DIY Video Projector Part II

[woneill]

Hi Aleksey,

I am not sure about this, but in my investigations, it appears that the Xenon HID Projector beam headlamps are only running at 35 Watts. Also they are very blue, which might not be good for colour rendering.

What I do know, is that unless you find a really cool source, they seem to cost more than the standard MH projector bulbs for commercial projectors - I have not seen a complete assembly for less than $350.

I was experimenting with some cheap halogen pod ones because they are small, cheap, and have an exit beam diameter of about 1.5". Oh, and did I mention that they were cheap???

If you know a source of the Xenon projectors, please let me know 'cos I want some blue eyes for my pet motorbike...

The big thing for me here is not the specific use of car headlamps themselves, it is the possibility that we can merge two separate beams from different fixtures into one single beam, without losing the quality of focus that comes from a small bulb in a well focussed assembly.

Also, for experimentation purposes, the lower colour temperature of halogens does not matter too much in my case, because my eyes seem to auto-adjust very easily to the colour balance of these bulbs. (My room lighting uses halogens, and my walls are cream. Before I stuck the shower curtain up, I was projecting onto a cream wall without too much discomfort...)

There are, actually, "ultra-white" car headlamp bulbs available, though, and some claim to be brighter than normal - check out the PIAA offerings. But, even if the light output per bulb is actually reduced, if we can feed an array of these things into one single beam, then it might not matter as much.

The main reason I am leaning in this direction is that it seems SO difficult to utilize all the light from the big 400 Watt bulbs without resorting to a massive reflector. I am just guessing, but if we could make use of maybe 80%-90% of the output of a lower powered light source, could we still get a brighter image than most people are getting from the big MH bulbs?

I don't know, and if someone can hit us with cheap, small, powerful HID bulbs that could be focussed with a small precision reflector into a well collimated beam, I would definitely follow that path instead!!!

All good fun!!!

Bill.

[woneill]

Hi Xblocker,

You make an interesting point about the dates these MLA layers began to be introduced. I must do more research, and get my microscope out!

In my experience, though, I have been playing with a number of panels of the RGB OHP type, mostly being originally manufactured by Sharp, and having manufacture dates from '92 to '97.

The non-TFT ones in the old monochrome panels are nice simple optical filters: you can hold the panel up in front of an image you are viewing (e.g. a computer screen), and not see any distortion.

For four out of five of the TFT panels I have played with, if I hold them up in front of an image, then I get some serious distortion. The distortion gets worse as the angle increases (panel gets tilted), and seems to be in some part due to the shutters acting as a diffraction grating.

However, even directly holding the screen up with the light passing through perpendicular to the surface, there is significant image disruption. The image is recognisable, and not completely obliterated, but "something" is definitely interfering with the light as it flows through the panel - creating a much more diffuse output.

I had believed that the MLAs were introduced into LCD panel manufacture in order to bring the TFT devices into the mainstream - they have always suffered from having much less shutter area than the STN types (because the transistors on the panel took up a large surface area), and they were originally very directional. They needed (and most still do) a much brighter light source than the STN types to be usable. My understanding was that the MLAs were introduced to panel manufacture to reduce the demands on the light source - funneling more light through the small apeture, and as a side effect of their design, increasing the viewing angle of the light coming out of the front.

I could well be wrong on all this. But, the fact still remains that in many of the panels I have played with, there was and is this image disruption effect - ranging from mild diffusion to full scale ghosting and total loss of focus. (No, it's not the vodka - honest!!!)

If it is not MLAs, then why are the TFT screens not as good optical filters as the STN devices?

These panels themselves seem fully functional in use, and work quite well as a projection panel - except that they are interfering, to some extent, with the operation of the fresnels between the panel and the light source, which would send the light to the objective. Light does get scattered, and while an image (often quite cool) gets projected, it bothers me that there is a potential loss of contrast and brightness to this phenomenon.

Looking for enlightenment,

Bill.

[woneill]

Hi Invictum,

I don't know much about the outputs of modern computer power supplies - I am a few years out of date, unfortunately.

For my experimentation, I have been using a car batery charger to drive the bulbs. It probably has too high a voltage, and will shorten bulb life, but the bulbs I'm using are cheap, and easy to replace untill I get things right.

If anybody is playing with this stuff, check out the reflectors, bulbs, and any lensing setups. Quite often car headlamp fixtures have opaque panels inserted to shape the beam so that oncoming motorists don't get blinded...

