Originally posted by EdB It is my common practice to have a good UV filter (mostly B+W, and a couple of Hoya) mounted on my lenses.
To me, the big plus is lens protection and sparing the lens from repeated dust cleaning
Dust, as I write further below, is not a real problem in 95 % of all shooting situations, but reflections are. There are a few shooting envirinments, where protective filters do make sense, especially near salt water, where salt water spray may end up on your lens and that is a sticky stuff. Also wind, together with sand can be dangerous to a glass surface and then protection makes sense. But otherwise, against simple mechanical bumps, a good lens hood offers usually enough protection.
However :
Originally posted by EdB 1) will this contribute to some image refractions/chromatic aberration/other problems (?...) especially on the picture edges ?
You will see more flare and ghosting and thus a reduction in contrast when you use filters, if you shoot anywhere near a light source. This is especially pronounced near the sun, or when specular highlights are within the image frame. Also, I have had significant flaring and loss of contrast, with flash outside of the fielf od view but aimed at my subject. Even a good lens hood would not prevent that.
With good filters, what I never have been able to detect was a loss in resolution.
Originally posted by EdB 2) do you see a difference in image quality/definition with or without filter ? What focal lenses would be more deteriorated (if true) ?
I used to say in the past, that wide-able lenses would be more prone to unwanted reflections by the filters due to their more curved front surface. But concerete experience shows, that even a short tele will suffer. So, I do not think, that in practice the focal length of the lens is relevant. Relevant is only the amount of the flare/ghosting/unwanted reflection compared to the amount of the light from the subject.
Originally posted by EdB 3) Given the enhanced glass coating on the DA* lenses, if no filter used, is dust accumulation a problem ?
Dust accumulation is hardly ever a real problem with lenses, unless you shhot in windy and dusty environments (beach, desert etc.) A few dust specs on the lens will do nothing to either the lens nor the final image. A lot of dust will deterioate contrast when shooting against a bright background etc. But usually some blows with a Rocket Blower or a very light use of a dedicated lens brush will remedy that without scratching anything.
Ben