HT1075 - Help with light leakage around screen - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 5 Old 05-25-2016, 06:34 AM - Thread Starter
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HT1075 - Help with light leakage around screen

I am a projector newbie. I ceiling mounted, about 10 inches off center, a Benq HT1075. Distance to the screen is about 11.5 ft. and the screen size is 120".

I've been trying to dial in the alignment using the on screen test pattern and have it in a decent place. The problem, as I hope is discernible in the pictures, is that that there is a light leakage around the frame of my screen, particularly to the bottom and sides. Sorry for the poor pic quality.

Is this normal? Any help is greatly appreciated.
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post #2 of 5 Old 05-25-2016, 08:57 AM
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If you're using digital keystone correction, you'll always have that issue. (Along with lower resolution/artifacts and unequal focus at larger correction levels).
Only solution is lens shift or placing the projector in the appropriate spot with no digital keystone.

You're just seeing the unused/"black" pixels from the actual rectangular 1920x1080 pixel image projected while your content is being squeezed into the parallelogram that matches the screen. Those unused pixels will only be as "black" as the projector's lowest black levels. I'd imagine if you had a projector with a dynamic iris on and tried a similar setup, it would be even more irritating with a pulsating light around the screen.
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Last edited by JustAnEE; 05-25-2016 at 06:48 PM.
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post #3 of 5 Old 05-25-2016, 11:31 AM - Thread Starter
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Quote:
Originally Posted by JustAnEE View Post
If you're using digital keystone correction, you'll always have that issue. (Along with lower resolution/artifacts).
Only solution is lens shift or placing the projector in the appropriate spot with no digital keystone.
Thank you. That makes sense now that I actually think about it.
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post #4 of 5 Old 05-25-2016, 12:41 PM
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Some folks on this forum say that using digital keystone is just fine because it's virtually undetectable. Thanks for providing a real world example of the kind of image degradation keystone can cause. Next time someone recommends using digital keystone we can point back to this thread as an example of why that's not such a great idea.
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post #5 of 5 Old 05-25-2016, 01:59 PM
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This isn't actually light 'leakage' - That's typically extraneous light that comes out of the lens or projector at an unusual angle to cause a spot of light on the ceiling or on a wall next to the image.

What you are seeing really is the natural image of the DMD chip. Is is typical of DLP projectors to have about a 1" ring around the edges which is the DMD chip edge itself. This is what the black of the screen sucks up.

When a projector is properly mounted with the lens on center, you don't notice the ring around the edge due to the screen, and there is no additional overlap of image onto the wall. Right now you may be losing 5% of the pixels available to you because you have the projector off center and are using keystone correction.

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