I 've asked a question about the diffraction of small f-stop diameter in my last post. And, now I'd like ask about caluculating DOF for my particular shooting situation. As I mentioned before, I am shooting 6 people, who are standing very closely each other in front of black seamless, in the studio using 8x10 with a 165mm super angular lens. Because I want to make people just fit in the frame, the lens is very close to them. (about 30 in.) Then, to make everything in focu s I think I have to stop down to f64 . (Near distance 30in. Far distance 70in) T hen, I'm going to make at least 30in x 40in prints from the neg. Now, I am wondering where to focus. I know that I have to fucus 1/3 of the po int in the area where to be focused and depends on circle of confusion. Since as we know, in the large format, when we move the focusing nob, the size of imag e changes a lot, I 'd like to know the exact point to be focused to get everythi ng in focus. Is there any fomula which I can caluculate the DOF in this particular situation. Thanks Joe