LCD Projection Distance
Projection throw distance is the distance the projector must be from the screen in order to fill that screen. This is mainly a concern if rear screen projection is used, as it takes away from seating space in the meeting room. Most LCD projectors have a rear screen and a front screen setting. Whether or not you are using rear or front, projection distances are the same.
Lenses and throw distances for LCD projectors are given in ratios to screen width. For instance, a 1.5:1 (1.5 to 1 ratio) lens will need to be 1.5 times the screen width in order to fill the screen. So if you have a 10 ft. screen with a 1.5:1 ratio lens, the projector will need to be 15 feet from the screen. A lens ratio of 2:1 (2 to 1 ratio) will need 20 ft. to fill the same screen.
Large Format Projectors
Most large format LCD, DLP and Light Valve projectors have interchangable lenses, so you can specify certain lens ratios. The most common ratio for short projection distances are 1.2:1 and 1.5:1. There are also many longer throw lenses and zoom lenses available. Check with your AV equipment supplier to make sure they have the lens you need. Remember a smaller ratio lens of 1.5:1 is a shorter projection throw distance than a 3:1 ratio lens.
Small Format Projectors
Most small projectors do not have interchangeable lenses. Each manufacturer uses it's own standard zoom lens. Most common is a zoom lens that will go from a 1.9:1 ratio to a 2.5:1 ratio.
With smaller projectors, check on the lens ratio by each model, but for a rule of thumb, use 2:1 as the ratio for a quick calculation, then consult your equipment supplier.
Screen Ratios and Throw Distances
|1.5 to 1||2 to 1||2.5 to 1|
|8 ft screen||12 ft.||16 ft.||20 ft.|
|10 ft screen||15 ft.||20 ft.||25 ft.|
|12 ft screen||18 ft.||24 ft.||30 ft.|
|14 ft screen||21 ft.||28 ft.||35 ft.|
|16 ft screen||24 ft.||32 ft.||40 ft.|
|20 ft screen||30 ft.||40 ft.||50 ft.|