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Are circular polarizers required with mirrorless cameras?

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JohnFrim

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I know what polarizers do, and I know the technical differences between circular and linear polarizers, so no need to explain any of that.

Circular polarizers became a necessity with DSLRs because of issues related to both autofocus and metering systems because these take their information from mirrors inside the camera box. The mirrors actually polarize the light going to the sensors to some extent, so depending on the angle of the linearly polarized light entering the camera (when using a linear filter) the combination of linear filter and focus/metering mirror could cut light intensity much like crossing two polarizers.

Since mirrorless cameras have PDAF sensors embedded right on the imaging sensor (not sure about CDAF) I was wondering if there is no longer a need to use circular polarizers. Linear polarizers are cheaper; alternatively one could spend the same $$ and get a very high quality linear polarizer.

J
 
Solution
S
JohnFrim said:
My typo -- should have read Brewster's angle. Wikipedia has quite a lot of technical info about polarization, but they end the article with a very broad comment about cameras that does not address the situation with mirrorless cameras. I think they need to update the page.

After much back and forth (and many tangents) on this topic, I think there are a few posters who actually understand the question, and there might be agreement that linear polarizers should work just fine on mirrorless cameras. Availability of good quality linear filters may be the problem.
Click to expand...
You already got your answer. The logic is sound and the real life tests confirm.

Ignore people who don't understand the q or just parrot the old "you can't use linear...
SirShootaLot said:
Zapirian said:
JohnFrim said:
SmoothGlass said:
A: No. But good luck getting high-quality linear polarizers. I gave up and kept my old cir-pols from the DSLR era.
Click to expand...
Thanks. If I break down and buy an a6000, and if I get an adapter for my older Minolta lenses (for which I already have polarizers) I may not jump to shelling out big $$ for new CPL filters.
Click to expand...
The majority of E-mount lenses, particularly the APS-C ones take 49mm filters. If you happen to have some that size, great. Otherwise if larger, just grab a stepup ring.
Click to expand...
I have not found the lens to have the same filter size:

Sony a6000 lens samples

Kit - Sony SEL1650 OSS = 40.5mm filter

Kit - Sony SEL55210 OSS = 49mm filter

Sony Zeiss SEL1670Z OSS = 55mm filter

My other "Legacy" lens are all different filter sizes.

As to the stepup ring:

I use only Zeiss or B & W filters. The standard B&W Cir Pol. has slight vignetting at 16mm. The same filter in the "thin" type does not. If I were to use a stepup I assume the problem would reoccur. Have not tried it but it seems so.

Also I have cir pol for each lens and do see an improvement in situations others have stated in this thread.

I would rather get the shot right with the camera and not try to correct later with software.

BTW. B&W Thin cir pol has a problem getting the lens cap to stay on.
Click to expand...
Off the top of my head (ones I've owned):

SEL1855 - 49mm

SEL55210 - 49mm

SEL35F18 - 49mm

SEL30M35 - 49mm

SEL16F28 - 49mm

SEL55F18 FE - 49mm

Other 49mm filter E-mount from Wikipedia:

SEL20F28 - 49mm

SEL24F18Z - 49mm

SEL35F28Z FE - 49mm

SEL50F18 - 49mm

Sure not all of them, as obviously some of the designs need bigger glass, but for me this is still a majority of E-Mount APS-C lenses. Can state it as "a large number of" if that sounds better.
 
SirShootaLot said:
Zapirian said:
JohnFrim said:
SmoothGlass said:
A: No. But good luck getting high-quality linear polarizers. I gave up and kept my old cir-pols from the DSLR era.
Click to expand...
Thanks. If I break down and buy an a6000, and if I get an adapter for my older Minolta lenses (for which I already have polarizers) I may not jump to shelling out big $$ for new CPL filters.
Click to expand...
The majority of E-mount lenses, particularly the APS-C ones take 49mm filters. If you happen to have some that size, great. Otherwise if larger, just grab a stepup ring.
Click to expand...
I have not found the lens to have the same filter size:

Sony a6000 lens samples

Kit - Sony SEL1650 OSS = 40.5mm filter

Kit - Sony SEL55210 OSS = 49mm filter

Sony Zeiss SEL1670Z OSS = 55mm filter

My other "Legacy" lens are all different filter sizes.

