Keystoning image, Loss of quality?

**tonyvdb** · **03-12-08, 03:33 PM**

My Sanyo Z2 is ceiling mounted about 10ft from the screen and level with the top but the image is slightly wider on the bottom than on the top of the screen.
My question is I can use the Keystone feature to fix this but does that affect the image quality?

**lcaillo** · **03-12-08, 03:52 PM**

I am not specifically familiar with that unit, but I thought it had a lens shift adjustment to allow you to correct for keystone optically and not electronically. If you correct optically on a projector you generally do not significantly affect quality until you go pretty far. If you have to correct it electronically on a fixed pixel projector, you will distort the pixels and have unwanted effects such as moire. On a CRT projector, of course, this is not a problem.

**tonyvdb** · **03-12-08, 04:48 PM**

The lens shift is working properly but there still seems to be a wider image at the bottom than at the top by about 1/4 inch on each side.
The projector is pointed directly at the screen. seen here

**Mr. Mike** · **03-13-08, 02:35 PM**

Tony,

Although the projector may be even with the top of the screen (same distance from the ceiling), both the screen and the projector must be level to avoid needing to use the keystone adjustment.

My guess would be that you will find a slight downward tip (at the front) on the projector. This would cause the image to be slightly larger on the bottom than the top. From your description, it should only be off a smidge.

The projector needs to be level in all directions. Side to side and front to back.

The keystone correction will indeed distort the image, causing stair stepping in the image. It sounds like yours is not far off. You may need to lower the projector a tiny bit to be able to level it off front to rear and have the image stay on the screen, or maybe raise the screen a touch.

When installing my projector, I worked it in reverse. I installed the projector, zeroed out the keystone, leveled the projector using a level and double checked it using the projected the image on my wall making sure it was square by measuring it twelve ways to sunday...and then hung the screen where the image was.

Perfect fit.

Good luck resolving the issue.

Mike

**<^..^>Smokey Joe** · **03-14-08, 02:02 AM**

To answer your question, 'yes' keystone effects quality.

The effects can be clearly seen in a bandwidth display test.

However getting a projector mounted perfectly is not always possible when the room is used for general duties. Quite often a compromise has to be made, requiring loss of best setup for the PJ.

The trick is to find the range of positions where you don't cause ill effects that you discribe and position the pj to be within this range. Then ask yourself if this fits the room for it's other uses?

Some things to consider as you do this though, is the screen level, virtical, square to the Pj; Is the pj level square to the screen. If you get where I am going you understand that alignment starts with the fundimentals. Ignore them and the result gets harder to resolve.

Laser levels and or string lines measuring tape and a spare pair of hands are the tools needed, checking levels and squareness can solve alot of ills.
I might add that most projectors have a natural central position of about 1/4~1/3 from the lower or upper edge(depending if you are roof mounted or not). Being set at the edge at a relatively close range of 10ft will make things hard to resolve.

A trick though is to angle the bottom of the screen up, drop the angle of the PJ down. A couple of degrees would be hard to notice but may remove the shape issue. Depends on how far you need to go.

Have a careful read of your manual for 'best pos'tion' then see how you are setup.

goodluck.

**Jodean** · **03-15-08, 01:09 PM**

glad i read this.....never even thought of raising the feet on the pj and lowering the lens shift to eliminate the +1 keystone i had before....

My pj is sitting on a shelf at ceiling height and this worked great!!!

Thanks guys!!

**tonyvdb** · **03-15-08, 04:54 PM**

Yup, I just had to angle up the front of the projector and adjust the lens shift and all is well.
Thanks everyone for the suggestions.

**Blaser** · **03-15-08, 05:13 PM**

While keystone will distort the image, I don't think a small amount will badly affect the viewing experience that much. At least it is better than watching a trapezoidal picture

**<^..^>Smokey Joe** · **03-15-08, 06:29 PM**

You can effectively turn a 1080 image into a 720 image by using keystone correction. It is very worthwhile to get alignment as good as one can. It is infact the fundimental first step in image calibration.

**lcaillo** · **03-16-08, 12:37 AM**

Quote:

blaser wrote:

While keystone will distort the image, I don't think a small amount will badly affect the viewing experience that much. At least it is better than watching a trapezoidal picture

I completely differ on that. I would much rather have a bit of keystone or have to tilt the screen a bit than have the distortion and reduction in resolution that electronically keystoning the image will effect. It is almost never impossible to properly place the projector and or screen so that it is not necesary, and if it is impossible, tilting the screen a few degrees is a perfectly good alternative.

**Blaser** · **03-19-08, 06:14 PM**

OK. But I do some keystoning and I can never see any difference (with or without), but a trapezoidal shape. Tilting a screen is not very esthetic as well BTW.
Can you tell me how much resolution will be affected?

**lcaillo** · **03-19-08, 06:16 PM**

A lot. Put a resolution pattern or multiburst pattern up and you will be shocked.

Or don't! Once you see what it is doing to the image in the test patterns you may see it in other images. If you don't see it now and you don't plan to modify your installation, STOP asking questions. Ignorance is bliss. Ignore my sig.

**Jodean** · **03-19-08, 09:33 PM**

man....after i do some (12 or so) keyston(ing) i usually cant even see the screen!!!!!

Esp if its keystone premium

**Blaser** · **03-20-08, 05:08 PM**

I am speaking about SLIGHT keystone I am using (+2). Of course I have run test patterns and the effects are neglectable in my setup....Full Stop! But tilting the screen is unthinkable!

**Prof.** · **03-20-08, 05:26 PM**

I'm inclined to agree with blazer on keystoning..
I've adjusted keystone with my DLP projector without any detrimental affect on the quality of the image..
I think it must be that some projectors handle it better than others,..

**Blaser** · **03-20-08, 05:35 PM**

Quote:

Prof. wrote:

I'm inclined to agree with blazer on keystoning..
I've adjusted keystone with my DLP projector without any detrimental affect on the quality of the image..
I think it must be that some projectors handle it better than others,..

Exactly, I forgot to mention that: Yes all projectors will have a degradation in picture quality, some huge and other not so: not all projectors are created equal

**lcaillo** · **03-20-08, 07:13 PM**

With respect to electronic keystoning they are all very similar. Just put a multiburst pattern up. You will see what happens to your fine resolution and the artifacts that result. Think about what has to happen to correct it. It is the equivalent at scaling an image to slightly incrementing frequencies on each line. You get a mess.

**muzz** · **03-21-08, 06:19 PM**

Quote:

Jodean wrote:

man....after i do some (12 or so) keyston(ing) i usually cant even see the screen!!!!!

Esp if its keystone premium

Hehehehehehe

Advertisement