DIY Video Projector

[HokieTT]

xblocker,

Thanks for the advice. The reason for the reflector, really, is trial and error. I'm just monkeying around with a few things, and I figured I'd try this. No big deal, really. What do you suggest I use instead? Should I rely on just the direct light? Thanks for the help.

[xblocker]

HokieTT,
trial and error, thats all we do! Now what can you do...? It depends of what you already have ! panel, bulb, fresnel, objective? If you prefere high resolution way, i would recommend to use or rip out a bright OHP in conjunction with a 10" projection panel or TFT monitor. You could these parts fit together in a case, like i showed a couple of posts before. Advantage: You have a working system as a starting point, you can improve or recombine, if something is not working.
If you would like more small panel route, have a look at the small panel thread !
Whatever you do, be carefull with heat !! We have seen here melted lenses, fresnels, damaged panels..

Good luck!
xblocker

[tech head]

spherical reflector with point light source at focus.
this gives almost all the light coming from the same point.
from there use a ferensl lens to condense the light through the lcd to the projection lens.

the reason I say to use spherical reflector is because:
1. a light will radiate in all directions.
2. light radiated from the center of a sphere will reflect directly back to the center of the sphere.

If you use a 180 degree spherical mirror (i.e. half of a ball) with the light at the center, theoreticaly, you could use all the light that the bulb produces. All of the light reflecting off of the mirror would apear to be comming from the same place as the light comming directly from the bulb and it could all be focused by one ferensl lens.

Someone please correct me if I am wrong.

[xblocker]

Yep!!

BTW, lightsource have to be at 2f which is the radius of the spherical mirror.

xblocker

[SuperZoboo]

hey, thanks to you guys, Undream and Cowan especially, Krazzyed and I have completed our projector. We have good results. In dim light our ELMO HP4kdx (4000 lumens) throws out enough light to get by playing games and watching movies. When we dim the lights and cover the windows, thats when things get rockin' though. Bright colors, no motion blur, 8 ft wide games of Goldeneye, what more could you ask for?

Again, our setup is simply the OHP + Panel route. Phase 2 involves retrofitting an OHP with MH bulbs for maximum colorage!

Here's the final project info:

Panel: Nveiw Z115 ($115) www.invsol-inc.com
OHP: ELMO hp4kdx ($72) www.invsol-inc.com (bulbs: $10, 50hrs)

Check out this site
DIY Projector Results for our results and info.

[SuperZoboo]

btw,

in favor of parkland plastics, we went with "blackout cloth" sold at most fabric stores. the avforum was hyping it up and so far we're happy with the results. is anybody else out there using this?

Blackout Cloth
at most fabric store, drapery section, made by Roclon
54 inches wide, $6 a yard
estimated 1.3 gain

DIY Projector Results

[biteon]

i checked out your website its pertty cool. but cheak out one more site that i found in my catalog: www.sylvania.com
they got alot of bulb that in the future might help you out at least for referance.later and good luck.

[jiggersplat]

okay... first let me say i've been reading this thread from the beginning, and damn it's long. i think i have a pretty good grasp of what the problems are with the lcd setups, mainly that of focusing the light and getting it parallel through the lcd. (polarization i haven't touched yet), but i had an idea, and i need someone to tell me why it won't work.

ohp - okay, these work pretty good, but to get more light through, we want it normal to the plane of the lcd. the two fresels don't do this, and we can't sandwhich the lcd between two fresnels because of image quality issues. furthermore, we can't seem to find lenses big enough for a reasonable price to use instead of fresnels, or a screen small enough with good resolution to use normal sized lenses.

take a look at the picture and i'll tell you what you're looking at. we starting with a light source with a parabolic reflector and either a small blind in front of it, or a very small 2nd reflector, whatever floats your boat.

light coming off the reflector is in parallel rays. it travels out through a honeycomb-like structure painted flat black, to assure that ONLY parallel rays are going through. one might want to put heat sinks on the outside edges of this honeycomb.

next the light passes through the lcd.

after the lcd is a one-way mirror tilted at a 45 degree angle. light from the lcd passes through the mirror. correct me if i'm wrong here, but the angle does not change when light passes through a sheet of glass or one way mirrow, but it may have some offset based on the thickness of the glass.

still all parallel rays at this point, enter the second reflector, facing the opposite direction. which is then focuse towars the reflector focal point.

it then bounces of the 45 degree mirror, and out of the projector, either straight onto a wall or through a set of projection lense.

bonus: i *think* you get free keystone correction with this by change the angle of the mirror slightly.

so what am i missing? i realize i'm loosing a lot of light through the mirror and the two reflectors, etc. but i think allows us to avoid using BIG lenses with BIG lcds. interference between light travelling in opposite directions? there's got to be something.

dan

[remp]

So what am i missing? i realize i'm loosing a lot of light through the mirror and the two reflectors, etc. but i think allows us to avoid using BIG lenses with BIG lcds. interference between light travelling in opposite directions? there's got to be something.

Jiggersplat,

Your idea would work. Just a couple of points. A fresnel can give you parallel rays if thats what you want. Depends where you put your light source. If a light source is at the fresnel focal point you get parallel rays out the other side. Or you can move the light slightly and get rays with a very slight convergence through your LCD panel but you have a long distance then to locate your projection lens.

Where you going a get a honeycomb structure with sufficient definition.
You would have to have thinwall structure otherwise it will block light including parallel rays going to the panel. It would have to absorb non parallel rays and the honeycombs would have to line up with the pixels in your LCD panel. Thats a tough job. 3 LCD projectors use a sheet of pixel size microlens on each LCD to take as much "useful" light as possible and direct it through their panels. Gives more contrast and more lumens on the screen.

There are several ways to get parallel rays. Point source light. Perfect shaped reflector with completely smooth walls. Normal reflectors and lights are a long way short of this but its suprising how well they work.
Direct your light into a fibre optic or light guide and a lens at exit end to make parallel rays. With practical devices you only get small diameter parallel ray bundle and can be costly.

Assuming you could find a honeycomb structure and parallel through your panel you could use an offset focus second reflector directly to your projection lens and not need the one way mirror.
You could find the losses in the honeycomb structure and the second reflector and if used, the one way mirror you would be short of light.

For practical purposes a projection panel and OHP does very well but can be short of contrast and sufficient light.

Your last sentance sums it up. I realise I am loosing a lot of light etc.

Thats the key point. You dont want to loose a lot of light you want to gain a lot of light at affordable price and minimum problems otherwise it gets to be an expensive projector.

[HokieTT]

Besides the handful of childish people clogging up this forum, there's been a lot of good discussion the last couple of days about reflectors. Unfortunately, I'm still not quite sure what I want to try first. I have that parabolic reflector coming in, so I'd like to give that a go, but I might not end up with it. Let me give a rundown of everything I have in my possession or on order that pertains to lighting and lenses, and maybe that will generate some ideas of the best starting point. I'm not really committed to any method yet.

1 400W metal halide bulb (the smaller of the 2 Philips models)
1 12" parabolic reflector w/3" focal point
1 12"x12" fresnel lens
2 8.5"x11" page magnifiers
1 surplus projection lens (not sure of the specs yet)
(LCD, ballast, mogul base, etc don't count here)

Now, short of special ordering more components (though I don't mind something else from the hardware store), what are my options? I want to experiment, but I'd like to start out with something mildly effective. Thanks!