What does a high gain screen REALLY look like - AVS Forum
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post #1 of 4 Old 09-14-2000, 01:52 PM - Thread Starter
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Jeff,

You would have to have one very wide room for the off axis problem to surface when using a high gain screen. With a 107" screen, your room would have to be about 18 to 20 feet wide for this problem to be noticed.

The biggest benefit to a Gray screen like the 2.5 that you are talking about is a higher light "throwback" to the viewer and a greater contrast ratio.

Some of the negatives (when using a 3 CRT PJ) can be color shift bacause the Red and Blue guns are offset and can show up on the screen with a blue tint on the right side and red on the left.

Another "problem" can be the uniformaty of the surface. This happens almost all the time with a Silver 4.0 where there are areas that have more "silvering" than others and when watching very bright scenes can show up as picture anamoly's.

Just as a reference point, I use a Stewart Micro Perf 107x60 Silver 4.0 fixed screen. I also have the 1.3 white micro-perf material which I used for the first 2 years of my PJ's life (Zenith PRO900X). When I ordered my screen I ordered both the 1.3 and the 4.0. As the PJ aged, the light output goes down as much as 40% so the 4.0 picked this up.

Another problem with 3 CRT PJ's is Hot spotting where the center of the image will be brighter than the sides.

But the "punch" that a high gain screen gives has to be weighed against the negatives. If you want an absolutely perfect image, then stay with the 1.3. But if you are willing to live with some imperfections in the image from time to time than a high gain is the way to go.

As far as DLP being as good as a CRT PJ...NO WAY. The contrast ratio is nowheres near the deep ink black that a CRT PJ will give. You will get more brightness and there are some good advantages to Digital PJ's. In fact they beat a CRT PJ in every aspect except one...contrast ratio.

Lee
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post #2 of 4 Old 09-14-2000, 03:55 PM
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And the contrast ratio, combined with the subtulties of such, is where the life is 'breathed' in to the picture. Without it you are dead in the water.

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post #3 of 4 Old 09-14-2000, 07:23 PM - Thread Starter
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KBK,

You are so right. On a 2D surface the human eye can percieve a 3D image if the contrast ratio is high enough. The difference between the blackest black and the whitest white is the CR. The numbers I have heard over the years are between 800 and 1000 to 1. At this point, the human brain is fooled into thinking it is seeing 3D on a 2D surface. The higher the CR, the better the 3D effect. Numbers of 1200 to 1 or better are obtainable with CRT PJ's using a small screen in a totaly blacked out room.

The best I have ever heard a digital PJ being was 600 to 1. It will be many years if ever that a consumer priced DLP or LCD or D'ILA will reach these CR numbers.

A person from JVC was discussing the D'ILA and it's CR right here on this Forum. When asked about improving the CR from 500/600 to something like 800 to 1, he replied, "yes...it is doable but the price would be prohibitive."

Lee
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post #4 of 4 Old 09-14-2000, 09:09 PM
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I know about all the numbers, angles, gain, etc., but what does it subjectively look like?

1) How much more light will a 2.5 get you over a 1.3 (which I now have)...ie is it as much as the difference between a 9' and 8' CRT (brightness only...I know it won't help resolution). Or would it effectively get you enough on screen lumens to go from 96" to 107" wide (not diag)?

2) More important...how bad are the off axis artifacts? I sit in the sweet spot (13-14') of a 107x60 screen...when I have guests, they get that spot and I move to about 9 or 1 screen width back from either side (straight back from the edge...so looking at the near edge, I'm at 0 degrees, but looking at the far edge, I'm at 45 degrees roughly). These are worst case angles. Even on my 1.3 gain screen I notice NO objectionable gradients of brightness or color... would a 2.5 screen look much different from one end to the other?

How about an extreme example... at super bowl parties 30 people sit way too close, on the floor, and way off to the side, and the picture always gets raves...would a 2.5 screen make it unwatchable at these extremes or would it still look good because of the huge size and nature of "viewing material"?

Basically I have the 107x60 1.3 screen up now but only use 80x60 on a 7" CRT without scaling...and want to move up to either a 9" CRT (worried I may need the high gain screen with its problems) or to a DLP (minimum 1024...prefer 1280) with more lumens and hopefully the gray screen mentioned in other posts to get the blacks and contrast I know and love with CRT). I figure street price on the Dwin or Seleco will be about what a used 9"CRT is...and hopefully the 1280x720 RPTV DLP chip will be available for FPTV this spring.

I welcome anyones opinions and experiences.

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Jeff

Finally went digital: RS20, ISCO IIIs, DIY 10.5' wide torus screen, Stewart StudioTek 1.3 G3 with 4 way masking and adjustable image size
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