I would imagine if you have access to a densitometer, it's easy. Otherwise, generally follow Fred Picker's advise (and others who have similar methods). Basically, focus on a grey card, make sure the light is even, meter normally, Then stop down 5 stops (or get to five stops down). Shoot. Then put the cap on. Shoot. I then take the cap off, and shoot again. But it's variations on this; some advise opening up also, to get to zone X. I guess you can. It's a good thing to do, because once you have found your N, you can forget about that part of the process. You should also look at N-1, N-2, N+1 and N+2.(posted 8237 days ago)Or, i imagine, you can find some standard scene, and see if different films, EIs, development times yield similar negs. I use the hallway outside my apartment at night, so there's no light coming in from the window at the end of the hall, only interior lighting.
RON