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Equipment

My Not Nearly Complete, But Rather Entertaining, Circular Polarizer Filter Article

Published September 15, 2017

So, a while back I wrote a not quite complete article on UV filters. To do that, I had to buy new testing equipment and learn to test filters. This was not what I wanted to do when I grew up. But somebody has to do it, and I did get to buy new toys.

More importantly, Tyler (Who handles the purchasing) asked me why, many years ago, I chose the Circular Polarizing filters that Lensrentals stocked. A better person than me would have confessed that I’ve never known the first thing about Circular Polarizers; that I just bought the most expensive to be our ‘best’ and the cheapest to be our ‘basic.’ But instead, I just said, “Well, we should do some scientific-type testing and a more thorough evaluation now.”

Like a metaphor for my life, the results ended up being the opposite of what I expected. I thought if we found tons of differences testing simple clear and UV filters, there would be many more differences in more complex polarizing filters. So today, instead of showing you amazing differences between the various brands, I’ll just save you some money on your next CP filter purchase. That should work out for both of us: you save money, I get a shorter blog post.

I should mention our methodology has improved somewhat since we did our first filter article. I used a red laser to measure transmission then, and several people made the very reasonable suggestion that a green laser might be a better choice, being in the middle of the spectrum and all. Other people said I should get a spectrometer and measure the entire spectrum. So I did both of those things.

This should give you some hints about me as a person. If someone asks me to test a lens at a different aperture, I have a screaming fit about testing taking up a few hours of my time. Someone suggests I spend $15,000 on new equipment, and I’m like, “Yeah, great idea, that would be cool to have.”

Finally, I had no intention of testing every polarizing filter on the market. I did what I usually do; bought the ones B&H Photo had in stock in 77mm size. So we’re going to compare, in no particular order, except alphabetical, with the current price for a 77mm:

  • B&W XS-Pro High-Transmission Circular Polarizer MRC-Nano         $102
  • Heliopan Circular Polarizer                                                                          $200
  • Marumi EXUS Circular Polarizer Filter                                                     $140
  • Sigma Water Repellent Circular Polarizing Filter                                   $150
  • Tiffen Ultra Pol Circular Polarizing Filter                                                 $103
  • Zeiss T* Circular Polarizing Filter                                                               $180

So, About the Polarizing Part

If you’re thinking about buying a circular polarizing filter, you probably want to know which ones polarize the best and which ones the worst, right? I know I did. Now we could have just gone outside and taken pictures in the bright sun and said this one’s good and that one’s bad. But we never do anything simple when we can complicate the crap out of it.

So what we did was take our laser transmission set up and modified it a bit. Primarily, this shines a laser into a power meter and gets a reading. Then we can stick mostly transparent stuff in the beam and see how much it reduces the power reaching the meter. Excellent lasers are almost entirely polarized, but I have a budget, and that budget didn’t include (much to my sorrow) $10,000 for the lab-grade, steel-melting laser I wanted. I got a little 5-mwatt green (530 nm) diode laser.

It’s sort of polarized. So we shined that laser through two sheets of polarizing film, each of which have a 1,000:1 polarizing extinction ratio. So basically, the light that passed through the film was really, really polarized. Then we put the filter in the beam of polarized light to see how much light it let through in the open position. For now, we’ll just call it ‘most of the light.’ Finally, we moved the lens to the polarizing position, which should have blocked all of our polarizing light if the filters were really effective.

Circular Polarizing Filters Test Circular Polarizing Filters Test

Here’s where I expected to put a table showing how efficient the polarizers were. Instead, I’ll just tell you that all of the polarizers we tested blocked all of the light, within our capabilities of measurement. They were all at least 99.9% efficient at doing their job, polarizing light. There’s something you don’t see very often; a photography product that completely does what it says it will do.

Also About the Glass

When we tested UV filters, we found several for which the glass wasn’t flat. We repeated the test on all of the CP filters, and all passed with flying colors, so I won’t bore you with repeating it. Again, my expectation was with two pieces of glass we might see more, not less, bad glass. But no, they all passed just fine. That may be that better glass is used in CP filters, or the polarizing effect evens things out. I don’t know. But they all passed just fine.

What About Light Transmission?

If you’ve ever used a CP filter you are probably aware that even when not polarizing it absorbs some light. You should be aware of this because, well, it’s darker when you look through it. We thought it would be worthwhile to see how much light it does absorb.

Why? Well, partly because we had that laser transmission bench already set up, but mostly because two of these filters claim to let more than 99% of light through. The Marumi claims it lets 99.4% of light through, and the B&W High transmission says it passes through 99.5%.

