DIY Video Projector

[Scot_lad]

How much did you say you were selling your OHP for? And roughly how much would it cost to post it to Britain?

[fender4]

SuperD,
I am with you on the problem caused by the non-reflected light coming directly from the bulb, but won't the fresnel refract the reflected light and negate the advantage of using an ellipse in the first place? I hope that makes sense.

If you wanted to eliminate scattered light caused by the non-reflected light, you could try this:

Parabolic Polarizing
reflector---> sheet------>fresnel--->LCD--->lens

Remember that OHP fresnels are actually TWO fresnel lenses---one to make diverging rays parallel and one to make the parallel rays converge. In this case, you would need a frensel like a page magnifier (but hopefully higher quality). I don't know of a good way to get the non-reflected AND the reflected light to travel uniformly---I'll think about it.

Good luck with the reflector! I'm at a loss for good ideas on that...I'm still playing with aluminum foil.

Question about the LED/laser projector:
First off, pardon my ignorance. Is the LED/fiber optic approach possible because the image is formed before the light has a chance to spread? And then it is projected using a lens? If so, would a smaller, pre-projected image equal a better projected image because of less "dispersion distortion"? Also, would using a higher frequency piezo produce a smaller pre-projected image, although with higher resolution? OK, I'm giving myself a headache.

Later,
f4

[tech head]

you cant focus both the reflected light and the direct light. you would have to block the direct light or reflect it back to the primary reflector.( lots of reflecting )
that is wyo most of the bulbs that you see in cars have the front of the bulb blacked.

[jamie]

http://patft.uspto.gov/netahtml/search-bool.html

its the us patent search ... do a search for lcd projectors and find out just what everyone uses?

[jamie]

http://www.glenbrook.k12.il.us/gbssc...ln/u13l3g.html

[remp]

You cannot focus a large size light sorce such as an led into a small size light source. The source can never be smaller than its original size. You can extract a small portion of a source but you loose the amount of light depending on the ratio of how small you extract compared to original size. This law of optics is in every optics text book is why it is impossible to get enough light from an led into a fibre optic to do any good. Basically you cannot turn a large light source into a small light source without loosing light otherwise they would not need to make short arc lamps.

[fender4]

Thanks, remp. That is what I originally suspected.
-f4

[piGuy]

If there's no way to efficiently get LED light into the fiber, would a laser be the only other alternative? I'm thinking it would be rather difficult to obtain red, green, and blue lasers. Red would be easy enough, green is just more expensive, and I don't know if blue is even possible to obtain....

[remp]

Lasers are used all the time to drive fibre optics. If you have questions about lasers might be best to hop into the laser projector thread. This one is for LCD projectors

[Scot_lad]

I don't understand how the fibre optic was thick enough or gave anywhere near enough light to produce an image - these things aren't well known for holding a lot of light are they? Hence the name 'fibre' as opposed to 'tube'.

I'm still not convinced of mountain's claim of aiming the LED into the fibre-optic. Surely it would be like filling a bucket by peeing into a straw?

Mountain - surely you know somebody with a digital camera you could borrow from? If you were in Britain I'd post you mine. Send us some photos