Hi, I was wondering if someone could help me:

My room setup does not permit me to have the projector directly in front of the screen. Instead, I would like for it to be off to the left of the screen, projecting at an angle. I was wondering if someone could tell me how to compensate for the resulting distortion. It would be rather far to the left, so I understand that it may not be possible for me to correct for such a wide angle, but I would still like to try anyway.

Do I angle the fresnel? LCD? Projection Lens?

I read in the forums that all you need to do is angle the fresnel so that it is parallel with the wall. This illustration shows an example of this but it is an extreme angle that I don't think would actually work without repositioning the triplet lens. Can someone correct me? I would like to know how to do this as well.

Click to view attachment

Devin's picture is correct, although I think there is a maximum you can correct for, although I do not know what it is. Your best bet if your angle is too far is to hang the thing from the cieling and correct for that angle instead, if space allows.

I don't know enough about optics to figure out if you can angle or reposition the triplet and get any results out of that.

Don't forget, with such an extreme angle, and in all keystone, the projection lens needs to be parallel to the screen also to produce even focus acrross projected image.

Don't you mean parallel to the lcd?

Ideally, the fresnels, LCD and projection lens should all be parallel to the screen for best results.

When this is not possible, getting the LCD and projection lens close to parallel to the screen is needed. Then some final adjustment with the field fresnel can be done my making it parallel to the screen.

Yes, the LCD and projection lens should be parallel to each other.

The problem with using the field fresnel for large amounts of keystone correction is that the distance ratio from the projection lens to the LCD changes, which results in part of the screen being out of focus. you are then forced to choose which part of the screen you are going to focus on.

With the LCD, projection lens, and screen all parallel to each other, the entire screen can be focused.

With the projection lens parallel to the screen, but not the LCD, focus improves, but it's a limited thing, much like tilting the fresnel to get keystone adjustment in the first place. Eventually the distance from the lens to the LCD changes by enough to cause the focal problems to return.

thanks, excellent posts, very informative. I will play around with it and possible post my results.