OK, I am in the planning stages of my pj and one of my goals is an externally adjustabel keystone. My first though was to simply put a pivot halfway down the fresnal and extend the axel outside the box so I can turn it. It was then i realized that the lense would no longer be perpendicular to the triplet.

So, do I need to be able to slide the lense up and down as I tilt it to keep it properly facing the triplet or will a simple pivot work?

No sliding needed. It seems like most just hinge it at the top and let gravity automagically™ adjust the fresnel for keystoning. Just make sure a minimum distance (see lumenlab guide) is maintained between the fresnel and lcd (doesn't touch).

whoa I didn't even think of that. Thanks!

Or...tilt your screen so it is at the same angle as the projector. Whatever is easier for you to implement. My projector will be in a fixed environment, therefor tilting the screen is practical.

well, it is not needed to have the fresnel slide up and down inside the box as long as you have it lined up on the same plane as everything else (light still passes through the fresnel in a straight line even though the fresnel is tilted).if you mount your frenel to a piece if glass and use glass door hindges you will have the ability to move the fresnel up/down if you need to by loosesing the screws to adjust it. however you may need to have it slide forward/ backward to accomadate the angle of the lens(depending on the locatin you have the projector set up in), and accomadate the min. distance from lens to lcd. you can set it up to handle a max angle of 15 deg.. that is the max. angle before you get funky things in the picture, and it is really hard to get the whole image in focus. if you need more you can set your focus box up to be able to tilt to projection lens and get a few more degs. i have mine set up as a floor model with a top hindged style, with a metal rod attached to the bottom, through the front of the box so i can adjust it, and it is set up at 13-14 degs.
hope this helps
toby

I like the idea of using a hinge on your Condenser Fresnel. I read some where else in the forum where someone used a bolt to move the Fresnel back and forth for focusing. Wouldn't it be easier to fix your hinged Fresnel and mount your projector lens inside of treaded piece of PVC which can be treaded into the oposite mounted piece of PVC. This way you can smoothly adjust your focus mm by mm by turning your projector lens.

not 2 mins later I think I found the answer to my question

http://www.lumenlab.com/forums/index.php?showtopic=996

I think you mean 'field fresnel'.

corrected

i just started an dthis is the way im going to sandwich my front frsnel with glass door pivots, and use it for keystoning also

another

will the gap between the glass and the side of the box pose any problems?

i just noticed all the little bits of dust in the picture, will that show up on screen?

will the gap between the glass and the side of the box pose any problems?

Hi jimm3030,

I hinged mine near the middle too.. works great! No sweat with the gaps between fresnel and box! A small foam rubber block in that gap makes a neat little friction lock for the position of your lense.

The dust particles won't really show, but may be creating some darker areas. You'll want to clean as well as possible before finish. Dry pressurized air helps a lot for cleaning the grooved side of the fresnels. Either canned or compressor.

Mark