Help with design

zackbass

Member
2002-07-03 12:56 am
NJ
I've been seuriously considering buliding an LCD projector for a while now, and have been trying to read everything that I can find on LCDs and projection but now that I have started to design a system I have run into a rew problems.

Before I put the question out I'll tell a little about myself. I am a student, I build and fix computers, and am an amateur machinist. I can make almost anything needed out of metal to a tolerance of .001". I also have built water cooling systems for computers, and have some good experience with water cooling.

My projector design includes a metal halide bulb in a reflector at the back end, an LCD panel for an overhead projector, and some sort of projection lens(es) so far. What I need help with is deciding exactly what lenses I need.

From reading undream's site I decided I need a plano-convex lens to project the image. What I don't understand is exactly how lens diameter and focal length affect how it projects light.

What other chioces do I have for a projection lens? I see some people are buying a Fujinon lens from Surplus Shed, can one of these be used after a large concave lens? Is it practical?

It seems that many designs use a fresnel lens (I don't know know if they are concave or convex) before the light hits the LCD panel. What does the fresnel lens do to the light before hitting the panel? Does it condition the light from the bulb to be more uniform?

I plan to place this projector about 120" from the screen, and hope to get a screen size of about 98" diag, in a 16:9 setup. Is there a prblem with this setup?

If it makes any difference, I can make most any fixtures needed from aluminum to extremely close tolerances, and can implement a water cooling system if necessary.

Thank you for you help.
 
you're trying to get out easy by not reading the original thread--but here's a little info, the fuji lens is made for crt projection at very short focal length. there's some nice lenses inside, though, which makes it worth buying(see lenses thread) the fresnel is actually 2 fresnels opposite one another, one to collect light and one to focus it toward your projection lens. you want your focal lenght to be close to that of your fresnel so that the light will be focused on the center of ypou projection lens. bigger lenses gather and focus more light, making you setup more efficient,. you could also uce a DCX lens, but they tend to have a shorter throw and can be more expensive for high quality.

BTW, it's not fair to start a thread to answer a question already presented and answered in another thread.

we'd love to hear about your ability to fabricate reflectors and cooling systems, sounds like a good idea for a new thread
 

zackbass

Member
2002-07-03 12:56 am
NJ
Thank you for your help.

I'm not sure of my ability to creatue reflectors myself, as I only work with sheet metal in auto body situations, mostly taking out dents and welding. I'm sure that I know someone that can make one for me. As far a machining reflectors from aluminum, I do have acess to the CNC equipment required, but not the skills to use it.

I was thinking that machined parts would allow a more exact and complex lens combination, as I can machine lens holders that connect together at exact lengths without a problem.

As for water cooling, it is definetly easier than it looks. I remember seeing somewhere an idea for sandwitching a water layer between to sheets of glass that light from the bulb would pass through. While it could work, it wouldn't work well. Glass is not a very good conductor of heat, so only a portion of the unwanted heat will ever reach the water. Also, introducing water into the lighting system will probably cut down the light actually reaching the panel.

I was thinking that a heat exchanger could be integrated into a metal reflector, probably by soldering pipe used in heat exchanges directly to the reflector. This would allow the heat to be removed from most of the area surrounding the bulb. At the other end of the system is a pump with a heat exchanger. The heat exchanger has a fan on it, and cools the water before it circulates back.
 

xblocker

Member
2001-12-20 5:10 am
zackbass,
if you don't know exactly what lenses do, it's little bit hard to explain.
First rule of thump: focal lenght (fl) of projection lens has to be minimum or more of panels diagonal size.
2.Projection lenses are mostly triplets. Single PCX lenses have spherical abberations, which don't allow to focus center and corners of the image at the same time. Many of the guys here don't seem to know that and are complaining of not getting the whole image sharp.
3. Fresnel lenses are simple convex lenses and act as condensors. It doesn't matter if they are doublesided or not as long they collimate the lightbeam into projection objective. This is an important point, because the lightpath after the LCD-panel has to match the image path. If the fl of the fresnel is too short, light is collimated before reaching objective and diverge again,.. bad!
If fl is too long, also not all light reaches objective...bad!
This all has to be considered and therefore, it might be a good idea, to use components of a well designed 'ready' system.

xblocker