screen brightness- How real? - AVS Forum
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post #1 of 14 Old 07-25-2001, 07:33 AM - Thread Starter
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I recently got a used Nec 6pg+(from Alan of course), and built a homemade screen (45 x 80) using the excellent advice in this forum. The idea was, that since I wasn't sure how everything was going to look, I might as well build a screen for $40 before I decide what I ultimately wanted. Anyway, the screen looks very good but I called Stewart and had them send me some samples for comparison. In case anyone is unaware, when you get a sample it is simply 8 1/2 by 11. I had one sample of 1.3 gain and one of 2.0 gain. With the samples up on the screen, the pictures were MUCH brighter and even appeared sharper. Additionally, the 2.0 seemed brighter thatn the 1.3 which stands to reason. Here is my question? Can the screen really make this dramatic a difference? Or, if I was simply to go into the settings of the projector (which I don't want to do), and raise the brightness and/or sharpness would I get the same results? However, if I do the latter, wouldn't I mess up all the settings relative to one another (ie.. tint, contrast etc)? How can this difference be so great and what am I missing?

-Jason
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post #2 of 14 Old 07-25-2001, 08:41 AM
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Don't worry, your eyes are not deceiving you! Gain screens actually performed as advertised. You don't want to go into your projector and raise the brightness/contrast, you will end up overdriving your tubes and they will wear prematurely. The sharpness control will not help with resolution, it only affects the contrast at edges in the image.

The difference in brightness is so great because the a gain screen redirects light that would normally hit the ceiling and walls towards the viewing area. There is a pretty good introduction to screens on a website somewhere, maybe someone has a link to it?

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post #3 of 14 Old 07-25-2001, 08:12 PM - Thread Starter
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Kam- I have no intention of raising the brightness of the projector but I am curious as to whether or not this would give me a comparable picture. In other words, do better screens allow you to achieve results that could only be achieved if one was to really push their projector or will better screens actually reproduce a better picture regardless of how much tinkering one does?
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-Jason
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post #4 of 14 Old 07-25-2001, 08:17 PM
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Because the phosphors start to bloom (the beam spot size gets bigger) as you drive the tubes harder, the screen gives you a brighter picture at the same sharpness if you don't adjust the projector, or an equally bright picture with less sharpness and shorter tube life.

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[This message has been edited by noah katz (edited 07-26-2001).]

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post #5 of 14 Old 07-25-2001, 08:32 PM
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If you have perfect light control, I have to think that the brightness of the projector or screen is not as important. If the projector is brighter, wouldn't your eyes just stop down their pupils to maintain the same apparent brightness anyway? After all, sunlight is thousands of times brighter than typical interior lighting, but we sure don't perceive it that way.

Do people who have a 2000 lumen projector really perceive a brightness that is 5-10 times brighter than a CRT projector?

It seems to me that brightness is mainly valuable in overcoming ambient light. The dimmer the projector, the more any stray light will pollute the image. If you can make your theater completely black, then up to a certain point I would think that brightness isn't that important.

I don't have experience with lots of different projectors. I've been using an 800 lumen DLP, and in a completely dark room it looks very bright, even just projected on the wall.
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post #6 of 14 Old 07-25-2001, 11:19 PM
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dhanson,

Sorry to refute so much of what you said, but...

"Do people who have a 2000 lumen projector really perceive a brightness that is 5-10 times brighter than a CRT projector?

No, because the eye responds logarithmically, but it's a worthwhile improvement nonetheless. If it wasn't, it wouldn't be such a sales point.

"If you can make your theater completely black, then up to a certain point I would think that brightness isn't that important."

A big if for many people. Many don't have a dedicated room where they can take all the necessary measures.

"I've been using an 800 lumen DLP, and in a completely dark room it looks very bright, even just projected on the wall."

The original post asked about a CRT projector; only the brightest CRT's put out 800 L.

