Originally posted by normhead Falconeye once went through a mathematical proof as to why the absolute best lenses are shaprest at ƒ2.8, and the next bunch like the 31 ltd and 77 ltd. being sharpest at ƒ4, and your standard every day kit being sharpest at ƒ5.6, I know enough to know he may be on to something, but not enough to repeat the proof. Apparently some ZIess lenses are sharpest at ƒ2.8. There are enough lens reviews around on Photozone you can check this out empirically if you choose.
Having your lens sharpest at ƒ4 or ƒ2.8 makes for some really nice smooth out of focus areas on portraits, without having to open to ridiculously wide apertures and killing your depth of field.
At least I assume it would. Those lenses are out of my price range.
I may have been a little unclear - I was specifically referring to f/5.6 being the sharpest point for the dfa100mm macro
. I've no comment on the performance of the lenses that are also out my price range
.
I don't think the dfa100mm falls into the 'absolute best' from an optical criterea alone, but I do wonder if it was intentionally designed to be sharpest stopped down a bit given how it's likely to be used or if this was just a given after other design considerations (size/cost). I've drooled a few litres over the
Voigtlander APO Lanther and it's interesting to see how it has an even smaller change in sharpness as you range across the aperture settings (tested on a different camera so the numbers aren't directly comparable to the dfa100mm chart you showed). The cost is double the weight and maybe 4 or 5 times the price of the dfa100mm (it's also tough to find).