Linear vs. Circular Polarzers

[rod_melotte]

Whats the difference. What I have found so far is that you need a

Circular pol for an Auto Focus camera. Is that the only difference?

 

(withoput gettign into a physics descussion LOL)

[michael_hohner]

Without the physics discussion, this is the difference. Search the archives for the physics discussion if you want to know more details.

[rod_melotte]

Well - THATS a help! LOL. I guess my question is - I have a choice - which one is used for what?? I didn't even KNOW there were 2 kinds until a few hours ago.

 

Sorry about fat finger syndrum.

[markci]

It's already been answered which one is used for what. Circulars are used for autofocus cameras. (Actually this isn't quite technically true. It's beam-splitting metering systems that are the problem, but those almost always correspond to AF cameras). That is the only practical difference.

[richard_cochran]

A couple more details: Manual focus cameras can take either (with the

caveat that, as has already been mentioned, it's really the beam

splitter that matters, but almost all AF cameras have beam splitters,

and almost no manual focus cameras have them). Both styles of

polarizers are used in the same way, and both have the same

photographic effect. Both are round, and both rotate in their

mount. The word "circular" doesn't refer to anything about the

shape of the filter, but if I were to tell you why one of them is

called "circular", I'd have to explain that it has to do with the

nature of the polarization of light that exits the filter, which

is getting dangerously close to a physics discussion, so I won't

talk about that.

<p>

So if you don't want to talk about physics, the two types of

polarizers are identical except for price tag, and the fact

that autofocus cameras don't work well with linear polarizers.

[curt wiler]

I believe that you will find that linear polarizers are capable of a slightly stronger effect - but it is stronger than needed for almost all uses. Cross-polarizing lights for copying might be an example of where linear is better. As has been said, they are also significantly cheaper. Personally, I only use the circulars for simplicity, even with cameras that don't require them; the chance of not having the right one in the field is reduced.

[svante.johansson]

I think some of the answers above are slightly inaccurate. Manual focus cameras with TTL light meters also use beam splitters. If you have such a camera (e.g. Nikon F3, Leica R or Rolleiflex GX) you will need a circular polarizer in order to get correct exposures.

[fmueller]

<i>Manual focus cameras with TTL light meters also use beam splitters.</i></p>

 

That's rubbish. There are hundreds of models of manual focus cameras with TTL light meter that do not use a bean splitter, and thus work perfectly fine with linear polarizers. I am no expert on other brands, but this includes ALL manual focus Minolta SLRs - from the good old SRT to the X-700.

[fmueller]

Make that a beam splitter, not bean splitter :-)))

[richard_cochran]

<cite>

Manual focus cameras with TTL light meters also use beam splitters. If you have such a camera (e.g. Nikon F3, Leica R or Rolleiflex GX)</cite>

<p>

The Nikon F3 is a manual focus camera that does NOT use a

beam splitter. Its mirror has many tiny pinholes that allow

light to pass to the metering cell, which is located below

the mirror. Unlike a semi-silvered beam splitter, those

pinholes aren't sensitive to the polarization of light,

so the F3, along with all other manual focus Nikons, can

use a linear polarizer just fine. In fact, the F3AF

is one of the rare autofocus cameras that can use a linear

polarizer, as its unusual design doesn't use a beam splitter,

either.

[markci]

<i>I believe that you will find that linear polarizers are capable of a slightly stronger effect</i>

<p>

You can believe in leprechauns if you want, but a circular polarizer IS a linear polarizer, plus a quarter wave plate behind it. Unless the wave plate (which is just a clear piece of glass) is somehow manufacturing light, that's a fairly absurd statement.

 

The quality of the polarizer might have some (likely extremely small for photographic purposes) effect, but mainly its a function of the degree of polarization of the light, which depends on reflection angle.

[markci]

Actually, correct that. A quarter wave plate is a birefringent material, not plain glass, but that doesn't affect the argument.

[__hank_boneroneo1]

The circular ones will thread easier.

[jbq]

The output of a CPL is circularly polarized. The output of a LPL is linearly polarized (without getting into a deep physicss discussion, both filters only let through the light that vibrates in one direction, but the LPL is such that the light continues to vibrate in that direction after the filter, whereas the CPL modifies the light so that it vibrates equally in all directions).

 

The difference only becomes significant when you use a camera that is sensitive to polarization (like most AF cameras, in which case the rear one needs to be a CPL) or when you stack polarizers (the front one needs to be a LPL).

[rod_melotte]

OK - answer this then. A Cokin A173 Blue/Yellow Polarizer. It does not say either. Can I assume that it is Circular and will not work on my older Digital Camera with AF? OR will results vary

 

What happens if the wrong one is used.

 

I'm relaly sorry for the (what seem to be dumb) questions - just trying to learn.

[markci]

<i>Can I assume that it is Circular and will not work on my older Digital Camera with AF?</i>

<p>

Huh? We just told you circulars will work on everything. Linears will not work on most AF-era cameras. It screws up the metering.

 

There's an easy way to tell if your polarizer is circular or linear. Take it off the camera and hold it up in front of your eye in front of a mirror so that you're looking THROUGH the filter AT THE FILTER'S REFLECTION in the mirror. Now flip the filter over and look through it the other direction. A linear filter will look the same -- grey -- either way. A circular will look grey if you're looking through it one way, but solid black the other.

[rod_melotte]

Thanks - the Conkin Blue/Yellow Polarizer looks the same - THUS it's Linear and will mess up the metering on my Digital - which is OK because I did not buy it for that purpose.