neutral, I see no difference with / without apart from a very low flare, inevitable I think (at least there are more uv hoya with the range (c) HMC). Logically enough when I get the filter and the sun visor I blatant vignetting has large aperture (gear: pentax k30 + 18/135), since the filter extends the target; to reduce I have to close a 5.6 or greater (or remove the visor :-); This filter has an external thread which allows to place a lens cap.
