DIY Video Projector

[Myren]

muzzman: actually, what would be ideal is to be able to have your contrast, brightness and volume settings all depend on the brightness of the scene. i started working on that a month ago - after picking up the DScaler source - and have been making fickle progress when i get enough time to code it.

that way you can custom tune the light and dark scenes and gradient between them. with gamma, if you've got a really dark scene, everything suddenly would jump up a fixed amount. with gamma a really bright scene would suddenly become not so bright. by fine tunning the gamma contrast and brightness (or beter yet, just do a photoshop style curves editing) for each scene, you can find something that looks good everywhere.

i think its the only way were gonna get decent pictures on both light and dark scenes without the high gain screen that are otherwise necessary to make em beautiful.

dont really have any EFFECTIVE ways of checking sccreen brightness, sadly.

myren

[Grumpy_Git]

jjasniew.

don't put your tire iron through that vga panel just yet, it may not be working great but hey I'm sure something could be sorted.

Or alternatively, any chance you'd post it to me in England??

Nick.

[Axeman]

I just had a thought.

Has anyone tried putting a mirror behind an LCD panel and shining light on the front? Sure, it means that you will lose 50% of the light, and it would be a pain in the a**, it would solve the problems those of us with ribbon cables are facing. If you put a mirror and fresnel together, you could focus the light back up to an OHP head and still slide the whole thing under any PCBs.

Doesn't do me much good until I get a new monitor/take mine apart again and try to fix it(shudder).

[jjasniew]

Myren,

Check out this http://www.barco.com/projection_syst...ces/advice.asp to measure screen brightness...

Nick, I'd post it to you, but it belongs to my employer! Luckly, I didnt make the mistake of buying it, just borrowed it to check out.

Axeman, well, they DO make OHPs where the light is on top (up with the lens assy) it shines down on a fresnel with a mirror behind it, then bounces back up through the lens to project an image of whatever "foil" you have placed on the stage.

Here's a like to show what this type looks like - http://www.dynadirect.com/bc-apovs3000.html (3000 lumens)

Putting the light up top solves a lot of cooling and noise problems, provided the bulb can operate being only convection cooled.

So its is logical that if you can sandwich a fresnel and a mirror just behind the LCD, that arrangement might - just might - be similar enough to a "foil" on top of the stage of the projector in the above link! The large aperature from the 15" LCD panel display might (again, just might) allow you to use a 3000 lumen unit with a satisfactory screen brightness.

Great idea!

[jjasniew]

http://www.do-it-yourself.netfirms.com/projector.htm

[jjasniew]

http://www.fresnel-optics.com/pdf/reflective_opls.pdf

[Bitch]

Portable ohp:s (light at top, mirror or such reflecting the light back to the lens) don't work with LCDs. Although I have got no experience on this, I've read about it.

I got my screen mounted today. It's quite cool, although it doesn't work with ambient light as the ambient light shines quite badly on it which sucks *** a bit. But it's movie screen anyway and works ok lights off. I get 120" (measured from top left to bottom right, does "diagonal" mean this?) windows deskktop on it.

There's still loads of stuff before I'll get happy with this. Firstly I need get that damn VGA Y-cable. Secondly I have some minor problems with the ohp cooling (it gets _hot_ and the thermal switch thing doesn't work on it so it won't cool it after you turn it off, so I have to open the "hatch" after a session). Fixing it wouldn't cost much but I just can't get around to take it to be fixed.

I would definetly want new LCD with better contrast and res. With 15"-lcd the image would get almost twice as big which normally I quess would be just good but it wouldn't fit to the screen/wall and there's no way the ohp is going to be at the middle of the room. But buying Viewsonic or such won't anyway happen before the price drops to reasonable level.
At least for now I would want to disable/lower the rpm of the cooler of the current LCD as the noise is just terrible.

Oh and then there's that DVD-decoder card still to get to improve the movie quality and blaablaablaa..

I'm up to bed.

I'll watch some movie tomorrow and see what are the feelings after it..

[jjasniew]

Bitch,

They dont work with an ordinary projection panel, because the panel puts some space between the bottom protective glass and the LCD - usually for air cooling. On top of that, the panel has feet which further lift the LCD up above and away from the reflective surface.

Axeman was thinking of putting the reflective part right up against (in physical contact with) the LCD element itself, which may or may not make all the difference.

Also on my panel there is a top glass, with another space between. Certainly all these glass panels and spaces are going to ruin the original operating principle; hence why the ordinary situation doesnt work!

[Gunawan W]

Axeman,
Long ago I did experiment with small lcd panel calculator.
The panel has reflective surface right behind it.
I put the lamp (300w halogen floodlight) in front of the panel (slightly above), the light beam shone the panel and reflected to the lens right in front of the panel and I can saw the image on the screen. This setup basically is opaque projector. Can't do it with larger panel, because my PS1 panel was broken. If this setup can really work, it will help us a lot.

see you.

[jjasniew]

Axeman,

Could you measure the thickness of your LCD element? (If you still have it apart?) Hopefully it'll be very thin -

If anyone else could contribute this measurement of the "bare" LCD array, please do.

Thanks,