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post #7 of 14 Old 07-26-2001, 12:45 AM
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Jason,

As you know I use a Stewart 1.3 gain 80"x45" with my NEC 6PG Plus, and my image is plenty bright, but I do have 100% light control in my room as well.

If your very picky about white field uniformity across the entire screen, then I'd highly suggest using the 1.3 gain material. The 2.0 gain material will likely cause "some" hotspotting that may or may not bother you.

FWIW, I went from a Draper 2.3 high gain screen to a Stewart 1.3 low gain screen and the difference using the low gain screen is well worth it, IMHO.



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post #8 of 14 Old 07-26-2001, 08:31 PM
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Too many variables for me.I will cut and try till I am satisfied.Like PJ choices refuse to take anybodys word.You never get apples against apples.Go out and use those fabulous instruments(eyes)but do meaningful comparisons.Yes,hard to come by.
You want to shout "it all depends."

This isnt "1 size fits all."Politics is rampant.X said this Y said that.
But some are experienced and balanced and they are good teachers.
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post #9 of 14 Old 07-27-2001, 07:33 PM
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I'm a person who feels that to get an image that you can really sink your teeth into you need a certain amount of reflected light . I have gone so far as to use the Stewart vidematte 200( 1.8 gain ) and two projectos stacked side by side for more light! Since this aspect is so important to me I wouldn't go down to the politically correct 1.3 gain screen. I do see some color shifting left to right in B&W films but even this isn't distracting enough to me to give up the added light. Even higher gain screens will require you to have total or near total light control to obtain the "dynamic range"(blacks) of the low end of the reflected light and achieve the most engaging image.

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post #10 of 14 Old 07-28-2001, 11:27 AM - Thread Starter
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OK, now I am really confused. Here is the question assuming a lot of variables: If one has absolute control of lighting and absolutely no regard for wear and tear on a projector, what difference does screen gain make??? In other words, can't one just turn their projectors brightness up to any level they desire to achieve the same results as a sceeen gain of 1.3,1.5,2.0 etc or is their something fundemenally different in the overall presentatiom if it is done by the screen?

Art: Am I correct that you are saying that extra light will indeed give you better contrasts between blacks and all other colors which is something that just turning up ones brightness inside a projector surely won't do?

