I agree with Drew. A rule of thumb for normal focal length lenses, regardless of format, is: for optimum sharpness, stop down so the aperture appears to have about a 1/4" or 1/5" diameter when viewed through the front of the lens. This gives a good balance between lens aberrations, DOF, and diffraction for many subjects. Long before digital calculators I went through the math for many lenses on several formats with pen, paper, and Rudolf Kinglsake's old Lenses in Photography. It was an education that many of us would find worth the effort. A calculator or computer can simplify the calculations. St. Ansel had good reasons to use f/64, and Weston could get by with smaller apertures with some of his subjects.
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