Screens
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 singleimage
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:
 Find the
distance to the last row of seats and divide by eight. This
will give you the ideal height of your screen.
 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 narroweraspect 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.
 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.
