I know we are all impressed by the quality of modern equipment: I was given a lesson today in what our older kit could produce.  In
researching an article I am writing, I went back to an image taken on a Voigtlander Vito CD 35mm rangefinder camera, the first
camera I ever owned.  Scanned some years ago on an Epson V500, I made an inkjet print 39x25cm, and the detail is so good the
portholes on a ship 300 metres away moving at 25 knots and taken from a small boat are tack sharp.
No wonder I don't need  to go shopping, not even for Pentax!

John in Brisbane

The one big improvement with many of the newer computer designed and manufactured lenses is sharpness in the corners. But when it comes to the full image at F5.6 or F8D many of the older lenses are equal to today in most respects. Of course, with digital sensors the coding change does help control reflection off the sensor surface. That’s what I’m told. But better old lenses under controlled lighting … I’m having no problem. Just keeping away from the sun flare.

That said, the newer computer designed zoom lenses are sharper across the range. But your classic prime lenses, no sense and not using them. They’re good. I did it a couple months ago with an old Konica AR lens, 57 mm f1.4. Optical design is everything, whether computer made or mechanically ground. That lens serves as evidence to me that rendering of the image is far more important than simple resolutions. The Konica has a much flatter field than anything else I have and that focal length range, including the Pentax.

In short, there are advantages to some of the newer lenses but as you have found many of the classics remain the equal of the newer models. For all practical purposes.

There are some older lenses which have more aperture blades than most
modern ones, good for bokeh. Jupiter 9 85mm f2 (~1960s Russian copy of
a ~1930s Zeiss design) has 15 & this m42 Pentax is the only lens I've
ever heard of with 18.
https://www.pentaxforums.com/lensreviews/Takumar-200mm-F3.5.html