As to the stepup ring:

I use only Zeiss or B & W filters. The standard B&W Cir Pol. has slight vignetting at 16mm. The same filter in the "thin" type does not. If I were to use a stepup I assume the problem would reoccur. Have not tried it but it seems so.

Also I have cir pol for each lens and do see an improvement in situations others have stated in this thread.

I would rather get the shot right with the camera and not try to correct later with software.

BTW. B&W Thin cir pol has a problem getting the lens cap to stay on.
Click to expand...
I checked the specs on the Zeiss Touit lenses in E-mount:

Zeiss 12mm has 67mm filter threads

Zeiss 32mm, 50mm have 52mm filter threads

ps This is a great thread, I've learned a lot here.
 
I wondered this also (are CPL's required for mirrorless), as I recently re-entered the hobby. I had a linear polarizer from the "old days", but wasn't sure how definitive the obvious test would be. My concern was that the AF might still sorta work sometimes, and give me a false positive. Also, I'm pretty sure I hadn't purchased the absolute best quality polarizer back then, so no big loss.

If linear polarizers do work, I'd guess it's just a matter of time before they become available again, as they must be cheaper to produce. Here, I'm assuming all circular polarizers are a combination of linear polarizer and quarter-wave plate -- is that right?
 
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TJ61 said:
I wondered this also (are CPL's required for mirrorless), as I recently re-entered the hobby. I had a linear polarizer from the "old days", but wasn't sure how definitive the obvious test would be. My concern was that the AF might still sorta work sometimes, and give me a false positive. Also, I'm pretty sure I hadn't purchased the absolute best quality polarizer back then, so no big loss.

If linear polarizers do work, I'd guess it's just a matter of time before they become available again, as they must be cheaper to produce. Here, I'm assuming all circular polarizers are a combination of linear polarizer and quarter-wave plate -- is that right?
Click to expand...
Yes, that is the structure of a circular polarizer. As for them becoming more available again, I suppose it depends on market share of mirrorless vs mirrored cameras down the road.

BTW, in order for the CPL to work properly the quarter-wave plate has to be on the camera side of the filter. Proper mounting of the filter in the holder can be checked with a mirror. I read a post of someone who had a polarizer mounted backwards in its holder, thus defeating the "circular" aspect of the filter and resulting in problems with AF and metering.
 
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JohnFrim said:
JohnMahl said:
I think my pics turned out better without one..
Click to expand...
Your reply does not really address the issue I am pursuing, but I am curious as to why your pics were better without a polarizer. Poor outcomes are often attributable to poor filter quality, using a very wide angle lens where sky polarization is variable and/or vignetting because filter is too thick. What are your issues?
Click to expand...
Polarising filters can improve a photo in specific situatons only. In most situations a photo taken with a polarizer may not improve the photo. In some situations it may even spoil a photo ( non uniform exposure of sky espcially with wide lenses). As for your specific question, the CPL works on mirrorless. So, as for Leanear Polarizer, question should be if it is better or worse compared to a CPL, rather than just price factor.
 
dotborg said:
...then you'll need to use a circular polarizer.
Click to expand...
I am not sure you are correct. My understanding is that it is not the PDAF, or CDAF, or metering sensors that are affected by polarized light, but rather the fact that in some cameras, such as DSLRs or SLTs, partially silvered mirrors are used to reflect some of the light to these sensors, and those mirrors themselves polarize the light to some degree. In other words, it is the mirror that confuses the focus and metering systems when presented with linearly polarized light; circularly polarized light is OK. So, I am hypothesizing that mirrorless cameras that have focussing and metering sensors built into the image sensor itself will work just as well with linear polarizers as with CPLs. I don't think you can broadly state the PDAF requires circular polarization... unless the anti-aliasing filter that might be in front of the sensor has some interaction with polarization.
 
