# Short Throw Projector - Foot Lambert?



## Checkov (May 11, 2015)

I'm a theater director, not a technician so please forgive my lack of knowledge on the topic...

I'm trying to backlight a 16' rear screen width on a set with 5' to 6' throw.

I've found an Eiki projector that will do the job, it's at 3100 lumens illuminating the screen with 19 foot lambert. I can't find 4000 or 5000 lumen projectors with short throw capability. We intend to use media when stage lights are low or in a black out.

I have no idea what a foot lambert looks like without buying the projector and trying it - hoping some guidance here might help.

The resolution isn't as important as the brightness. We're using rough animation and rough live action to create atmosphere through a ship's window.

tx!


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## lwinters630 (May 11, 2015)

Checkov said:


> I'm a theater director, not a technician so please forgive my lack of knowledge on the topic...
> 
> I'm trying to backlight a 16' rear screen width on a set with 5' to 6' throw.
> 
> ...


To me 3100 seems low. Viewing from 30' might work but 60' may be too dim.


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## gafftaper (May 11, 2015)

Are you buying? What's your budget. There are some very bright very wide angle options but they are also Very expensive.


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## Checkov (May 11, 2015)

We were hoping to buy three projectors (one foh, two rear projected) at about 1,500 to $2,000 each. We could probably raise another 5k or so towards the equipment, and yes we need to buy. Gaff - what's the angle options you know of?


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## Jay Ashworth (May 11, 2015)

If you are trying to evenly light a 16-foot diagonal screen from 5 feet away, you are almost certainly going to need to do that with a projector with interchangeable lenses. Eiki, Sharp and some other big names are in that market, but even today, those are not cheap projectors.


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## ruinexplorer (May 12, 2015)

The ultra short throw projectors with installed lenses will generally max out at around 3100 lumens. I would be a little hesitant that the focal capacity of these will give you a good image for that size screen (some might). On the other hand, the projectors with interchangeable lenses will likely be out of your budget range. Even if you purchase a used projector for around $500, you may find difficulty with the price of the short throw lens, which could run $2000 used. You can also increase the image size by using a first-surface mirror (commonly salvaged from old projection TVs) and bouncing the image to the screen (there will be some light loss).

As for the quality of the image, a few things come to play besides the brightness. What type of screen are you using? There will be variances in gain (the amount of light that gets passed on to the audience), variance in contrast (light to dark ratio, which will not be the same as what your projector advertises), the amount of ambient light hitting the screen (some are better at rejecting directional light), and the viewing angle (some are designed for an audience to be mostly in front while others are meant for the audience to be more spread out). Of course, if you are using something other than an actual projection screen, you won't be able to know these variables.

For your information, the human eye is most perceptive to changes in light to dark. This is why contrast is very important. The issue comes with keeping ambient light off of the screen to keep the deepest blacks and having a bright enough projector (with a high contrast ratio) to allow for whites to not appear grey.


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