How to calculate screen size of a digital projector?
 

I read a lot of specs of Digital Projectors in the magazines.
Only thing they talk about is the lumens in most of them
like (5000, 6000 etc..)

For example,
The PT-D7600U and PT-D7500U are super-bright models (6000 and 5000 ANSI lumens respectively) that display vibrant colors and crisp images in 1280x1024 SXGA and 1024 X 768 XGA resolution, respectively. They offer a remarkable, theater-quality contrast ratio of up to 1000:1 and are stackable for double brightness (up to 12,000 ANSI lumens).

If I want to setup a digital projection for commercial use,
my question is, how do I calculate the optimal (biggest)
screen size (which looks good like film projection)

Thanks everybody.

Wow, those sound like rocking projectors, very bright and good contrast!! You should be able to display them in a fairly good size room and screen.

I don't think there is any formula for screen size to projection distance. Each projector is different because of lens differences (for one)

If you want the biggest size possible, you will need to spend a lot on a good, huge screen (limited by the wall size of course).

I bought a cheapie home projector a few months back and during my extensive research it seemed nearly every maker has a chart on a website that documents distance from screen relative to screen size. There is always a minimum distance because most projectors won't focus too close. If you already have a room in mind, you will be limited to its dimensions and to the size of the screen you intend to project on, so be careful not to pick a projector that exceeds the room size or screen size.
All that info should be available on the maker's site. If it isn't, write them.

Good luck.

In general, viewing distance should be between 1,5 to 8 times picture hight. The higher the picture quality is in terms of resolution, line/pixel structures.., the shorter the viewing distance can be for optimal "viewing experience". Good DVD footage on a "good" projector" can be viewed at 2 times PH. Never make your picture bigger than needed... Contrast ratio specs in non CRT projectors are often more important than huge lumens outputs, if the ambient light can be fully controlled (dimmed) and the viewing allows some eye sensitivity accomodation time. High end projectors (like you mention) are in general available with zoom lenses and or lenses for different throw distances.So projector positiion (throw distance) in general is not a lens determined issue. It does more relate to the (accepted) noise levels from the projector cooling fans. Walls,...should be not to reflective Mat dark gray is the best.. Some minimal diffuse light surrounding the screen helps to keep the eye focussed on the image(screen) plane and helps reduce the shortcommings of the non infinite contrast ratio (brightness induction)

Forgot to mention: best viewing height is at about 1/3 of the screen.