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by Ed Cordes on Mon Oct 19, 2020 4:29 pm
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I have always been taught that DSLRs need to have circular polarizers due to the need to avoid "cross polarization" caused by prisms and mirrors in the system.  Is this still true for mirrorless systems?  Not having mirrors or prisms may avoid the cross polarization problem.  On the other hand, does it matter if we are using a CPL on mirrorless?  I have not noticed anything different in my images using a CPL on a mirrorless camera other than I am not sure if I always visualize the polarization effect in the EVF.  Thoughts?
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by Mark L on Mon Oct 19, 2020 4:55 pm
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I can't and won't comment on the DSLR points raised.  However, I can assure you that a CPL is a valuable tool on mirrorless cameras to reduce/remove reflections and glare as well as potentially darkening the sky.  For landscapes a CPL is often used.  Note that mirrors and prisms are only in the viewfinder light path of a DSLR; they are not in the image path through the lens directly to the sensor.
 

by Ed Cordes on Mon Oct 19, 2020 5:14 pm
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Mark L wrote:I can't and won't comment on the DSLR points raised.  However, I can assure you that a CPL is a valuable tool on mirrorless cameras to reduce/remove reflections and glare as well as potentially darkening the sky.  For landscapes a CPL is often used.  Note that mirrors and prisms are only in the viewfinder light path of a DSLR; they are not in the image path through the lens directly to the sensor.
Thanks for commenting Mark.  I totally understand how and when to use polarizing filters.  My question was for more of a scientific understanding of the need for circular polarizers vs linear (if they are even available any more) on mirrorless.  DSLRs have prisms and a mirror in the light path for the viewfinder, but they also have prisms sending light to the AF system.  Mirrorless have the AF sites on the sensor itself.  Do these sites work any differently than the DSLR sites when polarization is used?  Just seeking personal knowledge and learning.
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by E.J. Peiker on Mon Oct 19, 2020 5:28 pm
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It also affects the phase detect AF but almost all phase detect mirrorless cameras have a final step of contrast detect which it should not affect. It may still affect the metering system but then, personally, I don't use the camera's meter anyway preferring to rely on pre-exposure blinkies or zebras. I have shot my Fuji GFX with a linear filter on the Laowa 17mm f/4 (roughly 13mm f/2.8 on a full frame camera) and it worked just fine. That's a manual focus lens though.
 

by Ed Cordes on Mon Oct 19, 2020 6:36 pm
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Thanks E.J. It does make sense that phase detect AF points would be affected. This is the info I was looking for. With new technology new questions and new approaches often arise. Sometimes we only find out these things after the new tech is introduced. A friend of mine said he couldn't see the polarizing effect in his Sony mirrorless. I can see it in my Canon R5 but is sometimes a bit more subtle. My friend then paid more attention and then saw the effect in his Sony. I am guessing that the visibility of the effect in the EVF is related to the EVF brightness set by the user. Thanks again.
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