The same can be said for the bulbs - some are designed to only send light in one direction. If you play with these, make sure you are using your full output capabilities!

Bill.

[tech head]

Aleksey,

Rear screen projection screens are usually expensive. I haven't seen any material that is specifically made for that. And all the info that I have seen on them shows that the entire back of the screen is a frensal lens focused to a certain distance to increase brightness and the front is covered in micro lenses to increase viewing angle. If you can find one, you might try the screen from a rear projection t.v.

Undream,

The other day one of the bulbs in my proxima projector burned out ( don't worry, it has two :-) ) When I pulled the bulb out I found that it is integrated with a reflector. The interesting thing is that the reflector is a "color correction filter" it only reflects about 70% of the light that hits it. The bulb itself has a large coil that is tightly packed. IT IS NOT A POINT SOURCE! which really supprised me. Another thing about the reflector is that it is not smooth. It is a bunch of small rectangle reflectors that make a virtual eliptical reflector. and the bulb is not really powerful. it is 430w 82v.

What I am trying to say is, The cut mirror reflector is probably the way to go. If that is the way the big boys do it we might want to try it too.

Joe

[remp]

Woneill

Lack of efficiency in lighting is a real problem not easy to solve for DIY people.
For a start you loose 50 percent light because projection panels work with polarised light. Half the light we supply is wasted.

Modern manuifacturers use polarising recyclers by prisms and wave retarders so can utilise much more light than we can.

Also we use lights that do not have sharp point source so reflector efficiency not so high as manufactured items.

Some of our reflectors are not optimum.

In addition 3 panel manufacturers use polysilicon panels which have greater transmissivity. than projection panels.

3 panel manufacturers use MLA (micro lens array) to direct light parallel through panel which further increases light throughput and increases contrast by reducing stray light.

What can we do. Short of spending a lot of money on polarising recyclers and buying a sheet of MLA and buying a point source bulb and matching reflector, probably nothing.

People do what they can with whats available at good prices and some results are pretty darn good. But I take your point. Without investigation we get to a certain level and then stop.

Maybe we could find out how to use the half of the light that is wasted. Thats a big gain for a start. So we have firstly get it going, then improvements if economic and possible.

[eebasist]

ap0the0sis:
I dont have the perfect light source, I was just trying to help you with your suggestion, by all means go ahead and try those, but I don't think you will have much to be happy with afterward.....there is ~3inches of fillament in those to do the 300 or 500, etc watts, the light is distributed too much.

The best light source most likely like in the first set of posts says, is Metal Halide (MH) Ushio actually has some really cool MH assemblies of lower wattage ~150-250 watt that i want to get more info on, I think that they have some serious potential, but back to your bulbs.....you might get a decent effect out of them if you encase them in an old elipsoidal stage light....still not as good as metal halide, but it would work and would focus the light as much as possible

[Undream]

well, i decided I'm going to pickup a glass cutter. I think I've got a big mirror in storage that I can cut up. I might just glue the pieces right on my curved aluminum sheetmetal, I duno yet.

[SuperZoboo]

its been a while since i've done any projector work. but we did reclaim our cloth and still hope to build a screen sometime. really, we like our setup as is for the moment and we just enjoy watching movies, playing nintendo 64, and bigscreen soccer games.

funny thing is, ive never watched soccer in my life, but something about watching it 8 foot wide makes it exciting!

anyway, no new info, but i'd still like you guys to submit your results at our site. i think a list of 15 or 20 submissions with good results would be a good collection of information.


Submit you projector details here

[Invictum]

Will do Zoboo, as soon as I get a projector, and a panel, and a screen, and a...

I'm not so sure I should go with headlights now. For one, I'm pretty sure that one wouldn't be strong enough, and if the power supply can only power one, it's not really worth it. Even if it could power both, I'd need something to combine the lights etc.

I might screw around with it later today anyway though.

[*_if_I_know]

Hey,


I have a suggestion.

Maybe good information could be gathered if someone goes to the patent division in a local library and looks up, “projector,” technology. The details should have parts, measurements, scientific data etc., that we could use with the DIY project. It might be a good step forward. If somebody is willing [I don’t have the time now {soon}], that would be great.






Also a link for an LCD list: http://www.commspecial.com/resolutions.htm