If the
screen is 20'x20', then that probably means a 15'x20'
image, which is about right for general
PowerPoint presentations with the furthest viewer 100' away.
The
projector brightness required is the combination of several factors. One of the primary considerations is how much ambient light is on the
screen during use. Light on the
screen other than from the
projector tends to reduce the contrast ratio and
wash out the
image. This then requires greater output fron te
projector to compensate, so reducing any other light on the
screen can reduce the
image brightness and
projector output required. Another factor is the characteristics of the
screen material, so knowing the actual
screen material would help. If it is a flexible rear
screen combined with the short
throw distance noted, it is probably a fairly low
gain, maybe 07 to 1.0. Without knowing many of the details it is difficult to make an accurate recommendation, but 15'x20' is a big
image and for that size
screen a 5,000
lumen projector might be a typical general minimum with 10,000 lumens or more being a typical recommended solution.
Most projectors in that performance range have multiple
lens options that allow for flexibility in the
projector location. This is one example of how rental/staging and install projectors differ from the typical desktop projectors. However, some of the lenses are not inexpensive while others place severe restrictions on
projector location. If the
screen is 23' from the upstage wall and you have a 15'x20' rear projected
image, that suggests that a fixed, very short
throw, rear projection style
lens is required and even that may be tight. A couple of issues common with these types of lenses is that they are fixed
focal length so they have a fixed
throw distance, they typically reduce the
projector output compared to a standard
lens, and they require the
projector to be on the horizontal and vertical centerline of the
image with no
image shift capability.
A
projector and
lens for this application will be a significant investment. It would probably help to verify some of the details if you can such as the typical light levels on the
screen from other sources, the sscreen material and the projected
image size. It may also justify a few demos or even rentals to see how some different options work.
Manufacturers for projectors typically used in these types of applications include
Barco, Christie Digital, Digital Projection, Panasonic, Sanyo and Sony.
Not to make this more complex, but depending upon what your situation, this may also be a good time to assess going to 16:9 widescreen. It may not be justified in your case, but I have clients for whom WXGA laptops and computers are becoming the prevalent source and they are moving towards screens and projectors to support that format.