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Circular or Linear Polarizer

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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!
 
S

swoolf

Well-Known Member
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
 
M

mike_nunan

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 =-
 
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ou1954

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
 
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mike_nunan

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 =-
 
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arthur

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
 
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ou1954

>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
 
A

arthur

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
 
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mike_nunan

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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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.

Hi Mike

What you say is correct, could not remeber the term but I guess what I was trying to say is that for contax cameras the spot meter sensor has a beam splitter in the optical path which negates the use of a linear polariser. The C/W sensor on the Contax SLR's does not use a beam splitter so a linear polariser can be used in those cases. I don't know how the matrix metering is affected though or how spot or CW are implemented on other brands.

Cheers

Art
 
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ou1954

Hi Mike

What you say is correct, could not remember the term but I guess what I was trying to say is that for Contax cameras the spot meter sensor has a beam splitter in the optical path which negates the use of a linear polariser. The C/W sensor on the Contax SLR's does not use a beam splitter so a linear polariser can be used in those cases. I don't know how the matrix metering is affected though or how spot or CW are implemented on other brands.

Cheers

Art

O.K. Everyone-

I neglected the polarizing effect of reflecting light from mirrors or partially silvered mirrors in some exposure meters, so my first response was really incorrect.

Any time you reflect light it is partially polarized, and the same is true for light used in a metering system for exposure meters.

The light will be strongly polarized as the angle of reflection approaches Brewster's angle, which is not far from the 45 degrees in most or all metering systems.

Sorry for creating all the confusion.

I think the only good answer is that the effect will show up in some meter designs and not in others, so my general answer was not appropriate.

Don Williams
 
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colin

Well-Known Member
The need for circular polarisers long preceeds the autofocus craze. They were originally needed because of the beam splitter metering method. I first used them on my Leicaflex SL,(1969) due to metering mechanics. Remember, it is never incorrect to use a circular pol. but it maybe incorrect to use a linear pol.It is best to pay the extra cost, in case your camera system or design gets changed.
Colin
 
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tbc

Well-Known Member
[ Contax Real Time NewS, Vol 1 #4 (1995 or so) states that a Circular polarizer is needed for a camera with autofocus or a spot meter. The Contax system brochure states that a C-Polarizing MC allows a camera with half-mirror exposure metering system to deliver correct exposure. Of course, if any AF system does not make it's measurement through the lens, a linear polarizer will work fine. ]
 
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ht167

New Member
Hi everybody!
I own two Contax 167 bodies, so I'm VERY interested in this debate.
I think that the "linear polarizer question" depends from the sensor topology of your camera.
For instance:
Contax ST: has two sensors, one for flash metering and the other for C/W and spot metering
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On the diagram I coud not see any half mirror; flash metering is taken directly from the film, and normal metering (spot and C/W) is measured from an SPD behind a glass prism (they call it "aspherical lens", because one of the surfaces is aspherical).
Looks like the metering switch (C/W vs. spot) is done electronically... right?
If not, how can the meter cange measurement type? I see no mirror, and I can't imagine another way...

Contax 167
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It looks even simpler, the C/W and spot SPD is on the main prism.

Contax RTS III: ouch! This camera has THREE sensors...
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...and problems with linear polarizers.
Can you see the spot SPD under that mirror? Go buying circular PL... now! :^)

Contax RX: same as ST, but AF sensor could get confused.
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So: it looks to me that 167 and ST should not have problems with linear polarizers.

But I'm not shure.
Sometimes I get one or two overexposed shot with my 167s, I always attributed them to "forgotten" memory locks, as I use polarizers quite rarely...
 
jsmisc

jsmisc

Well-Known Member
Would not the easiest way to get the definitive answer be to ask = Kyocera?=20

John=20
 
M

mike_nunan

One would have thought so, and I am currently following the matter up with Kyocera in an attempt to obtain a satisfactory answer. So far, the responses I have received are a bit woolly and leave plenty of scope for wrong assumptions.
 
D

dre

Any thoughts on how a linear PL will work on the Aria? There is no auto-focus, but it has c/w, matrix, and spot metering. Sounds like the spot metering requires a circular PL, but I'd like to know for sure before spending the extra bucks.

Also, I noticed most brands offer a multi-coated version as well as a plain version of each PL lens (circular & linear). The multi-coated is obviously more expensive - what does this feature really do and is it worth the extra cost?
 
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marc

Active Member
Multicoating also improves light transmission, so it is really recommendable. However, coating polarizers is quite a difficult task for the manufacturers (resulting in a higher price level) since the optically important element is kind of a plastic material, whereas coating can only be applied to glass. So they have to put the plastic foil under a very thin glass or - if both sides are coated, which is not always done - between two glasses.
This is the case f. e. with the B+W MRC-coated polarizers (they come as linear and circular versions and also as "slim" construction for wide-angle lenses). Their coating is also very scratch resistant which might be an issue if they get heavy use and need to be cleaned frequently. I made very good experiences with them after having tried a lot of other brands. Hope that helps, Marc
 
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