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Photography Question 
Bill Belisle
 

Polarizing Filters


I have recently gotten back into photography after a 15-year hiatus and have what I hope is a simple question (okay, maybe a *few* simple questions). I am used to using polarizing filters, but now the prevalent polarizer seems to be a "circular" polarizing filter. I'm guessing that these circular polarizing filters work with the new breed of auto-focusing lenses which may rotate the filter during focusing, thus making the use of "normal" polarizing filters a nuisance. Does a circular polarizer deepen a blue sky regardless of its rotation? If so, how does one control the amount of polarization upon the image? Are "non-circular" polarizing filters still available? I often find that full polarization deepens the sky so much that it's obvious that a polarizer was used. I shoot mostly wide-angle scenery pictures here in the Southwest (Arizona), and want my photographs to appear as natural as possible. I have gone from using a Nikon F2 with 20mm, 35mm, 85mm, and 200mm lenses to a Nikon F100 with 17-35mm zoom, 28-70mm zoom, and 80-200mm zoom lenses (all AF-S), and the change has been somewhat staggering--I'm still not sure all of the automatic options are for the best; but perhaps that's better left for a different discussion. None of my lenses rotate the filter during focusing. I have been looking at (of all things) the "Moose Filter," which combines a circular polarizer with an 81a, and is guaranteed to not vignette images even with lenses as wide as 17mm. The filter is manufactured by THK/Hoya and costs close to $100 ($99 to be exact). Has anyone had any experience with this filter? Actually, any experience with "circular" polarizing filters as compared with "non-circular," or "regular" (as I know them) polarizing filters would be appreciated. Thanks in advance for any information you can provide. This is a wonderful site!


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3/25/2001 2:06:33 AM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Bill,
The two types of polarizers are "linear" and "circular." To my knowledge, the linear polarizers are still made; the B+W's are still available. A circular polarizer is used to prevent fouling up the auto-focus and auto-exposure on newer camera bodies that use "beam-splitting" half-silvered mirrors in front of the sensors for these systems. You use a circular just as you would a linear, and it is just as sensitive to any lens that rotates the front ring as you focus it.

A circular polarizer is a linear with a "quarter wave plate" laminated on the back of it (it's not a separate piece of glass). The polarizing part on front through which light passes first works exactly as it does on a linear. The quarter wave plate circularly polarizes the light that passes through the linear, a good portion of which is linearly polarized at right angles to the light that was blocked.

A "beam-splitter" is much like a linear polarizer in how it works, and presumes randomly polarized light to work properly. When aligned in certain positions, a linear polarizer can foul up the AF and AE systems behind the "beam splitter." Circularly polarized light reacts to a linear polarizer as if it were randomly polarized. The quarter wave plate that circularly polarizes the light passing through the linear in front of it ensures proper operation of the sensors behind the "beam splitter."

-- John


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3/25/2001 10:14:06 AM

 
Jim Miotke
BetterPhoto Member
BetterPhotoJim.com
Owner, BetterPhoto.com, Inc.
  Here are my two cents for you, Bill.

Like John explained, the circular is required for autofocus. You work it just like you would a linear; you can still control the amount of polarization with the filter. If you notice only part of your scene being polarized, you can keep polarizing until you get the effect you want. If it is too much and looks unnatural, you can back off a bit. You are right in that you have to be careful to not overdo it. Fortunately, with an SLR at least, you see what you are going to get and can therefore adjust it accordingly before shooting.

With both linear and circular, the polarizer is most effective when you are shooting at a 90 degree angle from the sun. So, if you are having a hard time seeing the effect, it may be that you are either facing toward or directly away from the light source.

Welcome back to the art - Enjoy!


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3/25/2001 10:45:25 PM

 
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