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Circular or Linear Polarizer

glenninduluth

New Member
I am looking to pick up a 55mm polarizer for my Contax lenses. I know the cicular ones are needed for AF cameras and in general linear ones are good for MF cameras. My question is this: All the ads I have been reading online regarding these filters say that "some MF cameras require circular polarizers". Can I get by with a linear for my 167mt? I have no other need for 55mm filters than for this system so if I can save a few bucks by not getting the circular I would like to do so. Thanks!
 
Can I get by with a linear for my 167mt? > I have no other need for 55mm filters than for this system so if I can> save a few bucks by not getting the circular I would like to do so.

The spot meter sensor will be affected by a linear polariser , so you should really get the circular one . Steve
 
Hi,

I have a similar question, but relating to the RTS II body. I suspect a linear polarizer will be satisfactory with this camera, but I would like to confirm it. Does anyone know the authoritative answer, or perhaps can someone suggest a conclusive way of testing?

Thanks in advance,

-= mike =-
 
Posted by Mike Nunan on Monday, April 28, 2003 - 12:20 pm:

Hi,

I have a similar question, but relating to the RTS II body. I suspect a linear polarizer will be satisfactory with this camera, but I would like to confirm it. Does anyone know the authoritative answer, or perhaps can someone suggest a conclusive way of testing?

Thanks in advance,

-= mike =-

Mike,

It seems to me that circular polarizers are only required by auto focus systems, at least most of them.

I wouldn't think the additional light loss (another stop added to the 50% loss you get with a linear polarizer) would be helpful and should be avoided if you don't need it.

Don Williams
 
Hi Don and Matthias,

Thanks for the replies. Don, it is possible for a camera's metering system to contain semi-silvered mirrors or beam splitters, which polarize the light, and thus will lead to metering errors if used with a linear PL. There are a few manual-focus cameras that fall into this category, for ex&le the Olympus OM4. I agree that using a linear polarizer is preferable, not only for reasons of extra light transmission but also because the polarizing effect is stronger, apparently.

Matthias, thanks for the confirmation that you have been using a linear PL successfully.

Regards to all,

-= mike =-
 
I asked the same question on the contaxslr list a while ago, the conclusion was that if your camera has a spot meter mode you will need the circular polariser otherwise you might get away with the linear. I went for a circular (contax) polariser as I have spot metering modes on both my RTS3 and 167MT.

Hope this helps,

Cheers,

Art
 
>Posted by Arthur Stanley Hood on Wednesday, April 30, 2003 - 2:10 pm: > >I asked the same question on the contaxslr list a while ago, the >conclusion was that if your camera has a spot meter mode you will need >the circular polariser otherwise you might get away with the linear. I >went for a circular (contax) polariser as I have spot metering modes >on both my RTS3 and 167MT. > >Hope this helps, > >Cheers, > >Art

I think I have to disagree with that post and one which was just prior to it.

I believe the requirement for a circular polarizer relates to some types of auto-focus systems, not to the metering system.

If you don't have a camera with an auto-focus system there is no need to consider using a circular polarizer which costs more and loses additional light in the process.

A circular polarizer does just as good a job at polarizing the light from the subject as a linear polarizer, so there is no loss in that regard.

Circular polarizers are simply linear polarizers with a quarter-wave plate attached to the back side at a 45 degree angle to the axis of polarization of the front section. You will get right or left hand circular polarized light depending on how the quarter-wave plate is mounted. In any case, it seems to be the consensus that the addition of this converter does lose additional light, beyond the one stop you might get from a simple polarizer. Circular polarized light appears to the auto-focus system to be very much like randomly polarized light so they aren't affected.

Going one step further, there are indeed auto focus systems which are not affected by polarization, but I have to admit I have lost track of which ones since I'm not a fan of auto-focus except for my little point-and-shoot camera.

If I'm wrong pleas correct me.

Thanks,

Don Williams
 
Don Williams wrote:

>I think I have to disagree with that post and one which was just >prior to it. > >I believe the requirement for a circular polarizer relates to >some types of auto-focus systems, not to the metering system.

Hi Don,

You may well be right, but the point was that as well as for autofocus, circular polarisers are required for spot metering mode on Manual focus cameras, as the sensing is achieved differently in this mode than in centre weighted and is simmilarly affected by polarised light. Normal C/W metering should work fine with a linear polariser. I have not tried a linear polariser with spot metering but have been assured by others who have tried it that the result can be severe over exposure. The advice I got was pretty consistent from several different contributors on the list. Maybe check the contaxslr archive, or even ask the question there.

Cheers,

Arthur
 
Oops, looks like I have unintentionally started a bit of a debate here! Don, the one fact I am sure of is that where you have a beam-splitter such as a semi-silvered mirror in the optical path, this will polarize the light. If you consider the way we all use polarizers to eliminate reflections from glass surfaces, then that makes perfect sense. I own an Olympus OM4Ti, and while this camera is manual focus, it DEFINITELY requires use of a circular PL for correct metering.

Arthur, it is not really a matter of whether the metering is spot, centre-weighted or matrix, it's a question of what lies in the optical path between the subject and the metering cell(s). Your statement that "normal C/W metering should work fine with a linear polariser" may be true for the Contax range, because of the particular way C/W and spot metering are implemented, but it is not necessarily true of other brands or models.

As for the point about the effectiveness of the two different types of polariser, I will chase up the reference on that, as I read it recently (I'm fairly sure it's mentioned in Ansel Adams' book The Negative).

Best regards,

-= mike =-
 
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