aint that the truth
JonK wrote in post #10694230
An 85mm 1.2 is a great lens I enjoy mine, but I don't often shoot it at 1.2. Not because its not sharp, but because the depth of field isn't what I am after
. It has the effect of miniaturizing subjects due to such isolation. That, and it's not as sharp at 1.2 as it is at 1.6
If the depth of field is too narrow, then there is nothing for it but to stop down, which you are right to do. It is commonly thought that isolation of subjects is the primary reason for wanting to restrict the depth of field and I tend to agree with this notion. Desired sharpness is a combination of the function of the viewing conditions and what you actually want to do with the final output. There have been several instances where I have seen photographers evaluating image sharpness of 16 or 32 bit images, on monitor screens which can only display 8bits of colour depth information, and yet they are using a restrictive colour gamut such as sRGB. Images are viewed by transilluminated light (display screens) when they are ultimately going to be viewed by reflected light (printed) within the smallest colour space... CMYK unless printing is going to be done using the six colour hexachrome process.
We all know about circles of confusion and eye to print distances and yet we are caught up in a concept of sharpness that is little more than theoretical... when we eventually send our image files for final output. If I supply a local newspaper with sports or hard news images, they want me to give them medium quality jpeg files sized for output at 75 lines per inch and converted to the CMYK gamut. This is approximately half of the resolution with which I would normally want to supply my client. (what price the difference between f/1.2 and f/1.6 here?) The only benefit to stopping down in this case is not one of sharpness but, primarily, one of depth of field and I doubt that such a small adjustment would be noticeable at 75lpi on newsprint. Secondarily, exposure adjustment could be cited as a reason for making the small adjustment but once again, I don't feel it would be noticeable on rough newsprint.
Does printed output require the perceived sharpness of a well-calibrated display? Likely it doesn't but when I prepare pre-press work for long-run printing on fine art paper which is intended to be printed by a photogravure printing process, I will take any help I can get and I use high resolution image files tied to very big colour spaces. The perceived sharpness on display screens is quite likely to be illusory and derives from the previously mentioned transillumination which, like the Kodachrome transparencies of old, appears to increase the sharpness of an image because of the apparent high contrast of the image on screen, leading to an edge effect that causes the observer to see an apparent increase in sharpness.
Once again, it is the real world everyday uses that determine what we need to do to increase our image sharpness. Photographers may realise that absolute sharpness is a theoretical construct and what we see with our eyes depends entirely on the conditions which obtain when we are viewing the image. A change in measured values of a couple of line pairs per millimetre is unlikely to be detectable by the human eye. All of the foregoing is apropos nothing other than to say that you should try to have fun and do what you think is best for your images.