far is the screen from the projector?

Answer 1

For any given projector, the width of the image (W) relative to the throw distance (D) is know as the throw ratio D/W or distance over width. So for example, the most common projector throw ratio is 2.0. This means that for each foot of image width, the projector needs to be 2 feet away or D/W = 2/1 = 2.0.