I have a 210 f5.6 symmar convertible to 370 f12. I think that the coverage is 29 7mm at f16 focused at infinity. Is there away to compute the coverage if I am focused at some other distances. Say, 8 feet. I think that the coverage at 370 should be the same as 210. The magic question i s that can I get away with it for 8x10 which requires 325. It is for full body portraiture, so I will be using 370.