Perfect Geometry for projector

[docferdie]

Is it possible to get perfect geometry with a ceiling mounted projector and a wall mounted screen? Are professional installers supposed to be able to get all four corners of the image to match your chosen screen? Am I asking the installer too much if want the geometry to be like that of a flat panel monitor?

 

[BMXTRIX]

Perfect is rare... Keep in mind plasmas put a nice rectangular trim up to make it all perfect.

BUT: Yes, it should be incredibly close. My installs put it at about 1/4" off at the most. Things like the heating and cooling of the room can minutely adjust optics and shift the image a teenie bit which can throw off the image a fair bit more. The house settling can shift joists that teenie bit which throws things off.

A cheaper projector without lens shift can DEFINITELY make things a good deal more difficult in achieving the perfectly squared up and centered image.

Most often though - it is a clueless and rushed installer than doesn't get the image really REALLY close to perfect on the screen. I've met people who install projectors regularly who still tilt projectors and use keystone correction before using lens shift to square up an image. Just crazy!

 

[RLA]

Am I asking the installer too much if want the geometry to be like that of a flat panel monitor?

A good installer would make sure the PJ is level and square to the screen regardless if it is fixed lens or has lens shift. The PJ should be installed first then project an image on the wall the size of the screen material when the PJ is level and square. Avia has several good geometry and convergence test patterns, circle hatch is good to use.

The installer should outline the projected image, then insure the image is at the correct height in relationship to the seated viewing position when the client is in the seat in a relaxed position. If the screen height is incorrect the drop distance of the projector should be adjusted mechanically. Lens shift should only be used to make fine adjustments.

correct screen height insures comfort, relaxation and rest. Keep in mind that many movies exceed 2 hours and it is difficult to sit in a chair for 2 hours if your not comfortable. The last step is to properly hang the screen insuring it is level vertically and horizontally and proper tension obtained between the top and bottom bracket on fixed screens. Too much tension can separate the joints on the mitered corners of the screen, too little tension can cause the screen to rattle and shake against the wall. Motorized screens should be adjusted for proper drop distance and smooth drop and retraction.

Selecting the correct screen material,gain and size is essential for good performance. The selection should be made based on the projectors specs, room ambient light conditions and viewing distance

Hope this helps

 

[BMXTRIX]

I forgot to mention - and RLA will know this better than myself - there is always the chance with front projection that there will be some geometry errors that can't be corrected. This would be caused by distortion due to the round lens. With digital projectors it may not be possible to correct for this distortion and if a line coming out of a digital projector is not perfectly straight, there may be little to nothing a dealer can do to correct for it.

A dealer should KNOW which projectors have this issue and how severe it is, but since front projection is not the same as a plasma/lcd which uses a fixed array of pixels and doesn't project from the rear so it can't really be framed perfectly, you are left with having to use the optics and design work of the company that made the projector in combination with solid installation work. Unfortunately - a lot of those factors may be to much for a manufacturer to live up to.

RLA: Lens shift is always used isn't it? I mean, most commonly the neutral position for lens shift will put a projector in the middle of the screen. Far to low for ceiling mounting. Most people want their projector as high as possible in a room which dictates lens shift. A properly designed and built optical system should not degrade the image quality or distort the image due to use of lens shift, though I realize it may to some degree, especially with cheaper projectors.

Either way, I have no issues with lens shift, but I have serious issues with digital keystone correction which immediately degrades image quality.

 

[docferdie]

Thanks for the replies. This saves me from spending several more hours of fine tuning. The image actually looks great. The only reason I noted the geometry imperfection was the fact that it was on the right side where most web page scrollbars are. When watching movies and playing xbox 360 it's beautiful. Now I can move on to ordering seats. By the way, I am using an epson procinema 800 with a vutec 1.3 gain fixed frame screen.

 

[RLA]

RLA: Lens shift is always used isn't it? I mean, most commonly the neutral position for lens shift will put a projector in the middle of the screen

Hi BMX,
Don’t confuse lens shift with vertical offset. Most new projectors have shallow vertical offsets (except for the HD72 My belief is if you can keep the light engine and the lens as square as possible to the screen using minimal lens shift you will increase performance. Installing a few of the Sharp Dt-200's and 300's confirmed this belief. The client was almost maxed out on vertical lens shift and the top of the image didn’t look as sharp as the center. We corrected this by lowering the projector about six inches giving the lens shift more headroom and the image became very uniform. Projectors with very good vertical lens shift capabilities such as the Panasonic and Sanyo don’t seem to be effected as much.

You are correct about barrel distortion, this is caused by improper lens alignment. The most recent projector to suffer from this problem was the Infocus 7200. It appears that most of the new projectors shipping have excellent lens geometry. The only problem I see today is LCD panel misalignment. Many of the Sanyo Z-2, Z-3 and Z-4 had terrible panel alignment; colors projected onto screen surfaces would be 1/2 to 3/4 of a pixel width off.

Have a great weekend all!