twowindsbear

Your photo could be 'in focus' someplace in the image, but not your main subject. That could indicate 1 type of problem

You could be calling 'out of focus' what really is camera movement, or subject movement. There are different reasons, and 'cures' for these issues.

Some cameras can indicate what the autofocus 'machine' actually focused on - assuming there is something actually in focus. And some cameras indicate the distance to the subject.

It could be as simple as the CPL reduced the amount of light below the level for your camera to be able to 'see' your subject and focus.

Pablo8 Loc: Nottingham UK.

***********************************************
Why did you not check the playback screen after a few shots?
That would/should have indicated whether shots were in focus or not. Saves wasting time and 200 spoiled shots.

Haydon

Recently I used a 3 Stop Lee graduated neutral density on my 70-300 4-5.6L and it struggled auto focusing in bright daylight numerous times until I cleared the filter from the lens. My 16-35L 2.8 II and 24-70 2.8L II don't have any issue whatsoever. I suspect the larger apertures make easier work with the substantial more light and contrast allowing accurate autofocus.

Crwiwy Loc: Devon UK

Definitely flawed when so often group tests show middle price items outperforming the outlandishly expensive ones.

For instance;
http://www.digitalcameraworld.com/2013/09/24/best-circular-polarizer-filter-5-top-models-tested-and-rated/4/

Showed the Hoya Pro scoring 88% and the B+W scoring 86%.
Naturally - anyone locked onto price or paid extra for the B+W will say it is rubbish.

FiddleMaker Loc: Merrimac, MA

I did not know that a filter can interfere with auto-focus. Good tip. Perhaps I should remove my protective UV filter or just use manual focus.
-FiddleMaker

jerryc41 Loc: Catskill Mts of NY

If polarizing filters were automatically bad, no one would use them. here are some links that might be useful. I use Marumi CPL's.

http://nikonrumors.com/2014/07/26/how-to-use-a-polarizing-filter.aspx/
http://www.lenstip.com/115.4-article-Polarizing_filters_test_Results_and_summary.html
http://www.lightstalking.com/polariser-mistakes/

wolfd Loc: Vancouver, Canada

I agree.
I have purchased several Hoya branded CPL filters off eBay over the years and not experienced any out of focus issues.

John N Loc: HP14 3QF Stokenchurch, UK

When we went to the U.S. some years back I borrowed my sisters 70-300 Canon cheapo lens. It would not focus sharply and it was not till I got home that I found out removing the filter cured the problem.

I get exactly the same issue with my Canon 400mm 'L' series lens.

It's not a filter fault - it's the way the auto focus works through the CPL (and some other filters). My neighbour bought a Canon 70-300 (the mid priced one) 2nd hand of EBAY and couldn't get a sharp focus. He sent it to CANON for a service who pretty much confirmed the above.

Go manual focus, using live view if possible. To prove the point do this, and shoot the same on auto focus and compare.

camerapapi Loc: Miami, Fl.

I am in agreement. I also want to mention that if in addition you are using matrix metering you could easily be compounding the issue since dark filters tend to confuse matrix metering.
I use old polarizers made by Tiffen. When I do I go with spot or center weighted metering although from the old film days my tendency is to focus and meter first and then use the filter and apply the filter factor. Because I use the rear AE-L button for focusing the shutter is disabled to achieve focus.
Another good point is to make sure the filter is clean prior to shooting.

Mac Loc: Pittsburgh, Philadelphia now Hernando Co. Fl.

I guess you didn't read or at least understand the last sentence in my post.
What I am saying is that if you buy cheap shit all you will ever get is cheap shit. If you buy a quality product from a respectable dealer you will get a quality product. Looking to buy on the cheap will wind up costing more in the long run.

rmalarz Loc: Tempe, Arizona

Doug, having limited finances I had to choose carefully and get the quality for the investment. After careful consideration, and calling the company with specific questions regarding their product line, I settled on a B+W brand. No problems with that product.
--Bob

Morning Star Loc: West coast, North of the 49th N.

Yes. And I'll give it to you at the risk of getting my wrist slapped - I promise I won't hit back.
My first thought was: Does he understand how a CPF/CPL works? This from the fact you say you took 4 exposures of each subject turning the filter 90 degrees with each exposure.
My second thought: You went out in the morning, how early? And considering the time of year, was the sun even out there to see?

So the sun should be at about 90 degrees to your camera. In mid-summer and in the middle of the day, when the sun seems to be right above you, you can point your camera in any direction except up, because the sun will always be at that 90 degrees.
This time of year though, at mid-day, you'll only have the sun at 90 degrees when pointing the camera east or west.

I think I remember, when using my old film-camera, that I could see the effect of the PF through the (optical) viewfinder.
My current camera has an electronic viewfinder, and I certainly can see the effect of the polarizer there. I don't use it a lot, because I really don't mind the sparkles on the water. On the other hand, I do like the more intense skies with the filter.

Of course, none of this answers your question regarding the sharpness (or lack thereof) of your photos. I saw your reply, about understanding "blurryness" - but there are different kinds of blurryness, and I know there are folks her on the Hog that will be able to tell you something about that by seeing a photo. I therefore respectfully request that you post such a photo, at full resolution (check the "store original" box).

OK, should I hold my wrist out now?

imagemeister Loc: mid east Florida

First point - You are focusing at approx. f8+ light values with the CPL in place - a challenging hindrance.

Second point- All filters will affect AF focus is some way and this is exacerbated with longer focal lengths - tis sad but true.

Try manually focusing and see what you get ???

Jerry Kos Loc: Milwaukee, Wi

No.

redhogbill Loc: antelope, calif

I can not find that brand, I searched the web, shows me refrigerators... do you have a link?