SL metering with linear polariser?

[dkCambridgeshire]

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I'll shortly be using a Canon FD 500/4.5 manual focus lens with my SL; lens has a drop-in filter holder (48mm filters). There is an accessory filter holder available for use with a polariser (with a wheel to rotate the polariser) which usually has a linear polariser fitted. Would the SL's metering (in any metering mode) be affected by use of a linear polariser? 

 

Regards

 

dunk 

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[steppenw0lf]

I have no linear polarizers - only circular. But I guess the difference will not be noteworthy.

A circular polarizer also influences linearly polarized light, so the effect is not completely different (I would assume the total effect of the linear polarizer is slightly weaker). The modern sensors offer so much DR, that even a wrong exposure (typically + or - 1 stop) will not result in unusable pics. As there is no mirror there is no inversion of polarity and no difference between what your eye and the sensor sees. (The EVF always shows the sensor image - while a DSLR finder shows a reflected image.)

But you will soon find out after your first tests, after all it takes only a few seconds from triggering the shutter to the final image.

 

More explanations:

http://www.bobatkins.com/photography/technical/polarizers.html

[dkCambridgeshire]

I have no linear polarizers - only circular. But I guess the difference will not be noteworthy.

A circular polarizer also influences linearly polarized light, so the effect is not completely different (I would assume the total effect of the linear polarizer is slightly weaker). The modern sensors offer so much DR, that even a wrong exposure (typically + or - 1 stop) will not result in unusable pics. As there is no mirror there is no inversion of polarity and no difference between what your eye and the sensor sees. (The EVF always shows the sensor image - while a DSLR finder shows a reflected image.)

But you will soon find out after your first tests, after all it takes only a few seconds from triggering the shutter to the final image.

 

More explanations:

http://www.bobatkins.com/photography/technical/polarizers.html

 

 

The point of my query is that I do not wish to spend ££ on an expensive s/h linear polariser drop-in holder if it might affect the metering in any of the camera's metering modes … the ancient Canon FD polariser drop-in holders are usually fitted with a linear polariser and a substitute 48mm circular polariser would add to the cost. I'm not sure how the SL's spot metering works in comparison to its centre-weighted and multi-field metering modes.

 

dunk 

[steppenw0lf]

The "problems" came usually from reflections at mirrors. (inverting polarity)

As there are no mirrors involved (as far as I know the camera takes the measurements from the sensor ?!), there cannot occur the classical problems.

I had no problems with a circular polarizer, so I expect more or less the same behaviour/measurements with a linear polarizer.

 

The question is if it pays to add a polarizing filter at all. If you use the lens for wildlife, then it is usually not necessary (the distances are not so big, the angles not predictable, and it reduces light).

The polarizing filter is usually most efficient for landscape pics, which are more or less wideangle. In a tele lens you would normally not be able to see much of a polarizing effect - only if the object by chance is in the necessary angle to the sun and/or contains reflections.

So I would not spend the money for this rare use case.

[ramarren]

Circular polarizers are a solution to the use of polarizing filters on cameras that include polarizing elements in the metering light path, typically DSLRs with their reflex mirrors and other optical systems required to provide viewing, metering, and autofocus. The reason you need it is that these systems' output can be influenced by the interaction of the polarizer with the natural polarization of light when it is redirected by a mirrored surface. 

 

The SL has no mirrors in the light path for any operation: the light coming through the lens falls directly on the main sensor and is used for metering, focusing, and viewing. A circular polarizer is unnecessary; a linear polarizer works with no issues. Metering patterns on the SL are made by limiting the area of the sensor and weighting the values of light in the metered area.