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michael abraham

how manage polarization issue through the beamsplitter

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Hi guys,

 

 

Does anyone knows how manage the polarization issue through the beamsplitter of a 3D rig.

I've heard using a IR polar filter.

 

 

Thanks a lot! :D

 

 

Michele

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A weak polarization retarder (reverse pola) will mitigate the issue. This retarder is the difference between a linear pola and a circular one. It is something you will need to have custom made, as the retarder needs to go BEFORE the beamsplitter. That means you need to get a large & expensive sheet of glass that goes across the front of your beamsplitter housing.

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The answer to this polarisation issue invloving a qaurter wave retarder has been familiar to stills photographers for some time. I hope this picture helps explain it

 

Cpol.jpg

 

Normally in a mirror rig there is an issue around linearly polarised light. The mirror will act like a selective filter and more of it will get through to one camera than the other, resulting in retinal rivalry, which looks hopelessly unnatural. By converting all the light to circularly polarised light both cameras see the same thing (in terms of brightness values).

 

It appears that 21st Century 3D have been using them for some time, but have been keeping quiet about it (still, many water borne insects have had them built into their eyeballs for millions of years and not told anyone either). It's a subject now recieving much discussion in the stereographic community. I saw one provided by Dzignlight on loan to OnSight recently and it seemed to work really well. They're quite cheap compared to a good mirror, so they double up well as a protective glass! They could have used them on Pirates for just that, where I heard they lost a lot of mirrors due to smoke particle precipitation!

 

Light loss is minimal. My guess is that all the major rig manufacturers will be providing them soon as an optional extra.

 

They're a godsend to shooting 3D on water - as any shrimp will tell you. :D

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