At what point does diffraction kick in and ruin a lens' sharpness?
And, how can I test to establish that aperture?
I bought a NEX-5N (with 18-55mmm kit lens) as a pocketable camera for when I dont want to lug my 5D and although the results are pretty good I find that for shots where I needed DOF and I stopped down to f16 and beyond, the results are inferior to when I shot at 5.6 or f8
Thanks for advice, links etc