No, I’m not a rocket scientist, I’m just a regular scientist. But high-tech scientific principles tell me that since everything looks a bit dark when looking through these CP filters, it’s unlikely that more than 99% of the light is passing through the filter. But maybe that’s just me being cynical. Or maybe there are alternative facts that say darker isn’t the same as less light.

Anyway, since I was rather fired up and my BS meter was pegged at full maximum, we removed the linear polarizers and measured absolute transmission for each filter in the non-polarizing position. If you remember, when we tested clear filters the best let 99% of light through, the worst was down around 90%.

The transmission results for CP filters were:

FilterTransmission
Marumi91%
B&W88%
Sigma68%
Zeiss66%
Heliopan58%
Tiffen55%

Now, the Marumi and B&W are nowhere close to 99% transmission, but I will admit that they did indeed have higher transmissions than the others.

Some, probably most, people don’t care about how much ND effect their circular polarizer has, and if they do they may well not want the higher transmission variety, they’d prefer a bit more light blocking. After all, if you need a circular polarizer, you probably are shooting where there is lots of bright sunlight. But the takeaway message is that higher transmission filters do tend to give more transmission. Just not as much as is claimed.

Let There Be Spectrometry

And so, in the days after the first article, the people spoke as one and said, “You show us but one wavelength of light, yet there are as many wavelengths as there are fish in the sea. Give us spectrometry, that we may see the effect on all manner of wavelengths, each unto its own kind. And make the graphs brightly colored.” 

It’s taken several weeks for us to get things calibrated and running, but this post seems a good place to start using our new spectrometer. We know that some polarizers give a bit of color cast, especially when polarizing, so we thought it would be interesting to see look at their transmission spectra.

We looked at transmission both in the open and polarizing position and did not see any changes with these polarizers. I’m told there are some that do have a color change with polarizing. I’m only showing you one spectrometry report for each filter, to keep this short post short. Also, don’t put much stock in the absolute transmission between the filters. We weren’t testing for absolute transmission since we’d already done it; we just wanted to look at the curves.

The High-Transmission CPs

The Marumi and B&W filters have similar transmissions and very similar spectra. Both tend to have some UV filtering activity and drop off a little bit at the blue end of the spectrum.

Marumi

Olaf Optical Testing, 2017

B&W

Olaf Optical Testing, 2017

The Standard CPs

These all have a stronger Neutral Density effect than the first two, and their spectra are different, too. The Sigma, Zeiss, and Heliopan filters are all very similar with a bit more transmission at the blue end of the spectrum and a bit less in the red-yellow range. The Tiffen has a similar pattern, although maybe a tiny bit more of a green peak.

Sigma

Olaf Optical Testing, 2017

 

Zeiss T*

Olaf Optical Testing, 2017

 

Heliopan Digital

Olaf Optical Testing, 2017

 

 

Tiffen

Olaf Optical Testing, 2017

 

So What Did We Discover Today?

Well, several things, one of which is really useful. So I’ll get that one out of the way first, and then let this post just steadily deteriorate. If you are buying a circular polarizing filter because you want some circular polarizing, it doesn’t seem to matter much which one you choose; they all polarize like gangbusters. So I saved you some money today.

The second point, one which I’ve been told before I did all this testing, is set the white balance after you put the CP filter on, not before. Because CP filters will have a color cast. Or just shoot in raw and fix it later, which is what we mostly do anyway.

There is a third point, and it’s a painful one:

Once Again, Roger Lets Technology Triumph over Common Sense

I didn’t want to test filters; I really didn’t. But people wanted me to. So I chewed up my testing equipment budget to buy laser transmission stuff and an optical spectrometer, spent a few weeks getting everything calibrated and establishing norms, and then a couple of days testing these CP filters. I did this in clear violation of Roger’s Third Law: No Good Deed Goes Unpunished.

After I was done, I told Aaron I had just documented that CP filters had different light transmission percentages and different color casts. And that high transmission filters had one look, and it was different than regular CP filters, which all were really similar. Because I was proud that my investment in time and money had paid off.

Aaron took the filters from me, put them on a piece of paper, took this picture with his cell phone, and said, “Yeah, you’re right.”

 

 

Oh, and BTW – I know what you’re thinking. Yes, I’m going to publish spectrometry reports on the clear and UV filters we tested in the last article. Next week, I promise. I need a few days to recover my pride.

Roger Cicala and Aaron Closz

Lensrentals.com

September, 2017

Addendum: MTF testing

Several people made the very pertinent comment that they would expect some effect in sharpness and contrast. FWIW I took a moderate telephoto, very sharp lens (Batis 135mm f/2.8) and MTF tested it first with no filter, then with a B&W Multi-coated clear filter, then 4 of the CP polarizing filters we tested above.

