DIY Video Projector

[tim0]

Hello All,

i have bought a used projector now. The optics is no good for me to DIY. I can do alot with electronics but mechanics is just not my thing. So i got a Polaroid Polaview 105 projector, 400W metal halide bulb, 640x480 for about 500$.
We will see how the bulb holds up. The noise is really annoying... However, there comes not much light out of the lens, so yes it seems the optics and LCD panel is very lossy.
BTW; i was just looking around for possible cheaper light sources and found metal halide lamps for about a third of what projector makers charge. These lamps are made for projection lights (light shows).
Also, the car "xenon" lights, or generally car lights, might be an alternative. These bulbs are cheap and should be quite bright. Power supply for the 12V versions is easy. The life time of the car bulbs is very high (7500 h).
Well before i think about a replacement light bulb i need the service manual for the projector. I hope this is available.

If there's any interest i'll let you know what i do, and what i can find out from the service manual.

later,
Timo

[hifiZen]

has anyone considered using an old 35mm camera lens?

...seems to me you could probably pick up a pretty high quality lens for an older/common mount like Canon FD, Pentax, Nikon etc., and have some really nice quality optics. Even something with a large aperature probably wouldn't cost too much. Of course, you may have to worry about using another lens before the LCD to direct more light into the lens. Something like a fresnel lens would probably do for that purpose. I did recently come across some plastic fresnel lenses in a dollar store, so with enough hunting, you can probably find fresnels for a very good price as well.

[Edited by hifiZen on 10-13-2001 at 02:06 AM]

[Fiat1]

You can get 100watt 12volt Halogen globes very cheap, here in Australia they are $3.45 at Jaycar electronics but probably cheaper at a light globe replacment store so I am sure they would be cheap in America. You could set 4 of them up all with reflectors aimed at a cold mirror and you would have a really bright 400watt light source ! A few fans, maybe house each globe inside a metal case with a heat sink! The only downside is thta they last about 300-400hours, but since they are so cheap it is not a huge problem!

[hifiZen]

hmmm... one problem with many light sources is that they need to be colour balanced (eg 5000K colour temp.) in order that the projected image has the right colours. So, I don't know if automotive Halogen or Xenon bulbs will give a white that looks white... I think this may be one of the reasons that projectors use expensive bulbs.

However, upon further consideration, i can think of a few things which need true white light sources... like scanners and photo lighting. Obviously, photo flashes are out, but studio lighting may provide some useful clues. Photography lighting techniques prescribe different colour correction filters for various light sources. The usefulness of this is debatable, since another filter would just be subtracting more light... But, the scanner light source could be useful - they often use these cold-cathode flourescent tubes, and it may be possible to find a bunch of these and hook them up in an array to make a large flat rectangular light source, which would be colour balanced and probably very bright...

[vdi_nenna]

Looking through an old Newark Electronics catalog. I found medical lighting (bulbs). The price seemed reasonable. They seem to be on the white side. I don't know the temp., but it something to look into.

Vince

[dwalls32]

I have been experimenting with this whole lens thing...using an 8 1/2 by 11 fresnel and a delta 68 projector lens and my bank of leds... I get the light shooting through the fresnel and lcd (8.5''), but I have to increase the distance between the led bank and the fresnel and the fresnel and the projector to get the image small enough to view the whole frame through the lens...from leds to fresnel/lcd to projector was over 4 feet long ( even though it was placing the whole image on the wall...

[vdi_nenna]

Can you tell us more about how it looked?
I have pretty much the same setup. Did the whole image 8.4" image pass through the projector lense?

[dwalls32]

It was kind of blurry, but I think that may be the spacing between the leds...I got them fairly close, but it's hard to get the individual beams to "converge" in to one picture. My array is not yet complete. As far as the whole panel, it was there, but just fuzzy. I think I might be having the same optics trouble as you Vince...I need to tast later this week when I can add more leds for additional brightness...

[Edited by dwalls32 on 10-14-2001 at 08:13 PM]

[Grumpy_Git]

Just a thought, has anyone tried using Photographic condenser lenses, (for example out of an enlarger) This might give better light passing than a fresnel, the only real probem I can see with this is the large size of LCD display that most people are using.
Also, for a reasonable Display, partsexpress have some small modules for about $150, they also have a wide screen module, now that would be cool!

Nick.

[faidzir]

im still waiting good results for white leds experiment. Any good news?. i will spend a lot of money if succesful.

* i play arround with flashlight camera, i built high speed
flashlight at 50 hz. Result is very very bright and white source light. May be can be used as a light source to project lcd?. Any suggestion?.