# Three edges are square and one isn't? How is this possible?



## Rancho5 (Aug 20, 2009)

My PJ screen is 110 inches and I have an Epson 6100 HD PJ with an Onkyo 705 and a PS3.

I'm on my 2nd PJ (the other was replaces under warranty) but with the 1st one being taken down when the bulb burnt out (they sent me a new one) and switching PJ back and forth, somehow I can get the top and both sides square but not the bottom. When we first put up the PJ months ago we got it all square then affixed the velvet tape, etc. Now the bottom is off.

What's REALLY weird is that when I shrink the picture down so it is nowhere near the velvet tape, it's still messed up. Top and sides square, bottom slopes up to the right.

Am I going nuts? Is their some kind of "one corner" keystone option I am not using?

Any help appreciated.


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## Alan Brown (Jun 7, 2006)

Never use digital keystone correction in a permanent setup. Doing so will reduce resolution and cause moire distortion in the image. Digital keystone correction is helpful for quick and temporary computer presentations but compromises picture quality in every case. You have an alignment problem somewhere between the projector and the screen wall. 

It sounds like you use a painted wall for a screen. If you had an independent screen, you could try adjusting the screen slightly. Walls are not reliably straight and flat. Perhaps you had a little error in the first projector's alignment when the tape was installed, but this time a little error in the opposite direction, making the deviation from square more pronounced. I appears you are left with having to adjust how the projector is physically mounted or move the tape that defines the edge of the screen. 

Best regards and beautiful pictures, 
Alan Brown, President
CinemaQuest, Inc.
A Lion AV Consultants Affiliate

"Advancing the art and science of electronic imaging"


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## Rancho5 (Aug 20, 2009)

I was actually being sarcastic with the "one corner keystone" thing. Sorry. I should have put an emoticon or something.

The wall is perfectly flat. I took painstaking time to make sure when I constructed the theater and besides the upward slope of the bottom right side is pretty drastic. Like three inches over the span from left to right. And it worked perfectly before I unmounted it. I've played with it forever and it's driving me nuts.:dumbcrazy:


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## Alan Brown (Jun 7, 2006)

It's difficult to comment without being on site to examine the details. I can't imagine how the projector could be defective in such a manner as to cause such a problem. Do I understand you correctly, that this is a replacement that is the same model you had originally?


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## Rancho5 (Aug 20, 2009)

You are correct. Both PJ's have done this so it seems it would be "my" problem, right? I took the whole thing down just now and refitted the ceiling bracket just to sort of start from scratch then I put up the PJ and projected the test screen and the same thing happened.

We measured the screen as defined by the velvet tape and it was square. Then we did the math on the 16:9 ratio and discovered that we were off a bit off on the tape, which is weird because we projected a movie and did the velvet that way. But then we actually shrunk the screen to as small as it would go so it was nowhere near the velvet tape and measured it and it was not square. The right vertical edge was an inch shorter than the left.

So I crept back behind the projection wall (it in the attic and I left space all around to have access) and measured and the left side is 25.5 inches out from the front wall and the right side is 25.25. I don't think a 1/4 inch over 15 feet would make a 1 inch difference on the image.

I'm baffled.


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## lcaillo (May 2, 2006)

Measure from all four corners to the lens. You will likely find that the distance is not the same top to bottom or left to right on the corner that is out (relative to its adjacen corners) compared to the other corners. Your screen plane may not be as perpendicular to the center line to the projector as you think or the projector may not be centered.


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## Alan Brown (Jun 7, 2006)

If your wall is screwier than you think, and you aren't going to invest in a manufactured screen, a little bit of over scan onto the velvet tape that defines the frame is a reasonable compromise.


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## Rancho5 (Aug 20, 2009)

Solved!!! I was not going nuts. Instead of measuring the distances like it was suggested I looked at the PJ and saw that it was not perpendicular to the side wall at all. It didn't even occur to me to look before. SO I lined it up and boom, the screen was proportionate once again!

I have 1/4" over on the black velvet which I am totally fine with.

Thanks hometheatershack.com!


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## lsiberian (Mar 24, 2009)

Alan Brown said:


> Never use digital keystone correction in a permanent setup. Doing so will reduce resolution and cause moire distortion in the image.


I use digital keystone in my setup and it still looks great. I think it's best to avoid, but a little doesn't hurt IMO.


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## Alan Brown (Jun 7, 2006)

> I use digital keystone in my setup and it still looks great. I think it's best to avoid, but a little doesn't hurt IMO.


Many projector users tolerate optional compromises to image quality for various reasons. As an imaging professional I don't advise causing compromises when they can be avoided. It is poor practice to use digital keystone correction in a permanent installation. If one has a passion for excellence in the home theater arena, the objective should always be to eliminate distortions and defects whenever possible. 

Some projector owners must settle for inferior imaging due to a limited budget. I've seen many low priced 1080p three chip LCD and LCoS projectors, or single chip DLPs with poor optics, produce such soft images that certain defects are partially masked as a result. Some screens mask defects as well. The projector listed in your profile uses a 4x3 XGA DLP imager chip, which will also soften any program signal sent to it other than its native resolution. Combined, such inferior display components can hide a variety of problems otherwise more readily noticed in a better designed system. Of course, real picture information gets lost in the process as well.


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## Rancho5 (Aug 20, 2009)

Are you talking to me or lsiberian?


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## Alan Brown (Jun 7, 2006)

Rancho5 said:


> Are you talking to me or lsiberian?


I quoted Isiberian, so I was addressing his comment. However, it's also for the education of anyone reading this thread, this being a public forum.

Best regards and beautiful pictures,
Alan Brown, President
CinemaQuest, Inc.
A Lion AV Consultants Affiliate

"Advancing the art and science of electronic imaging"


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## lcaillo (May 2, 2006)

I agree with Alan completely on this matter. It may be acceptable for some to compromise the image in many ways, but if one wants to maintain picture integrity, digital keystone correction needs to be avoided. With proper installation there should be no need for it. I would never design nor install a system with that kind of handicap unless there was some very unusual limitation on the location of the projector or the screen. Everyone has their priorities, but this is one compromise that makes little sense to me.


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## Rancho5 (Aug 20, 2009)

I'm in total agreement. I'm glad the PJ was just a little off and that it wasn't my wall or PJ. Keystoning, to me, is what you use on your PJ at work when you have to project onto a mammoth screen that's 10 ft above your PJ and you don't have a choice because you are presenting to 300 people. Flat wall, flat screen, good mount= no keystone. 

My best guess is that while taking down the broken PJ and putting up the new one I went straight to fitting the picture on the screen with out even looking to see if the PJ was even lined up properly. Live and learn.


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