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Photography Question 
Steven W. Lepak
BetterPhoto Member Since: 4/22/2006

Use of a polarizing filter w/Canon 20D

I purchased a polarizing filter for my Canon 20D some time ago - only recently noticed that the auto focus does not perform well while using it.

I did read the thread at
which confirmed my experience.

I am wondering what, if anything can be done about it. Are there some specific camera settings I can use while shooting with the polarizer to help alleviate the problem?

Any advice would be greatly appreciated.

Best Regards,


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7/9/2007 10:23:23 AM

Jon Close
BetterPhoto Member Since: 5/18/2000
  First, confirm whether it is a Circular Polarizer or Linear Polarizer. All polarizing filters rotate, the circular v. linear refers to how the filter orients light. Autofocus SLR/DSLRs require a circular polarizer for the autofocus and metering to function properly. If it is a linear polarizer, return/exchange it for a circular.

How to tell? A circular polarizer should have some indication on it, either the word "circular" or an abbreviation such as "C. Pol.". I've seen this test, but haven't confirmed it myself: "Look in a mirror through the polarizer once with the male threads toward you and then with the threads flipped toward the mirror. If the flip makes no difference, the polarizer's a linear polarizer. If the flip causes the polarizer to turn black or nearly so, then it's a circular polarizer."

Secondly, a polarizer blocks a significant amount of light. The lower light level reaching the AF sensors will adversely affect their performance.

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7/9/2007 11:38:34 AM

Suzanne Colson
BetterPhoto Member Since: 7/31/2006
  What lens are you using the filter on?

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7/10/2007 2:19:13 PM

Carlton Ward
BetterPhoto Member Since: 12/13/2005
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  I use my circular polarizer for landscape/waterfalls to get as much depth of field (f/22 - f/40) as I would like and to allow me to shoot slower shutter speeds. The circular polarizer will allow you to control reflections off of water and some control over the direction of incoming light which can bring out bluer skies and more saturated color. A tripod is a must and if you are using a tripod, manual focusing is easier. I have encountered some slowness using auto focus when hand holding and shooting faster speeds with my 17-40mm & my 100-400 lens which is why I usually take it off when shooting this way. I love my circular polarizer but I use it selectively.

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7/10/2007 3:31:27 PM

Steven W. Lepak
BetterPhoto Member Since: 4/22/2006
  Thanks for the input - seems to be more of an issue on my Canon EF 50mm f/1.4 lens.

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7/11/2007 10:23:52 AM

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