About f/8 or f/11 for most lenses. Most are great (especially the M-LA lenses and longer APOs) from f/5.6 but the DOF might be problematic and by f/16 you'll be seeing the beginnings of diffraction.
While I like that people can measure concrete numbers and always advocate for quantifiable metrics, I don't really think the numbers posted in that link above are correct or at least, they don't match the performance of my lenses. Either I've got strange ones or they've got strange ones, but the sample count is far too small to draw any conclusions. Specifically, the link claims nearly aperture-independent performance from the 110/2.8 whereas in my experience, it is noticeably softer and with more coma at f/2.8, better by f/4 and reaching full sharpness by about f/8. A secondary effect is that performance varies with distance somewhat, and most lenses (except the 140) are not anywhere near flat-field so testing them against a flat target is inherently problematic.
Last edited by polyglot; 04-09-2013 at 07:57 PM. Click to view previous post history.