Little benefit from rotating modern circular Käsemann polarisers

[wlaidlaw]

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I recently bought a 55mm B+W circular Käsemann polarising filter to use on my 50mm Summicron-R ROM lens for my R9. Fitted on the Summicron and looking through the R9 viewfinder, I could little to no difference on rotating the filter. I wondered if the R9 viewfinder was just not showing a difference that might appear on film. I also wondered if this was a characteristic of the relatively new Käsemann  type filters, which have the advantage, especially for film, of being about 1½ EV or more lighter than a traditional circular polariser.

I have a whole lot of polarisers and step up rings for different lenses and thread sizes, as when I am travelling, I use them for most of my daylight outside shots. I found a non-Käsemann 60mm Heliopan circular polariser and a 55 to 60mm step up ring. The Heliopan polariser did show a little more variation than the B+W but it was only just perceptible and would not make a huge difference to the final result. Finally I put on a Cokin P filter holder and then a Cokin linear polariser. Rotating this did make a substantial difference but the exposures shown in the VF, as might be expected were haywire. I repeated these experiments on my SL with an R adapter L, with identical results.

For the most part, I am now using Käsemann filters both B+W, Schneider and Rödenstock. From the foregoing, I feel it may be just nor worth the bother of often having to remove a lens hood to rotate and then re-attach. For some time, I used to put a "12 o'clock" paint mark on the filters, so I could rotate them according to sun direction but I am far from convinced it makes much difference. I am sure there are circumstances, like taking pictures over lapping water, marine scenes and early morning in misty mountain scenes, where the prevalence of polarised light, would make more of a difference but for the most part, I think there is no need to rotate or benefit in doing so. 

What do others think and do they rotate or not? Obviously no need to rotate, makes life much easier on rangefinder cameras and must be better than the clunky Leica swing up - swing down polarising filter arrangement I have used in the past. 

Wilson

Edited February 1, 2019 by wlaidlaw

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[masjah]

Wilson, I can only suggest that if the rotation makes little difference, then the light from your subject intrinsically has little polarisation. Again,  I can only suggest trying it with an obviously highly polarised subject, such as those that you mention. The polarisation effect you see in the viewfinder should be what you get on the film.

When testing circular polarisers, if you have two circular ones, then you have to put their outer faces face-to-face to get them to "cross" and go dark. I know it's not quite what actually happens with the physics, but if you think of a circular polariser as a conventional polariser with a "de-polariser" behind it, you get the idea. The conventional polariser first does its business, cutting out light polarised at right angles to the filter's polarisation angle, and then, having done that, the de-polariser behind does its job so that the metering is not upset by subsequent polarisation of the camera mirror.