Originally Posted by rdjam
I asked you for a source and instead you just say that is how it works. Honestly, I get the feeling that you don't really know, are making an assumption, and passing it off as fact here. Maybe you actually do have some information to back this up, so please provide it if you have it. I'm not trying to get personal, but I know your history enough that I'm not going to be naive and just trust what you say without something to back it up. Especially when my initial measurements don't seem to support what you claimed (although it can get complicated and I wasn't mapping wavelengths, just total measured light).
Originally Posted by omicronian
What happens when you put the left lens over the right lens ? is it black ?
Good question. It is pretty dark, but not black to my eyes. But our eyes can adjust a lot. At one point I calculated that this blocked about 299/300th of the light (letting about .3% of the measured light through), but that could have been off depending on changing room conditions, which could have put it closer to 1% of the light that a high end meter measures making it through both lenses.
I also found that the angle of the lenses was very important. A little tilt could change the measured light significantly. I'm just going to give my final figures after realizing it was important to make sure the lenses were very perpendicular to the projector lens and meter lens.
I used a Minolta LS-110 that measures light off the screen and all measurements are in cd/m2. One of the lenses lets light through that looks very green and one very red, so I'll call them by those colors (and refer to them as filters). My room was getting a little bit of light into it and with the projector blocked and no Dolby lens on the meter I was getting about .01 cd/m2 near the end.
Here is what I got for measurements with a 100 IRE full screen image with an Epson 9500UB:
No filters: 51.8
Green filter on projector: 33.9
Green filter on projector and green filter on meter: 26.9
Green filter on projector and red filter on meter: .23
Red filter on projector: 8.8
Red filter on projector and red filter on meter: 7.4
Red filter on projector and green filter on meter: .16
I should probably mention that when I first started doing the measurements my room was getting enough light in that I measured .11 with the projector blocked and it wasn't too long after that when I tried putting both filters over the projector and measured .23 off the screen with no filter on the meter. But I don't know if the room light had changed by then.
As far as total light loss with this projector with a UHP lamp it looks like it goes from 51.8 to 34.3 if both eyes are added, or 17.2 if both eyes are averaged. Or a 67% loss if using the average of both eyes. I suspect that the 94% loss claim was not with a UHP lamp like this projector uses. Of course my figure doesn't take into account any color balancing.