DIY Video Projector

[dwalls32]

I have used opaque projectors for some time being an artist and all. Their image is based on reflection. I don't want to be negative, but if you shoot light at a shiny LCD panel, you're image is going to be flooded with reflected light. I did try this at first with my overhead projector and a casio portable lcd tv. thoughts?

[Toni]

Hello everybody,

did anyone try the Sharp QA-1150 LCD Projction-panel? If yes, what kind of controller is compatiple with pal-Tv system ? It was offered here on ebay germany for 25$ !

Futher, here some of my tips for sucessfull projection:

From the world of optics:
1. Distinguish lightsources, they can be selfradiant or lightend by another lightsource. CRTs are lightsources, lcds, slides films are not. The projectionlens has to be in a distance >F(focus lenght) from the object to get a real picture.

2. If the objct is transmitted by light from lamp behind, the lightbeam ideally should come from a small lightpoint. That light can be amplified through a sphaeric- or polaroid mirror or condensor-lens or both. If you take cluster of leds with condensor the the outerborded leds may not reach the the projectionlens. then it would be better to place them directly behind the panel.theoretically every led needs its own little condensor.

3.the condensor-lens must be larger than lcd. The beam through condensor and lcd panel must (!) converge to the aperture of projection-lens. You can say the light source must be projected right into the main projection-lens. if not then you loose the outer parts of the picture.That means also the distance of the condensor lens from lightsource must be >F.

4. i think it's a good idea first try with tranparentfilm, black cartoon boarder(lcd size). With a marker draw symetric grids onto this film and by projecting you can easy fix geometric distortions.

5.Projection-lens: as a thumb rule you can say, the larger the aperture of a lens the better the brightness. But there is unfortunatly a relation between focuslenght, size of aperture and distortion of the picture, especially with large sized lcds. there will always be a compromise; good projectionobjectives are made with 3 and more lenses to correct abrevations(achromats).This is a mix of convex and concav lenses.

6.don' loose patience!


[Edited by Toni on 11-10-2001 at 08:11 PM]

[Toni]

Using a mirror behind the lcd will lead to a double loss of brightness! Remember: Only 30% of light will pass the panel. If the light passes back after reflecting again only 30% will pass! I would prefer 1-pass transmission.

[remp]

I have been doing some work on a laser projector if anyone is interested. The results so far have been less than spectacular but I think there is a way forward. Costs so far about $20.

[jdogg2]

ok so my lcd display is on order, i have a lens (electronics goldmine - $3), and now its time for a light source. cheap halogen is what i am thinking now as they are cheap and dont require to me wire up 150 leds. and they seem like they should work. to keep from burning up the lcd i guess i'll need a cold mirror. Are there any inexpensive sources and just how big of one do i need? the lcd is 4" diagonal. The lens is about 75mm diameter.

thanks

jeff

[Fiat1]

Here is a web page with some various information regarding LCD and DLP video projection systems I thought may be of use to you. The 3 colour LCD setup is the first one and it could be simplifyed by using colour filters as oposed to using dichroicn mirrors wich seperates the light into it various colours.

[JoeBob]

Remp, I'd be interested in your laser projector, start up a thread about it, I'd like that, and if not mail me with what you've got so far (I gather it isn't completed).

[remp]

I want a large screen projector like you folks. LCD panels are next to unobtainable here in New Zealand. Our dollar is 40 percent of yours so to buy a panel from USA would be expensive and you dont know for sure the condition of a panel. I will start a new thread on my laser projector and descibe progress so far.

Richard

[Fiat1]

For those of you having trouble locating fresnel lens I have this to say, you can't be looking very hard. I live in Perth Western Australia and I have found them at department stores, newsagents, and my optomitrists. Theye were all page magnifiers. I did some tests and found that 1 of these is no good for a projector, I think if you combine two it would work. I have one in my overhead projector and they are no were near as powerful!

[Gunawan W]

Here's my progress:

Ideal lamp:
>10.000 lumens, cannot convert to ANSI lumens because it's depend on many factor inside the projector.
>5000 degrees Kelvin light temperature (daylight temperature is 5600 d.K)

White LED, >5000d.K light temp. but too small lumens / costwise.
http://www.e-insite.net/ednmag/conte...ges/149134.pdf
Halogen lamp, very cheap ($5 complete set),I use this type of lamp for my first experiment (floodlight, 300W/220V (my country standard voltage),5000 lumens,3000d.K, 2000 hrs life), output is not bright enough and some kind of yellowish color, (like watching old movies with old projector in old cinema sometime in 1930es).
Metal-Halide lamp, moderate ($60 complete set), for my second experiment (floodlight, 150W/220V, 11500 lumens,4300d.K, 10000 hrs life), output is very bright and real white!
Both lamps very hot. Temperature in front of it (30 cm, with powerfull cooling fan) measured: 40d.Celcius.

Lenses:
I use basic formula to calculate:
1. 1/dIMAGE-1/dLCD=1/f
2. hIMAGE/hLCD=dIMAGE/dLCD
3. 1/ftotal=1/f1+1/f2
http://www.education.eth.net/acads/physics/light-X.htm
Using bigger lenses is better, because more light can pass thru it.
My first experiment using 3 lenses from reading glass magnifier ($1 each) with f=300mm, dia=75mm.

Setup:
I use 14" diagonal transparency picture to substitued not yet come LCD panel at the same size, about 25 cm in front of it I put 2 of the lens together (f become=150 mm),it will reduce 14" object to around 4,5" size.
http://www.education.eth.net/acads/physics/light-X.htm
case #5.
Third lens is 70 cm in front of previous lens and will produce 70" image on the screen (the screen is 16 feet from projector unit).
http://www.education.eth.net/acads/physics/light-X.htm
case #3.
The image has good brightness (with MH lamp), but not sharp enough with some rainbow effect around dark/black spot, due to poor lenses I use.
Ambience light comes from 5W incandescent lamp.

Next step:
Replace the lenses with good quality lenses, actually I need only 1 lens with f=50 cm to get the same result for the above setup.
Replace transparency picture with real LCD panel. (can't wait it's come)

Questions:
1. What is the best color for inside the projector box?
2. Is it true using more than 1 lens will reduce rainbow effect?
3. How to spread the light evenly to LCD panel?
4. What is the best but cheap material for the screen?
5. How big should I put an AC unit? because it's so damn hot and noise like inside a chopper but without rocking!

Note:
Guys, please update your progress and let us know what's your setup in more details and the important thing is how your projected image looks like. We hope it'll become better and better, ready to put in our livingroom and dramatically changes the way we're watching video!

see you.