The Filters We Need With Digital...

Started Oct 5, 2008 | Discussions thread
OP Joseph S Wisniewski Forum Pro • Posts: 34,130
All polarizers are "gel", sort of...

BorisK1 wrote:

JensR wrote:

And usual crossed polarisers act as a defacto IR pass filter

I knew this applied to gel filters, but thought the ones made out of
glass weren't IR-transparent. Good to know, thank you!

Polarizers aren't actually glass, nor are they really "gel", but they are "gel like". They're actually a vinyl polymer, loaded with shards of iodine crystals. Single solid optical grade iodine crystals big enough to make a decent polarizer would cost a simply insane amount.

Edwin H. Land figured out that if you put a bunch of microscopic crystals in a polymer, and applied physical stress (stretching) or an electrical field as the polymer hardened, the crystals would all orient themselves along the field, and you end up with enough of them stacked on top of each other so that you have nice, uniform polarizer with no holes...

To make them easier to handle, the vinyl is glued between two sheets of optical glass, which is what you see when you handle the polarizer. They're typically PVA, and that absorbs water and swells, gets gooey and sometime cloudy. And the glue fails, because it's difficult to do a good job gluing dissimilar materials like PVA and glass. That's why B+W makes such a fuss about their Kaeseman polarizers with the sealed edges...

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

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