Linear Polarizer more effective than Circular Polarizer? at

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Old March 16th, 2007, 04:32 PM   #1
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Linear Polarizer more effective than Circular Polarizer?

A few days ago I found these two Tiffen polarizers at work (seems like nobody had used them for a while), both 72mm screw-on. One is a circular pol the other a linear. I just did a quick comparison with the reflections on a nearby glass door and found that the circular pol was not able to remove the reflection totally, it got a lot less and changed color (I've seen that phenomenon with other circular polarizers and reflections on glass). Then I tried the linear and was shocked because it totally removed the reflection - no change in color or anything, the reflection just totally vanished.

I always thought circular polarizers were just as effective as linear polarizers, only more expensive - but now it seems they are more expensive and less effective. Am I right with that assumption?
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Old March 16th, 2007, 05:55 PM   #2
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Here is information I copied after a quick internet search on "circular polarizer". Until I needed to purchase a new 72mm polarizing filter I always used my older linear polarizers on my auto focus 35mm cameras. My 35mm auto focus cameras (Pentax) had no issues regarding focus with a linear polarizer.

The quality of a polarizing filter will vary significantly from one manufacturer to another as well as one production run to another regardless of manufacturer. Once you find your favorite filter, guard it jealously!

What is the difference between the Polarizer and the circular polarizer ?

A circular has an additional quarter-wave plate or scrambler behind the (still linear) polarizing foil. Although not scientifically correct, it more or less restores the natural 50/50 vertical/horizontal balance of polarization, without affecting the initial pictorial result.

Only by restoring this natural balance it will allow the light metering and AF sensors to work properly, as they use polarizing beam splitters. With a linear filter, you would risk a cross-polarizing effect, ie a black-out. Bad for both light metering and AF.

In spite of what most people will tell you: the main reason to buy a circular polarizer is *not* the AF sensor, but the light metering system. You can *see* when AF goes haywire (it won't shift focus, it just has more difficulty to lock on), but you can only guess what happens with your light meter!

Actually, the first circulars were required long before AF existed, and are still required for non-AF cameras today (Rollei 600x series is a nice example).


TIP #1: How much a polarizer filter will darken a sky depends on the type of sky and your shooting angle in relation to the sun.

TIP #2: On a sunny day, position your shoulder towards the sun and your subject at a right angle to your shoulder. When the sun is high in the sky, maximum polarization will result along the horizon. When the sun is low in the sky, maximum polarization will result in all areas in front of and behind you.

TIP #3: A polarizer has very little effect when used under a gray, overcast sky.

TIP #4: Remove any protective lens filters when using a polarizer.

TIP #5: Use a polarizing filter indoors only for reducing relections and glare. Any color saturation will be minimal. Remember, a polarizer filter will effectively reduce your lens aperture by up to 2 f:stops.

TIP #6: Use a polarizer filter to control depth of field. This is similar to using a Neutral Density filter, except that the Neutral Density will render "neutral" colors, while the polarizer saturates colors. Neutral Density filters are available in greater light reducing densities than polarizers.

TIP #7: To distinguish a Circular Polarizer from a Linear Polarizer, turn the filter backwards and look through it into a mirror. If the filter image in the mirror is black, you have a circular polarizer. If the image is clear, you have a linear polarizer.

Tip # 8: A Polarizer tends to cool down the image. I find adding a Warm filter will restore warmth and a more natural image.

Jim Dees
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