RS50/RS60 Positioning Question - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 6 Old 03-29-2011, 11:39 PM - Thread Starter
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I am about ready to pull the trigger on either an RS50 or RS60. I am looking at having the projector recessed inside the soffit at the back of my Theater room rather than on a mount. My problem is that due to existing structure the opening that will hold the projector will be 3 inches off of center of the front screen. I am aware that there is lens shift and I believe that the 3 inches could be corrected for with minimal if any image reduction. Can anyone confirm that? also in addition to being off 3inches from center (at screen), the projector will be above the top of the screen, so the lens will have to adjust downwards for about 10inches also. Can anyone confirm my assumptions above wrt the image quality not being impacted?

thx,
Jim

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post #2 of 6 Old 03-30-2011, 08:38 AM
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Jim,
I had the same questions wrt my RS-50. Page 21 of the installation manual has a couple of charts describing acceptable combinations of vertical and horizontal lens shift. It's a bit of a head-scratcher, as they refer to a % of the image height and width. In my case, with a 52" H screen, the 80% point is 41.6". Subtracting that from 52", I get a maximumm drop of 11.4" from the center of the lens to the top of the screen. That's a number I understand from my CRT days.

For your install, calculate the % of vertical shift you'll need to accomodate the drop you have, and see if you've got enough left over to handle the horizontal shift.

Others here may be able explain it better or correct me if I've interpreted the info incorrectly. Bottm line, this calc method worked for my installation.

I have the RS-50 nestled pretty close to the ceiling on the Unistrut mount that held my G70 for 10 years, and the lens shift has enough range to cover my drop and then some. No issues with distortion, no electronic adjustments needed.

P.S. you can download the IM from the JVC website.

Regards,

Tom

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post #3 of 6 Old 03-30-2011, 10:05 AM
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Tom has the numbers right, but I think a bit confused on the execution. That is if I understand it correctly (which is iffy...)

My understanding is this:

The maximum allowable shift is up to 80% of the total projected image height in the vertical, as measured from the centre of the screen. So if you have a 52" high screen, your maximum allowable shift up or down is 41.6" from the centre point. Meaning you can mount the projector as much as 41.6" away from the centre of the screen. That would be 41.6" - 26" = 15.6" above the top of the screen.

The shift allows I think up to 34% in the horizontal, but combining the some horizontal with some vertical will reduce the percentage allowed. As tom mentioned, there are diagrams and a graph in the owners manual which you can download from JVC that may help you out.

As for how it impacts image quality, I've heard conflicting reports but I don't think you'll find any substantive detriment using lens shift. Having the projector high-shelf mounted or ceiling-mounted is quite common, so I would well imagine that JVC took every effort to maintain a very high image quality using this sort of setup.
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post #4 of 6 Old 04-26-2011, 09:55 AM
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My callibrator was emphatic that ceiling mounting the JVCs at the top of the screen results in noticeably better ansi contrast than shelf mounting at the middle of the screen.

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post #5 of 6 Old 04-26-2011, 10:19 AM
 
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I am sure the projector can handle 3 inches of horizontal shifting. The only thing you have to take into consideration in that horizontal and veritical shifting influence each other so the more you lets say horizontal shift, the less amount of vertical shifting you will be able to do
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post #6 of 6 Old 04-26-2011, 11:38 AM
 
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Also take air flow into consideration. Need to make sure that you allow for the projector exhaust to work.
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