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Old Jan 19, 2008, 1:03 PM   #11
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I believe that a linear and circular polarizer produce the same effect (i.e. it polarizes the light entering the lens), except that a linear polarizer apparently can affect the autofocus mechanisim in cameras. I do not know how, but reportedly a circular polarizer doesnot affect the AF mechanism at all. Having said that, I've used a linear polarizer on an AF SLR and found no impact.

One other bit of information re. polarizers: in order to get the max darkening affect of skies, shoot from a position wherethe sun is 90 degrees to the right or left of thelens. Here is an example of a picture that I've posted before where the I was shooting North with the early morning sun coming from the East.

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Old Jan 19, 2008, 7:18 PM   #12
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Harriet, thanks for sharingthese examplesreminding how polarizers help with saturation andeven exposureas well asits expected role of eliminating thereflections
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Old Jan 19, 2008, 7:31 PM   #13
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I've used a linear polarizeron a couple of Pentax dSLRs, with both manual and FA lenses (the M 50mm 1.7 and the Phoenix FA 100mm macro). My results were quite mixed - sometimes it would be fine, and at other times the camera would over-expose. Same thing with the auto focus lens - sometimes I'd get a focus lock and sometimes it would just hunt and blink at me. That's one of the reasons why I bought a circular polarizer, rather than a less expensive linear - I couldn't count on the linear giving me good results.

The advice about how to maximize the effect of the polarizer is good - a friend of mine once told me to have the sun at my shoulder with my subject in front of me (90 degrees). The two pictures I took yesterday were taken between 12 and 1 (lunch time) and I was surprised I got as much effect as I did.
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Old Jan 19, 2008, 7:46 PM   #14
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Those are excellent photo's Harriet, Shows how good a polarizer does work. I have a 52mm sitting here on the desk, I will need a couple step down rings I will probably order them tomorrow, it made me want to try it again.
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Old Jan 20, 2008, 9:51 AM   #15
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A shot with my CP and some PP. Clouds way better than w/o filter. Sigma 28-300.
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Old Jan 20, 2008, 10:06 AM   #16
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Remember that when you step down you will get vignetting and lose the corners of your picture (the filter won't cover the whole opening of the lens). If you aren't stepping down too much it might not be a big deal, but I've never actually tried it.

Stepping up doesn't causethese problems as the filter is larger than the lens opening. The couple of things I noticed doing it is that you can't use the lens hood, and you can't use the lens cap (cap is smaller than the filter). That meant that if I wanted to put the camera in my camera bag, I had to take the filteroff, which more or less means disassembling it. That's not such a bad thing - I found myself slowing down and thinking about things more, rather than just grabbing, shooting, sticking the camera back into the bag and rushing off somewhere else. You have to be more careful with it, too, since the filter extends beyond the lens.
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