The clear filter made absolutely no MTF difference.

All tested polarizers (B&W, Marumi, Zeiss, Tiffen Ultra, and Helipan) caused a slight decrease in MTF at high frequencies. There was no detectable change at 10 and 20 lp/mm. At 30 lp/mm there was a consistent 1-2% drop, at 50 lp it was about 4%. All of these CP filters were very similar, I could detect no difference between them.

This is a quick, off-the-cuff check. I’ll look at things in more depth when I have time. But the bottom line is fine detail in photos is affected a bit. I don’t find that the least bit surprising.

I’ve also ordered a couple of $40 filters and we’ll see how those compare.

Author: Roger Cicala

I’m Roger and I am the founder of Lensrentals.com. Hailed as one of the optic nerds here, I enjoy shooting collimated light through 30X microscope objectives in my spare time. When I do take real pictures I like using something different: a Medium format, or Pentax K1, or a Sony RX1R.

Posted in Equipment
  • Ally Aycock

    I told a customer that his Switronix PowerBase 70 battery needed to charge “for a hot minute” on a tech support call today. I amended my advice once I realized that “a hot minute” was neither quantitative nor helpful. At any rate, the customer seemed to find it charming. On a side note, I’ve never been called out for saying, “y’all” on a phone call.

  • Brandon Dube

    Well, a polarizer is a polarizer and a waveplate is a waveplate. On thorlabs, thin film polarizers have about 80% transmission for the state they select, and about 40% for unpol light (no surprise there, ~0% for the state they block and 80% for the state they select, average the two). I can’t find transmission numbers for a 1/4 waveplate, but a quartz or calcite crystal is clear to the eye so it is pretty high.

    To find what is reflected and transmits to flare/stray light and separate that from absorption, we would need a scatterometer. They’re $80k and would serve no purpose to us except for testing filters. Not likely to happen.

  • odddave

    Yes I realized after I posted I omitted the absorbtion part of this. I’m not an optical engineer and really didn’t want to deep dive into the physics. You say that it’s a huge part but the question begs, how huge?

    Looking at the pictures I’d say some filters are definitely darker than others. Time for more measurements.

  • Brandon Dube

    Light that is not transmitted is either reflected or absorbed. For the components of a CP filter (linear pol & 1/4wp), absorption is a pretty huge part.

  • odddave

    How about “Y’all hold my beer and watch this”?

  • odddave

    This can introduce moisture into the lens. I use wide rubber bands wrapped around the filter. Works like a champ.

  • odddave

    Light that isn’t transmitted is reflected. If you are stacking filters that reflected light can start bouncing around your filters creating all kids of undesired effects. Transmission efficiency does matter. Also it’s B+W.

  • Jay Dee

    We’ll only start worrying when “Like” starts the sentence. Every sentence.

    I was a bit surprised at the spectrometer curves as they seem quite different from those presented by the new kid on the block–Breakthrough:
    https://breakthrough.photography/products/x4-circular-polarizer
    So (he-he), I’ll say their stuff needs a thorough examination in the near future, because I almost bought one instead of B+W.
    BTW, your testing is, like, bitchin’–THANK YOU!

  • Michael Sandman

    Or wrap a wide rubber band around it, pull tight, and turn.

    And — Thanks, Roger. Informative, useful and fun.

  • midluk

    Did I miss something, or did you not test for the “Circular” part of CPL? You tested for the proper selection of one linear polarization direction on the input, but did nothing to measure the amount of residual linear polarization on the output. Only then you can draw your conclusion that every filter does exactly what it is supposed to do.
    You should try to put a linear polarizer behind the fut (filter under test) and see if there is any difference in transmission between different orientations of the second filter. The difference between minimum and maximum transmission divided by the sum should give you the amount of residual linear polarization.

    BTW: Did you check that your sensor is equally sensitive to all possible light polarizations?

  • Pete Cockerell

    The number of stops lost is log2(100/t), where t the is the transmission percentage. So for 90% it’s log2(1.111) or about 0.15 stops. Since most calculators don’t have logs to the base 2, you can use log(100/t) / 0.3 instead, where log is base 10 log.

  • appliance5000

    Use a lens shade?

  • appliance5000

    When they started rotating the Venn Diagrams, I passed out. I am now in a dark place…….

  • SpecialMan

    The key to usage is intentionality—if the writer is conjuring a specific effect by starting a sentence with for, and, nor, but, or, yet, or so, that would be an appropriate use. If a forbidden word appears because the writer is just fumbling around for a different way to start a sentence, then it’s wrong and the perpetrator deserves a long stretch in grammar prison.

