Film-Tech Forum ARCHIVE: Maximum Throw

This is topic Maximum Throw in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Barry Floyd (Member # 385) on 08-24-2000, 09:38 AM:

In preparation of preliminary plans for our upcoming drive-in, we are moving to the next phase of design and are trying to determine the best use of our lot, and trying to determine the maximum suggested throw for a 4kw lamphouse.

Any "rules of thumb" or design criteria available anywhere?

Posted by Brad Miller (Member # 2) on 08-24-2000, 10:06 AM:

What make/model of lamphouse? I am assuming this is with a new reflector as well?

There's a big difference in light output between a something along the lines of a Strong Ultra80 as opposed to something like an ORC or CFS.

Posted by Barry Floyd (Member # 385) on 08-24-2000, 10:14 AM:

I've got a 4kw ORC, but will more than likely replace it with a Xenex II or a Christie - both 4kw minimum.

Posted by Pat Moore (Member # 380) on 08-24-2000, 11:30 AM:

Unless you're at one extreme or another (really short or really long focal length lenses), throw doesn't count as much as screen size does to determine light and power requirements.

Assuming you've got a "normal" sized drive in screen, 4kw is usually required, but there are plenty of exceptions. Consider ambient light conditions and general air quality -- if it's naturally dusty, longer throws will cost you some light. I always found drive-ins easier to light in winter because the air was cleaner -- less stuff floating around in it.

Have to say, you should include Strong in your considerations -- very good 4kw lamphouse and optical system. And yes, I'd say that even if I didn't work for us.

Posted by Ken Layton (Member # 133) on 08-24-2000, 02:10 PM:

250 feet is about as far away as you want to put the projector without losing too much light. Try for a screen size of 40 by 90 feet.

Posted by Steve Guttag (Member # 268) on 08-24-2000, 08:45 PM:

I'll second Pat's suggestion about considering Strong for the light source. I haven't been disappointed with an Ultra-80 yet. Have safely run 5KW on 35mm film too (7KW on 70mm).

The best light vs heat I have come across is Kinoton though. It is the only lamphouse I would consider for say 16mm and 3KW (which we just installed)...you can put your hand in the projection beam (between the film gate and the lens even) and not feel uncomfortable after a minute.

As Pat said, throw really isn't a significant factor in light, unless you are close to pollution or live in a foggy area. About the only factor that will crop up is that at 141.2mm your f/stop will start increasing on standard lenses (thems the physics). If you are anticipating being in the 6 - 7" range, consider finding some B&L Super Cinephors (4" diameter)...they actually really work quite well for their age and are actually coated! I believe they have a typical speed of f/1.7 which, for a drive in, every little bit helps!

Steve

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"Old projectionists never die, they just changeover!"