Hello neighbour (greetings from Lower-Saxony ),
Originally Posted by baachitraka
probably I can help giving some data:
The Xenar is a 4 element Tessar design.
The Yashinon 3,5/80 in the Yashicamat 124G is also the (same) 4 element Tessar design.
We've tested the Yashinon 3,5/80 in our optic lab.
This lens has its best performance at f8.
With an object contrast of 1:4 (two stops) we achieved 80 clearly separated linepairs per millimeter on Provia 100F.
The resolution at f11 was only minimal lower. The difference can only be seen at 100x enlargement under the microscope.
For normal daily photography the difference is irrelevant.
At f16 there is a visible resolution loss due to diffraction, and of course even worse at f22.
But as you say your print sizes are now not bigger than 10 inches (which is a very small enlargement factor for 6x6), using f16 would be no problem.
Depending on your requirements concerning quality, maybe even f22 will work (well for me it does not work well, I stop down max. to f16).
Just try it and look if you like it.