Do I really need a low gain screen? - AVS Forum
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post #1 of 5 Old 03-08-2013, 07:52 AM - Thread Starter
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I'm moving my JVC RS45 to a new, shorter room.

My throw distance will drop to 9' 9" and I plan on putting a CineVista anamorphic lens on.

I am aiming to have a 87" wide 2.35 ratio screen (37" high).

Since the CineVista widens the projected image by about 33% I only need to have the projector set up to throw a 66" wide image.

According to the Elite projector calculator, the RS45 throws a 66" wide image from a throw distance of 9' 9" at a zoom of 1.72.

What concerns me is at that throw distance and zoom the brightness levels for the Minimum/Iris Closed scenario (this is a 2D film set up only and I run low lamp mode, fully closed iris for the great JVC D-ILA blacks) with a 1.0 gain screen the brightness measurements projected are too high (27.5 fL on a new lamp and estimated 20 fL after 500 hours).

If I dial down the screen gain to 0.7 those numbers are respectable (19.3 fL on a new lamp and 14 fL after 500 hours).

I'm planning on either buying, or making a new screen anyway. Based on what I see with the projector calculator looks like I should aim for about a 0.7 gain.....would people agree with this or is there something else I should be thinking about. For what its worth the room is a basement room with complete light control, although walls and ceiling are white and the screen wall is black velvet.

Thanks,

Dave M

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post #2 of 5 Old 03-08-2013, 08:42 AM
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Quote:
Originally Posted by dave in gva View Post

27.5 fL on a new lamp and estimated 20 fL after 500 hours.

That seems awfully optimistic.

Anyway, just try it with a white sheet or paper, which are pretty close to unity gain.

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post #3 of 5 Old 03-08-2013, 11:34 AM
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Well, in low lamp with a new lamp, and your iris closed, it might be more like 368 lumens, which gives you more like 21 foot lamberts. I like it bright, so I wouldn't worry about that. Your screen is mighty small though. IMO 21 FL is perfect. cool.gif

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post #4 of 5 Old 03-08-2013, 10:44 PM - Thread Starter
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Originally Posted by Craig Peer View Post

Well, in low lamp with a new lamp, and your iris closed, it might be more like 368 lumens, which gives you more like 21 foot lamberts. I like it bright, so I wouldn't worry about that. Your screen is mighty small though. IMO 21 FL is perfect. cool.gif

Alright, so what I am hearing here is I shouldn't fuss so much about the gain. Sounds like a gain of around 1 could be fine. I am thinking I will DIY my screen anyway so being able to go with a gain around 1 could give me more variety.

Craig when you say my screen is pretty small....I dunno....is it really so small? It's not a long room so I'm constrained by the width the RS45 can throw and I also have the door entrance to the room on the side I am going to project on to. I'll be sitting about 9 feet back from the screen as well, so according to the THX and SMPTE guidelines the angle of view I'll be having is greater than 36 degrees.

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post #5 of 5 Old 03-10-2013, 08:13 PM
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If that size works best for you, go for it. I personally feel that projector brightness is over stated anyway - better bright than dim IMO.

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