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are there differences in CPL filters

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TJTigger

TJTigger

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Is there a big difference in circular Polarizing filters?

the local big box store has one on clearance for less than $10. Often I see Hoya or other CPL filters around $40 or more. Is it worth it to buy the cheap one? are there things i should look for that would make it not worth buying the cheap one?

Thanks for your advice.
 
I have a cheap marumi CP. When shooting out in the snow, the corners are a tint greener than the rest of the image. No such thing with a B+W MRC CP. So yes it does matter. I don't know about all other brands though. Another thing is how easy it is to clean them. Some are reported to be very difficult to clean. The B+W version isn't difficult to clean, neither is my cheap Marumi. I think I've read Tiffen is difficult to clean.

For $10 you can always try of course, if you're not happy you can always get a more expensive one.
TJTigger said:
Is there a big difference in circular Polarizing filters?

the local big box store has one on clearance for less than $10. Often I see Hoya or other CPL filters around $40 or more. Is it worth it to buy the cheap one? are there things i should look for that would make it not worth buying the cheap one?

Thanks for your advice.
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I own and use Hoya's, B&W's and Marumi's and really can't tell the difference. Stick with a name brand, make sure it's multi-coated and circular has been my personal guide line, it hasn't failed me yet.

Here's a pretty comprehensive test on polarizing filters by some folks that know much more about the subject than I ever will. Surprisingly Marumi ranked pretty high, making it a great bang for the buck.

http://www.lenstip.com/115.1-article-Polarizing_filters_test.html

Regards,

Roger
 
In general, even a cheap CPL is better than no CPL. They're THAT useful.

However, as the Lenstip article reveals there are some excellent price per performance deals to be had. IIRC, I picked up my Marumi DHG CPL 58mm for ~$25. Since then the Fujiama DHG has also emerged as a very good price per performance CPL. The extra performance is definitely worth $10-$20 more than the cheapo $15 CPLs.

As you go shopping, the difference between the Marumi DHG & Marumi DHG Super is that the plain ol' Marumi DHG is significantly darker - but the light that it does let through is just as well polarized as any of the others.
 
I should be clearer - the light that it lets through is "just as well selected by polarization" as the others.

What a CPL does is first to select the light by linear polarization (the same as a linear polarizer) and then adds an extra layer (called a "quarter wave plate" or "retarder") essentially "depolarize" it because your autofocus and exposure metering systems are designed on the assumption that the light coming in isn't polarized.

In other words, the camera doesn't see circular polarized light as being (linearly) polarized at all, which is the goal.

Thankfully, the quarter-wave plate doesn't have to be anywhere near perfect - just good enough to enable the autofocus and exposure meters to do their respective jobs. The sensor itself doesn't care about polarization.

As an aside, any mirrorless camera is OK with a linear polarizer, its just that economies of scale have made CPL's cheaper than linear polarizers these days.
 
The brand is Platinum Plus by Sunpak. Not sure if they have reputation or not.
 
They have a reputation - El Cheapo. However, as I said to begin with - el cheapo CPL is better than no CPL. I still recommend that you see if you can find a deal on a better CPL, though.
 
I think I will do that. I looked at the reviews for the filter on BB's website and they were not overly positive. i will shop around. thanks again.
 
Check on Amazon and EBay - there is a US vendor selling the two versions of the Murami CPL for what seems to be good pricing compared to list prices. I am thinking of the Super version myself unless someone can tell me the regular version is just as good. The referenced review gave a better rating to the Super.

Steve W.

Edit: See one of the standard Murami CPLs on EBay for Buy It Now or Best Offer. May try the Best Offer for the amount I see others got it for. Can't hurt - he can only say NO.
 
Hi

I'm not sure if this is a bit out of topic; I have two quite cheap polarizing filters, linear & CPL one, they work exactly the similair way with my lenses (focus, exposure etc.). The question is, why do they work well with 18-55, but with 55-250 I'm really not able to use zoom, the image gets blurry after ab. 60 mm focal length...

Is this normal behaviour with longer lenses, or do I just have bad filters? Maybe there are some diffraction issues with polarizer & longer focal length or...?
 
It is possible that both are linear polarizers and one is just "mis"labeled.

To determine if it is, put the linear polarizer behind the circular one. If the darkness changes as you turn one in comparison to the other, you have been jipped. If that is the case, then I think it is just the linear polarizer interfering with your autofocus system. (The effects on the autofocus system are much more significant than those on the metering system.)

I've never seen a cheap polarizer do this, but I have never mounted a linear polarizer on an autofocus camera just to see how it messes it up :).

