Question about CPL


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loboclerk

Senior Member
Jul 28, 2002
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#1
Hi everyone

A noobish question...

I've a CPL filter on my kit lens, and noticed that as I turned the filter while pointing my lens at the sky, the sky gets blue or green tones. I thought CPL only polarizes by stopping down reflected light at certain angles, how did it affect the color tones? :think:

Any explanation appreciated. :)
 

mrericlee

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Sep 27, 2008
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#2
CPL is meant to increase colour saturation. I think you need a UV filter.
 

loboclerk

Senior Member
Jul 28, 2002
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#4
Thanks for the replies!

I understood the basic functions of CPL and how they worked. But what I didn't understand is, how did the color tint change? Its between blue or yellow tones as I rotated it (sorry typo in first post, not green).
 

Octarine

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Jan 3, 2008
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#5
Apart from the factors that a cheap CPL can bring in due to low quality the filter will only modify the existing light. Depending on the polarization plane of the light and the position of the filter certain portions of the light will be blocked and others can pass. If those that can pass carry the wavelength of yellow tint you will see the result in your picture. Thats one possibility
Another possibility: White Balance - which one have you used? Using Auto WB could lead to a "correction" by the camera resulting in such a tint. Reason: the CPL blocks stray light (usually whitish) and as result the sky turns out more blue (the desired effect). Auto WB could sense this as "too much blue" and will shift the WB towards the "warm side". As result you'll get a yellowish tint. Reason: complementary colours, see here: http://en.wikipedia.org/wiki/Complementary_colours
 

scorpioh

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Jul 17, 2007
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#6
Apart from the factors that a cheap CPL can bring in due to low quality the filter will only modify the existing light. Depending on the polarization plane of the light and the position of the filter certain portions of the light will be blocked and others can pass. If those that can pass carry the wavelength of yellow tint you will see the result in your picture. Thats one possibility
Another possibility: White Balance - which one have you used? Using Auto WB could lead to a "correction" by the camera resulting in such a tint. Reason: the CPL blocks stray light (usually whitish) and as result the sky turns out more blue (the desired effect). Auto WB could sense this as "too much blue" and will shift the WB towards the "warm side". As result you'll get a yellowish tint. Reason: complementary colours, see here: http://en.wikipedia.org/wiki/Complementary_colours
AWB should work on the taken image. But I think he's refering to looking through the view-finder?
 

thenomad

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Nov 17, 2008
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#7
Yes, you can rotate a CPL, and when you look through the viewfinder, you'll notice a more blue or orange tint. It is filtering different lights from going through.

I suggest you experiment by turning it until blue, take a shot, then turn it to orange, then take a shot again, and see what's the difference.

A major difference is light reflection. If you set it right, you'll get a lot of reflected light filtered, e.g. you can see through glass, water, even when there's sunlight reflected from them. You'll also get more saturated colours as a result of this light filtering.
 

giantcanopy

Senior Member
Feb 11, 2007
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#8
They are suppose to cut down the haphazard scattered light and hence giving whats underlying it abit more saturation.
 

Rashkae

Senior Member
Nov 28, 2005
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#9
CPL is meant to increase colour saturation. I think you need a UV filter.
No, CPL is designed to reduce stray reflected light. The saturation increase is a welcome side effect.
 

loboclerk

Senior Member
Jul 28, 2002
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#10
Thanks for all the replies!

Yes I was referring to what I saw thru the viewfinder. Somehow even a normal cloudy sky could give a slight yellow tint when I rotated it at certain angles. Using a Steinzeiser CPL. It felt more like a yellow/blue tinted filter at times rather than what I expected of a CPL. Guess I'll experiment more with it. :)
 

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