I'm getting started with constructing my theater so that I can finish off my pj. I have found that it makes sense in my room to mount the projector about 7' high with a 5 degree tilt to the screen. This is going to cause a small amount of keystoning.

Rather than use a split fresnel design to correct the keystoning, I'm currently planning on tilting the screen 5 degrees as well.

Has anyone tried solving keystoning this way before? what was your experience with it?

Thanks,
WH

While not ideal, this could work well enough.

Two problems I think might crop up:

1. The optimal "viewing cone" in front of your screen will be angled up as well, so if you are sitting in front of it, you will be toward the bottom of that cone, and may notice a brightness loss, particularly toward the top of the image.

2. Watching an angled screen will produce a keystone effect in itself, though maybe not as noticable as simply projecting on a perfectly vertical surface. But the bottom will be closer to you, and therefore seem larger than the top.

If I am way off on these points, someone please jump in here. I don't want to steer somebody wrong.

EDIT: I am on a lot of cold medicine right now, so bear that in mind.

Ya know, I've thought about what you're saying here. I'm not sure about the viewing cone that you mentioned. It's possible that there may be some loss but I'm hoping that with a screen with a little gain to it that I'll be able to overcome it.

With regards to the angled screen creating a keystone effect. I don't think it would because I'd have both the pj and the screen mounted so that there was no keystone between them. (They'd be at the same angle). Perhaps the best thing to do is to grab a bed sheet, make a cardboard box with a light in it, take it to my basement and test my theory.

I do know that some others on avsforum were talking about it at one point and it seems that some believe that movie theaters use a curved & tilted screen.

WH

Right, they will be at the same angle, so the projected image will be perfectly square, I agree with you there. What I was trying to say is that the bottom of the screen will be closer to your eyes than the top of the screen is, so the bottom of the screen will seem larger. Like I said, not by much, but it will be there.

Actually, I am hoping to do some screen tilting to correct keystoning when my PJ is done, so I hope this does work out. Let us know how it turns out! Good luck!

I would not want to watch a screen that was tilted up.. youre going to be sitting below it anyway most likely, so now it'll be like sitting in the front row of a movie theater. Are you against tilting the fresnel because you want to use an unsplit setup? You could get 5* keystone using lens shifting with unsplit.

Lots of people have done this. I have done this and it works great for a screen tilt less than 5 degrees or so. As long as your watching position is where it should be (about 1/3 up from the bottom of the screen or higher) you will not even notice the tilt.

Let me repeat that. You don't even notice the tilt when watching movies or playing games.

Another way of dealing with the problem is to simply put a black border to mask the trapazoid sides of the image. For a very slight keystone (<5 degrees) it is virtually impossible to distinguish that there is a keystone from the image alone.

I have an extreme keystone in my setup (about 20 degrees or so), but built only a 15 degree keystone in the projector. I have done both, tilted the screen and put on a black masking border. They both work great.

Another issue you may have to take into account: My projector is cieling mounted. So the reflected image is closer to the watchers when the screen is angled up. If your projector is floor mounted then that may produce slightly different results.