What do you then the gain of the blackout fabric is? - AVS Forum
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post #1 of 21 Old 05-22-2001, 03:50 PM - Thread Starter
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What would you guess the gain of the blackout fabric is. I'm guessing that the gain is about 1.3, but I am wondering what others think.

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post #2 of 21 Old 05-22-2001, 06:24 PM
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Colin,
I have some and compared to screens of 1 to 2.5 my guess is 1 to 1.3(but contrast is good.)
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post #3 of 21 Old 05-22-2001, 08:11 PM - Thread Starter
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Great - I'm wondering if by averaging all the responses we get will reach the reading we would have if it were actually measured. Has anyone actually measured this. How is this done professionally.

Also, what does 1.3 correspond to. Does it mean that there is 30% more light reflected than a 1 rated screen. If so then we should be able to calibrate a photographic spot meter on a perfect 1 and measure another piece of screen material under the same conditions and figure out its gain. An increase of one third of a stop equals a 1.3 gain an increase of 1.5 stops equals a 2.5 gain screen and so on. Has anyone done this or are gain numbers not linear like f-stops?
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post #4 of 21 Old 05-22-2001, 08:13 PM - Thread Starter
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Actually, F-Stops are not linear they are logrhymthic, but in any case they are consistent.
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post #5 of 21 Old 05-23-2001, 06:44 AM
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I would be interested in this also, I have a blackout fabric screen, and was wondering if I should go to a higher gain screen. Maybe a 1.5 to 2.0. Comparing mine to some screen samples I would say the blackout is around 1.3 maybe a little less. No real way to measure it for sure though.

Tim

P.S. I am using the vinyl side.

[This message has been edited by TGroom (edited 05-23-2001).]
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post #6 of 21 Old 05-23-2001, 07:56 AM - Thread Starter
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I just assumed - though I probably should've specified - that I was talking about the vinyl side. Does anyone know about how screen gain is measured?
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post #7 of 21 Old 05-23-2001, 02:44 PM
 
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I attached a 6" square of Da-Lite Pearlescent (1.5 gain) onto my blockout screen and if it were not for the outline, you couldn't tell it was there. I would say it is almost a perfect match for the 1.5.
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post #8 of 21 Old 05-23-2001, 03:54 PM - Thread Starter
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Gee, my estimation of the blackout meterial being about 1.3 was because I had the same six inch swatches of Da-Lite stuff and I thought the 1.5 pearlescent was somewhat brighter than the 1.3. The 1.5 Video Spectra is somewhat brighter than the 1.3 and the blackout - also stranger. Did you have a swatch of the 1.5 nearby when you saw the 1.3 and blackout ? Maybe we have different blackout meterial - I got mine from JoAnn fabrics - how about you?
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post #9 of 21 Old 05-23-2001, 05:01 PM
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I taped a swatch of Draper M1300 to my blackout fabric from JoAnn's and I thought that the M1300 was ever so slightly brighter.

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post #10 of 21 Old 05-24-2001, 06:42 AM
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I was also using the Da-Lite samples for comparison. This is getting interesting. http://www.avsforum.com/ubb/smile.gif

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post #11 of 21 Old 05-24-2001, 08:44 AM - Thread Starter
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Tim - whats you're estimation of the gain of the vinyl side and where did you get the material?
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post #12 of 21 Old 05-24-2001, 12:52 PM
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Got blackout from Hancock .. there's been discussion lately when someone found it to be whiter than the JoAnn fabric... and it IS quite white.. if only someone with measurement tools could establish it.

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post #13 of 21 Old 05-24-2001, 02:51 PM
 
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I also purchase mine at Hancock.
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post #14 of 21 Old 05-24-2001, 03:10 PM - Thread Starter
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I don't suppose that this will help us differentiate small differences, but depending on what 1.5 'means' we should at least be able to differentiate between 1.0 and 1.3 - maybe more. I am still thinking about whether an accurate photographic light meter could be employed to measure differences. Does anyone know what a 1.3 or 1.5 means in terms of its relationship to a perfect 1.0?
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post #15 of 21 Old 05-24-2001, 09:18 PM
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I got some of JoAnn's blackout fabric the other day, to line the drapes in the windows, and noticed there was atleast three _slight_ color variations there. Two had a blue-ish tint to them, one ever so slightly bluer then the other, then there was one that looked white compared to the other two. This may account for what the verious reports of different gains you are seeing. Although, note I was seeing this in the store with flourecent lights, which may or may not have made things worse.
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post #16 of 21 Old 05-24-2001, 10:23 PM
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Here is a link on how to measure screen gain.

Enjoy
http://www.avsforum.com/ubb/Forum9/HTML/000118.html
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post #17 of 21 Old 05-25-2001, 01:41 PM - Thread Starter
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Thanks Don, the photographic part will will be a cinch, but maybe I'll find a high school algebra student to check my math.
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post #18 of 21 Old 05-29-2001, 09:21 PM - Thread Starter
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Well. lately I've been experimenting with my blackout screen surface. Playing with matte white spraypaint over a layer of silver - looks like a promising idea, but it really was a demonstration of how bad my spraypainting skills are.

Anyway, I was having friends over to watch Baraka (if you haven't seen it do so soon) and decided that the inconsistencies of the screen were not cool so I switched to some blackout material from Hancock and it seems to be somewhat less than the JoAnn stuff I was using before. This new stuff is maybe 1.2.

I am moving in about a week and next time I get some free time I am going the route of painting my own screen. I'm going to use some artist paints on a stretched canvas as well as a bunch of Magnesium Carbonate and some Pearlescent powder. Maybe with a backing of something very reflective. I know that KBK has done a good deal of the footwork in making a screen paint, and I'd be reinventing the wheel, but like most of us in this forum I am as interested in the journey as I am in the destination. I'll post my progress when I start.

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post #19 of 21 Old 08-28-2001, 08:56 PM
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I just had to bring this up again... I too have the blackout material from JoAnns... I'm taking a swatch to work in order to compare it to a Stewart Studiotek 130... we'll see.

My big question was vinyl or cotton side? I simply flipped a big piece of the extra material over, against the projected image... I noticed that the 'fuzzy' side seems to 'bleed' the colors a bit more in detailed areas. I also believe that the vinyl side reflected slightly more light too.

Just curious if anyone else has done any further experimenting or not...

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post #20 of 21 Old 08-29-2001, 06:44 AM
 
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From reading the forum I got the idea that most people use the cloth side which is the side I use.
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post #21 of 21 Old 08-29-2001, 09:18 PM - Thread Starter
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I used the vinyl side. It seemed a little bit brighter, but since I have switched to my own concoction of Magnesuim Carbonate mixed with a binder applied to canvas and I really like it. I was not able to use any pearlescent because it brought down the whiteness of the MgCO3. Sometime I'll get around to writing up what I did, but it really is pretty simple. The biggest deal is mixing it sufficiently. If anyone really is interested say so and I'll motivate myself to write.
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