I always found diffraction on film highly overrated, If your goal is to make a contact print, I'd guestimate 1/3 of the way from the closest flower to the wall and stop down to F64.
If enlarging, I'd back up, focus on the same spot, shoot it at F32 and crop. Or get a 210 lens.
Use this DOF calculator, it makes a good calculation of the theoric circle of confusion with different settings. Using it a bit you will get a clear idea on how "Focus management" is optimized.
Anyway each lens has a particular behaviour in the DOF, there is a graph named Through Focus MTF that plots the "blur level" through the depth, some proficient cinematographers use those graphs to understand how a particular lens works.
http://cinematechnic.com/optics/super-baltar
Sure, measure and calculate . . .its all good.
But check it out on the ground glass. I took a workshop at Santa Fe3 years ago (mid-1990s) and one thing really stuck with me. /the instructor said to us, "The ground glass is truth." and "If you don't see it there, it isn't there."
So check it out. I use a set of bar codes to check focus in diffident spots of a composition. Stopping down haqrd does make it dim. I turn on extra hot lights to let me see what-is-what , then turn them off to expose with strobes or natural light.
I guess what I am saying is use all the tools and techniques you have.
Drew Bedo
www.quietlightphoto.com
http://www.artsyhome.com/author/drew-bedo
There are only three types of mounting flanges; too big, too small and wrong thread!
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