JohnFrim said:
...partially silvered mirrors are used to reflect some of the light to these sensors, and those mirrors themselves polarize the light to some degree. In other words, it is the mirror that confuses the focus and metering systems when presented with linearly polarized light....
Click to expand...
To take your comment one step further, I think the issue is simply the loss of light to the sensor as you orient your linear polarizer perpendicularly to the polarization of the mirror. This is what makes the "just try it" test dangerous, because it may seem to work fine for some orientations of your polarizer.
 
I have used an old Canon linear polarizer on a NEX-5R with manual focus lenses without any problems.
 
JohnFrim said:
Zapirian said:
SmoothGlass said:
jackalopemaui said:
Won't the on sensor PD sensors need the CPL?
Click to expand...
No. CPL needed only for mirrored cams.
Click to expand...
Good article on it.

http://www.lightstalking.com/polarizing-lenses-are-you-doing-it-wrong/

CPL still good for reducing reflections and improving saturation with mirrorless. Linear, no.
Click to expand...
Not enough techno-savvy in this article to convince me that he knows the right answer to my question. He addresses mirrored and mirrorless in a single statement.

SmoothGlass and I are on the same wavelength (sort of a pun) on this issue, the point being that neither the focussing sensor nor the metering sensor are affected by linear vs circular polarizers; rather, it is the interaction with the mirror(s) which themselves polarize the light to some degree.

It would be good to hear a truly definitive answer from the camera tech folks or a statement from a mirrorless manual. If I had a mirrorless camera I could try it myself since I have both types of filters.
Click to expand...
Practical experience trumps erudition all day long.

I have to be honest. In many years of photography I have never seen reference to CPLs having any relationship to the mirror's acting as a polarizer. Either I just learned something new or that's inaccurate. Not sure which.

That said I can tell you that I use CPLs on three mirror-less cameras and in all cases they eliminate reflections and increase the saturation of color; exactly as they did on my film cameras.

The fact that the outcomes are identical is what makes my question your assertions as clearly there is no mirror to "cross" with.
 
TJ61 said:
JohnFrim said:
...partially silvered mirrors are used to reflect some of the light to these sensors, and those mirrors themselves polarize the light to some degree. In other words, it is the mirror that confuses the focus and metering systems when presented with linearly polarized light....
Click to expand...
To take your comment one step further, I think the issue is simply the loss of light to the sensor as you orient your linear polarizer perpendicularly to the polarization of the mirror. This is what makes the "just try it" test dangerous, because it may seem to work fine for some orientations of your polarizer.
Click to expand...
Yes, I think that is the issue. I would expect that the metering system would read low light when the polarizations are "crossed", so to speak, resulting in overexposure under those conditions. SLRs where the mirror is present during composing/metering but flipped up during actual exposure will also respond differently from SLTs where the mirror is always present. And I have read that partially silvered mirrors do different things with polarized light than fully silvered mirrors, so careful testing is certainly required to really understand what is going on.

No doubt, simply sticking with CPLs is probably best, but I was looking for a better understanding of the interactions and not just a recipe for a quick fix that skirts around the real issue.
 
i have used 3 or 4 different liner polarizes on my 5Dc and 20D and never had any AF or metering problems the makes are cokin,vivitar ,hoya and a Minolta ..i do now have a hoya cpl will have to try it to see if any different
 
DFPanno said:
JohnFrim said:
Zapirian said:
SmoothGlass said:
jackalopemaui said:
Won't the on sensor PD sensors need the CPL?
Click to expand...
No. CPL needed only for mirrored cams.
Click to expand...
Good article on it.

http://www.lightstalking.com/polarizing-lenses-are-you-doing-it-wrong/

CPL still good for reducing reflections and improving saturation with mirrorless. Linear, no.
Click to expand...
Not enough techno-savvy in this article to convince me that he knows the right answer to my question. He addresses mirrored and mirrorless in a single statement.

