[Leica] Question about A42 M Polarizer #13351

[leica at screengang.com (Didier Ludwig)]

Thanks, Henning and Fred

Btw, Fred, "dutch" is not "deutsch" (german) but the name of the language
spoken in the Netherlands. It may sound similar for anglo-saxons, but in
fact is so different that I for instance do not understand one word of
Dutch.

Didier


> Thank you for this explanation.
> I could not have done it better, maybe in Dutch...;-))
> Fred Hess



>> Right, it's a linear polarizer. The M's don't
>> need circular ones. The circular ones are for
>> cameras that use semi-silvered mirrors as part of
>> their operation, either for metering such as the
>> Leica reflexes or for AF. In those cases the
>> polarized light coming through the back of the
>> filter can interfere (cross-polarize) with the
>> polarization that occurs in the semi-silvered
>> mirror and a) cause overexposure or b) not AF
>> correctly or at all.
>>
>> The circular polarizer has a so-called 'quarter
>> wave plate' at the back, which depolarizes the
>> light again. That's OK, because it's the
>> relationship of the reflection of the light off
>> non-specular parts of your subject and the
>> polarization direction of the entrance of your
>> filter that causes the effect, and if it gets
>> de-polarized after that it doesn't matter to the
>> effect on the film or sensor.
>>
>> Circular polarizers are somewhat more expensive
>> to make, but don't create a better polarization
>> effect.
>>
>> As mentioned before, 0? is the same as 180?, for either type.
>> Henning J. Wulff