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Does using lens shift degrade the projected image?

post #1 of 12
Thread Starter 
Hi guys, I'm planning to install the latest 2D/3D Epson or Panasonic home theater projector in my large living room (45 ft x 35 ft). My size screen is a DaLite 159" diagonal the projector will be mounted on the ceiling and I might have to use lens shift feature to install the projector closer to the ceiling. My question: does the moderate use of the lens shift degrade the picture or dim the brightness?
Thanks!
Alex
post #2 of 12
If only using a moderate amount of lens shift, should not effect the image. A ground and polished lens is usually best in the middle and not as good toward the edges, so you want to avoid shooting the image near the edge of the lens. Also due to the curvature of the lens, you can get some distortions, as you move away from the center. You might see some of this with test patterns, but most of the time, you don't see any problems with actual material. Some projector lens are better than others and with cheaper lens, you are more likely to notice.

I should add, I am talking about vertical lens shift. You never want to use horizontal lens shift.
Edited by AV Science Sales 5 - 2/13/13 at 6:40am
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post #3 of 12
Alex,

I tried both the AE8000 and 5020UB. I found the lens shift controls on the Epson to be terrible. The dial action had a ton of slack before actually starting to move the picture, and one dial would drag the other unless you held it in place. Basically you can't legitimately call one horizontal and the other vertical, because one doesn't stay in place while you're adjusting the other. It's possible I had a bad unit, but I much preferred the Panny's lockable joystick.

I don't find any significant image quality problems induced by using lens shift, but then again, my projector is pretty near the center of the screen to begin with so I'm not using much.
post #4 of 12
Thread Starter 
Thanks guys!
post #5 of 12
Quote:
Originally Posted by Xank View Post

I found the lens shift controls on the Epson to be terrible. The dial action had a ton of slack before actually starting to move the picture, and one dial would drag the other unless you held it in place. Basically you can't legitimately call one horizontal and the other vertical, because one doesn't stay in place while you're adjusting the other.

It's interesting that it's exactly the same in my Optoma HD8300.
post #6 of 12
Quote:
Originally Posted by Ilya Volk View Post

It's interesting that it's exactly the same in my Optoma HD8300.

That's kind of sad considering the HD8300 is more expensive than either the 5020 or the 8000.

With the Epson, it wasn't impossible to shift the lens into the right position, but it was frustrating to do. Since I don't have a fixed install, it's just one of those anxiety things where I know if the projector has to move at all, it will be a pain to get the lens shifted right again. With the Panasonic, I'm confident it will be quick, direct, and easy to fix if my projector has to move.

I'd be interested to learn more about how the mechanism works. I assume there's some kind of reason or constraint that forced them to design it that way, because otherwise no one in their right mind would design those dials to suck so much.
post #7 of 12
Quote:
Originally Posted by superfrognyc View Post

Thanks guys!

Good luck! Let us know how it turns out.
post #8 of 12
Quote:
Originally Posted by Xank View Post

That's kind of sad considering the HD8300 is more expensive than either the 5020 or the 8000.

Not really. I've seen it $2400 new on ebay.
post #9 of 12
Quote:
Originally Posted by Ilya Volk View Post

It's interesting that it's exactly the same in my Optoma HD8300.

Adjusting the vertical always effects the horizontal on projectors that have both horizontal and vertical lens shift. Same goes for adjusting the horizontal, it effects the vertical location of the image. That is why lens memory is such a big deal to people that have scope screens.
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post #10 of 12
There are many many posts throughout the history of AVS on lens shift.

At this point in my life all I will spend typing an answer is. Yes it does, it depends on several factors if you will notice it, and projectors have been designed without lens shift because it can hurt PQ, and some projectors have just vertical lens shift (because many need it despite its nasties) and do not include horizonral lens shift because there are alternatives in physical mounting to get around not having it (sort of do it right and don';t FU the horizaontal mounting location). And never rely on someone who tells you I use it and it doesn;t affect PQ. That said. I would never ever use horizontal lens shift and I would use vertical lens shift as needed but try to keep away from the extreme shifts.
Edited by mark haflich - 2/13/13 at 9:12am
post #11 of 12
I think it also depends on how much zoom you are using: I'm at minimum zoom and I made a point of moving my old HD350 to a higher position specifically so I could use some vertical lens shift to help resolve an issue caused by internal reflections in the lens. It worked very well in this regard so was a simple choice for me since it didn't seem to make any difference in terms of CA or sharpness even close to the screen, but I could see the effect of the reflections in the 'dead centre/no shift' position even back at my viewing position.

However, with the same projector I found that if I used zoom for 2.35:1 instead of my A lens that the image wasn't as sharp as using the lens (which seems opposite to what you'd expect putting an extra piece of glass in the way) so the zoom plus shift may have been at fault here. Since it seems popular on here to have the projector closer and using zoom, I wonder if this is why many users tend to prefer not using shift.

Interestingly, I've seen measurements posted that compared ANSI contrast on JVC projectors with different amounts of shift and the no shift position gave the worst ANSI figure and JVC projectors aren't particularly high ANSI contrast to start with.

My new X35 is in the same spot with maybe half shift (no horizontal) and is sharper still than the HD350, but again at minimum zoom (with A lens for 2.35:1).
post #12 of 12
You are right on all counts. when one is at long throw, the imiging exiting the lens is at its smallest and there is more glass surrounding it. So you can move it a bit without really hurting optical performance. At long throw, projectors just perform better all around except for the amount of lumens out,

Now it is true thtcontrast might go up a tad using extreme lens shift so that the light beam is closer to the interior of the lens barrel. But other performance factors would decrease such as sharpness in the areas away from lens center.

also high gain screens need long throws to avoid hotspotting at least in the case of angular refletive screens.i
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