What cameras need a Circular Polarizer? The explanations of linear vs. circular polarizes vary in clarity as to what is affected. Is difference important because of autofocus, modern...

nadelewitz Loc: Ithaca NY

The explanations of linear vs. circular polarizes vary in clarity as to what is affected.
Is difference important because of autofocus, modern metering, or both?

It's clear a DSLR needs a CPL.

Is a CPL needed on a film camera with autofocus? Film cameras with some meter types but not others?

DSLR if using manual focus?

Etc.

rjaywallace Loc: Wisconsin

I have found a circular polarizer to be useful on digital cameras whether an SLR-style body, a rangefinder or an advanced fixed lens compact. I am aware that others disagree. When buying such a polarizer it is important to choose high quality filters from sources such as B&W, Breakthrough or Marumi (just to name a few). Linear polarizers work on 35mm film cameras, but not on digital bodies.

nadelewitz Loc: Ithaca NY

rjaywallace wrote:

I have found a circular polarizer to be useful on digital cameras whether an SLR-style body, a rangefinder or an advanced fixed lens compact. I am aware that others disagree. When buying such a polarizer it is important to choose high quality filters from sources such as B&W, Breakthrough or Marumi (just to name a few). Linear polarizers work on 35mm film cameras, but not on digital bodies.

A CPL is good for ANY camera. The question was....Where is a CPL NECESSARY, as opposed to a Linear polarizer?
What is negatively affected by a LPL....autofocus, or metering, or both?

E.L.. Shapiro Loc: Ottawa, Ontario Canada

A linear polarizer, if employed on a modern digital camera, can cause various automatic functions like exposure metering and autofocus to malfunction and work inaccurately. A circular polarizer is required, when necessary, for full functionality on current digital cameras. Linear polarizers will work properly on older film camera. Circular polarizer are compatible on both kinds of cameras.

speters Loc: Grangeville/Idaho

rjaywallace wrote:

I have found a circular polarizer to be useful on digital cameras whether an SLR-style body, a rangefinder or an advanced fixed lens compact. I am aware that others disagree. When buying such a polarizer it is important to choose high quality filters from sources such as B&W, Breakthrough or Marumi (just to name a few). Linear polarizers work on 35mm film cameras, but not on digital bodies.

Linear PL's are not recommended on 35mm film cameras either, if they have autofocus, it's exactly the same as with digitals!

nadelewitz Loc: Ithaca NY

So, let me try so sum up so far...
1. a linear polarizer messes up AF on ANY kind of camera. Or is it okay on AF film cameras?
2. a linear polarizer is BAD for METERING on "modern" cameras (DSLRs, bridge cameras, etc.)?

I'm trying to keep metering and autofocus separate here.

rgrenaderphoto Loc: Hollywood, CA

nadelewitz wrote:

The explanations of linear vs. circular polarizes vary in clarity as to what is affected.
Is difference important because of autofocus, modern metering, or both?

It's clear a DSLR needs a CPL.

Is a CPL needed on a film camera with autofocus? Film cameras with some meter types but not others?

DSLR if using manual focus?

Etc.

All imaging cameras can benefit from a circular polarizer. Type of meter and weather it's film or digital makes no difference.

I found a lot or wordy, hard to understand articles on the web on the differences between the two. This, from The Luminous Landscape, was the easiest to understand:

"There are two types of polarizing filters available linear or circular. Linear polarizers are more effective and less expensive than circular ones. But circular polarizers are needed with just about any camera that has a through-the-lens metering system, or auto focus.

The reason for this is that both of these systems use semi-silvered mirrors to siphon off some of the light coming though the lens. If that light is linearly polarized it renders either the metering or the autofocus ineffective. This means that you’re going to have to buy circular polarizers unless you’re shooting with a pre-1970’s camera, or a view camera."

https://luminous-landscape.com/polarizers/

nadelewitz Loc: Ithaca NY

rgrenaderphoto wrote:

All imaging cameras can benefit from a circular po... (show quote)

Thanks, rgrenaderphoto. This about as clear and simple as it can be.

Linear polarizer for manual focus, unmetered cameras only!

larryepage Loc: North Texas area

nadelewitz wrote:

The explanations of linear vs. circular polarizes vary in clarity as to what is affected.
Is difference important because of autofocus, modern metering, or both?

It's clear a DSLR needs a CPL.

Is a CPL needed on a film camera with autofocus? Film cameras with some meter types but not others?

DSLR if using manual focus?

Etc.

You are correct...there is a lot of misunderstanding around this topic. I'll try to explain based on the physics of the situation.

When light reflects off a surface at an angle, it is partially polarized at an angle parallel to the surface. The shallower the angle, the greater the polarization. This includes light reflecting at 45 degrees off the mirror in a SLR...film or digital. A linear polarizer may be at such an angle that it is "crossed" with the angle of polarization due to the mirror reflection, reducing the light that gets through to the metering sensor. When the mirror raises and the shutter opens, the light hitting the film or sensor gets no cross-polarization effect, resulting in overexposure...sometimes a little, sometimes a lot.

So the answer to your question is that a linear polarizer shouldn't be used anytime on a SLR/DSLR with through the lens metering.

To a much lesser extent, it may reduce light levels enough to interfere with autofocus operation, but that is not the primary reason.

nadelewitz Loc: Ithaca NY

larryepage wrote:

You are correct...there is a lot of misunderstandi... (show quote)

Your last two sentences sum it up nicely. Thank you.

rjaywallace Loc: Wisconsin

speters wrote:

Linear PL's are not recommended on 35mm film cameras either, if they have autofocus, it's exactly the same as with digitals!

I successfully used Linear Polarizers on my Nikon FILM cameras for years.

JohnFrim Loc: Somewhere in the Great White North.

None of the answers so far have addressed modern mirrorless cameras, where focussing and metering is done from the image sensor itself. With no mirror in the light path of anything there is no polarization taking place due to reflections.

I believe linear polarizers will work just fine on mirrorless cameras.

larryepage Loc: North Texas area

JohnFrim wrote:

None of the answers so far have addressed modern mirrorless cameras, where focussing and metering is done from the image sensor itself. With no mirror in the light path of anything there is no polarization taking place due to reflections.

I believe linear polarizers will work just fine on mirrorless cameras.

The theory says that you are correct. I'd be interested to know if anyone has verified that linear polarizers work fine on mirrorless cameras.

JohnFrim Loc: Somewhere in the Great White North.

When the need for CPLs arose, prices went up. They are, of course, more expensive because of their construction (linear polarizer + quarter-wave plate). If mirrorless cameras flood the market I doubt that linear polarizers -- at lower price points -- will come back to popular use.

I do not have a mirrorless camera to verify the theory that a linear polarizer is OK for metering and autofocus. The only other possible interaction is with the anti-aliasing filter mounted over the sensor, but I don't know if there is a detrimental effect there.

Maybe someone with a mirrorless camera and both linear and circular polarizers can verify for sure.

Pablo8 Loc: Nottingham UK.

I had both types Linear and CPL ages ago. With the onset of Auto-Focus and TTL exposure settings, the Linear filter became redundant, except for using in the light path of my Nikon Microscope, when doing crystal photography. A test for Linear or CPL if there are no markings on the mount. If the CPL is viewed and rotated in the reverse direction to normal mounting, no Polar' effect is seen. It only polarises in one direction.