My apologies if this has been answered elsewhere (couldn't find it in a search)...

The JVC site is telling me the RS1 can do 80% +/- vertical lens shift, but I don't quite get what this means. I'm trying to figure out how low the top of the screen can be in relation to the middle of the lens (w/o keystoning of course). Does this mean I can go 80% of one screen height below the lens (so, the top of the screen is below the middle of the lens)?

Basically its optical shift to allow for non ideal positionong. I would strongly suggest you use the minimum shift you can, ideally zero. 80% is a ludicous shift so try to stay at zero. Use a test patteren to determine the centre of travel as some PJ have thier lens shift off centre OOTB. Just note the 2 extremes and half it.

DigitalAV,

Let say you have a 16:9 screen of 100" diagonal, which is 49" vertical screen height. To calculate take 49" x .80 = 39.2" to get total vertical lens shift. However, the lens shift starts at the center of the screen so take 49" / 2 = 24.5" or half the screen width. Now, if you take 39.2 - 24.5, you have 14.7" which mans at max vertial lens shift for a 100" diagonal screen, the projector can be 14.7" above/below the top/bottom of the screen.

hope this helps.

My apologies if this has been answered elsewhere (couldn't find it in a search)...

The JVC site is telling me the RS1 can do 80% +/- vertical lens shift, but I don't quite get what this means.

It's been discussed in the "Owners" thread, but here's a picture from the JVC website that should help. As coldmachine said, you'll want to keep shift in either direction to a minimum.

http://pro.jvc.com/pro/attributes/PRESENT/images/rs1/rs1_lensshift.gif

Thanks so much!

As coldmachine said, there are negatives to pegging the lens shift. But, if your installation requires it, optical shift is much better than using any sort of digital keystone, so this projector will fill a lot of niches.

No one has posted what the 'negatives' are with the lens shift. I've been following all the threads and even this one say's don't use the lens shift when possible. So, what are they? Additional Convergence issues? Loss of lumens? I don't think anyone has actually cranked the lens shift to the max and reported the results.

I ask, because I would like to use some shift to get the PJ higher up to lower the fan noise right above my head.

What I have noticed is a softening of the image somewhat at the extremes. Convergence doesn't really change, but the illusion of it can since more CA can occur.

geometry suffers too, even worse if you scope.

Somewhere I saw a post that stated pegging the vertical offset @ 80% also resulted in a 12% loss in lumens.

Lumen reduction would be a benefit as it will bit too bright to start. But, geometry and/or focus issues are not acceptable. My ceiling mount can go from top of screen up, so I'll just have to see when I get my RS1. I had a demo unit in house to test, but forgot to try for lens shift issues.

Ernie...top of the screen is much better than above if you can.

From Projector Central's review (http://www.projectorcentral.com/jvc_dla-rs1.htm) "One final note on lumen output—the projector loses about 12% of its light output when the lens shift is set to the extreme ends of the lens shift range as compared to having the lens in the neutral position. That brought the lowest reading we could get from the RS1 down to 340 lumens (low lamp power, max telephoto, max lens shift). "
But no comment on other effects (of the kind one might expect at the edge of an image circle from a lens - CA, loss of sharpness etc) so far from anyone. One might expect those to be worse as one goes more wide-angle from the max telephoto. I'm resigned to testing it out myself beofre finally mounting it (the room's not ready and the unit's not ordered ytet, so perhaps someone will be able to provide some update before then :D )