Yes, "filter factor"... To do this on the GSN, you'll want to set the ASA dial to a number less than the number you would use for the given film without a filter.
Col. Sebastian Moran, ret. (not really)
SLR, dSLR, and compact RF's. Black Yashica RFs; Nikon & Contax/Yashica SLRs; Nikon digital.
Where did all these cameras come from?