Film-Tech Forum ARCHIVE: Is my screen too bright?

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Posted by Sam Hunter (Member # 1119) on 07-23-2003, 11:18 AM:

My screen size is 4' x 8' (Matte White) and my throw is about 20' with a ORC 1000 Watt light source, Brenkert BX80, scope lens (Sankor 4' F2.0 with B-L Scope Attachment (Silver face) and Flat lens B-L Super Cinephor 2.50" F1.8.
According to the rule of thumb of 5W per square foot I come up with a required light source of 160 Watts. I am 6.25 times above that. I really don't see a problem with blinding light or anything and I am happy to have the level of light that I do have as I worked hard and paid a lot for it but was just interested in your comments.
I wish I could have went to a bigger screen in my setup but alas I went as far as I could go with it under the circumstances.
Thanks.

Posted by Gordon McLeod (Member # 33) on 07-23-2003, 12:29 PM:

If you have too much light you will see a noticible strobing flicker in bright skys
It is easier to get rid of light than add it

Posted by John Pytlak (Member # 331) on 07-23-2003, 01:42 PM:

You really should MEASURE the reflected light:

http://www.kodak.com/US/en/motion/newsletters/pytlak/spring98.shtml

http://www.kodak.com/US/en/motion/newsletters/pytlak/march2000.shtml

http://www.kodak.com/US/en/motion/newsletters/pytlak/june2000.shtml

See if you can borrow a screen luminance meter.

As Gordon said, it's easier to handle too much light, than to try to get more if you are underpowered.

Trade all that extra light for one or more of the following advantages:

1. Use a three-blade shutter to eliminate flicker

2. Defocus the lamp slightly to get more uniform illumination

3. Use an aperture/iris in the lens to gain better depth of focus

4. Lower the gain of the screen (e.g., paint it gray) to get a better black level when there is some stray room light

5. Run the lamp at the lower end of the recommended current range to save electricity

Posted by Frank Angel (Member # 248) on 07-25-2003, 04:56 PM:

Ah, what a joy....figuring out how to get rid of too much light! [Cool]

Frank

Posted by Sam Hunter (Member # 1119) on 07-25-2003, 05:07 PM:

Really, it doesnt bother me and it doesn't hurt to view it but I ran the figures and was surprised. I have one print that is a little dark and it plays just fine so I think I will leave well enough alone. That homemade lamphouse I built and used at the OLD SDH Cinema worked great as well. I still have it in case I need another one or somebody wants it.