  • Brandon Dube

    4% reflection is for the fresnel losses of an interface of two mediums having a refractive index of ~1 and ~1.5.

    Different technologies to achieve polarization and achieve the conversion from linear to circular polarization are used by some of these filters compared to others. Some of those technologies are most costly to the transmission of polarized light than others.

  • Ren Solomon

    It seems to be strange to observe such HUGE deviation in transmission among aforementioned specimens! It is close to impossible to obtain the polarizing film with such a low transmission of polarized light (garbage in another word).
    The only explanation would be in reflections between glass-adhesive-film-adhesive-glass interface.
    Then when you add up about 4% REFLECTIONS FROM EACH INTERFACE (I ASSUME THEY DID NOT USE materials with matching RI then everything looks quite possible!
    But then one will inevitably get a high level of hase thus reduced sharpness and reduced contrast.
    Gary

  • OK, on further thought, I’ve made some assumptions with that and they may not be pertinent. I’m going to run CP filter tests on known lenses on the MTF bench to make sure. You have a very valid criticisim.

  • Thanks Mike, I thought most people knew of those tests, but glad to have the link up.

  • Matt

    Those words are called conjunctions, and according to The Chicago Manual of Style (and others) ” CMOS includes Bryan Garner’s opinion that there is “no historical or grammatical foundation”
    for considering sentences that begin with a conjunction such as and, but, or so to be in error (see paragraph 5.206). Fowler’s agrees (3rd ed., s.v. “and”), citing examples in the OED that date back to the ninth century and include Shakespeare”
    http://www.chicagomanualofstyle.org/qanda/data/faq/topics/Usage/faq0013.html

    Conjunctions connect one thought to another, and thoughts, thankfully, don’t have to be included in the same sentence to be connected.

    I believe teachers started telling their students to stop doing it because they were tired of reading papers that had every sentence start with “and.” It’s easier to tell little kids to not do something at all than it is to teach them to do something sparingly, and thus a fake rule was born.

  • Mike Earussi

    That’s for doing this. Polarizers are a important part of photography, so having more info really helps.
    BTW, here’s a link to some earlier polarizer tests just in case you didn’t know they existed:

    https://www.optyczne.pl/7.1-Inne_testy-Test_filtr%C3%B3w_polaryzacyjnych.html

    https://www.optyczne.pl/8.1-Inne_testy-Test_filtr%C3%B3w_polaryzacyjnych_-_uzupe%C5%82nienie.html

    https://www.optyczne.pl/23.1-Inne_testy-Test_filtr%C3%B3w_polaryzacyjnych_2015.html

  • We’ve tested a ton of filters, even bad ones, on the MTF bench. If they weren’t plane parallel we’d have expected some change in MTF side-to-side, but we’ve never seen one bad enough to do that. Irregularities in the glass seem to have the much greater effect on images.

  • Stefano, we did the same ‘distortion of pinhole’ testing we did with the UV filter. All of these passed easily, which I mention in the text, but didn’t want to take up the space of posting all the images.

  • Exactly. I will try to add some cheap ones and maybe some color-changing ones. This was one of those “here’s the test I need to do so I’ll show you what I have” posts.

  • Vincenzo Miceli

    Isn’t the first property of a photographic filter to have plane and parallel faces? Is there any way to measure that? Thx!

  • Stefano Allari

    my main concern with polarizers is that they could affect the resolving power of the lens and the level of sharpness in my photographs. I never looked thoroughly into this but noticed it sometimes, especially with the wide angles. Have you made or plan to do any measurements about that, Roger?

  • Nice to see a test of CP filters, that taught me to use whatever I can get hold of, at the best price!

    If someone want to give me a Marumi, OK, but I would not say no to any of the other!

  • John Warren

    Also it’s B+W, not B&W…lol

  • Jan-Pier Loonstra

    Well, how about flare?

  • Ed Hassell

    A professor of linguistics was once explaining emphatics in certain languages and dialects and discussing double negatives and double positives. He made the statement that in English, a double negative is actually a positive — not more negative — and that the double positive does not exist at all as a grammatical construct.

    A student in the rear of the class responded, “Yeah, right.”

  • Brandon Dube

    You can make a thin film monochromatic waveplate. You cannot (or rather, no one has) made a thin film achromatic waveplate. Those films essentially make a small cavity with interference that allows perhaps millions of trips back and forth for the extraordinary polarization state in the coating, building up 1/4wave OPD. This is extremely sensitive to the wavelength, where a birefringent crystal (or other material…) naturally is reasonably achromatic.

    The polarizer can be a thin film. There are many common ways used to make them.

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