Adjusting Keystone on AE900U

[hometheaterman]

I have a Panasonic AE900U I've had for a while now. Probably a year and a half or so. Anyway since I've mounted it on the ceiling which it took me a while to get around to I've had an issue where the screen seems to angle in at the top. It's not too noticable on 16x9 stuff but on 4x3 stuff where you have black bars on the side you can really notice it because the black bars are quite a bit wider at the bottom than the top. I measured once but can't remember how much difference but want to say it was around a inch. I've just lived with it. It bugged me but it was the only thing that bugs me really about the projector and was well worth putting up with it as I love everything else soo much. Anyway I read on here about how Keystone adjusts it but that it's not a good idea to use that to adjust it to use the lens shift. I'm assuming the lens shift is the thing on the projector itself that adjusts the lens up and down and what not. This is how I adjusted it and tried to get the projector level but it still had this issue.

Anyway, I tried adjusting the keystone tonight and if I put it at -1 it gets it close and -2 is about perfect. Is there any harm in leaving it at -2? I've read it's not good to adjust but why? Can I leave it at -2 without hurting anything? It looks really good right now. Would even more than -2 say -3 or -5 or anything hurt? I love how it looks now and it basically fixed the issue I was having. I think it's really close now but I might tweek it more but I measured and it seemed the same. Can I safely leave it like this? Thanks.

 

[jayn_j]

That's what it is there for. Greg has pointed out in other threads here that using keystone will lower your resolution. However, a -2 is a pretty mild adjustment.

You would get a better picture if Greg or another certified calibrator was to go in and adjust the keystone optically, but if an ISF calibration (recommended) is not in your plans, this is a good solution for now.

 

[Gregg Loewen]

-1, -2...it makes no difference....it is not ZERO adjustment.

The setting of 1 or 2 clicks will kill your resolution and add a BUNCH of artifacts.

Why? ....
think straight vertical lines....pixel on top of pixels..
As soon as you do ANY electronic keystone adjustment the vertical lines will have to be electronically shifted, this will cause jaggies and moire artifacting in your images.

Continuing but not related...
vertical and horizontal sizing...
when this done...you lose 1 to 1 pixel mapping and there for you will lose resolution once again.

Regards

Gregg

 

[JimMcC]

I don't see why you would need to use keystone at all, since you have lens shift on the projector. Unless your ceiling is really high. I think most people with lens shift projectors place it on a rear shelf.

 

[jayn_j]

Greg, with all due respect, I don't see it. I would agree that a mild keystone (+1 has no real scale or meanng) would add a small number of stairsteps to a vertical line. I can also see that it would cause some pixel interpolation and potentially SOME loss of pixels at the extreme ends. But isn't the statement "killing your resolution" just a bit extreme here. I'm talking about real world pictures, and not test patterns that are designed to display the flaw, as I know I can create fine line patterns that will show moire patterns, but these are not realistic.

 

[JimMcC]

Theoretically he's right. But we don't live in a perfect world. Some of us(like me) need to use keystone, due to a low ceiling. I see no difference in the image by using keystone.

 

[Gregg Loewen]

not at all theoretical, just use some test patterns...that is what they are there for.

 

[JimMcC]

I didn't buy my projector to watch test patterns. I bought it to watch movies and football games. And I see no difference in the image when using keystone.

 

[Gregg Loewen]

then you simply dont know what to look for, your display probably has never been calibrated either?

 

[JimMcC]

Not by a professional. I did it with the DVE-HD disc.

 

[Gregg Loewen]

on a related note....(the same note).

I would not be able to count the # of internet threads I have read about the "obsessive need for 1 to 1 pixel mapping". Moving the keystone control by even 1 click would eliminate 1 to 1 pixel mapping.

I did it with the DVE-HD disc.

Ah...so you do watch test patterns !!! lol

 

[teachsac]

Ah...so you do watch test patterns !!! lol

Almost as exciting as watching the grass grow

S~

 

[Citation4444]

I agree wholeheartedly with Gregg recommending against the use of any electronic keystone adjustment. It is guaranteed to destroy your image quality, even if you can't see it. A far better way to deal with this is to insure that your screen is perpendicular with the projected beam. Use the offset optical control first after making sure the projector is level in both planes. If this is not enough, then angling the screen can be used. This usually requires angling the bottom of the screen away from the wall slightly until the geometry is correct.