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Mounting a projector off center of the screen?


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5 replies to this topic

#1 of 6 OFFLINE   micah bjj

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Posted July 16 2004 - 11:07 AM

Hello. I am having difficulties finding out where I will eventually put my projector. My room seems very difficult for a projector setup. I have a vaulted ceiling and a fan coming down from the ceiling. If I were to mount the projector on my side wall and have it not completely centered with the screen, how much picture quality would I lose? Someone explained to me that you can do this with a keystone correction(?) and it will work but will lose some quality. If I did this method the projector would be about three or four feet left of center on a 106" 16:9 screen. Is this to far off center or would I be alright and not lose to much quality? Thanks for all the help.

#2 of 6 OFFLINE   James Buhler

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Posted July 16 2004 - 11:30 AM

Sorry for not having an answer for you but I will be interested to see what the responses are going to be. I have held off on a projector as a basement support jack enclosure would mean that the projector would have to be about 1' off center. Hopefully this works out!! Posted Image
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#3 of 6 OFFLINE   Jim Mcc

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Posted July 16 2004 - 12:58 PM

Micah, you need a projector with horizontal lens shift(lets you move image left to right by moving lens). I'm not sure if 3-4 feet would be too much though. A couple examples are the Sanyo Z1 and Z2. Go to Projectorcentral.com and read up on all the good info. Good luck.

#4 of 6 OFFLINE   Daman

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Posted July 16 2004 - 06:15 PM

faced this problem today when i got my ceiling mount, mounted the projecter about 4 feet offset and the picture was getting angled.. keystone couldnt correct it so had to remount it at the center of the room. My projector doesnt have the horizontal offset i guess- its an infocus 4805

#5 of 6 OFFLINE   StephenHa

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Posted July 17 2004 - 05:46 AM

any keystone correction will lower the picture quality, but it may be something you can live with. I don't know of any projectors that will allow for that much distance, but there are external type keystone pieces that do that (one of the magazines did a test of one and he was quite a ways off center and it worked)

#6 of 6 OFFLINE   Leo Kerr

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Posted July 17 2004 - 06:06 AM

There are two types of keystone correction, and both are available in a wide variety of 'scales.'

Digital Keystone Correction is applying a distortion to the signal going to the display panels in hopes of compensating for the optical irregularities. This is a powerful bandwidth filter, and should be avoided at all costs.

Now, some projectors do single-axis keystone correction, others can do bi-axial correction.

I think that the best way for it to work is if you can seriously oversample the image... in the style of, "I've got a 720x480 source (DVD,) I need a projector with a native resolution of 1440x960 (minimum) to make this work well."

On the other hand, I've heard of an external box that you can use to 'correct' for all sorts of ills, including spherical surfaces. With its level of signal processing, it may not cause too much trouble.

Optical Keystone Correction is much more expensive. On the other hand, if you need to do keystone correction, this the best way to do it. Again, you can get single or bi-axial correction lenses... in my experience, a single axis lens adds roughly 400% to the cost; bi-axial correction at least doubles that cost again.

Then there's lens-shift for when you want to adjust the image globally... Manufacturers have gotten pretty good about being able to build in a fixed degree of lens shift without adding too much distortion without breaking the bank. (Virtually every small digital projector on the market today has this.)

One of the places I used to work, we had a number of slide projectors with fancy lenses... the Kodak slide projector was the standard Ektagraphic III projector, costing, what, $350? Each one in the main lecture hall had a nice Navitar lens with biaxial keystone and a fair degree of lens-shift adjustment in it. I think MSRP for these lenses was in the range of $2500 each.

Leo Kerr




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