I have found filters a real pain and found the coating's are easily damaged with cleaning. I used a filter in front of cooled CCD and found that after a couple of incidents where condensation mist formed the coatings became damaged.
For comparision when I first got my 100mm Canon lens I managed to dew up the front element a number of times (before I got smarter with avoiding condensation) and each time I cleaned the lens afterwards to remove the residue. But the coatings are still perfect.
I only use filters when necessary.
Terry
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