Polarizing Film Experiment

[afxman80]

I just ordered a couple sheets of Polaroid polarizing film from surplus shed. I don't have them yet, but when I get them, I was going to try an experiment. I've played with polarizers from calculators before, and I noted that when you rotate two of them together, they become less transmissive. I know that one of the effects pre polarizing has on LCDs is to improve the contrast. I was thinking, if you made a circular pre-polarizing lens large enough to cover your light source, rotating it may help to further inhance contrast, or at least remove some of the screendoor effect, at the cost of lost brightness. I know if you go too far with it, barely any light would pass. But if you rotated it just slightly, it may improve contrast dramatically. Just a thought. I'll be using it with a 5 inch lcd projector I'm building to replace a rear projection unit that is burned out (160 dollars per tube times 3, I think I'll just build my own projector for 120 bucks). Using a 5" cheapo legacy panel from ebay, I figure screendoor is going to be horrible(hopefully watchable at the 48 inches of the screen). Maybe this would help. Since its an already built commercial rear projection cabinet, it shouldn't need too much brightness. Gonna try with a 100 watt halogen, and see what I can come up with. Anyways, let me know what you think or if anyone has already tried this. Thanx,

--aphex

 

[Axeman]

I tried a similar experiment. I took a polarizing sheet from a laptop LCD screen and tried it between my LCD and the projection lens. By rotating it I could either see the picture, or reduce the brightness. It did not increase the contrast since it just made the entire picture darker. Try taking the sheets and lining them up with the polarizers on either side of your LCD. If black level is dependent on the quality of your LCD's polarizers(extinction ratio I think it's called), which I think it is, then mabye the higher quality Polaroid sheets in conjunction with what's already there will improve it. If black level is dependent on the twisting ability of the liquid crystals, you are probably out of luck.

Anyone else want to jump in on this who knows more than me? It might improve our black levels if it does work this way...