Liquid Crystals

[Andy Resnick]

A colleague and I scavenged some liquid crystal material from a broken LCD display, smeared on a slide and covered with a standard coverslip.The material is imaged 4 different ways using the same 16x phase contrast objective (clockwise, starting from top left): phase contrast, crossed polarizers, replacing the (illuminating) polarizer with a Cokin A171 varicontrast filter, and replacing the (illuminating) polarizer with a circular polarizer.

There are all orthoscopic views of the sample and the top left was the only one using the (illumination) phase ring. Cropping and scaling only (jpg camera output, etc. etc.). Illuminating the sample with circularly polarized light rather than linearly polarized light has the effect of removing all of the isogyres, leaving only the isochromes. The Cokin filter is a little hard to describe, I think it color-codes the two polarization states as either red or blue.

[ModelZ]

Interesting comparison study, nicely done. Taking a fresh look at an ubiquitous material is always good!
Thanks for posting, Karl

[rjlittlefield]

The material is imaged 4 different ways using the same 16x phase contrast objective (clockwise, starting from top left): phase contrast, crossed polarizers, replacing the (illuminating) polarizer with a Cokin A171 varicontrast filter, and replacing the (illuminating) polarizer with a circular polarizer.

Visually interesting and very thought-provoking -- nice!

Thanks especially for introducing me to the Cokin A171 filter. I'm sure that I have periodically seen references to varicolor filters, but I had never thought to track down what they actually do. Certainly adjusting the color depending on subject polarization had never occurred to me. Unfortunately it looks like Cokin has discontinued the 171-- everywhere I look they are described as "out of stock", except that B&H specifically says "discontinued". Yesterday eBay showed one for sale, but it's gone today. B&H does advertise the X-Pro 171 variant, but that's very expensive (over $1000) and "special order, expected availability 6-10 weeks". B&H also lists a P170 variant, red/green, also special order but only $65.

BTW, Cokin describes those filters as "varicolor", not "varicontrast". The term varicontrast is also associated with color filters, but they were not polarizing and instead were used to adjust the contrast of black-and-white printing papers such as Kodak Polycontrast (also discontinued, 2005) and Ilford Multigrade (still available).

--Rik

[Andy Resnick]

Interesting comparison study, nicely done. Taking a fresh look at an ubiquitous material is always good!
Thanks for posting, Karl

Thanks for the kind comments!

[Andy Resnick]

The material is imaged 4 different ways using the same 16x phase contrast objective (clockwise, starting from top left): phase contrast, crossed polarizers, replacing the (illuminating) polarizer with a Cokin A171 varicontrast filter, and replacing the (illuminating) polarizer with a circular polarizer.

Visually interesting and very thought-provoking -- nice!

Thanks especially for introducing me to the Cokin A171 filter. I'm sure that I have periodically seen references to varicolor filters, but I had never thought to track down what they actually do. Certainly adjusting the color depending on subject polarization had never occurred to me. Unfortunately it looks like Cokin has discontinued the 171-- everywhere I look they are described as "out of stock", except that B&H specifically says "discontinued". Yesterday eBay showed one for sale, but it's gone today. B&H does advertise the X-Pro 171 variant, but that's very expensive (over $1000) and "special order, expected availability 6-10 weeks". B&H also lists a P170 variant, red/green, also special order but only $65.

BTW, Cokin describes those filters as "varicolor", not "varicontrast". The term varicontrast is also associated with color filters, but they were not polarizing and instead were used to adjust the contrast of black-and-white printing papers such as Kodak Polycontrast (also discontinued, 2005) and Ilford Multigrade (still available).

--Rik

Thanks! Spike Walker turned me on to these things a while ago, I scored mine off eBay. I've used it for 'normal' photography, and it does produce interesting color effects, but it's not something I would regularly use.