Warning for cheap polarizers? Or, don't use them at 200mm?

Started Aug 5, 2010 | Discussions thread
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Warning for cheap polarizers? Or, don't use them at 200mm?
Aug 5, 2010

A few weeks ago, I got myself a really cheap polarizing filter for the 52mm thread size so I could use it with my 9-18mm, 20mm (with a step-up ring) and the 45-200mm. I've mostly been experimenting with the 9-18 and 20mm but yesterday I tried it on the 45-200 and got pretty horrible results:

With polarizer:


In order to make sure it wasn't because the auto focus was being tricked, I took this manual focus closeup of some clothing, too. With polarizer:

(Original: http://bit.ly/cSHRhp )

...and without:

(Original: http://bit.ly/aIHZdT )

What's up with this? Is this due to the poor quality of the polarizer or are there other optical things coming into play here (e.g. some rule that I don't know of like "don't use polarizers at 150mm and above")? It was completely impossible to get a sharp image with the polarizer and the zoom set to 200mm.

In comparison, the 9-18mm images look sharp even down to the pixel level.

(All sizes: http://www.flickr.com/photos/djst/4860729883/sizes/z/in/set-72157624652066074/ )

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David Tenser
My camera equipment: http://djst.org/camera/

 djst's gear list:djst's gear list
Olympus PEN E-PM1 Olympus M.Zuiko Digital ED 9-18mm F4.0-5.6 Panasonic Lumix G 20mm F1.7 ASPH Panasonic Lumix G Vario 45-200mm F4-5.6 OIS Olympus M.Zuiko Digital 14-42mm 1:3.5-5.6 II R +1 more
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