Good article about polarizers here:.

Http://www.luminous-landscape.com/tutorials/polarizers.shtml.

Basically either type will work as intended for the shot, but circular polarization is required in order for the AF and metering systems to function correctly...

Cheap isn't always the least expensive..

If you purchased a top of the line Hoya vs. that cheap Hoya and you compared them with the same shot, you will notice a difference. The higher grade multi-coating processes to make professional class filters are worth every penny..

Look at it this way, the reason that you purchased the 18-200 was because it was the best wide to zoom available. Sure it cost you more, but you know for a fact that it is a better decision than any 3rd party lens out there. Why go cheap on that good lens now?.

For myself, I purchased a step-up filter to 77mm which makes my filters cost more, but also most of the best zooms from Nikon are 77mm thread. Then I purchased a Kaesmann B+W Circular Polarizer that cost me well over $100. I've owned cheap filters before and I know the difference. Don't go cheap. You'll only end up selling it & buying what you should have in the first place. Cheap isn't always the least expensive...

Sorry to intrude in this thread but I felt it may be relevant, but when you say cheap first expensive Hoya filters, do you refer to i.e. Pro1 digital filter vs Standard filter of the Hoya range? I'm looking to purchase one myself from ebay but have realised that there are quite a few different ones out there in the Hoya range..

HOYA UV FILTERS*.

Filter Series Ring-Thickness Coating Threading Effective-Light-TransmissionGreen Series 5mm Uncoated Double ~85%Standard (purple box) 5mm 2 Layers Double ~92%HMC (gray box) 5mm 3 Layers Double 97%Ultra Thin (red box) 3mm 3 Layers Single 97%Super HMC (black box) 5mm 12 Layers Double 99.70%PRO1 Digital DMC (blue box) 3mm 3 Layers Double 97%Super HMC PRO1 (black box) 3mm 12 Layers Double 99.70%.

The price from Green to Black goes up dramatically just like anything else from the consumer to the professional level of any manufactured item of any category..

I realize that these are not Circular polarizer filters and that they are UV filters, however this is the research that I had performed and know about. I figured you'd want an answer rather than no answer..

I have to tell you though that I wasn't really impressed with Hoya in the first place. Whenever I tried to clean the things, they just smear. I got hooked on B+W MRC filters and I never ever looked back. But I also hear the Tiffen's top of the line stuff is really high quality as well...

Something is wrong I think. Ordinary plain glass has a transmission of 92% .Single layer coatings on both sides of plain glass would give 97 to 98% T..

How can "uncoated" filters have a 85% T and "double coated"filters have a transmission of 92% ? Perhaps a bad translation?..

It's not like the glass is clear, it's UV glass...