I am gearing up to finally through down and build my diy projector. I have a LCD screen ready to go but I wanted to see what the final brightness might be so I made a little test setup.

To start I took apart a small 7" 640 x 480 LCD from a imported DVD combo unit and plopped it on an overhead projector. The results were terrible. The OHP I was using has a 600W halogen in it and it wasn't working. At first I couldn't even see the LCD being projected it was just a dark rectangle... then I realized that it was projecting through it it was just so incredibly dim that it looked like a black rectangle.

What is the deal here? I thought those LCD units that are made for OHP were dim but viewable. I took off the diffuser and polarizer it was a straight shot to the focusing lens.

I don't understand. The only thing that I can think of is that the light isn't going through the screen parallel so it is not hitting the focusing lens the way it should be.

Any thoughts here?

I obviously understand that a real set up with the right lenses and metal halide lamp will be brighter, but this still should be brighter right?

The LCD requires the polarizer in order to run.

errrrrrr.... what are you talking about? Perhaps it was not the polarizer that I took off. There was a diffusion sheet and a sheet that looked like a fresnel.

That's it though.

read this - all of it

The above link is form this compilation

Happy reading

I have a feeling the other members mistook some of your description to say that you removed the polarizer from the LCD when in fact you just removed the backlight defuser glass and thin sheets from behind the LCD leaving the LCD panel intact.
To answer your question "yes" you should be able to see a nice clear semi bright picture from a OHP with a 600 watt halogen ....even if you don't completely mask your LCD or create a light tunnel (se my plog)
I would have to assume that either:
*You have some focusing issues
*Your LCD is damaged
*Your LCD has wayyyyy too many anti-glare layers

Try to post some pics of the set-up and results and I bet you will get your answer and many helpful hints

Good luck

I would almost bet that the OHP does not have a fresnel in it

When you look at the LCD on the OHP bed, can you see an image?

LCDs only allow 4-8% of the light to pass through them. Therefore, if you do not "mask off" the LCD from the surrounding OHP bed, the image will be comparatively dim. Try blocking off the rest of the OHP bed.

Because of the above, this is not going to be an incredibly bright projector, you will have to ensure that the rest of the lights in the room are off.

I posted this in another thread a while ago:

A while back, I came across a website called "Tom's Hardware" that discussed using an OHP as a projector.
That was my first introduction to this type of a DIY project.

You can find the guide here:
http://www.tomshardware.com/2004/11/13/sup...e_your_tv_for_/

It has detailed instructions and should answer almost any question you'd have.

You'll eventually want to switch to a MH bulb as the OHP bulbs only last about 75 hours. When you get to that point, you'll probably want to build your own box to house it.

hahaha, wouldn't that suck

Alright, here is the deal.

Dirt. Turns out that there was a nasty film in the ridges of the fresnel lens and that was dimming it down a bit. Not enough so that you couldn't see the lines in the fresnel when focusing, but enough to make a difference. It looks a little less bright as my 3 gun Zeinith CRT projector, but in a heck of a lot smaller area.

I did mask off the rest of the bed and it was better than when when I first tried this experiment. Also I think I might have looked to many times into the fresnel with the lamp on the first time..... I am sure that didn't help.

It does work it is just dim ass dim. This lamp has about 16,000 initial lumens but I am guessing that a crap ton of those are lost in the reflecting mechinism, or lack there of. The only thing behind the lamp is a 2" cup that is a dark silver color and textured. I imagine the texture is so that it diffuses the light on the fresnel. surrounding that is a black metal box that comes up about 4 inches on all sides. Nice and efficient, eh?

I think that this experiment actually worked because my goal is to build 2 projectors. Once for my living room and one for my bedroom (to shoot on the ceiling pimp style.) The brightness of this projector is just adequate for sleepy time viewing, but I am not running a 600W lamp that sounds like a window fan all night. What I need is something with similar brightness that is ultra quiet.

I would double that more than 2/3's of the lumens are making it to the fresnel so that puts me at about 10,000 lumens. It doesn't sound likley that I could get an array of 200 leds to kick off that kind of light (although it is much more directional) but I think it is possible to do it with compact fluorescents or a 150W metal halide. I want it to consume a reasonable amount of electricity so that I won't feel horrible leaving it for 4 hours while I fall asleep.

Thoughts here?

Suggestions on where to get a higher color temperature lamp in the 150W range?

I do plan on making an enclosure and re working the OHP for maximum output and efficiency.

I would personally recommend a CMD-150/TD/942 - either double-ended RX7S bases or single-ended G12 base. This type of lamp is sold under various brands (Ushio, Philips, etc.).

You can read all about this bulb type here:
http://www.lumenlab.com/forums/index.php?showtopic=13358

Ok I have found Lamps for $46 and I have found http://bulbster.com/lightbulbs/bl150s55-p-5547.html for what looks like a balast that might work. But I don't know if this is the proper balast for this lamp and I am not finding more specific information about what kind of balast goes with what kind of lamp.

Will this one work?

Where might I find a base for the lamp?

I also noticed that there are 2 acrylic fresnels in the OHP that are glued together. Would it be beneficial to dremel them apart and put the LCD in between them? My thinking is that the light will be more parallel passing through the LCD because setting it on the top most fresnel does not get the light to pass through parallel so there is probably transmission loss there. Or might this mess up something?

I flipped the LCD so that the light was entering the anti glare side first and had the shinny side fading up, and that seemed to make it a bit brighter. Would removing the anti-glare buy me noticeable amounts of brightness? I am sure there is some sort of calculation in a post somewhere, but who knows what an X number of lumen increase will actually look like? What I want to know is if it is a noticeable difference.

Guys, I really appreciate the advice on this forum. It is really nice to know that people who have done lots of hard work are still in it to help people like me who are ghetto DIYers. It gives me a warmish fuzzyish feeling to know there are a community of people who actually care about betterment of the average man's viewing experience.

Thanks.
Dave