DIY Planar Stereo Mirror, linear polarization.

[Carandiru]

I'm building a Planar Stereo Mirror rig, have the stand finished and the monitors mounted. Waiting on the glass to be cut, then I'll apply the Supertint film I bought for for 51% reflectance.
I do not know yet if my lcd monitors are 45 degree polarized, hoping so LG W2442PA - if anyone knows please post !
I have to order some linear polarized glasses to find out, and eventually use it for the final finished 3d setup.

BUT I'm wondering if it would be possible to convert a Planar Stereo Mirror rig to circular polarization using waveplate - quarterwave ? IF so how, or where would you apply it ?

[Likay]

I don't understand why you wants to go circular (it ghosts twice more than linear) but about the theory you're quite on spot. A circular polarizer is simply a dual layer construction with a polarizing film and a quarterwave retarder. In a circular polarizer the retarder is rotated 45° in regards of the polarizerfilms polarizationangle.
Practically since the output from an lcd already is polarized you can turn the polarization into circular by applying a simple qw film. If the monitors have 45° internal polarization the retarders should be aligned straight. If they have 0° then turn the retarder 45°. Simple as that. Turning the polarizer clockwise gives clockwise circular polarization and vice versa.

About permanently applying the retarder to the polarizer i'm not able to help you sorry. I guess you need a nondepolarizing glue and a way to get rid of airbubbles during the application process. However: I've trid both professional circular filters as well as linear filters with my projector rig and i had quite similar results to the professional filters (well, actually better since the linear filters are spars) by simply holding a qw-retarder in front of the spar filters. I had the same amount of ghosting but as a tiny bonus i could reduce the slight colortint i've got using circular a little. You should expect more reflectionlosses without using a proper glue but i'm not sure how much though.

You should be fine converting to circular by simply applying a qw film to each monitor. I don't think it's going to work if applying to the mirror. However i have slight concerns about the supertint film. Is it verified working with planar rigs? In my experience (there are exceptions!) most plastic/celluloid materials messes up polarization real badly.

Hope this been helpful!

[Carandiru]

I didn't know that circular polarization ghosts more than linear, thanks for the information - I'll stick to linear.

As for the supertint film, I'll just have to wait and find out. Its a two-way mirror film from a professional shop local here used mostly for interior windows. Tried to get as close to 50/50 reflectance/transmittance. I couldn't find a two-way glass mirror any where for a decent price (less than $100).

If it does mess up polarization badly, what can I expect to see through the linear polarized glasses ?

[Likay]

If it messes up polarization you'll see a lot of "rainbow effects". The phenomena is so bad that you won't even notice any ghosting.
I once took pictures of the phenomena and posted here (can't find the thread but here are the pics):
A waterfilled etchingtank does not affect polarization, either the water nor the glasscontainer.

These on the other hand are examples on the effect:
Emty cd-case
Emty cd-spider
Plastic wrapping

The pictures are taken by putting the objects between an lcd-screen and a blocking polarization filter just to show if they interfere with polarization.

Tip: if your monitors have the polarizationangle at 0° they won't work directly in a planar rig (45° becomes 135° when mirrored while 0 and 90° keeps their orientation). Fear not: You can turn the polarization 90° by using a halfwave or qw retarder (halfwave is theoretically right to use but quarterwave seems to work just as nice) in combination with a polarizer. If you change one monitors polarization you can use 0/90° glasses. You will of course loose some light on the "modified" lcd but on the other hand you can use this monitor to equalize eventual brightnessdifferences in the rig caused by the mirror.
If you modify both (45° only which also is fine with the retarder/polarizer) to 45/135° they will of course give the same lightintensity.

[Carandiru]

Wow thats some really good information, and helped me determine that the tinted mirror I made will not work
I made the tinted mirror, and put it infront of my monitor. Looking thru some RealD glasses I got from the theatre (waiting on my linear polarized ones) and I could see the rainbow effect you explained.

Fortunately I believe the monitors I have are 45/135 polarized, as I used the RealD glasses and could see the color change when moved to a 45 and 135 angle thru the glasses. On my LCD tv, it changed color at 0 and 90 (horizontal and vertical) - though circular polarized, I believe this is a could indication that I atleast am lucky with the LCD's I have.

This information you posted would be extremely helpful to anyone else trying to make a mirror, tinting film will not work. I went this route because it was cheaper for the glass to be cut and the film, about 40 bucks for 26 by 23 inch plate.

Turns out I need a smaller size, ooops, 23" by 19.5" so its been learning process to say the least. I'm hoping I can get as close to 50/50 transmittance and reflectance, maybe even 60/40 here at a local glass and mirror shop. The stereomirrors I've seen online are outrageously priced. Beamsplitters the same.

IF anyone knows of a cheaper way to get a suitable mirror please let me know.

[Likay]

Someone maybe had success using acryllic (plastic yes but some might do well in these rigs) semireflective mirrors which indeed was a lot cheaper than glassmirrors. However i wasn't able to either find the thread, manufacturer nor remember if there was any success with these sry.

ps: if you made a similar try as i did but used real-d glasses you should keep them "backwards" from you when testing materials because the polarizationlayer is the one facing your eyes. This will make them work like a linear filter (giving more clear results when testing with a lcd-monitor/tv), however both left and right eye polarizationlayers in the real-d glasses usually have the same orientation since the retarderlayer instead is rotated.

[Carandiru]

Alright, first off I want to thank you again for all the great information. I got a two-way mirror cut, $65 and have installed it into my stand the other day. Adjusting the brightness of the two LCD's in the planar stand have yielded acceptable results.
For anyone looking for a 50/50 visible light transparency/transmittance two way mirror / beam-splitter - GOOD LUCK. Either your going to pay a lot of money or you will have to compromise.

With all your information, I was able to use the RealD glasses I have to "preview" the 3D effect and make sure it is working. I took the lenses out, reversed them so we have linear polarization and rotated one 45 degrees, and the other 135 degrees.

LUCKILY my monitors, 24 inch LG FLATRONS, are polarized at the right angle.
I can see great depth / popout already with these make shift glasses and I'm very satisfied. When I get my glasses from Berezin Stereo 3D, it will be even better.

One thing I wanted to point out, maybe someone has some suggestions. but ALIGNING vertically and at the right angle is very difficult. How important is it if say its out 1/8 or 1/4 inch vertically in alignment ? What difference does it make?

I'll be posting some pictures one I have finalized everything, might paint it too. But its a planar stand, like the one that costs your a few thousand bucks, and its all aluminum, brackets no welding.

[Likay]

Cool your monitors fitted directly! And it's always fun to see poeples work and solutions. Glad to help even if i don't have a planar myself.

[Carandiru]

Here are some pictures of my finished setup. I have also included a picture of the RealD glasses, lens flipped and rotated 45, 135 degrees just for kicks. Waiting on my "real" linear polarized glasses from Berezin

Whats amazing is the stereo 3d quality, with these makeshift glasses - unreal.

[Likay]

Great rig! It looks slimmed and discrete for a planar rig. Gotta love the glasses!!!

[cybereality]

Very nice.