Projector Lens Shift and Layout Planning (1 Viewer)

Jay Mitchosky · Mar 31, 2003

Hey All

It's a toss up whether or not this could be located here or in display devices...

Working on the layout and details of my pending HT construction and have run into a snag with projector positioning. I am considering the Sharp XV-Z10000U projector (with a 96" wide 16:9 Stewart FireHawk screen). The predominant recommendation for projector placement (on the vertical plane) is to have the center of the lens line up with the top of the screen (I am ceiling mounting). The screen will be placed such that my eyes are lined up 1/3rd from the bottom, which places the top of the screen (and hence the center of the projector lens) at 19" from my 8' ceiling. Not happy with the way that will look hanging out into space - be it an 8' or 80' ceiling it's going to be constrained by the screen position.

Here's where I'm confused. The Sharp includes an optical lens shift, which if I understand correctly allows you to compensate for vertical positioning up to one screen height with the projector placed anywhere between the top and bottom of the screen without having to employ digital keystone correction. What precisely is the benefit of this feature? I would imagine the goal of a lens shift would be to allow you to place the projector higher than the top edge of the screen (for ceiling mount) and then shift the image properly onto the screen plane - thereby keeping the projector up and out of the way.

Given that you are able to shift the image down while lined up with the top of the screen, why can you not have the projector elevated above and shift to the "normal" position? You would obviously not be able to cover the same range on the screen, but what value is there is moving the whole image below center anyway? What experience has everyone here had in their projector installations?

Jay Mitchosky · Apr 1, 2003

Going to try this in Display Devices...

mark alan · Apr 1, 2003

I am not sure what you are asking. The main purpose of the lens shift (in my opinion) is to allow you to slighly adjust your picture in order to exactly center your picture on the screen without degrading the image using a digital correction. That way, if you are a little off on your screen or mounting placement, you can still get the picture exactly right.

When I set up my Z1, I thought that I measured all my dimensions exactly, and I wouldn't have to shift my lens all the way down. Of course, I ended up using all the shift. Without it, though, I would have had to redo everything.

I don't see anyway you can have a projector which is flush against the ceiling and projects an image which begins two feet (or whatever) below the ceiling without sending the light at an angle and distorting the image. You either have to have the screen against the ceiling or accept that the projector will hang down from the ceiling. My ceiling in the basement is only a little over seven feet high, so I hung my projector on a wooden platform with chains. I lower it to use, and raise it up against the ceiling when it is not in use.

Doug_B · Apr 1, 2003

Jay,

I think you're out of luck with the Sharp. From my readings at AVS, it is true that the Sharp needs to be vertically between the top and bottom of the screen for its lens shift to work. However, a possible alternative to digital keystone correction may be tilting the projector and screen enough so that the projector "thinks" it's in line with the top of the screen (and perpendicular to the top). I do agree with you that there is added value in supporting a lens shift where the lens is vertically higher than the top of the screen. My Infocus 7200 does just that; however, it supports only a fixed vertical offset.

I don't see anyway you can have a projector which is flush against the ceiling and projects an image which begins two feet (or whatever) below the ceiling without sending the light at an angle and distorting the image. You either have to have the screen against the ceiling or accept that the projector will hang down from the ceiling.

There are projectors made just this way. The light is sent at an angle but does not distort. This is just an extension of how it's done for the projectors that line up with the top or bottom of the screen; it's just an angle shift as to where the image begins (not to say that it's easy to do, but it has been done). Why they all don't support this, I don't know. Maybe there are some tradeoffs, but the implementation does not imply picture distortion.

Besides the 7200 (in the HD2 pj category), I believe the (upcoming?) Dwin TV3 also supports a mounting higher than the screen but also has a flexible vertical lens shift (instead of the fixed shift of the 7200).

Doug

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Jay Mitchosky · Apr 1, 2003

The light is sent at an angle but does not distort. This is just an extension of how it's done for the projectors that line up with the top or bottom of the screen; it's just an angle shift as to where the image begins (not to say that it's easy to do, but it has been done).

This is where I get confused - how is it any different making that adjustment whether the projector lines up with the top of the screen or above? Either way it's a linear adjustment. That said, I did not realize the 7200 supported that type of shift.

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Doug_B · Apr 1, 2003

This is where I get confused - how is it any different making that adjustment whether the projector lines up with the top of the screen or above? Either way it's a linear adjustment. That said, I did not realize the 7200 supported that type of shift.

I don't claim to know the implementation well, so I really can't answer your first question. I take it on faith that the feedback I have read concerning many of the HD2 projectors (incl the Sharp) that they are limited to vertical shifts based on the lens height being between the top and bottom of the screen is in fact true.

As to the Infocus, it's basically a fixed vertical offset that amounts to ~16% of the screen height. In other words, multiply the screen height by 16%, and that is the vertical distance required (in the downward direction) between the center of the lens and the top of the screen, for a ceiling mount.

Doug

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Rob Tomlin · Apr 6, 2003

I believe the (upcoming?) Dwin TV3 also supports a mounting higher than the screen but also has a flexible vertical lens shift (instead of the fixed shift of the 7200).

That is correct. This, combined with the "two box" design, makes the DWIN a frontrunner in my potential projector purchase. These units are now being shipped to dealers, so you may want to hold off purchasing a Sharp until you give the DWIN a shot. I am!

From what I understand, all Japanese made pj's require the pj to be mounted between the top of the screen and bottom of the screen (i.e., the pj cannot be mounted any HIGHER than the TOP of the screen, or any lower than the bottom of the screen). I agree that this is not a good way to set up the pj.

American made pj's (including the InFocus and DWIN) allow you to mount the pj between the top of the screen and the ceiling (withing a certain distance, as mentioned by Doug), which is much more convenient.

Why the difference between the Japanese and American pj's in this regard is beyond me!

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Jay Mitchosky · Apr 6, 2003

Why the difference between the Japanese and American pj's in this regard is beyond me!

Ditto. Considering that living spaces in Japan are typically much smaller than those in North America. I would think the design differences would be the opposite. The Dwin has definitely caught my interest. The shorter throw vs. the Sharp is definitely offset by its ability to be mounted flush to the ceiling (at least in my installation). I'm really hoping the Dwin has the colors down because this is the Sharp's greatest strength IMO compared to every projector out there. Unbelievable control over color!

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Rob Tomlin · Apr 6, 2003

I'm really hoping the Dwin has the colors down because this is the Sharp's greatest strength IMO compared to every projector out there. Unbelievable control over color!

I'm with you there, Jay! Also, it has really good brightness too (better than the Marantz and HT300+). Did you read Greg Rogers review in Widescreen Review? A glowing review indeed, but, ironically, one of the things that he didn't like was the fact that the pj had to be lined up somewhere between the top and bottom of the screen!

I have high hopes for the Dwin. I am also sensitive to fan and color wheel noise (the Marantz rules in this regard) so I am hoping it will be quiet.

Some people on AVS Forum have recently indicated a problem with loud (faulty) fan noise on their Sharp's.

Just another reason to wait for the Dwin. Will it be perfect? Not likely, no pj is...but with the two box system and being able to mount the pj almost flush with the ceiling (along with glowing reviews from CES)....the Dwin has a lot going for it.

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Projector Lens Shift and Layout Planning (1 Viewer)

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Jay Mitchosky

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mark alan

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