SmoothGlass and I are on the same wavelength (sort of a pun) on this issue, the point being that neither the focussing sensor nor the metering sensor are affected by linear vs circular polarizers; rather, it is the interaction with the mirror(s) which themselves polarize the light to some degree.

It would be good to hear a truly definitive answer from the camera tech folks or a statement from a mirrorless manual. If I had a mirrorless camera I could try it myself since I have both types of filters.
Click to expand...
Practical experience trumps erudition all day long.

I have to be honest. In many years of photography I have never seen reference to CPLs having any relationship to the mirror's acting as a polarizer. Either I just learned something new or that's inaccurate. Not sure which.

That said I can tell you that I use CPLs on three mirror-less cameras and in all cases they eliminate reflections and increase the saturation of color; exactly as they did on my film cameras.

The fact that the outcomes are identical is what makes my question your assertions as clearly there is no mirror to "cross" with.

--
¡Viva la Resolución!
http://www.flickr.com/photos/dfpanno/
http://www.flickriver.com/photos/dfpanno/popular-interesting/
On Flickriver chose "Scale to Fit Screen" (upper left) for highest resolution.
Click to expand...
You are right -- CPLs work on mirrorless cameras just fine. I never doubted or questioned that at all.

The question is whether linear polarizers are OK with mirrorless cameras, because they are NOT OK with many DSLR and SLT cameras that use mirrors to get light to the focussing and metering sensors. If the light is linearly polarized then it will interact (i.e., cross) with the polarizing effect of the mirrors as the filter is rotated, leading to incorrect exposures and possibly poor AF performance because of reduced light. To be very specific, the best orientation of the linear polarizer for removing unwanted glare under certain conditions might be the worst angle for the metering system.

As for your disbelief that mirrors act as polarizers, look up Brewter's angle. That is exactly why polarizers are able to cut glare, which are the unwanted reflections from non-metallic surfaces.
 
JohnFrim said:
DFPanno said:
JohnFrim said:
Zapirian said:
SmoothGlass said:
jackalopemaui said:
Won't the on sensor PD sensors need the CPL?
Click to expand...
No. CPL needed only for mirrored cams.
Click to expand...
Good article on it.

http://www.lightstalking.com/polarizing-lenses-are-you-doing-it-wrong/

CPL still good for reducing reflections and improving saturation with mirrorless. Linear, no.
Click to expand...
Not enough techno-savvy in this article to convince me that he knows the right answer to my question. He addresses mirrored and mirrorless in a single statement.

SmoothGlass and I are on the same wavelength (sort of a pun) on this issue, the point being that neither the focussing sensor nor the metering sensor are affected by linear vs circular polarizers; rather, it is the interaction with the mirror(s) which themselves polarize the light to some degree.

It would be good to hear a truly definitive answer from the camera tech folks or a statement from a mirrorless manual. If I had a mirrorless camera I could try it myself since I have both types of filters.
Click to expand...
Practical experience trumps erudition all day long.

I have to be honest. In many years of photography I have never seen reference to CPLs having any relationship to the mirror's acting as a polarizer. Either I just learned something new or that's inaccurate. Not sure which.

That said I can tell you that I use CPLs on three mirror-less cameras and in all cases they eliminate reflections and increase the saturation of color; exactly as they did on my film cameras.

The fact that the outcomes are identical is what makes my question your assertions as clearly there is no mirror to "cross" with.

--
¡Viva la Resolución!
http://www.flickr.com/photos/dfpanno/
http://www.flickriver.com/photos/dfpanno/popular-interesting/
On Flickriver chose "Scale to Fit Screen" (upper left) for highest resolution.
Click to expand...
You are right -- CPLs work on mirrorless cameras just fine. I never doubted or questioned that at all.

The question is whether linear polarizers are OK with mirrorless cameras, because they are NOT OK with many DSLR and SLT cameras that use mirrors to get light to the focussing and metering sensors. If the light is linearly polarized then it will interact (i.e., cross) with the polarizing effect of the mirrors as the filter is rotated, leading to incorrect exposures and possibly poor AF performance because of reduced light. To be very specific, the best orientation of the linear polarizer for removing unwanted glare under certain conditions might be the worst angle for the metering system.

