Circular Polarizers

[BananaRepublic]

What is the difference between the Hoya polarizers there seem to be a few different types or at least that's what the letters suggest NXT, HD, HMC, HDPro I don't know what the difference is, or is it just a marketing thing. Hoya is just an example brand.

Also when it comes to ND filters is it better to get the circular or the adapter type

 

[sscarmack]

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