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05-26-2011, 05:50 AM   #1
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Polarizer tint question

Hi
Here is a question I am trying to find the answer to for quite some time. Can't make any headway and so I call on all the learned forum members here to help out.

Question: Why are all Polarizers tinted in that grey colour?

Every time I walk into a photo shop and enquire (yes the spelling with "i" or "e" is optional) for a clear polarizer they look at me as if I have just flown in from outer space. Yet let me point out that at one stage I owned a clear polarizer which belonged to my ROBOT camera I had purchased second hand in 1975. The clear polarizer fitted in front of the Schneider-Kreuznach Redionar 1:3.5 38mm . (I still own both camera and lens today) The filter of course was of the linear variety.

Unfortunately the filter fell out of my hands during an ocean razing event I participated in (the year was 1976) and rests now at the bottom of the South Pacific Ocean somewhere between Australia and Fiji.

So, can anybody tell me why polarizers are grey tinted and are not available in clear glass?

Greetings

05-26-2011, 06:06 AM   #2
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because polarizer cannot be clear. UV filter can, not polarizer.
05-26-2011, 06:12 AM   #3
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Hi Shraub.
I have a Camray linear and its is not tinted (well,not visually, until I try it on a card).
What do you mean by "tinted in that grey colour" ? Tint is a colour cast away from grey, no?
The one here has about 1 stop of light reduction when rotated to peak transmission
You can test by rotating the filter viewing a thin film monitor, it should go from peak to almost black.
05-26-2011, 06:24 AM   #4
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QuoteOriginally posted by aurele Quote
because polarizer cannot be clear. UV filter can, not polarizer.
Your answer does not explain why it cannot, you only say it cannot.

Greetings

05-26-2011, 06:38 AM   #5
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QuoteOriginally posted by Schraubstock Quote
Your answer does not explain why it cannot, you only say it cannot.

Greetings
Grey is not a tint. It is the absence of white; grey is less than fully bright. In computer numbers (red, green, blue) white is (255 255 255) and grey is (127 127 127).

Unpolarized light is polarized 50% in one direction and 50% in the other. A polarizer removes light from one of those directions. Therefore after passing through a polarizer, light is only half as bright as it was before the polarizer; ie. it is grey (50%) compared to the original unpolarized light.

Actually most polarizers remove more than 50% of visible light (they remove a fraction of light polarized in any direction).

Last edited by newarts; 05-26-2011 at 07:05 AM.
05-26-2011, 06:38 AM   #6
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QuoteOriginally posted by wombat2go Quote
Hi Shraub.
I have a Camray linear and its is not tinted (well,not visually, until I try it on a card).
What do you mean by "tinted in that grey colour" ? Tint is a colour cast away from grey, no?
The one here has about 1 stop of light reduction when rotated to peak transmission
You can test by rotating the filter viewing a thin film monitor, it should go from peak to almost black.
The clear polarizer I had (now at the bottom of the ocean) itself did not change colour when it was rotated but of course the intensity of the light changed as it was passing through.

As far as I know (I stand corrected) polarizers are made up of a sandwich of two pieces of clear glass with a polarizing foil in between. So the glass itself is not body tinted and the grey colour is in the foil.

My question is why has the filter got to be coloured, grey or any other colour.

Greetings
05-26-2011, 07:06 AM   #7
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Hi Shraub.
If the partially polarized light ray entering your lens happened to be pure white, then it would go grey as you rotate the ideal filter.
Eventually it will be black. That is what should happen and is what you would want and hope to happen mostly.
As to whether a practical polarizer casts a tint by imperfectly transmitting the spectrum, I don't know, I expect that would occur.
You have me reading about Snell and Brewster and Huygens, while I am supposed to be working on more mundane stuff!
05-26-2011, 07:09 AM   #8
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QuoteOriginally posted by Schraubstock Quote
polarizers are made up of a sandwich of two pieces of clear glass with a polarizing foil in between. So the glass itself is not body tinted and the grey colour is in the foil.
not entirely correct, with circular polarisers which are much more common these days, there is a quarter wave plate as well as the polarising foil. This quarter wave plate turns linear polarised light into circular polarised light, some older film cameras that used beam splitters couldn't meter or AF properly with linear polarised light - so the circular polariser came into existence. You can still get Linear polarisers, in fact I use one on my 50mm f/1.2 however they aren't perfectly clear either. They still use polarising foil which knocks the light down by a stop or so - Linear polarisers let in a fraction of a stop more light than circular polarisers do.

05-26-2011, 07:39 AM   #9
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QuoteOriginally posted by Schraubstock Quote
Question: Why are all Polarizers tinted in that grey colour?
I`d say CPL filters are tinted in deep dark magenta cast
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