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Circular or Linear Polarizer

>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
 
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
 
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
 
[ 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. ]
 
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
http://www.contaxinfo2.com/broshures/ST/pages/page08.htm
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
http://www.contaxinfo2.com/broshures/167MT/pages/page12.htm
It looks even simpler, the C/W and spot SPD is on the main prism.

Contax RTS III: ouch! This camera has THREE sensors...
http://www.contaxinfo2.com/broshures/RTS_3/pages/page13.htm
...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.
http://www.contaxinfo2.com/broshures/RX/pages/page10.htm

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...
 
Would not the easiest way to get the definitive answer be to ask = Kyocera?=20

John=20
 
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.
 
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?
 
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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