My experience with filters is that they keep me from getting the actual lens dirty, which even with careful cleaning etc. will eventually lead to a degradation of IQ. It's much cheaper to buy a new filter than to buy a new lens. That is the big thing for me. I have never had a finer print, or any other dirt on any of my filter protected lenses. The lens I have that can't use filters are a constant source of worry. Even things as simple as condensation on the lens during star trails is a worry. How do i clean that off without affecting the coatings?
That is why I use filters... but, if you ignore that benefit and pretend like it's irrelevant, then I guess you can make a case for not using them.
---------- Post added 03-16-16 at 10:41 AM ----------
Originally posted by Simen1 The zoom factor of this class of lenses have been increasing from time to time. The last decade from 18-200 to 18-250 to 18-270 to 18-300 to 16-300. What is next? 15-300 or 16-320 (both 20x)? Maybe we get a Pentax 15-300 or thereabout in the near future, or a 28-300 for FF or both.
Only the Pentax 55-300 is optimized to be strong in the long end as far as I know.
While zoom factor has increased, other factors such as the characteristics of out of focus areas has remained pretty much dismal, especially in zooms that go from wide angle to telephoto. These zooms give you the 95% of what you need for a great image. If you want the last 5% of what's possible, you have to upgrade.
You just have to ask yourself, what am I going for here?
More zoom range could be the answer. More IQ could be the answer, but usually those two things are not answered by the same lens.