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I'm going to ceiling mount my projector.. ???


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#1 of 9 OFFLINE   FranklinD

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Posted May 01 2008 - 11:51 AM

I'm thinking about getting this mount for my Sony VPL-HS20: Projector-Gear Sony Projector Ceiling Mounts for projectors

I need to know if I can get away with using a 3" extension with this mount. This will put the projector about 12" or so above the top of the screen. I've been messing about with the vertical/horizontal keystone features to get an idea how this would work out. The HS20 does not have a lens shift except in certain modes so I guess I'd have to point the projector at the screen and adjust the keystone from there?
I was just hoping that someone here could tell me if these tolerances will work for this specific projector. I haven't been able to find information about this online. Should I maybe get the longer extension bar?
Any help with this is appreciated.

#2 of 9 OFFLINE   Brent_S

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Posted May 01 2008 - 03:42 PM

I've always read keystone adjustment was something to avoid. If it doesn't have lens shift, the Sony's manual should tell you the offset required for proper screen-projector relationship. Usually it's lens center aligned with top/bottom edge or some percentage of screen height above/below the top/bottom screen edge. For instance, my Infocus has a 33% offset. For my 44" screen height, the projector lens needs to be 14.5" above the top of the screen for a ceiling mount. If my ceiling is 108" from the floor and the top of my screen is 72" from the floor, I need 21.5" of drop from the mount/pole combination. I don't know anything about the mount you linked. I have seen positive reviews on the universals that monoprice carries and they're considerably less expensive if budget's an issue. -Brent

#3 of 9 OFFLINE   FranklinD

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Posted May 02 2008 - 08:41 AM

Ok, I'll check out the manual again for offset. I probably missed it. I'll check out monoprice, too. Thanks for the info.

#4 of 9 OFFLINE   Leo Kerr

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Posted May 02 2008 - 10:21 AM

there is keystone correction, and then there is keystone correction. Digital and/or electronic keystone correction is... bad. Not quite "don't cross the beams" bad, but it's a brutal, lossy transform that's done to the picture. Optical keystone correction depends a great deal on the lens. It won't be harmless, but depending on how far out from "neutral" it is, it can be invisible. (Generally, I imagine you'd see a little bit of geometry distortion, some haloing and/or flare, and maybe some general softening of focus as the side effects of optical keystone correction. But again, it depends a great deal on the quality of the lens.) Leo

#5 of 9 OFFLINE   Brent_S

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Posted May 02 2008 - 03:43 PM


From trying to reverse the math in the charts on page 11 for 16:9 ceiling mount, it looks like the neutral position for the HS20 is lens center aligned with vertical top of the screen image area and centered horizontally. I don't know why they couldn't have added one sentence saying that (maybe I missed it) instead of referencing the screen center and lens center heights from the ceiling. Their screen size numbers appear to be referring to diagonal measurements, in case that helps.

For example. An 80" diagonal 16:9 screen has a vertical height of 40", making the vertical center 20" from the top/bottom of image. Sony's p. 11 chart says the screen center should be the (lens center distance from ceiling + 19 7/8") from the ceiling. Instead of referencing both to the ceiling, why not reference either from lens height or screen image top/bottom...it's so much simpler. This logic held up for the 4 or 5 different screen sizes I checked.

Don't forget to take into account all of the distance from the ceiling to the bottom of the HS20's case and then add another 2.5" for the distance from the base to the center of the lens.

They also give you the math to figure out how much freedom you have to adjust the image from an non-neutral mount. I'll leave that as an exercise for the reader. Posted Image

-Brent

#6 of 9 OFFLINE   FranklinD

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Posted May 02 2008 - 11:24 PM

So, basically, for a neutral position, the lens needs to be parallel with the top of the screen in the center? Is that you you/they are saying? Since this projector uses digital keystone correction, I guess I will avoid using it as much as possible. Actually, after messing with it more, I noticed that it's nearly impossible to get a perfectly square image. Does digital keystone correction decrease the quality to the entire image? Like it's either on or it's off? I would guess it would since it's digital and all of the information would have to be processed. Is that how it works? Thanks for the help.

#7 of 9 OFFLINE   Brent_S

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Posted May 03 2008 - 02:24 AM

Yes, if I interpreted Sony's math right...and I did review my thoughts a couple of different times. The center of the lens should be aligned with the top of the screen image area in a ceiling mount...reverse for table top. Also, you want to align the lens horizontally with the center of the screen image as well...the manual includes dimenional numbers for both the lens center from the case bottom and the horizontal offset from the center mounting screw. I'll have to let someone else speak to the badness detailes of keystone. At a minimum, it's got to reduce resolution since it can't add image to square up the tilt...somehow it's got to make the fat part skinnier. As far as picture squareness. I think keystone only corrects for up/down tilt. If the projector's not square to the screen from left to right, you're probably still going to be left with an out of square image using keystone. Even if is square there's a limit to how much keystone and Sideshot can correct...just work out the bizzaro math Sony used and it'll all be clear. :-) Good luck. -Brent

#8 of 9 OFFLINE   GeorgeAB

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Posted May 03 2008 - 05:13 AM

Digital keystone correction reduces resolution and induces moire' in the image. If you feed a multi-burst, or one-pixel-on-one-pixel-off pattern to your projector, you will usually see that only one click in either direction of keystone adjustment will visibly affect the image quality. NEVER use it for anything but static images, such as Power Point presentations and the like. If you value image fidelity and picture quality for motion programs, avoid it like the plague. Digital keystone correction is for convenience, not quality viewing of moving pictures. Attention to detail in following the manufacturer's mounting instructions is the best path to optimum image quality and realizing the most value from your projector. Best regards and beautiful pictures, G. Alan Brown, President CinemaQuest, Inc. "Advancing the art and science of electronic imaging"

#9 of 9 OFFLINE   FranklinD

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Posted May 03 2008 - 05:54 AM

Thanks for the help, guys.




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