Help is needed before I go out for this shoot. I am planning to photograph the interior of Grand Central Terminal's Main Floor. My camera will be situated next to one of the main staircases on either end, if I can get the necessary permit to set up a tripod for eight hours. The camera is a Leica M3. The lens is a 12mm Voigtlander. The film is Ilford SFX. Thanks to an APUG member, Simon R. Galley, I now have an Ilford SFX filter mounted in a Cokin P holder, which I will mount in front of the 12mm lens. I estimate that the average exposure during the eight hours is four seconds @f/22, without compensating for reciprocity failure and the 16X filter factor. I can only make one exposure in one day, so I want to get as close to a perfect exposure as I can. Does anybody have experience with this sort of thing? Can anyone calculate the correct exposure factor? Thanks in advance.