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Discussion Starter #1
I've got a JVC RS20 and I'm finding that I'd like a little more brightness. I only have 500 hours on the lamp, but it seems a bit dim. My screen is a Sintra 120" 2.35:1 screen, but unpainted. I'd like to paint it or do something to it to get more gain, but without sacrificing much color accuracy. What would be best for me?
 

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I've got a JVC RS20 and I'm finding that I'd like a little more brightness. I only have 500 hours on the lamp, but it seems a bit dim. My screen is a Sintra 120" 2.35:1 screen, but unpainted. I'd like to paint it or do something to it to get more gain, but without sacrificing much color accuracy. What would be best for me?
How are is the PJ mounted from the screen?

You are going to have problems making a screen that has more gain than unpainted white Sintra without introducing a visible viewing cone and possibly getting other screen artifacts such as image graininess or color shifting with viewing angle. Keep in mind that the gain values stated for DIY screen mixes found elsewhere are not accurate. The same goes for commercial screen mixes.
 

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Discussion Starter #3
I'm aware. The projector is currently shelf mounted 16 feet from the screen. I can move the shelf to whatever the optimal height is for high gain formulas.
 

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I'm aware. The projector is currently shelf mounted 16 feet from the screen. I can move the shelf to whatever the optimal height is for high gain formulas.
Did you calibrate your PJ? According to one review they got 722 lumens in Cinema 2 mode and normal lamp (the low power setting on the RS20) which would give you over 20 fc of image brightness on a screen your size with your mounting distance, which means you are probably getting around a 22-26 fL image from the unpainted Sintra. You would have to be wearing sunglasses to call such an image dim. I'm beginning to wonder if something isn't wrong with your PJ. You might give some thought to getting a light meter that reads in fc (foot candles) or lux (it's easy to convert from one to the other). This will tell you EXACTLY what image brightness you are really getting. These meters are quite inexpensive (less than $20 shipped) from Amazon. There meters ARE accurate. I have one of these and it gives me the SAME lux readings as my $400 photographic light meter that measures in lux and fc.

If you really do need to get a high gain screen, the best one for the job is actually a commercial screen (the Da-Lite High Power) that has a gain of 2.4. This is a retroreflective screen so to get the brightest image you would mount the PJ at the same height above the floor as your eyes are when viewing.
 

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Discussion Starter #5
Sounds good. I bought the LX1330B on eBay since I had some eBay bucks to burn. I'll take some readings and let you know what they are when I get the unit.

Also, keep in mind those readings that Art got are with a fresh bulb. Mine has seen 500+ hours of use, so it's probably only about 14fL, if even that.
 

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Sounds good. I bought the LX1330B on eBay since I had some eBay bucks to burn. I'll take some readings and let you know what they are when I get the unit.

Also, keep in mind those readings that Art got are with a fresh bulb. Mine has seen 500+ hours of use, so it's probably only about 14fL, if even that.
Cool. Looking forward to some real numbers instead of the guesstimates we usually have to go by. :T

BTW, what you want to measure is the amount of light falling on the screen and not the light being reflected from the screen. Place the sensor on the middle of the screen and pointing at the PJ then slowly pivot the sensor up, down, left and right until you get the highest reading.
 

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Discussion Starter #9
I am reading 7.87 foot cancels and 84.8 lux at the screen with a 100ire test image. My 16:9 screen area is 83.5"x47" which equals 27.2 sq. ft. This results in 215 lumens at the screen. What the !? The lamp has 615hrs but it shouldn't be THAT dim. Throw is 15ft and the RS20 iris is at -4. I set it to 0 and its barely brighter so I put it back to get better blacks.
 

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I am reading 7.87 foot cancels and 84.8 lux at the screen with a 100ire test image. My 16:9 screen area is 83.5"x47" which equals 27.2 sq. ft. This results in 215 lumens at the screen. What the !? The lamp has 615hrs but it shouldn't be THAT dim. Throw is 15ft and the RS20 iris is at -4. I set it to 0 and its barely brighter so I put it back to get better blacks.
I assume you followed the procedure described in post 6 by Don and took a reading of 84.8 lux from the center of the screen. Ok!!

Your screen is 120'' 2,35 which means 127'' in 16:9 (remember your panels are 16:9 and not 2,35). So, we have an area of 4,44 square meters. Therefore:

84.8 x 4.44 = 376,5 Lumens aka 84.8 : 10.76 = 7,88 FL. That's a pretty low number and you have to stick with a screen gain at least 1. So, any shade of gray is probably out of the question. You need the whiter white that's available.


PS

Your lumens are probably less than 376,5 because usually the projectors are far more brighter at the center than in the edges of the screen. So, if you want really know exactly of how many lumens your pj is capable of, you have to measure up 9 points on the screens and divide by 9 to have the exact number.
 

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Discussion Starter #11
Thanks for the reply. I actually zoom to achieve 2.35 but I took these measurements zoomed out. So that 16:9 fits on the screen with leftover space to the left and right. My 16:9 diagonal is actually 95". The calculations I did were correct for that number. Im thinking that instead of painting I may be better served by just buying a new bulb.
 

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Discussion Starter #13
That seems a bit odd for a lamp that only has 500 hours on it - it may not be a bad idea to contact the manufacturer and see if there is anything amiss with the lamp and if they would replace it.
Oops, I misspoke. It actually has around 615 on it, but your point still stands. it shouldn't be THAT dim.

Now, when I open the iris, I get about 10fL, which is around 280 lumens. Better, but still pathetically dim.
 

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Thanks for the reply. I actually zoom to achieve 2.35 but I took these measurements zoomed out. So that 16:9 fits on the screen with leftover space to the left and right. My 16:9 diagonal is actually 95". The calculations I did were correct for that number. Im thinking that instead of painting I may be better served by just buying a new bulb.
A, ok, sorry then for the mixed up...
 

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Silas, at this point I wouldn't recommend painting your white Sintra screen until you talk with JVC and find out if there is a problem with your bulb or not. At the lumens you are currently dealing with there is no DIY solution that is any higher gain than your screen and color neutral.

Please keep up apprised of your situation.
 
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