MF projection and screen distance

[doug_foster]

Some time ago, a contributor to this forum noted a formula for how far

back to set a MF projector (6x6) to fill up a square screen. The lens

and the screen size, of course, are factored into the equation. I've

searched the archives and so far unable to locate the information.

I'd appreciate this information being sent in again. Many thanks in

advance.

[gerald_di_giampaolo]

Hello Doug. I posted the following in May, 2000. I hope it's what you remembered and is helpful to you.

 

A=BxC

 

where A=Projection Distance B=Full Height of Screen C=Lens Constant

 

Example: for a 150mm lens, C=2.9

 

If using a 48 inch high screen, the projection distance required to fill the screen with a 150mm lens is 11.6 feet.

 

For a 75mm lens, C=1.4 and projection distance=5.6 feet

 

For a 250mm lens, C=4.8 and projection distance=19 feet.

 

Jerry DiGiampaolo

[Rob F.]

Here's another way to do it, that doesn't depend on having to look up a constant. First, divide the screen width by the slide image width. Use the same units for both. For MF, the film width will be about 2.125 inches. Now as an example, we'll say we want a screen 72" wide. divide 72/2.125, which equals approximately 33.9. Next, add a one, so now we have 34.9, or for convenience, call it 35. That's the distance from the film plane to the screen, measured in focal lengths. Now let's figure that distance in inches. So let's say we have 150mm a (six inch) lens. the projection distance is then 35 x 6 = 210 inches (17 feet, 6 inches).

If working in metric, just be sure to use millimeters throughout, or centimenters.

 

Simple? (Hope it helps)

[werner boeckelen]

I'd suggest, that you use that freeware Screencalculator:

http://www.baessgen.de/binfiles/screen.zip

Hope you're fine with "Meters".

 

Werner