I am replacing my Infocus IN76 with a Optoma HD65 (perhaps something else). I needed a new mount because my old one didn't fit. I did the math and positioned it almost exactly where I figured it needed to be. My mount is the Sanus Universal mount (lots of play in different directions).

http://demo2.webslingers.ca/demo/h051VMPR1-fp.jpg

My image looked about perfect when it was set up in 16x9. The Pro-Trim of my Stewart screen caught anything spilling over (and the spillover looks consistent around the screen). However, I threw in a 4x3 DVD of the original Star Trek series, and I noticed a slight trapezoid effect. Here is rendering of what I am seeing (albeit a more exaggerated example for this thread).

http://demo2.webslingers.ca/demo/trap.gif

I will not move my screen, and I don't believe in tilting the screen out at the top or bottom because the trapezoid still exists... it is just masked by the now trapezoid shape of your screen. What I am looking for is what is the best way to correct the trap shape (tilt the projector back, forward, drop the projector or raise it)? I have lots of play in the mount for little movements, plus I can also raise or lower the mount as it is recessed in a drop ceiling and I can get away with alot above the tiles.

Thanks.

What you want to do is swivel the projector very slightly to the right - just to the point where the right and left sides are at the same slant. Then tilt the projector up slightly until you have a square image.

1) If your replacement projector erroneously has trapezoid correction turned on (it might be called SideShift, auto-levelling, et c), disable it.
2) If your replacement projector has optical lens shift, use that.
3) Otherwise, do like Ghost said, but if you can't tilt the projector up enough to correct the trapezoid, you might need to mount the projector lower (i.e. extend the mounting pole)