Throw to Screen Size Ratio

From Lumenlab

Basically two things control the throw (for any given screen size). The LCD size and the triplet FL. The smaller the focal length of the triplet, the smaller the throw for a given size screen, and the smaller the LCD, the longer the throw for a given screen size. For an example: 17" screen, 500mmFL triplet, and 120" screen gives a throw of 158"... if you change the triplet to the 320mm, the throw becomes 101" (158-101 = 57" shorter throw). If you now change the LCD size to 15" (using the 320mm triplet) the throw becomes 113" (113-101 = 12" longer) for the same 120" screen.

The Focal Calculator II can be down-loaded from here.