How do you get your projector "Perfectly Square"?

If your projector has adjustable feet try raising the lower side's feet or just stick a quarter or something under one side until both are level. I've used the quarter trick in the past to level one side with the other.

If the problem is that the image is rotated so that one side is higher than the other, then you need to adjust the feet to get the projector level with the screen.

If one side is longer than the other, then you need to turn the projector. The shorter side is closer to the screen than the longer one, so move that edge away from the screen. When you do this, you will then have to either use lens shift, or physically move the projector over to one side to re-centre the image.

Here's a quick sketch of what I mean:



First adjustment on the left if the image is rotated, second adjustment on the right if it looks trapezoidal.

Just in case you have not figure it out, this is a link for post on the 6800 forum that may help you...There are a few posts ahead of this one that tells the story...

http://www.avsforum.com/avs-vb/showp...&postcount=422

If the screen is mounted to a wall, and the walls of the room are slightly out of square, you will also have this problem.

I have my screen suspended from the ceiling, and have had the devil's own time properly aligning it to the PJ.

If repositioning the PJ doesn't help, try shimming the screen on one side so that the side with the taller image is brought closer to the PJ. You shouldn't have to shim it more than an inch or so. This should be easier to do than shifting the PJ a foot or more to either side to correct the problem.

Edit:

If you have a laser rangefinder, you can measure the distance from opposite screen corners to the center of the lens. Adjust PJ and/or screen until the distance measurements match.

I used the LH side wall as a datum wall, all measurements from that.

Centered the PJ, attached to ceiling.
Measure to LH wall, mark front wall same centerline.
Measure screen, put centerline on it. Center screen.
Hang screen. Level screen.

Level PJ; Shoot straight line PJ>Screen, get level within 1/8" across room length. (ceiling is datum)
Level PJ side/side. Shoot laser line to RH and LH side wall, get level within 1/8" across room width. (ceiling is datum)


Turn on test pattern, confirm test pattern center line matches screen.

Basically, square, true, and plumb everything.
Sounds simple, a little time consuming but not hard,
If "issues", you may have to adjust the PJ like mentioned above, I think you want the screen to look "correct" in the room.
Write dimensions down for history, nice to have for future reference.
Good luck.

run 2 same length strings from sides of screen to center of lens. move screen or proj to center setup

How about when you have just the bottom right corner slightly on an incline? Something like this.
The rest of the image is square?

I think you'll find that you have both of the problems, each in small amounts. I bet that if you hung a plumb bob along each of the image edges you'd see they are not quite vertical. The bottom of the image will be right of the plumb.

If that's true, rotate the right side of the projector down a hair to get the edges plumb, then shift the whole thing left so that you can aim it back right to stay centered on the screen.

Correct one and then you'll see the other more clearly. Or I could be wrong...