[thuan98]

Hi all,

My PJ NEC260K was installed ceiling mounted. But there is a keystone problem: on right side of the screen no trapezoid (no keystone correction needed). But on the left screen, there is trapezoid shape, the top is wider than bottom, about 5 inches !


Which way should I move the PJ to fix the issue ? The PJ is at center and perpendicular to the screen (to my best)


Tilt to left, right, up, down ?


BTW: I try to avoid using digital keystone correction as possible

TIA

Thuan

 

[Cyrano]

Quote:

Originally posted by thuan98 Hi all, My PJ NEC260K was installed ceiling mounted. But there is a keystone problem: on right side of the screen no trapezoid (no keystone correction needed). But on the left screen, there is trapezoid shape, the top is wider than bottom, about 5 inches! Which way should I move the PJ to fix the issue ? The PJ is at center and perpendicular to the screen (to my best)

That's a lot!

What axis adjustments can you make with your mount? You are not perpendicular to the screen or your screen is not flat. It is odd that the right side is perfect and the left side is so off.


Can you move your PJ? If so, move it about and see what happens onscreen. If you have hard mounted it to the ceiling - create a different method of mounting it. You need to be able to adjust it in several axis'. (It's better if it can move in all axis', but Yaw and Pitch are pretty essential to remove trapezoidal shapes.)


If it was professionally done, get them back and have them do it again - it just needs to be adjustable.

 

[Ericbres]

*Thinking back to horizon painting in art class back in elementary school*


I believe if the upper left corner is wider ... you will need to turn the projector to the right.

However, if you are about 5" off ... you will probably end up now with a couple inches worth of keystone adjustment that need to be done.


But to correct it, I would first tilt the nose of the projector UP.


Best of luck to you.

 

[Cyrano]

Quote:

Originally posted by Ericbres I believe if the upper left corner is wider ... you will need to turn the projector to the right. However, if you are about 5" off ... you will probably end up now with a couple inches worth of keystone adjustment that need to be done. But to correct it, I would first tilt the nose of the projector UP. Best of luck to you.

Good advice - except won't tilting the PJ up make the top wider?


If you have adjustability - move it about and see what happens. It will become apparent.


I echo Ericbres' wish for luck.


And Ericbres has a Great tagline!

 

[Ericbres]

Thanks Cyrano ... on the comment and the correction.

Yes, tilting the projector upwards will not work. He would need to tilt it downwards ... bringing the light path from the top of the lens closer to the screen. Sorry about that!

 

[thuan98]

I understand that tilt PJ downward will make the bottom wider.


I guess I should rephase as: which way PJ needs to move to get equally trapezoid shape on both left and right screen.


Quote:

"I believe if the upper left corner is wider ... you will need to turn the projector to the right."


No, I think it only true for horizontal trapezoid (left side is longer than right side)

I imagine a flash light with square hole to shoot the light out


My PJ is wall mount (on shelf) so I can move anyway I want. I did turn left and right, don't see much differences


Thanks

Thuan

 

[Cyrano]

If you've got adjustment capability in all axis' (Pitch, Yaw, rotate on axis - if there's more, somebody, tell me.) then either your screen has a defect or your PJ does.

Pick it up. Aim it like a flashlight. Aim it at a known flat surface. If you can't make a rectangle with 90 degree corners then something is either broken or not flat.


I'm out.


Good luck.

 

[Kysersose]

You could try NEC's 3D Reform if it's impossible to fix by moving the PJ. I have my 240K on a shelf that is attached to the ceiling and I've never had to use keystoning. Is it possible that the wall the screen is on is not straight? Or the screen itself?


Cyrano, with NEC's 3D Reform you can sit the PJ against one of the side walls and still project a perfect image on a screen in the middle of the room. I've done it myself just to see it with my own eyes.

Still, I chose to ceiling mount it and use no keystoning to avoid any distortion.

 

[Cyrano]

Quote:

Originally posted by Kysersose Cyrano, with NEC's 3D Reform you can sit the PJ against one of the side walls and still project a perfect image on a screen in the middle of the room. I've done it myself just to see it with my own eyes. Still, I chose to ceiling mount it and use no keystoning to avoid any distortion.

It sounds like you're talking about keystoning, if distortion might be involved. Or is NEC's 3D Reform an offset?


The problem presented here sounds odd in that he is treating the two sides of the projected image as though each side is separately adjustable. I don't think of a trapezoidal problem as being restricted and correctable on one side only. I think of it as a whole image that needs correction. He needs to move the PJ so that the problem is equal on both sides. (this is what Ericbres was trying to cure by yawing the PJ to the right.) Whether or not it can shoot a "square" image sideways isn't at question. I'm sure there are capabilities I know nothing about in a PJ I know nothing about. I just wondered if his PJ can shoot a "square" image.


But, I could be wrong. There's more to this than meets the eye.

 

[Kysersose]

It's beyond keystoning. The 240K has a seperate "keystoning" function as well as 3D Reform. I've only played with it but it's a little like a CRT's convergence and beyond. You can really play with 8 points within the image.


The 260K should be able to project a "square" image without any real tinkering.

 

[Kysersose]

Here's a bit of info on it.

Quote:

The new NEC chip is the result of exhaustive research by NEC Viewtechnology, who have developed ASIC scaling for converting picture elements, making NEC unique among projector manufacturers. Independent algorithms manage the vertical, horizontal, or angled corrections, thus increasing the range in which the projector can be placed. Angled projection ability lets you place the projector anywhere you like. A newly developed NEC chip provides the 3D Reform function, a keystone correction feature that corrects trapezoidal distortions -something which was beyond the capabilities of traditional "up-down-left-right" correction functions. The result is vivid, razor-sharp image projection. If the projection is distorted, simply set the four corners of the screen to activate the keystone correction function and square the picture. This allows greater freedom in setting up the projector, because it can now be set up at an angle in relation to the screen. The projector no longer needs to be placed right in front of the screen where it can block the audience's view of the screen. 40° vertical and 30° horizontal (25° for the LT240. 27° for the MT1065/1060 ) from the angle of projection.

 

[Cyrano]

Kysersose:


Well now you've done it. I can see I'm going to have to limit myself to only commenting on things I know.


That's rather restrictive, you realize. Thanks for the info.


But, after all is said and done, does the picture suffer any degradation due to this rather sensible way of doing keystoning. (Simply setting the four corners of the screen up as "targets".)


Would the image look better shooting perpendicularly straight at the screen than it does by electronically straightening itself? I could see a situation where a DMD chip could be "floated' to align itself with the screen but electronic conversions usually leave a footprint.


Anyway, I hope you're looking at a nice rectangular picture thuan98!

 

[Kysersose]

I think that electronically straightening it does cause some "minor" distortion. So minor in fact that I don't think anyone would notice unless they walked right up to the screen and looked at the pixels. That's the only way that I could see any.


Still, I chose to project from the ceiling "straight on" to avoid altering the image.


thuan98, any luck?

 

[thuan98]

Thanks for all response,

Yes, I can fix this problem with 3D-reform (keystone not use, set to 0)

But I try to physically relocate the PJ to avoid any artifacts when using digital adjustment which might loss some pixels/mirrors in the total resolution.

If no digital adjustment, the edges are sharp but if using 3D-reform the edge become stair-step which mean some pixels have been turn off to make the image perfectly square at corners.


I can live with it, just a curious if I can totally avoid digital keystone/3D_reform adjustment


Regards

Thuan