Here are some helpful and commonly used terms to help you familiarize yourself when projecting your backdrops.
Strictly defined a lumen is the amount of light that falls on an area of one square foot from one candle that is one foot away. When it comes to projection, however, “lumens” is a measure of how much lighting a projector puts out. The the higher the lumens the brighter the projected image will be.
Throw is the distance between a projector lens and its screen. It is the distance the image is thrown onto the screen, and it has a large effect on screen size. Some theater installations may often have an incorrect throw distance in the room but this can be corrected by use of a short throw lens. There are also “long throw” lenses available.
A related measurement, throw ratio, is the ratio of the distance from the lens to the screen (throw) to the screen width. A larger throw ratio corresponds to a more tightly focused optical system.
Throw Ratio = D / W
Is when you are projecting the image from the same side it it is viewed.
Short Throw Projection
Allow users to create big pictures in tight spaces, without concerns about shadows obstructing the image or light shining in the presenter’s face. These projectors have very short throw ratios, the distance from projector to screen compared to the screen size.