Rear Projection or high angles from the front?
In any case, pay special attention to the ambient and stray light hitting the
screen. The more light hitting the
screen, the more
power is going to be necessary to light it.
By the way, Backstage Handbook has a very useful chart on figuring out
projector sizing and ranges.
That in addition to this: (but I'm not sure where I got it from so that's a bad thing. Probably either Architectural Graphics Standards or Architect's Handbook of Formulas, Tables & Mathematical Calculations.)
Lenses and Focal points:
Screen Projection
The relationship between the positions of
the light source or the object (slide) and the
point where the transmitted rays from an
image is determined by the “
Lens Formula”,
When P= the distance from the object to the principal plane of the
lens,
Q= the distance from the principal plane to the
image, and
F= the
focal length of the
lens; than 1/P + 1/Q = 1/F.
The maximum distance between the first row of the audience and the
screen is determined by the maximum allowable angle between the sight
line from the first row to the top of the
screen and the perpendicular to the
screen at that
point. 30 to 35° is recommended.
The maximum distance between the
screen and the most distant viewer should not exceed eight times the height of the
screen image. A most distant viewer two to three times the
screen width is preferred.
Screen width is determined by the use of the appropriate
aspect ratio between the
screen image height and width.
Curvature of screens may reduce the amount of apparent
distortion for a larger audience area. Curvature of a larger screens may help to keep the whole of the
image in focus and may provide a more uniform distribution of
luminance.
Tilt all projection screens back half the angle of projection whenever the projection angle is over 15°.