I'm working on the sled design for me fresnels and lcd and I had a couple quick questions.

Is there any visual improvement having the lcd in front of the condenser fresnel?
If yes:
- How noticible?
- How close can you put the lcd to the fresnel? Distance between fresnels?
- If the lcd is directly in contact with the condenser fresnel, will this allow for keystoning?

If you go with the spacing indicated by the guide, fresnel, lcd, fresnel, do the same spacing rules apply?

Also, what is a safe distance between the heat barrier (using Lexan) and the rear fresnel.

You ask quite much. The values in The Guide are guite good. I tried once to have the fresnels together, uncut and in that test rig it seemed quite ok. I still think that fresnels at both sides of lcd give the best result.
If the fresnel is too near the lcd you may get fresnel-rings visible on screen. The min allowed value depends on your taste, but to me it could be something like 10mm (=half inch).
Condenser (lamp-side) fresnel does not affect keystoning or focus ! It just collects as much light as possible to the lcd and makes the light come in the correct direction so that the other (=field) fresnel can direct it in the lense.
The field fresnel can used to keystoning, but remember that it is good for only about 10 degrees. And even that makes the picture wider on the far side than on the near side. Above 10 degrees it will be impossible to get a sharp image. The factory made PJ's do the keystoning with software i guess (they scale down the resolution on bottom/top edge !?)

???

Zero ? My fresnel s are not straight (anymore?) so there always is a gap.

Tux

Don't mind me. When I can't sleep and I start posting past 3am, they seem to be very long winded and unclear.


I understand how the PJ works. I just assumed that you'd have a clearer picture when the light goes through the LCD to the PJ Lense, rather than through the LCD, a fresnel, and then the PJ Lense. From your reply I'm assuming that allowing the condenser fresnel to warp won't have any major negative effects down the road? SO I guess I'll just slap the condenser and the fresnel together.

Don't we all...

When the light comes through the lcd it should be directed to the lens. Without the field fresnel most of the light would be wasted --> dark picture. If the both fresnels would on the lamp side then the light direction is good. The fresnels have to be slightly bigger than lcd.

The fresnel warping (about 10 mm) has not yet caused any trouble. I think that my picture is very good, among the top five seen here in LL forums. The only problem is that top-right corners is slightly blurry and I think it is coused by the Pro Lens. My set-up is 15´ lcd, 1024*768, Pro Lens, design almost as in The Guide but with a mirror just before the lens. Throw distance 4.1 meters (13.5 feet) and the pic is 2.5 meters wide. I'd like to make it smaller, but then I have to reposition the PJ ja the screen.
See the attached close-up. The pixels and even lcd's color-dots can be clearly seen on all the surface except top-right-corner. Some say that the pic should be un-sharpened to hide separate pixels from the viewer...

Edit: somehow I cannot get the attachment to join....
Tux