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10-31-2012, 02:20 AM   #1
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Confused about circular polarizers

I recently bought a couple of Hoya circular polarizers. I purchased a 52mm and 58mm version of this:
Hoya 58mm Circular Polarising Filter: Amazon.co.uk: Camera & Photo

I then found the following video on YouTube and a few others that explain how to check the quality:

However, I'm getting some strange results and wondering if I have been sold a linear polarizers in one case, or maybe a fake. Both have "CIRCULAR PL" written on the side of the polarizer.

Here is what I see for the 52mm filter:
If I look through at my LCD display with the threaded side nearest me and rotate it then it goes from light to dark (completely dark so seems good). If I spin it round so the threaded side is away from me and rotate it then it goes from blue to orange but never goes dark.

Here is what I see for the 58mm filter:
If I look through it from the threaded side then it goes from light to dark (very dark again), same as above. However, if I spin it round it does exactly the same thing, light to dark, whereas the 52mm one goes from blue to orange.

So in other words, the 52mm one has a different effect depending on which side I am looking through, but the 58mm is exactly the same effect on both sides. That seems odd to me but am I missing something i.e. is it normal for a larger filter to behave differently from a smaller?

10-31-2012, 05:14 AM   #2
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Having read that one way to tell the difference is that a linear polarizer looks the same in either orientation, sounds like the 58 is a linear polarizer. My CPLs both behave like your 52.

You might want to experiment with it on the camera before deciding whether or not to replace it. Question is whether or not you can find any conditions under which autofocus fails.
10-31-2012, 05:54 AM   #3
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I already have a linear polarizer for it. I think the guy at the shop spotted I was a noob when I bought my 55-300 lens and sold it to me and it was only when I got home and researched that I found you're not meant to use them with DSLRs. I put that down to experience and then bought the Hoya ones on Amazon.
10-31-2012, 05:59 AM   #4
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I've just done the "mirror test" as well and it definitely seems like my 58 is in fact a linear. I will get in touch with the seller.

10-31-2012, 06:17 AM   #5
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More to the point... I have found that a nice Tiffen 72mm linear polarizer I have still works well with my K-5 AF. I was under the opinion that circular polarizers were necessary for AF systems but this seems not to be the case.
10-31-2012, 07:07 AM   #6
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QuoteOriginally posted by SRT201 Quote
More to the point... I have found that a nice Tiffen 72mm linear polarizer I have still works well with my K-5 AF. I was under the opinion that circular polarizers were necessary for AF systems but this seems not to be the case.
It shouldn't be AF that would be the issue with linear polarizers but rather the proper metering of light. That said, I have a couple of old linear polarizers and I have yet to encounter problems with them in that respect.
10-31-2012, 07:24 AM   #7
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The problem with linear polarizers is not consistent. The metering, and the AF in some circumstances, is affected adversely by a linear polarizer. I take no chances and emptied my wallet a bit more to buy a top of the line circular polarizer just in case. The problem that happens is with a specific alignment of the polarized light with the partial transmission section of the mirror which has some polarizing effect on the light passing through.

If you have never had a problem with your good quality linear polarizer, just check the LCD when you are using it to make sure you don't hit the problem and continue to use it until you do have the problem. Then you buy a CPL so the problem never occurs again.
10-31-2012, 07:53 AM   #8
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Another quick way to check if a filter is a circular or linear polarizer is to look at the reflection in a mirror through the filter. Look through the filter from the lens side (as if you were the camera). Then flip the filter over (looking through the side that is normally pointing to the objects). If the reflected image of the filter goes dark it is a circular polarizer. A linear polarizer will look the same either way.

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