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04-06-2011, 03:53 PM   #1
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Polarizing filter for Sigma 10-20 EX DC non HSM

Nooby here, just bought a Promaster 77mm circular polarizing filter for my Sigma 10-20 4-5.6 EX DC. A couple of questions.

* the filter rotates easily, does the orientation of the filter affect the outcome of the picture?

* do I need to remove the filter for low light situations?

Any other tips or advice would be helpful.

Thanks in advance.

04-06-2011, 05:56 PM   #2
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Yes, rotating the filter changes the polarization of the light allowed through the filter. Some filters have a dot on them that's supposed to be pointed at the sun. I just turn it until the viewfinder darkens.

The sky is naturally polarized to the north. The effect is easy to see here, especially in the winter, but it's not obvious everywhere.

With an ultra-wide angle lens, you can have a scene that includes light that's polarized differently. You might notice a sky that's deep blue in some places and pale in others. That might even happen without a filter because of the above effect. Just know when it happens, and maybe try the photo without the filter.

A polarizer filter absorbs some light all the time. It varies depending on the brand and type. Circular polarizers absorb more. So remove it if you don't need it for higher shutter speeds. You might get more flare with a filter also.

The viewfinder will look weird with polarized sunglasses
04-06-2011, 07:42 PM   #3
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You sound like you are considering using the filter sort of "by default", but you don't want to. You only want to use it when it produces an effect you want.

With the 10-20mm Sigma, my experience is that you don't have to worry about the filter cutting off the corners of the image, but you should check with your filter just to be sure. it's not fatal even if it does, but just something to keep in mind.

You do have to be careful with clear blue skies, particularly with a lens this wide. You'll get some unevenness anyway, just due to discrepancies in the lighting across such a wide area of sky.

The filter will cause light fall-off to varying degrees, depending on how you rotate the filter. The light loss can be handy (if you don't have an ND filter), or not (makes focusing difficult/impossible, and makes handholding more difficult.)

You'll see the polarizing effect as you rotate the filter, but you don't always want the maximum effect. Sometimes just a moderate effect is best, because full polarizing can make some subjects looks somewhat dull and flat.

Any filter will compromise image quality, and while I have only very inexpensive filters for this lens myself (it's possible to spend as much for a generous set of filters as this lens cost), you do want to be conscious of flare, and consider not using the filter when there is a significant light source in the image itself. Usually I find that a polarizer isn't that helpful when photographing into a light source anyway, but that suggestion would apply to any other inexpensive filter you might use as well.

Paul
04-07-2011, 04:49 PM   #4
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  • The general recommendation it that a polarizing filter gives the best results when pointed at 90 degrees to the sun.
  • They are wonderful when you want to emphasize clouds or cut reflection on water.
  • The generally increase contrast when used at right angles to the sun.
  • When pointed more or less at the sun, they generally flare. (this depends on the lens, too.)
  • When you have a large expanse of sky you might find uneven exposure. (especially with cheap filters)
  • When pointed away from the sun, there will be little positive effect unless you want to cut down light as in smoothing water motion.


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