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Beware cheap "circular" polaizers
Posted By: kevindt, 07-08-2009, 10:07 PM

A good polarizing filter is probably the single most useful filter for color photgraphy, and is still useful in black and white work. If used properly, it can reduce reflections from shiny surfaces, heighten sky contrast, improve foliage contrast by removing flare and double as a 2x ND filter for some situations (and two stacked linear polarizers can also make an infinitely variable ND filter).

Polarizers come mostly in two types - linear and circular polarizers.

Most normal light has a mixture of polarizations that is mostly pretty random.

Linear polarizers selectively remove that part of the light that is not polarized in the same plane as the filter. What remains and passes through to the camera lens is mostly polarized in the same plane as the filter is oriented. (that is very similar to an red filter for B/W that removes mostly green light, passing primarily red light on to the lens).

Circular polarizers are really two filters stacked one behind the other. The filter furthest from the lens is a regular linear polarizer. Immediately behind that (in the same mount) is a "quarter wave plate" oriented at 45 degrees from the polarizer. That converts the "linear polarized" light coming back from the front polarizer to "circularly polarized" light that contains all polarizations again. Just how it does it is complicated, but I can post a more in-depth article if interested.

Reflected light is partially polarized in the process of being reflected, whether it is from an object in the image that you are trying to photograph, or reflected from the beam-splitting mirror in your DSLR that allows autofocus/metering. That means, in theory at least, that feeding the camera with linearly polarized light might interfere with light metering and/or autofocus, while feeding it with circular polarized light should not. Because of this, the normal dogma is that you need a circular polarizer on a DSLR to allow autofocus and metering to work properly. In actuality here, I have found little or no problem with linear polarizers (which are often better, cheaper and less prone to other artifacts including color casts). That has been true with istD, istDS, K100D and my current K20D.

The simplest test for whether a polarizing filter is really and truly a circular polarizer is very easy. Look through it into a mirror. This is a Hoya PL-CR filter that is first held in the normal orientation (male threads toward the camera lens or my eye). Light is reflected off the mirror and passes back through. There is some darkening (about 1-2 stops with each pass through the filter) but the camera is clearly visible in the reflection. There is very little color cast visible.



Now reverse the filter. This is the same Hoya PL-CR filter with the male threads pointed to the mirror, away from the camera. Now the mirror image of the filter is very dark, making it harder to read the logo and much harder to read the lens lettering..



(Just why that happens is fairly complicated. Again, if there is interest I can post a more in-depth explanation).

If you try the same test with a good linear polarizer, there is absolutely no difference on reversing it - the image looks identical, and with minimal color cast.


Now look at a cheap Visico CPL circular polarizer bought off ebay. This is in normal orientation, male threads to camera lens.



And this is the Visico CPL reversed, female thread to the lens.



The first thing that is obvious is the lack of darkening when the filter is reversed, but there is also a definite yellow color cast in both orientations. This "circular polarizer" is only circular in shape, not in type!

This holds true for other filters I have acquired over time, some with lenses, some on their own. The Hoya 67 and 77 mm PL-CR filters are true circular polarizers with minimal color cast. The Hoya 49 and 52 mm PL are true linear polarizers, again with very little color cast. In contrast, each of the cheap Asian filters from Visico or no-name from Korea fail this simple test, both obviously as true circular polarizers and also by introducing unwanted color casts.

Try it with your own filters and see which others pass the test!
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10-06-2009, 12:46 AM   #2
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Thanks so much for this article
It really broadens my knowledge.

I was looking for a circular polariser a week ago and decided that I would get the PRO1 Hoya CPL. At USD ~60 (ebay) it represents good value (to me).
10-07-2009, 10:16 PM   #3
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Thanks for the article. I stick to what's known as filters make or break the shot. You pay more for quality, and Hoya, B&W, Tiffen, Pentax are what I stick with.

A lesson there for all of us.
10-09-2009, 10:51 PM   #4
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This is too true. I experienced trying to buy a good quality cpl on eBay last spring and even then ended up with a bad copy that scratched up as soon as I cleaned it (with a clean microfiber cloth). After I returned the item I got a Hoya Pro1 from a reputable store, and have loved the results.
I have also recently tried using the bigger cpl hand held on my 49mm threaded 50mm lens with great results.
Thanks for the tips.

