You don't really need a filter.. and they can degrade IQ, and add artifacts to the photos. If you always use a lens hood.. that will protect the lens.. and also give good protection against flare. If a filter breaks.. it will do more damage to your objective lens than would have happened without it.
If you absolutely feel you must have a filter... a very good, multi-coated Clear filter would be your best bet! Along these lines...
Amazon.com: B+W 77mm XS-Pro Clear with Multi-Resistant Nano Coating (007M): Camera & Photo
If you use a lens hood, it gets in the way of focusing a macro lens.
The hood will actually hit the subject in some cases, and send it flying away.
I use a Marumi UV filter on my Pentax 100mm WR.
I did a comparison, I think on this forum , over a year ago
With a UV filter and without.............NOBODY could tell the difference.
Most people picked the image that had been shot using the UV filter, as the image shot without a UV filter.
Which I found remarkable , considering the advice against the use of UV filters for protection, and for image degradation.
The rally against UV filters in my opinion, is ridiculous considering the obvious, that the human eye can't detect the difference.
I have never had to clean the front element of my macro lens. This after , over a year of use.
On he other hand, I have had to clean the Marumi filter that sits on top of it, many times.
This was gunk and crap that otherwise would have landed on the front lens element, coating.
Some consider the Pentax designated SMC coating as the best there is.
I don't want to have to clean anything off that coating if I can help it. So far I haven't.
Heliopan is another that I'd recommend. Bit pricy, but a good filter.
And it comes with a lens hood. So I guess I'll just save the money on filters for that lens and invest in circular polarizers for my other lenses. Thanks for the input!
