My recent question to the PhotoTakers forum …
Generally I always take shots like this
CAMERA -> POLARISING FILTER -> SKYLIGHT FILTER
From what I understand every extra bit of glass (filter) added in front of a lens takes away some light so should I remove the polarising filter for dusk/ nightshots ?
Resulted in some conjecture, but the consensus from searching several sites was that any filter or glass in front of the lens degrades image sharpness (except for the filter manufacturer sites and, of course, they swear up and down they don’t). The consensus also says that the use of more than one filter at a time is a definite no-no and can cause all kinds of problems (chromatic aberrations, etc). Bottom line – pretty much everyone agrees that you should never put a filter on unless you need it.
However a minority did claim that using a UV (skylight) filter was still worth it to prevent the lens getting damaged, scratched or accidently finger printed, providing no other filter was being used at the same time.