B New Optics Toy: A 'Varicolor' filter

Andy Resnick

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Check out this new (to me) cool optics toy.
Spike Walker, whom I semi-regularly consult with about my Ultraphot III, recently told me about a really cool optical device: a 'Varicolor' filter, manufactured (and discontinued) by Cokin. I found one for $10 on eBay, received it yesterday, and I can't put it down. Here's a set of images of the clear plastic holder held against my laptop screen, take as the filter is rotated through 90 degrees:




The object being held is the clear plastic cover and the fringes are due to strain-optic behavior. When used this way, the filter is a polariscope. Notice also that the background screen changes color as the filter rotates. That's because LCD screens emit linearly polarized light.

The filter consists of (I think, don't know for sure) a linear polarizer sandwiched between two retarders, the spectral retardance of each retarder ranges from 0 degrees in the blue to 180 degrees ('half wave plate') in the red (or vice-versa). There are other color combination filters out there, the essential aspect is the use of (highly) chromatically aberrated elements.

What I'm going to try to do is incorporate the filter into the Ultraphot and see what results.
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