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How to buy the right size screen

Your goal in sizing a projection screen is to find a screen large enough so that those in the back of your audience can see your subject matter easily, but not so large that those in front have difficulty seeing the full width of the projected image.

This can be a tricky task, particularly if you’ll be showing computer text or side by side images. The basics of sizing a single-image screen follow, but please realize that you don’t need to do these calculations yourself. Your United Visual representative will be more than happy to help.

Start with your farthest audience member
In the days when film was the medium of choice, the rule of thumb for screen sizing was the "2 and 6 rule." You would measure the distance to the last row of seats and divide by six to find the screen’s width. Next you would multiply the resulting width by two to find the minimum distance to the first row of seats. Because of the various screen formats in use today, most experts recommend that you start, instead, with the screen’s height. To do so:

  1. Find the distance to the last row of seats and divide by eight. This will give you the ideal height of your screen.
  2. Use the aspect ratio of the media you’ll be using to find the screen’s width. For video, personal computer images and 16 mm. motion picture that’s 3:4. To keep these proportions you need simply to multiply your height by 1.33. For slides, the aspect ratio is 2:3, so you would multiply the height by 1.5. For HDTV, the aspect ratio is 9:16, so multiply height by 1.78. If you’re using more than one medium and your calculations indicate more than one screen width, buy the larger, but don’t feel obligated to fill it with the narrower-aspect medium. If you’ll be showing both horizontal and vertical slides, find the height needed to show a horizontal slide, then find the needed width, then buy a square screen where both the height and width equal the width you found.
  3. Once you have the screen width, simply multiply by two to find the minimum distance to the first row of seats.

Be ready to modify your results
Though this method is the most widely used for sizing a screen, note that there is room for compromise. If you can’t fit a screen that’s perfect for the most distant and the closest viewers, you need to decide who will suffer more if the screen you choose is larger or smaller than what’s calculated.

If small computer text is to be shown, some experts recommend a screen larger than the method above would indicate. Instead of using 1/8 the distance to the farthest viewer for the screen’s height, they suggest using 1/6 for computer data.

Putting these two guidelines together,
we calculated the following table:

screen diagonal screen height closest viewer farthest video farthest computer
72" 43" 9.5' 28.7' 21.5'
84" 50" 11.2' 33.3' 25.1'
100" 60" 13.3' 40.0' 30.0'
150" 87" 19.3' 58.0' 43.5'
300" 174" 38.7' 116.0' 87.0'

Planning seating
Once you’ve run these calculations, you’ll have the screen size plus the distance to your nearest and farthest seating. Next, you’ll want to take your screen’s viewing cone into consideration to determine how wide your rows of seating can be.

Once again, it’s important to realize that, despite the specifications stated by the screen manufacturer, you want to keep seating within a 60 viewing cone–that’s 30 to the left and right of the screen’s center axis. If you need to go wider, a 90 cone should be your absolute maximum. Beyond that angle, the image will look distorted and text will be difficult to read.

Holding to either of these viewing cones will typically limit the width of your first few rows of seats. There’s a rule of thumb to help you plan seating: no row of seating should be any wider than its distance from the screen.

Height off the floor
One mistake you don’t want to make is placing the screen too low. You need to position your screen high enough that the backs of people’s heads don’t block the view of those behind them. How high the bottom of your screen must be depends on whether the floor is level or sloped and whether seats are directly behind each other or offset. But, since the average seated adult is about 48" tall, you’ll want the bottom edge of your screen at least 48" from the floor (although you can go as low as 36").

Positioning a projector
You may also want to figure out where your projector must be positioned, or what kind of lens you’ll need if you wish to position your projector at a particular point in the room.

A simple formula will provide the answer, and we’ve included the calculations for slide and overhead projectors in their "how to choose" sections of this catalog. There’s a problem using this formula with LCD and CRT projectors, however: the numbers going into the formula will vary with every manufacturer and model. This is an area where you’ll definitely need to get United Visual involved.

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