start to assemably

I'll try to answer some of your questions here:

1. The fresnels are GENERALLY 15mm - 25mm from the LCD. The closer the better, but not too close because you will start seeing the rings from the fresnel lens on the screen. One fresnel goes before the LCD, one goes after in a split design.

2. IR and UV filter.... Well, the closer you can get them to the bulb, the smaller the IR and UV glass has to be. But if the IR or UV filter can't handle the heat, then they will have to be placed further from the bulb. I've heard some people place the glass very close to the fresnel lens and some have put it 100mm from the bulb.

3. Ahhh... The field fresnel (your 330mm fresnel lens). To find the place where the field fresnel goes, first use this equation to locate where your LCD should go:

1 / (Projection Lens Focal Length) = 1 / (Distance from LCD to projection Lens) + 1 / (Throw)

Once you find where your LCD goes, place the 330mm fresnel 15mm - 25mm from the LCD (between the LCD and the projection lens). Remember that the focal length of the field fresnel (330mm) plus the distance between the field fresnel and the LCD (15mm - 25mm) must equal the "Distance from LCD to Projection Lens" you got in the equation above. Otherwise, you get a dark picture.

4. Not sure, but it's been covered. Search for this question.

5. I think you are asking if you need another glass sheet to protect the fresnel from warping (bending) due to heat. The IR filter should remove most of the heat that would warp the fresnel. Again, this has been covered. Just search for it.

So you measurements would be something like:

Bulb (center of bulb) -> Back Fresnel (220mm) = 220mm
Back Fresnel -> LCD = 15mm - 25mm
LCD -> Field Fresnel (330mm) = 15mm - 25mm
Field Fresnel -> Projection Lens = 330mm

The IR and UV filters, like I said above, are going to be placed between the Bulb and back fresnel. Something to remember as well... Often times, when measuring the Field Fresnel -> Projection Lens distance, you want to measure to the CENTER of the projection lens not the edge. That's a general statement and you'll want to experiment with that.

2 & 4

Good answers. Two small additions:

2. Put your UV filter before any fresnels. Acrylic fresnels will absorb UV. (They are actually pretty good UV filters themselves.) But that process will damage the polymers and turn them yellow over time. The UV filter should protect your fresnels as well as your LCD.

4. I use one mirror in the image path. I can stand in front of my projector (my back to the screen) and look down to see the LCD with a normal (not-reversed) image. If you are building a projector with an even number of mirrors (ie. 0 or 2) in the image path, then you need to reverse the image. You can do that by sending the light through the LCD from front to back, or by using a PC video card that has that capability as a special mode.

This is the kind of thing you discover as you go, if you try some experiments. Since you are doing your own design, it is important to try stuff before you commit to a particular non-adjustable setup.

fresnel function

Yes, in a split design the field fresnel should be about 20-30 mm from the LCD. It will have very little effect on the image (it will magnify it just a bit), but that is not why we use it. The purpose of that fresnel is to converge most of the light into the projection lens. It would do that even if the LCD to fresnel distance was 0, but then you would see fresnel rings in the screen image.

sid58ney said:

Then Why we aim the light from front of LCD not from back is there have more meterial to protect the LCD on front ?

Click to expand...

I think this will depend on your setup. If you don't have any mirrors, then you want to aim the light from the front of LCD, coz if you don't, you will be watching the right side of LCD on the left side of the projected image.