Throw Ratios and Viewing Distances
A projector's throw ratio is defined as the distance (D), measured from lens to screen, that a projector is placed from the screen, divided by the width (W) of the image that it will project (D/W).
The ratio, like any ratio, is dimensionless. For example, if D equals 10 feet and W equals 5 feet, then 10 feet divided by 5 feet equals 2. The dimension of "feet" is thereby cancelled out.
So, in knowing this formula, a projector's throw ratio will provide you with all of the information you'll need to set up a room. The following examples will better explain how this works.
Example 1: You know what screen size you want, but need to know how far back the projector will need to be placed.
If the screen width is 7 feet and the projector's throw ratio is 2.0 - 2.4:1 (because projectors have zoom lenses, they also have a range of throw ratios) then you can place your projector anywhere from 14 to 16.8 feet away from the screen. (7 * 2 and 7 * 2.4 = 14-16.8)
Example 2: Maybe you don't know which screen size want, but you do know that the space available in your room for projector placement is limited.
The projector should be placed 15 feet away from the screen. So, how big of a screen can you use? If your projector has a throw ratio of 1.8 - 2.22:1, your screen can be between 6.76 and 8.33 feet wide. (15 / 2.22 and 15 / 1.8 = 6.76 and 8.33)
Viewing distance (V) is defined as the distance between your audience and the screen. A viewing ratio is V/W or the viewing distance divided by the width (W) of the screen.
Micro display technologies are all fixed resolution devices, hence the images are actually made up of tiny individual elements called "pixels". If you stand of sit too close to the projected image, you will actually see the individual elements, effectively destroying the illusion of a seamless image.
The distance from the image that you need to be, in order to view a seamless image, varies for each technology; it even varies with the resolution of the projector you are watching. Simply put, the higher your projector's resolution is, the closer you can sit to the image.
We suggest the following
- If you have an LCD projector with 600 or less vertical lines of resolution (800 x 600 or 854 x 480), a viewing ratio range of 2-3:1 (V/W) is optimal. If you sit closer that two (2) times the width of your screen, you will start to see the individual picture elements, or a grid pattern known as the "screen door effect," which gets its name by its resemblance to a screen door having been placed over the image. Conversely, if you sit farther away than three (3) times the width of the screen, the "home theater" effect will be lost.
- If you have an LCD projector with more than 600 vertical lines of resolution, we suggest a viewing ratio between 1.8 - 3:1
- If you have a DLP™ projector with 600 or less vertical lines of resolution, we suggest using a viewing ratio between 1.8 - 3:1
- If you have a DLP™ projector that has a resolution of 1024 x 575 or 1024 x 768, but use it only in 16:9 mode, we suggest using a viewing ratio between 1.6 - 3:1
- If you have a DLP™ projector that has a resolution of 1280 x 720, we suggest using a viewing ratio of between 1.4 - 3:1
- If you have an LCoS projector, your resolution is going to be above 720 lines, guaranteed. We suggest using a viewing ratio between 1.4 - 3:1
We will tie together throw ratios and viewing distances in our section Setting up a Room for Front Projection.