polarizers...linear vs circular

[frogpoet]

Just trying to sort out the differences...and decide which is better for me.

..advice is another lamp at the crossroad..you still have to make the choice..its just easier to see which way you might prefer.

[TCampbell · Accepted solution]

A "circular" polarizer is simply a linear polarizer that has a quarter-wave plate on the backside of it.  This means that only the light matching the polarized direction of the lens can pass through... but once it passes through you can think of it as getting a slight "twist".  Without that quarter-wave correction, the polarizer would make it difficult for both the auto-focus sensors and also for the built-in light meter.

This is why virtually all cameras with built-in metering and auto-focus need a "circular" polarizer.

You may use a "linear" polarizer (sometimes called a "top" polarizer) on manual focus cameras that lack built-in metering such as an older film camera.

You can even create a variable polarizer by stacking a linear polarizer in front of a circular polarizer.

[ebiggs1]

All Canon cameras I am aware of require a 'circular' polarizer. So, this pretty much makes the choice for you doesn't it?

[hsbn]

All cameras that use through the lens metering and autofocus must use Circular polarizer (that's almost all of the camera in the market today).

[TCampbell · Accepted solution]

A "circular" polarizer is simply a linear polarizer that has a quarter-wave plate on the backside of it.  This means that only the light matching the polarized direction of the lens can pass through... but once it passes through you can think of it as getting a slight "twist".  Without that quarter-wave correction, the polarizer would make it difficult for both the auto-focus sensors and also for the built-in light meter.

This is why virtually all cameras with built-in metering and auto-focus need a "circular" polarizer.

You may use a "linear" polarizer (sometimes called a "top" polarizer) on manual focus cameras that lack built-in metering such as an older film camera.

You can even create a variable polarizer by stacking a linear polarizer in front of a circular polarizer.

[MikeSowsun · Accepted solution]

Circular Polarizers are recommended for any camera that uses a beam-splitting mirror to direct some of the light entering the camera to the AF sensors.  This includes most (if not all) Auto Focus Film SLR's or Digital SLR's.

If your camera is "Mirrorless" (like all Point and Shoots or the new breed of "Mirrorless" cameras), then a Linear Polarizing filter will work just fine with no errors to either the Focus or Metering systems.  This is because Mirrorless cameras use "Contrast Detection AF which reads the focus right off the image sensor and there is no mirror to interfere with with the Linear Polarized light entering the camera.   

I would still suggest getting a Circular Polarizer as Linear Polarizers are actually pretty hard to find these days, and you might want to upgrade to a Digital SLR one day.  

[frogpoet]

I was just wondering as I noticed that with a circular polarizer I am aware that when rotating it the "darkened sky" effect shifts and rarely includes the whole horizon where the linear darkens the sky pretty uniformly.

Thanks for the informative reply,
Bruce

[frogpoet]

Thank you for the reply. It was informative..which is what I ask questions for in the first place.

Bruce