i have been working on this projector for about a week now. i have two 300W Halogen bulbs as my lamp. a dissasembled 15" lcd bonded to a 12.25"x12.25" fresnel lens. the problem is when i try to project an image by manualy moving the lens (with my hand) i can only get an image that is a portion of the screen, when the lens is held close to the lcd. i move the lens out and do not get any image, in focus or not. i have tried fresnel in front and back along with many types of lenses. mainly a 200mm camera lens and a delta-77 sony rear projection tv lens. any help or advice would be great.

Might help if you clearly draw up your setup with what measurements your using etc and post them

attached is a rough diagram of my setup, hope that helps

edit: the fresnel lens is a bifocal 220mm-320mm purchased off of ebay

First, have you used the Focal length calculator at this thread Focal Calculator II, rev1.43 ?

Second, if you are using a camera lens, chances are that it doesn't have a large enough field of view to be able to "see" the entire LCD. That's why it is only projecting a portion of the LCD.

Do you get the image that is just a portion of the LCD when the camera lens is just a couple of inches from the LCD? Camera lenses are designed to focus an image just an inch or two inside the camera body onto the film. That is called the back focal length. It doesn't look like you will be able to use the camera lens with a 15 inch LCD.

The rear projection TV lens is a great lens, but it is designed with a back focal length of about one-quarter of an inch. It has to be just about in contact with the LCD and will only project the part of the screen that it is in contact with. It would work great with an LCD that has the same diagonal measurement as the diameter of the rear part of the lens. For instance, a five inch diameter tv projection lens would work great with a 5 inch diagonal PSOne Lcd.

The fresnel in back of your LCD should work fine, you just need the right kind of projection lens. Use the focal length calculator to find the projection lens focal length that you need, and go from there.

We'll help you out.

Tgreenwood

thanks for the reply. no, i have not used the calculator cause it wont start, i think its cause im 64-bit windows. i do get the image portion when i hold it like 1 inch from the lcd. so what your saying would make a lot of sense. i guess ill just have to find another lens. thanks for the help.

You may also have some problems having your LCD so close to your fresnels. Sounds like ya got 'em smack dab together?

Most here would frown upon using two halogens like that. How are they configured?

Best results will be achieved by approximating a "point" light source as closely as possible.

Anyway, since you've started fiddling you'll likely find you've got a new addiction and you'll be swapping stuff around like crazy trying to get better and better results.

BTW: It's highly likely I will be selling an M135 ballast and Ushio T15 Pulse Strike 400W Metal Halide bulb along with mogul in the Trading Post in the near future just in case you're in the market sometime soon.

I was thinking that same thing. I really didn't have any success
with the amount of light I was getting through the projector until
I went with a very focused source. That dual setup might be
throwing something off.

i dont think light is the problem, im getting a nice bright image, its just only a portion. the bulbs provide 12,000 lumens, witch isent alot, but enough that you think you'd see somthing. i think im going to buy a triplet lens from lumenlab store in a while and give that a try, either way it should give better results because its made for projection.

both bulbs are in a flood light fixture with a reflective coatig, almost the light from them is going right on the fresnel.

You can't use multiple light sources in a dual fresnel design!!

You need a POINT light source. The rear fresnel effecitvely focuses on a point, so you will only be utilising a fraction of the light being produced.

However, this is not your problem. The problem is almost certainly a mismatch of focal lengths between the fresnel lenses and the camera lense.

When you get the right lens, I suggest you compare your dual light setup to a single bulb positioned at the focal point of the rear fresnel.

HOWEVER, if your bulb is one of the long thin halogen variety, it's not much of a point source anyway, so your brightness is likely to suffer.

Let us know how you get on!

You will never get it to work with these lenses. They are designed to work on a very small LCD (or film in the case of a camera.

The light source will never work either. Too hot, not the right colour and not the right size.

If you can get a Metal halide lamp and control gear, as well as a standard triplet you'll be a lot closer to getting an image on the wall.