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Photography Question 
Garry Mack
 

Polarizing Filters - Linear vs. Circular


I'm wanting to buy a couple of polarizing filters. I looked at ebay and they have linear and circular polarizing filters.

What is the difference and which would be best for me?

I use a manual focus 35mm cameras.


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2/1/2002 7:09:02 PM

 
Gadi Eidelheit   Hi Garry,
The difference is in the way that the polarized rays enter the filter. It has almost no effect on the final outcome. However, if you use lens with autoFocus feature you will need the circular version, otherwise the AF will not work properly.

Also, polarizer means less light will enter into the camera and you should compensate for that (done automatically most of the times, but should be aware of).


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2/13/2002 5:40:19 AM

 
Jon Close
BetterPhoto Member Since: 5/18/2000
  Circular Polarizers can be used with any camera. Linear Polarizers can only be used with cameras that do not use "semi-silvered mirrors or prisms to split the light entering the viewfinder in order to calculate exposure and focusing distance. PL (Linear Polarising) filters can sometimes interact with these items to give unpredictable exposure or focusing. So we recommend that you choose a PL-CIR filter unless you have a manual focus camera which has no beam splitter." (courtesy of Hoya, http://www.thkphoto.com/catalog/h/011pl.html ) Check your camera's user manual, but if you have any doubt, use a circular polarizer.


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2/13/2002 6:23:27 AM

 
Jeff Grove   Garry,

One thing that wasn't mentioned in previous responses was price. If you haven't noticed already, circular polarizers are more expensive, sometimes significantly so. Even if you have an auto-focus camera lens you can still use a linear polarized filter. Just switch the lens to manual focus and focus manually. You'll still get the effect of a polarizer without the excessive cost.


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2/13/2002 10:26:51 AM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Jon C. has provided the technically most accurate answer. If the camera has a "beam splitting" mirror or prism, for whatever reason, use a circular. Nearly all current SLR's (made within the past few years) use beam splitting.

I emphasize what he mentioned about affecting *exposure* in addition to focusing. Two of my manual focus camera bodies require circular polarizers because the internal exposure meter uses a beam splitter. I don't recommend using a linear polarizer and manually focusing a camera with an auto-focus system. Very, very likely the same beam splitter is also used to feed light to the camera's internal exposure meter sensor.

Gadi almost has how it works correct, but its not how it enters the filter, it's how it exits the filter that's different. A circular polarizer *is* a linear polarizer with a quarter wave plate added to the back of it (usually they're cemented together). The linear polarizing plate in front acts just as a pure linear polarizer. The quarter wave plate behind it circularly polarizes the the light that has been filtered by the linear polarizer. A "beam splitter" is similar to a linear polarizer. To the beam splitter, the now circularly polarized light reacts as if it were randomly polarized, allowing the beam splitter to direct the correct portion of light to the camera's internal exposure meter and auto-focus system (if it has one).

Using a linear on a camera that uses a beam splitter, at least for its exposure meter, won't always throw off the metering. It will only occur when the polarizer is rotated into certain positions (or near them). When it does happen though (and it's unpredictable), how badly it throws off the metering is pretty dramatic.

-- John


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2/13/2002 7:21:04 PM

 
Garry Mack   Thank you Gadi, Jon C., Jeff G. and John L. for the information. Since I am in doubt about my camera's meter I will pay the extra and buy circular polarizing filters.

The best thing is that now I know the difference.


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2/13/2002 8:39:19 PM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Garry,
What make and specific model of camera do you have? That may help answer whether you can use a linear or need a circular for your specific camera.

-- John


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2/13/2002 10:05:19 PM

 
Garry Mack   John,
I use a Nikon F3 and FE2. They share lenses.


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2/19/2002 7:16:41 PM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Garry,
Took some searching, but according to the specs I was able to find, you can use a linear polarizer on the F3 and FE2 and not worry about it messing up the auto-exposure system. Some details about your camera metering follows . . .

FE2 Metering:
It is very much like one of my manual exposure OM bodies with the meter sensors inside the prism housing. The reflex mirror is NOT a half-silvered beam-splitter. All the light is reflected by the reflex mirror into the prism where the metering is performed. This means the metering can be fooled a little by strong backlighting behind you. You may have noted this effect at times with bright sun immediately behind you. If working in AE mode on a tripod using a cable release, ensure you shade the viewfinder from direct sun.

F3 Metering:
While two of my three Olympus OM bodies have metering similar to the F3 (behind the mirror), how the light gets there is different. Mine have half-silvered beam-splitter mirrors which reflects most of the light into the prism and the rest passes through to the meter cells. The Nikon F3 has a unique "pinhole" in the center of the mirror. This also allows some light to pass through to the meter cells behind it. However, unlike half-silvered mirrors, the pinhole method is unaffected by linear polarizers. Unlike the FE2, the "behind the mirror" metering is unaffected by bright sunlight shining on the viewfinder.

-- John


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2/19/2002 9:34:43 PM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Garry,
Should also mention IMO the FM2n, FE2 and F3 are among the very best pro-grade SLR bodies ever made. They (and the AI/AIS Nikkor's) should serve you well for a very long time.

-- John


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2/19/2002 9:45:56 PM

 
Damian P. Gadal
BetterPhoto Member Since: 4/22/2002
  Very useful information - thanks!


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3/27/2004 9:43:33 AM

 
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