As for your disbelief that mirrors act as polarizers, look up Brewter's angle. That is exactly why polarizers are able to cut glare, which are the unwanted reflections from non-metallic surfaces.
Click to expand...
I have been scouring the internet for info. Haven't seen anything that words things quite the way you do but it sounds reasonable.

My current understanding is that mirror-less can use either type without problems but that reflex cameras require circular for reasons touched on by you.

--
¡Viva la Resolución!
http://www.flickr.com/photos/dfpanno/
http://www.flickriver.com/photos/dfpanno/popular-interesting/
On Flickriver chose "Scale to Fit Screen" (upper left) for highest resolution.
 
Last edited:
DFPanno said:
JohnFrim said:
DFPanno said:
JohnFrim said:
Zapirian said:
SmoothGlass said:
jackalopemaui said:
Won't the on sensor PD sensors need the CPL?
Click to expand...
No. CPL needed only for mirrored cams.
Click to expand...
Good article on it.

http://www.lightstalking.com/polarizing-lenses-are-you-doing-it-wrong/

CPL still good for reducing reflections and improving saturation with mirrorless. Linear, no.
Click to expand...
Not enough techno-savvy in this article to convince me that he knows the right answer to my question. He addresses mirrored and mirrorless in a single statement.

SmoothGlass and I are on the same wavelength (sort of a pun) on this issue, the point being that neither the focussing sensor nor the metering sensor are affected by linear vs circular polarizers; rather, it is the interaction with the mirror(s) which themselves polarize the light to some degree.

It would be good to hear a truly definitive answer from the camera tech folks or a statement from a mirrorless manual. If I had a mirrorless camera I could try it myself since I have both types of filters.
Click to expand...
Practical experience trumps erudition all day long.

I have to be honest. In many years of photography I have never seen reference to CPLs having any relationship to the mirror's acting as a polarizer. Either I just learned something new or that's inaccurate. Not sure which.

That said I can tell you that I use CPLs on three mirror-less cameras and in all cases they eliminate reflections and increase the saturation of color; exactly as they did on my film cameras.

The fact that the outcomes are identical is what makes my question your assertions as clearly there is no mirror to "cross" with.
Click to expand...
Click to expand...
Click to expand...
 
davev8 said:
i have used 3 or 4 different liner polarizes on my 5Dc and 20D and never had any AF or metering problems the makes are cokin,vivitar ,hoya and a Minolta ..i do now have a hoya cpl will have to try it to see if any different
Click to expand...
The fact that you have not noticed any issues sounds encouraging, but it is not definitive. The cameras you refer to are DSLRs that everyone says require CPLs to work properly. Perhaps you have never noticed the problem that is supposedly there.

To really prove the point a test setup would require conditions where on a DSLR you could see the difference between a CPL and a linear polarizer, with the linear polarizer giving problems with metering/focussing and the CPL alleviating those problems. Then, switch camera to a mirrorless style and again check both filters under the same lighting conditions. I suspect there would be no difference between filters on the mirrorless. If there is a degradation in performance, then there is more to this than the polarizing effect of partially silvered mirrors in the optical path of the sensing systems.
 
JohnFrim said:
dotborg said:
...then you'll need to use a circular polarizer.
Click to expand...
I am not sure you are correct. My understanding is that it is not the PDAF, or CDAF, or metering sensors that are affected by polarized light, but rather the fact that in some cameras, such as DSLRs or SLTs, partially silvered mirrors are used to reflect some of the light to these sensors, and those mirrors themselves polarize the light to some degree. In other words, it is the mirror that confuses the focus and metering systems when presented with linearly polarized light; circularly polarized light is OK. So, I am hypothesizing that mirrorless cameras that have focussing and metering sensors built into the image sensor itself will work just as well with linear polarizers as with CPLs. I don't think you can broadly state the PDAF requires circular polarization... unless the anti-aliasing filter that might be in front of the sensor has some interaction with polarization.
Click to expand...
It's widely held that polarized light will fool the phase detectors. You're welcome to invest in a linear polarizer and try it for yourself however.
 
