Polarizers: What causes cooling effect?

Discussion in 'Large Format Cameras and Accessories' started by MMfoto, Aug 22, 2009.

  1. MMfoto

    MMfoto Member

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    Can anyone explain why polarizers tend to cool as they polarize?

    This is a well known effect, but I've never heard an explanation of what causes it. One interesting thing I've noticed is that if you take a polarizer (in my case a MC Rodenstock) and look through it from the front towards the rear, the polarization is not seen, as the filter is backwards, but you do see the image cool as the filter is rotated towards what would be maximum polarization if looking through in the correct direction (as the film sees). I hope that made sense.... Try it if you don't believe me!

    Thank you.
     
  2. randyB

    randyB Member

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    Cooling effect? My experience has been that they every so slightly warm the scene because they remove the reflected sky light. I see the effect most on forest/landscape scenes where the sky light is reflected from leaves, grass, water, etc. Polarizers also act as a really good UV filter. I can actually see the warming effect in the viewfinder as I rotate the filter. I have experienced a great variance in the polarizing effect depending on the quality of the filter.
     
  3. Sirius Glass

    Sirius Glass Subscriber

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    I do not see either warming or cooling. Please explain or show examples.

    Steve
     
  4. keithwms

    keithwms Member

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    Offhand I don't think there is a general statement that can be made that a polarizer warms or cools a scene. The haze we typically see is some combination of Mie and Rayleigh scattering; the Rayleigh will tend to give a bluish look, the Mie more whitish. Most haze I see is bluish white, i.e. a combination of both components. (Not like the coloured haze that people used to see, you know, back in the 60s, but I digress)

    Anyway, a polarizer will tend to reduce both components, and what effect you see will depend on the proportion of the components in the first place and the colour temp of the incident light.

    Regarding colour temp, the way I think of it, the colour temp of the incident light is mostly determined by upper-atmosphere scattering, i.e. scattering off particles/molecules not between the subject and the lens. But haze is caused by scatter off particles/molecules that are between the subject and the lens. So you can have a warm or cool colour temp, with haze masking that and reducing saturation. Whether you see warming or cooling effect through a polarizer will depend on what the colour temp was for starters.

    These are the thoughts that appear logical to me at this hour.
     
  5. epatsellis

    epatsellis Member

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    regarding the lack of polarization when viewing the filter "backwards", only circular polarizers will exhibit that effect, linear polarizers are the same both ways.
     
  6. Peter De Smidt

    Peter De Smidt Member

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    It depends on the manufacturer. I have one, a Rokunar, that's very cool. A long time ago there was an article on polarizers in one of the camera magazines. At that time (mid-1990s), most "neutral" labeled polarizers were on the cool side, but this varied quite a bit from manufacturer to manufacturer. In a number of cases, a company's warm polarizer was more neutral than their "neutral" one.
     
  7. Sirius Glass

    Sirius Glass Subscriber

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    Some manufacturers make warming [and cooling?] polarizers, but I do not think they would sell them as polarizers, but as warming polarizers [cooling polarizers].

    Steve
     
  8. MMfoto

    MMfoto Member

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    While the cheap polarizers I've had in the past have been quite cool in general, with the Rodenstock MC polarizer I currently use, if you hold it over a white sheet of paper, and look through it backwards (so that the polarization effect is not seen) you can observe the color balance change as the filter is rotated. The white sheet becomes goes from cooler to warmer to cooler, etc, as the filter is rotated...
     
  9. markbarendt

    markbarendt Subscriber

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    My first polarizer was a cheap one with no instructions to fit a Cokin holder.

    For a while I used it backwards not knowing any better and it had that warm/cool shift, it also wasn't working well. I thought it was just cheap, then one day out of curiosity I just held it up to my eye the other (right) way and it worked just fine and had no color shift.
     
  10. pgomena

    pgomena Member

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    I've noticed some polarizers with a green shift, not just cooler. As others have said, it varies with the manufacturer.

    Peter Gomena