Polarization doesn't have any focal length dependent effects on its own, but if your lens has a rotating front element, it could play games with the AF system at one position and not another.
 
Shorthand said:
It is possible that both are linear polarizers and one is just "mis"labeled.
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Sure, who knows about ebay stuff...
Shorthand said:
To determine if it is, put the linear polarizer behind the circular one. If the darkness changes as you turn one in comparison to the other, you have been jipped.
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Thanks for the tip to check the filter, I'll do the test one day
Shorthand said:
I've never seen a cheap polarizer do this, but I have never mounted a linear polarizer on an autofocus camera just to see how it messes it up :).
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Actually they both work the same way, and I have not experienced any issues with focusing itself although people seem to have problems with linear ones
Shorthand said:
Polarization doesn't have any focal length dependent effects on its own
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This exactly is the issue, as far as I see it, with short focal lengths the polarizer works well, but when I mount the same filter into a longer lens then the images start to get blurry (with longer focal lengths). This is not an issue of focusing since I have tried manual focusing as well.
 
I'm trying to think but I have no good answer then if it occurs with manual focus as well - the true test is live view zoomed in manual focus instead of AF-sensor-confirmed or through-the-viewfinder manual focus.

The interaction of ghost images with the real one could also be a factor of focal length - this is actually my best guess.

Other WAGs:
  • If the filters are thicker on one edge than the other, the difference in optical path length could prevent it from ever achieving focus (the AF system would seriously freak out in this case), but I am having trouble thinking about how that would change with focal length. In this case, there would be a vertical or horizontal line in focus and the rest would be soft - kind of like a tilt-shift lens.
  • It is also possible that the filters both have a curvature to them that makes them into long focal length lenses, which might just be enough to prevent a long lens from focusing at infinity.
Most other imperfections would be plainly visible to the naked eye.
 
Thanks for taking time to figure out this issue, I think I have to try take a few photos if the effect could be seen from them...

What I was thinking was that maybe the filters have coating or layer of "polarizing material" which then interfere with the path of light when zoomed...

Anyway, must do the test and then come back to subject.
Shorthand said:
I'm trying to think but I have no good answer then if it occurs with manual focus as well - the true test is live view zoomed in manual focus instead of AF-sensor-confirmed or through-the-viewfinder manual focus.

The interaction of ghost images with the real one could also be a factor of focal length - this is actually my best guess.

Other WAGs:
  • If the filters are thicker on one edge than the other, the difference in optical path length could prevent it from ever achieving focus (the AF system would seriously freak out in this case), but I am having trouble thinking about how that would change with focal length. In this case, there would be a vertical or horizontal line in focus and the rest would be soft - kind of like a tilt-shift lens.
  • It is also possible that the filters both have a curvature to them that makes them into long focal length lenses, which might just be enough to prevent a long lens from focusing at infinity.
Most other imperfections would be plainly visible to the naked eye.
Click to expand...
 
Ok, so I did the test. At first don't mind about other things that general outlook of the images, I used relatively slow shutter speed because of dusk, but I think that the difference is quite clear. Manual focus used with CPL & 250 mm, that was the best I could get...

With 55 mm focal length, there are no issues, but after increasing the focal length, the images start ot get blurry. I know that cheap is cheap, but would the situation be any better if I invested several times more to CPL?



















 
There is definitely some kind of aberration in the glass (i.e. it isn't the same thickness all the way across). I can't tell from the photos, but I'm surprised that the aberration isn't visible to the naked eye.

The other thing that is odd is that you should be losing at least one stop of light when you put a polarizer on (it absorbs at least half of the light), but your exposures seem to not have been effected. I have to wonder if these are polarizers at all. Do they appear to be mid-grey or something lighter?
 
Something must be wrong with the pola, that is clear since I doubt that it should act like that... I never assumed that these cheap ones would be perfect, but this issue with longer focal length has really bothered me. As said before, with short focal lengths (less than 60 mm) the polarizers work as expected.

There is difference in ISO if you check the exif's, I've noticed ab. 1,5-2 stops of difference with pola attached. The polarizer effect can be seen if I use the kit lens (18-55) for example, so something is happening quite correctly.

Not very important issue since usually polarizers are used with wide angle lenses, but this is just something that do not understand...
Shorthand said:
There is definitely some kind of aberration in the glass (i.e. it isn't the same thickness all the way across). I can't tell from the photos, but I'm surprised that the aberration isn't visible to the naked eye.

The other thing that is odd is that you should be losing at least one stop of light when you put a polarizer on (it absorbs at least half of the light), but your exposures seem to not have been effected. I have to wonder if these are polarizers at all. Do they appear to be mid-grey or something lighter?
Click to expand...
 
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