08-25-2010, 02:34 AM   #5
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Another very easy way to test a circular polarizer, is holding it in front of a TFT screen. Hold the male threads pointed to the screen and turn the filter. At some point, it should block all the light from the screen.
05-19-2011, 05:20 PM   #6
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Ok. Well I purchased a filter pack (1UV and 1 CPL) from SUNPAK brand. It was cheap so I expected it to fail this test, but it actually works! It does have a very faint yellowish tone, but not too interfering in my opinion. It also blocked off the light from a screen. The filter pack was $20 at walmart. It has worked really good for me. I even have shots of minnows, turtles and aquatic snakes under water and they look very nice.
06-23-2012, 11:19 AM   #7
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Besides the problems listed above with cheap polarizers, there is also a difference in flatness of the surfaces. The cheap ones are sometimes cut from glass stock and not ground as an optical flat. The surfaces on the better filters are ground flat and tested.
06-23-2012, 02:05 PM   #8
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And here lies the problem with the Pentax (a real pancake and not a Canon Biscuit) 40mm xs... The most major disadvantage of the lens is actally finding most any filter that will work with it - a mere 27mm.

Outside of "protective types" of filters there aren't that many filters made in that size. I've never seen a polarizer in that small of a size. So one is almost stuck to have to use step up rings in many sizes and varieties. BTW also wondering how a step up ring might effect a close up filter??

06-24-2012, 08:25 AM   #9
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Thanks for the easy check - my 'bargain' cPL passes the mirror test, though I don't have calipers to measure the evenness of its surface . My old Kalt PL from the '80s fails the test, as expected.
06-24-2012, 10:13 AM   #10
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I'll have to check this out. I use Hoya Pro1 67mm and B&W 49mm. I bought a dirt cheap 62mm for my 18-135. It's mechanically challenged. The ring won't turn when I use the hood and port. I have to remove the hood so I can rotate the ring with no lateral force. If I press the ring in toward the lens at all, it jams and won't turn. If it fails the mirror test, it's going in the trash and I'm $14 wiser.
06-24-2012, 05:35 PM - 1 Like   #11
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A tip for those who need to clean their filter. Run it under a hot water tap (not boiling water) for about 15 seconds per side. Any smears (usually human body oils) or dust are removed. Then polish with a clean microfibre cloth. Also works with eyeglasses/safety glasses...
08-09-2012, 11:53 PM   #12
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I just wanted to point out that although the Hoya pro 1 Digital are great filters, I recommend you get the twin brother Kenko pro1 digital W (Wide Band), reason being although they look identical the kenko has superior performance.
links to test here:

Polarizing filters test - Kenko PRO1D Wide Band C-PL(W) 72 mm - Lenstip.com
Polarizing filters test - Hoya Pro1 Digital MC PL-C 72 mm - Lenstip.com

I own Hoya HD, Hoya Pro1D and Kenko pro1D (W), and consider the last one the best value, I even see a clear change in color rendering while turning it, with the HD it's not as evident and it seems to warm up the scene with some degree of orangy shift, I like the colors of the kenko much better, they feel richer and more saturated and no it doesn't have that warming up feel.
Another thing that I hate about the HD is that the frame is ultra thin and this, more often that not, makes it hard to get grip to take it off, especially if you screw it on tight.
(subliminal message: buy kenko from now on)
12-14-2012, 08:33 PM   #13
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QuoteOriginally posted by Medium FormatPro Quote
And here lies the problem with the Pentax (a real pancake and not a Canon Biscuit) 40mm xs... The most major disadvantage of the lens is actally finding most any filter that will work with it - a mere 27mm.

Outside of "protective types" of filters there aren't that many filters made in that size. I've never seen a polarizer in that small of a size. So one is almost stuck to have to use step up rings in many sizes and varieties. BTW also wondering how a step up ring might effect a close up filter??
My 40mm pancake lens lives on my K-x and, since with it, my camera's so light and small as to easily shoot w/1 hand, I simply hold the 1st polarizer I can find and hold it over the front of the lens and turn it as needed w/my other hand! No need to buy a special polarizer for this lens!
12-14-2012, 08:41 PM   #14
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Just tried my cheap $15 polarizer from "Worst Buy" and it passes both the mirror test and the computer-monitor test w/flying colors, or should I say, flying shades of darkening when turned the right wayz!
05-28-2013, 11:49 AM   #15
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Just buy a Marumi Super DHG and be done with it. You know what you're getting, which is quality equal to B+W or Heliopan at a fraction of the price. Lenstip rated them as #1 in their test, beating out the "premium" brands with their Super DHG and just barely coming in under them with their still cheaper plain-DHG series. They both trounced cheaper filters like Tiffen and Hoya.

Polarizing filters test - Results and summary - Lenstip.com
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