-Jason
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post #11 of 14 Old 07-29-2001, 02:50 PM
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Please allow me the ease of reply, by quoting myself from another thread:

~~~~~~~~~~~~~~~~~~~~~~~~~~
Not really, as far as the 9" unit goes.
You see, depth of field, or 3-d effect, is tied to sharpness/contrast depth..which CAN be a fucntion of the screen. Higher gain screens are less sensitive to being infected by the light being shone upon them, compared to lower gain screens. For instance, it is possible, to see the light in a given bright area, create a situation where there is a slight lightening of adjacent dark areas of the screen. This even happens with 1.5 gain screens.. if they are too thin a maerial, or mounted directly on a white wall as well (thin materials), for example... blackout fabric can be the worst for this effect. Matt screens (1.0 gain)are the worst in this respect (to me, they are so soft, contrastless and flat looking, they are disgusting). They have a lower contrast ratio, than that of a 1.5 gain screen.

So, the studiotek 130 is slightly less capable of producing this '3-d' effect than the ultramatte 150. It's a thing that has to be looked at on a WHOLE screen for comparison, which most people cannot afford to do, and cannot easily do, even if they have the cash to get both. Dealers get to see this effect, but only if they switch screens on the same PJ,and have a PJ good enough to see the differences, AND they are capable of making this understanding. So, the 'blocks' in finding this sort of thing out are rather hgih...I have had as much as 19 different screen formulations in the house at one time.

the reason I can, Is I am making my own screens,and screen materials (screen paints, with different gains and characteristics), So, I get the info rather often and clearly. I have changed screens three times in one day.. on numerous occasions, as this is how to assess materials properly.. no other test is valid. Full screens are the only testing method or evaluation method of any real merit.

As for the comparisons of Stewart materials, I have truthfully, incidental knowledge of such surfaces, other than the samples that Don sends out. The studiotek 130 has this 'loss in contrast depth modualtion' less than that of other 1.3 gain materials..that I have seen. It is an extremely well designed material. However, for the 3-d 'pop-out' effect, the Ultramatte 150 is superior. But, hotspotting and colorshift does begin to intrude, but to a fairly minor degree. Truth be known, it is ufair of me to make comparisons of ANY stewart materials, as I am close to being a manufaturer myself. I don't mind too much, as I am not 'dissing' Don's product in any way, they are both excellent screen materials.

The effects that I speak of are directly related to gain characteristics of materials and screens. They will affect any screen that has a gain cahracteristic, and WILL be an arbiter of what could be considered their 'ultimate image fidelity',and the directions and resultant of the choices made in that particualr design, insofar as trade-offs that are inherent in the way it was finalized.

9" CRt units are capable of throwing enough light onto a larger screen with lower gain (1.3), so the losses with contrast depth and sharpness (due to higher output) are not as readily apparent, as they would be with a 700 lumen unit, likea Electrohme ECP 4100. I would suggest a slightly smaller, higer gain screen for a ECP 4100, just to keep the pressure off the unit, the contrast modualation up, and the sharpness up. It reslts in a longer lasting PJ, with less pressure on it, and a sharper, deeper-looking image. 1.3 gain in this case, will up the pressure on the tubes signifigantly, and shorten the life of the PJ's tubes, at the same time the image softens, due to the screen,and the increased output of the PJ. I have friend who has preamturely weakened his previosuly MINT blue tube on his ECP 4000 PJ, specifically due to this sort of situation. Too low a gain, and too hiogh a pressure on the PJ.

You will get slight darkening in the corners of the image as well, due to the higher gain material, and the light drop off inherently in the tube's corners. It will be more noticable in the higher gain screen, due the fact that it is more mirror like (the screen), and you are further off axis from the corners, compared to the center of the screen...

The trick is to see diferrent screens in action, before you buy. Make a small trip to do so, if at all possible. it is wroth the effort to get the right screen for you, due to the fact that it is fully HALF the equation, when it comes to image fidelity and quality that you get.

More people should be aware of this fact. The screen is VERY important. It is FUNADAMENTALLY a LARGE part of the ACTUAL DISPLAY DEVICE.

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post #12 of 14 Old 07-29-2001, 08:00 PM
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Thanks Ken,
I was trying to get the basics in there as best I could.

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post #13 of 14 Old 07-29-2001, 09:29 PM
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Well, yeah. the explainations I had seen are fine. But, it is always uesful to get a bit more.. it cuts down on the un answered questions... It also has overlap, so all the bases are covered, and in multiple ways, thus leading to fewer mistakes and better understanding.

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post #14 of 14 Old 07-29-2001, 10:13 PM
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There are many variables to consider when comparing the ways available to get more light from your system. Increasing screen gain is one way and going from a screen that has a gain of 1.0 to one with again of 2.0 will result in twice the reflected light to the viewing area. This has some down sides however.One is the hot spotting that occurs(the center looks much brighter than the edges) depending on your taste some of this in my estimation is acceptable. Another issue is color shifting. This occurs because the red green and blue tubes themselves begin to reflect in the screen and you see this in the reflected image (one side looks a little red one a little blue).Again a little of this is acceptable since I personally see it only in B&W material and even then it isn't distracting to me at 1.8 gain. The veiwing area is also important since the higher the gain the more narrow the viewing area becomes.What occurs is the higher gain screen concentrates the light to a more narrow area as the technique to get more light to the center but if you sit vary far left or right (or higher or lower) the reflected light begins to diminish.
The increase in light which occurs by cranking the projector will reduce tube life geometrically and if carried too far will also cause blooming resulting in a less clear image since the beam spot gets larger.

[This message has been edited by Art Sonneborn (edited 07-29-2001).]

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