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Optical ideal is with projector height at the center of screen, even in ceiling mode?

post #1 of 13
Thread Starter 
Newbie first time projector owner.. I just took my Panasonic PT-AR100 out of the box to check the ideal ceiling extension column height. I set the menu to project from front/ceiling.

All of the diagrams in the manual (and everywhere else I've seen) show the image lined up with the top of the screen and top of the lens when it is in ceiling mode.

However when I have the optical shift lever in the center, the image is not lined up like this. Instead the image is lined up so that the projector would have to be vertically dropped down quite far, vertically centered with the screen.

I am trying to avoid moving the optical shift lever down so I don't have to use keystone correction.

Am I missing something obvious? Some other setting? Shouldn't the image line up so the lens is at the top of the screen image when it is in ceiling mode, and the optical shift lever is in the center?
post #2 of 13
In ceiling mode, the projector needs to be mounted to the ceiling upside down. Do you have it upside down?
post #3 of 13
Thread Starter 
yep, it's upside down.
post #4 of 13
Yes, that is the way most projectors work when they have a lot of lens shift - they throw the image with the lens at the center of the screen both vertically and horizontally. It will not make a visible difference to the image to use enough lens shift to put the lens at the top of the screen. Those projectors work great either way, ceiling mounted or shelf mounted.

You will not need keystone correction, you'll see.
post #5 of 13
Quote:
Originally Posted by DDBear View Post

Newbie first time projector owner.. I just took my Panasonic PT-AR100 out of the box to check the ideal ceiling extension column height. I set the menu to project from front/ceiling.

All of the diagrams in the manual (and everywhere else I've seen) show the image lined up with the top of the screen and top of the lens when it is in ceiling mode.

However when I have the optical shift lever in the center, the image is not lined up like this. Instead the image is lined up so that the projector would have to be vertically dropped down quite far, vertically centered with the screen.

I am trying to avoid moving the optical shift lever down so I don't have to use keystone correction.

Am I missing something obvious? Some other setting? Shouldn't the image line up so the lens is at the top of the screen image when it is in ceiling mode, and the optical shift lever is in the center?

One of the best visual depictions of what is involved with an LCD projector with lens shift is the online Epson calculator.

http://www.epson.com/alf_upload/land...ce-calculator/

Under Select choose the Home projector tab, the Epson 8350 (as an example), change the Installation Type to Ceiling and turn Lens shift on. There you will see the "0" lens shift position is at mid screen, the blue-gray area around the screen is the amount of lens shift possible with this projector. i don't know of anyone who has mounted their projector at the mid screen position although some shelf mounting may come close. I have my AR100U ceiling mounted (8 foot ceiling height) a few inches below the top of the screen and use lens shift to place the image directly on the screen (avoid any keystone adjustment) and the picture looks great.
post #6 of 13
My new 8350 is mounted 21.25" above the top of the screen. I am pretty much using all the available lens shift the projector provides. The Epson 8350 does not have keystone correction but you don't need it as long as your projector is level and parallel to the screen.

Why is my projector located so high above the screen?

1) Because I can, the lens shift allows much placement flexibility.
2) The projector is as far away from my ears as possible, even though the 8350 is the quietest projector in its price range, I don't like to hear projector noise.
3) I didn't feel like installing ceiling mounting plate and down tube extension, just more cost and if I don't need it I didn't want to bother.
4) The projector mount, even though it's only 5" from the ceiling, gave me the space from the ceiling that I needed, even reused some of the existing mounting holes from my last projector mount.
post #7 of 13
Thread Starter 
Great responses. From a physics perspective isn't lens shift essentially the same tilting the projector down? So wouldn't both result in a slightly trapezoid image unless it is keystone corrected (but in most cases it's too small to notice)? Or does lens shift apply an "optical" keystone correction at the same time when the light beam is shifted?
post #8 of 13
Quote:
Originally Posted by DDBear View Post

Great responses. From a physics perspective isn't lens shift essentially the same tilting the projector down? So wouldn't both result in a slightly trapezoid image unless it is keystone corrected (but in most cases it's too small to notice)? Or does lens shift apply an "optical" keystone correction at the same time when the light beam is shifted?

Using a projector's keystone function causes an algorithm to kick in which allows you to change the shape of the screen and introduces image degradation. Lens shift is the physical movement of the lens within the projector, it does not produce a trapezoid as long as the projector is square to the screen.
post #9 of 13
Thread Starter 
I read that optical shift can create a little bit of pincushion?
post #10 of 13
Quote:
Originally Posted by DDBear View Post

I read that optical shift can create a little bit of pincushion?

Several years ago Art Feierman wrote an article about lens shift and keystone which is still applicable today. He talks about a slight bowing when using lens shift although I've never encountered it myself on any of the projectors I owned.

http://www.projectorreviews.com/advi...alkeystone.php
post #11 of 13
No pincushion on mine and I am using nearly all the available lens shift.
post #12 of 13
Quote:
Originally Posted by DDBear View Post

Great responses. From a physics perspective isn't lens shift essentially the same tilting the projector down? So wouldn't both result in a slightly trapezoid image unless it is keystone corrected (but in most cases it's too small to notice)? Or does lens shift apply an "optical" keystone correction at the same time when the light beam is shifted?

It's hard to explain what it does from a physics perspective, but yes, it is as if it adds optical keystone correction to the shift, but the projector is not tilted and neither is the picture. The lens shift just throws the picture further down, or to the side, however you set the shift.

That's why lens shift is soo cool. Anybody could just tilt their projector, but you need lens shift to get your image shifted without the trapezoidal distortion. (or you must mount your projector in that one position that works for that projector.)
post #13 of 13
Drastic amounts of lens shift in either direction can effect your focus, it's best to avoid using lens shift when possible. That said, if you have to use it then you have to use it.

Jason
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