JohnFrim said:
My typo -- should have read Brewster's angle. Wikipedia has quite a lot of technical info about polarization, but they end the article with a very broad comment about cameras that does not address the situation with mirrorless cameras. I think they need to update the page.

After much back and forth (and many tangents) on this topic, I think there are a few posters who actually understand the question, and there might be agreement that linear polarizers should work just fine on mirrorless cameras. Availability of good quality linear filters may be the problem.
Click to expand...
You already got your answer. The logic is sound and the real life tests confirm.

Ignore people who don't understand the q or just parrot the old "you can't use linear polarizers with PDAF" line because someone somewhere told them so. It ain't true unless you have a mirror that is redirecting and potentially polarizing some light down into off-sensor AF. And metering. Mirrorless cameras with on-sensor PDAF and metering don't care, so use whatever polarizers you want. Unfortunately since so many people moved to SLRs, you will have a hard time finding top-notch linear polarizers and that will probably continue being the case for quite a while.
 
Last edited:
Solution
SmoothGlass said:
SmoothGlass said:
My typo -- should have read Brewster's angle. Wikipedia has quite a lot of technical info about polarization, but they end the article with a very broad comment about cameras that does not address the situation with mirrorless cameras. I think they need to update the page.

After much back and forth (and many tangents) on this topic, I think there are a few posters who actually understand the question, and there might be agreement that linear polarizers should work just fine on mirrorless cameras. Availability of good quality linear filters may be the problem.
Click to expand...
You already got your answer. The logic is sound and the real life tests confirm.

Ignore people who don't understand the q or just parrot the old "you can't use linear polarizers with PDAF" line because someone somewhere told them so. It ain't true unless you have a mirror that is redirecting and potentially polarizing some light down into off-sensor AF. And metering. Mirrorless cameras with on-sensor PDAF and metering don't care, so use whatever polarizers you want. Unfortunately since so many people moved to SLRs, you will have a hard time finding top-notch linear polarizers and that will probably continue being the case for quite a while.
Click to expand...
I had originally asked the same question on the Sony Alpha SLR/SLT forum because I currently use the A57, and someone there suggested the NEX E-mount forum as another place to poke around.

I agree I have my answer on both forums, and I marked your response as answering the question in this forum.

I have been following several photography forums over the past few years, and while I am often truly amazed by some of the expertise out there, I am more often very entertained by the "expertise" out there. After awhile you get to know who you can trust for opinions and advice.
 
Hi John,

contrast-detect AF is obviously fine with linear polarizers. And linear polarizers are more interesting to work with anyway because you can select which direction of the light waves you block - that's much more interesting than a circular polarizer which blocks all directions.

However, I'm sure you're aware that some more recent mirrorless cameras (btw I hate this term - it suggests that somehow the norm would be to have a mirror, but it's not) manage quite decent AF tracking by using both CDAF and some PDAF pixels on the sensor. Quite clearly I think that just like phase detection is hurt by a linear polarizer on DSLRs, it would also be affected on these cameras - it's just optics.

JohnFrim said:
I know what polarizers do, and I know the technical differences between circular and linear polarizers, so no need to explain any of that.

Circular polarizers became a necessity with DSLRs because of issues related to both autofocus and metering systems because these take their information from mirrors inside the camera box. The mirrors actually polarize the light going to the sensors to some extent, so depending on the angle of the linearly polarized light entering the camera (when using a linear filter) the combination of linear filter and focus/metering mirror could cut light intensity much like crossing two polarizers.

Since mirrorless cameras have PDAF sensors embedded right on the imaging sensor (not sure about CDAF) I was wondering if there is no longer a need to use circular polarizers. Linear polarizers are cheaper; alternatively one could spend the same $$ and get a very high quality linear polarizer.

J
Click to expand...
 
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