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
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
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.
Viewing Distance
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.
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