Does anybody know if it’s possible to use any of the lenses from cameras (SLR) instead of that Triplet lens?

i doubt it, a camera lens is much different than a projector lens i think, you could try it but im not sure if it would work

isn't Triplet just a zoom lens?

i think so yea

No I believe a triplet is consisted of 3 lenses in one housing that corect the light pattern to be projected enabling a sharper picture as opposed to a regular lens singlet or eaven doublet. I do know that they do have a triplet focusing lens sold right here in the lumenlab store but quite pricey. As far as the camera lens you asked about the focal length is not compatible with the fresnel lens optics that the diy comunity use also back into the price issue the lenses are very expensive for a DIY projector.

I tried using several different optics as the projection lens...

Telescope eyepieces don'te work, although they make a good image, it focuses less than an inch away from the eyepiece. Hopelessly short focal length.

Telescope mirrors actually work pretty good for long throw applications. I was throwing the screen 60 feet with a 10 inch f5 mirror, even then at 60 feet the screen was only about 6 feet. The down side was, every aberation in the mirror was clearly visible. Also, at $500, that telescope mirror is kinda pricy for a substandard projection.

The problem you will have with the lens from a camera lens, is going to be similar to the telescope eyepieces, hopelessly short focal length. Also the aperature is going to be way too small to be practical. IIRC camera lenses are designed to reduce aperature.

Nicely put you really threw an image that far how did it affect the brightness and contrast?

I was thinking about this extact question just the other day... I will try it out whenever I get my supplies and start building my projector.

The only problem that I see using a camera lens is that a good lens cost more than this whole project.

How would I test the lenses (I have no part for the projector yet)?

Another question: are there any fresnels made out of lexan (tempered glass), so that we wouldn't need tempered glass (or lexan) infront of it. One less layer = more light.

And one more question: Have anybody tested hot mirrors (or know if it'll work here)? They are expensive new, but also found in copiers, which could be purchased for almost nothing (if copier is old/broken). This way we wouldn't need to cool LCD with fans(s).

Couple of things...

First, the telescope mirror was only an experiment to see if it worked at all. Most telescope mirrors are going to have a parabolic shape rather than a spherical shape. Optics in layterms means, the edges were dim, while the center was bright. My telescope mirrors astigmatism (which his hidden in the shadow of the secondary normally) was clearly visible. As well as some scratches i didnt even realize i had. It was interesting only because I was able to focus the screen 60 feet away. If I were to make a projector with a telescope mirror as projection lens it would be about 6 feet long. As it was, I was holding the mirror with my hands about three feet in front of projector.

In short, Use one of the lenses you find in the store, they are made exactly perfect for our application, and at $20(iirc) for the basic lens you can do no better for the price.

Also, The cooling/tempered glass is only partially to support the fresnel. It is specifically to cool the LCD which must remain below 105 degree F.