In reply to:
you should try to minimize not only the keystone correction but the lens shift as well.
Absolutely right... home projectors do lens shift and k/s correction digitally from what I understand (I've used a lot of commercial projectors - never any home ones)
Check out this diagram:
Which means - say your projector has 600 lines of resolution (SVGA) - your image with the projector mounted is 25% too high, so you adjust the vertical lens shift to compensate. If you follow the top centre line, that's where the middle of the projector image is - 300 lines above, 300 lines below. But since the bottom of the image now contains 75% of the projected image in only 50% of the projector's resolution, it gets soft or otherwise ugly - depending on how the projector handles it.
A lot of the projectors I've used do keystone correction optically which is quite a bit better, but you're still using another lens or mirror in the light path.
Bren R.
