Originally posted by ChrisJ though how a thin piece of glass can offer any 'protection' eludes me
It doesn't elude me.
I worked in so many countries I have difficulties to name them all, but I have no difficulties to name the regions where, after just one day outdoors, everything was covered with a thin oily film. It was mainly from getting energy by burning coal with a high percentage of sulfur. And there were often very fine metallic particels included.
Western part of Turkey, East Germany, Taiwan, and some regions of what is today Czech Republic, Slovakia, Slovenia, and Bosnia come to mind.
Whatever you used for the daily cleaning of the front lens, after some years you would own a fine soft portrait lens, increased flare included.
The environmental situation I just described has improved a lot since, but in the film days - since multi-coated filters were available - even a lot of professionals used a combination of lens hood AND filters. I did, and removed the filter only in situations where a light source was within or near the AoV.
Indeed UV filters aren't needed with DSLRs for getting sharper images at the seaside and above 1200m from sea level, or if you have snow/white sand with a blue sky.
But I also sometimes ask myself why the general bashing of filters to protect the front lens started only when the digital age enabled serious pixel peeping.
I know and have experienced myself that filters in some situations can reduce contrast and increase flare so much that you can really see it. But in many situations I decided to risk this.
Personally, I don't use protecting filters with all of my lenses, and when I do, in special situations I may remove them. But I always use a lens hood.
EDIT: By the way, I used mostly original SMC Pentax filters.
Last edited by RKKS08; 09-08-2013 at 09:38 PM.