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circular polarizers and legacy lenses
  
 
stan2
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p.1 #1 · p.1 #1 · circular polarizers and legacy lenses


what's the scoop on this? I poked around a bit and didn't see anything specific on what kind of polarizer to use on old lenses mounted to new digital sensor body cameras. It seems that a circular polarizer would be the right choice, vs a non-circ polarizer? The sensor is still a digital sensor, after all. But, when I've used a good circ pol on a lens like the Pentax SCM 28/2.8, I'm not seeing much effect, if any. The filter is B+W F-PRO MRC 49mm, btw.

Any ideas? I suspect there is an answer already out there somewhere if I just googled better, but I also figured someone here would know! Thanks!



Jan 20, 2017 at 06:48 PM
JohnJ
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p.1 #2 · p.1 #2 · circular polarizers and legacy lenses


Film or digital, modern or vintage, a polarising filter (circular or linear) will have the same effect. I suspect the reason you didn't see any (or minimal) effect is because there are situations where the PL doesn't really do much. If you tried the filter in different circumstances then chances are you will see an effect. Reflections in glass/paint/plastics are often attenuated. Clear blue sky approx 90 degrees to the sun is also heavily affected, but not when the sun is directly behind you.

Not sure about the relevance of circular vs linear with mirrorless bodies. Maybe this was more relevant to SLR's due to the methods they used to measure light reflected from film for exposure determination.



Jan 22, 2017 at 07:10 AM
Bob Kane
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p.1 #3 · p.1 #3 · circular polarizers and legacy lenses


Linearly polarized light screws up the phase detection autofocus systems in DSLRs, hence the need for a circular rather than a linear polarizer ahead of the lens. To the eye, both behave about the same way since each contains a linear polarizing element. A circular polarizer includes some form of quarter-wave plate, presumably in the form of a retarder foil, at the exit side which transforms the polarization state from linear to circular.

There may be some subtlety that I'm not aware of with mirrorless systems, but it seems to me that one should be able to use either type of filter with these cameras to the same effect.



Jan 23, 2017 at 04:05 AM
stan2
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p.1 #4 · p.1 #4 · circular polarizers and legacy lenses


hmmm. There are parts of that I understand. Here's one part I think I get: 'Linearly polarized light screws up the phase detection autofocus systems....' Since I'm using old glass, I don't have autofocus. Does this mean I CAN / SHOULD use linear filters with old glass, since the Circpol didin't seem to work?


Jan 23, 2017 at 06:04 AM
Bob Kane
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p.1 #5 · p.1 #5 · circular polarizers and legacy lenses


stan2 wrote:
hmmm. There are parts of that I understand. Here's one part I think I get: 'Linearly polarized light screws up the phase detection autofocus systems....' Since I'm using old glass, I don't have autofocus. Does this mean I CAN / SHOULD use linear filters with old glass, since the Circpol didin't seem to work?


Two things: IF there is no interference with exposure metering (could happen if the primary mirror affects the polarization state, I guess) then it makes no difference which polarizer you use. The apparent result is the same to the eye even though the polarization states are different. Check the camera reading against an external meter.

Secondly, rotating a polarizer often produces no clear change in the viewfinder. Polarization is not isotropic, especially noticeable in a cloudless sky. You can predict the pattern by shooting the sun with your finger; rotate your hand around your finger and your thumb traces out the zone of max effect.



Jan 23, 2017 at 02:12 PM
AJSJones
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p.1 #6 · p.1 #6 · circular polarizers and legacy lenses


If you are not using AF, there's not much difference between them - I preferred the LP over the CP because I find the effect without the wave plate is a bit stronger.


Jan 23, 2017 at 10:46 PM
kwalsh
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p.1 #7 · p.1 #7 · circular polarizers and legacy lenses


For u43 you can use either linear or circular regardless of the lens being used or the body being used.

For DLSR bodies usually you should use circular regardless of the lens being used (even with a MF lens on a DLSR exposure will get screwed up with a linear polarizer).



Jan 24, 2017 at 01:09 AM
 

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AJSJones
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p.1 #8 · p.1 #8 · circular polarizers and legacy lenses


kwalsh wrote:
For u43 you can use either linear or circular regardless of the lens being used or the body being used.

For DLSR bodies usually you should use circular regardless of the lens being used (even with a MF lens on a DLSR exposure will get screwed up with a linear polarizer).


Not my experience that LP vs CP affects exposure - at least in any significant way.



Jan 24, 2017 at 02:02 AM
Bob Kane
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p.1 #9 · p.1 #9 · circular polarizers and legacy lenses


AJSJones wrote:
Not my experience that LP vs CP affects exposure - at least in any significant way.


I'd say it depends on the camera. In the past the reflex mirror probably didn't affect the polarization of light going to the exposure system, but newer (i.e., DSLR) mirrors probably can, and therefore could affect the exposure. You might not notice a half-stop (say) shift, and even less with largely unpolarized sources, but in some instances the effect might be significant.

But with a mirrorless camera, either type of polarizer should give the same result, assuming equal transmission and polarization efficiency.



Jan 24, 2017 at 02:26 AM
kwalsh
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p.1 #10 · p.1 #10 · circular polarizers and legacy lenses


AJSJones wrote:
Not my experience that LP vs CP affects exposure - at least in any significant way.


Depends on the DLSR. Indeed for many it does not affect exposure but for plenty it does. In the digital era of course things are more forgiving, but many a transparency was ruined in the past by linear polarizer induced exposure errors

It is of course easy to test if your particular DLSR has exposure problems from a linear, but for someone who doesn't own a polarizer and is asking which to purchase the safest advice is circular for any DLSR. For mirrorless (including those with on chip PDAF) linear is always safe.

Cheers!



Jan 24, 2017 at 03:29 AM
AmbientMike
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p.1 #11 · p.1 #11 · circular polarizers and legacy lenses


This might tick you off, but you are rotating it, right?


Jan 24, 2017 at 06:37 PM
stan2
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p.1 #12 · p.1 #12 · circular polarizers and legacy lenses


haha.. yeah. I rotate it. I'm used to using a circular pol on my big canon, where it's easy to see the effect. I think it's been pretty overcast lately so the 'dial-a-sky' effect is not as pronounced, at least on my Oly mirrorless with old glass. I'll do more experimenting.

appreciate all the replies!



Jan 26, 2017 at 01:07 AM
Michael Gordon
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p.1 #13 · p.1 #13 · circular polarizers and legacy lenses


Linear pol seems to have more effect--my theory is the quarter wave plate often has a warming property and partially offsets the cool color shift of the pol. Though metering and AF should not be affected by linear pol, if the mirrorless has an AA filter there could be a deleterious effect. The AA filter is made of two layers of birefringent material and there should be a theoretical interaction with linear polarized light. I have not been able to see it, but it depends on many things including strength of AA filter.


Feb 15, 2017 at 10:33 PM







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