Originally posted by AfterPentax I have a number of old lenses amongst which the F F1.4/50mm, A F1.4/50mm, F4/K200mm, Takumar Bayonet F2.5/135mm and the F3.5/35-105. I have tried all these lenses on my different camera's: Samsung GX-10, K-7, K-01 and the K-3II. The results are always the same. They are soft, very soft I would say. A professional photographer once told me that they are all designed for film camera's and that it is a problem to adjust digital camera's, that is the sensors, to that old glass.
F F1.4/50mm - this autofocus lens should focus reasonably well, but shots made wide open through f2.8 may show a lot of softness compared to the DFA 50 1.4. The lens will also show larger vignetting and ca/fringing. However it should be sharp at higher 5.6 or so. If it isn't try love view focusing.
A F1.4/50mm - similar to above, but manual focus. Manual focus of fast appeture lenses is very difficult to achieve without practice. The same focusing screen that allows a slow lens to look bright in the viewfinder is pretty terrible for manual focus. Magnified love view is pretty good but it takes practice. Replacement of the focus screen and calibration are options to improve results.
F4/K200mm - manual focus issues noted above, it can improve using good methods, but often a tripod may be needed for love view based focus.
Takumar Bayonet F2.5/135mm - as above. This lens may not be as sharp some variation exists in user reports.
F3.5/35-105 - there are multiple versions. Non auto focus versions will work as discussed above but it will not be as complex as the 50mm due to a less critical focus due to narrower f stop. The A series manual focus version of the lens is reportedly very very sharp. It is often called a "stack of primes". The solutions to poor focus are the same as the 50 from above. The F type autofocus version shares similar issues to the f 50 listed above.
I can also point you to this to dispel the myth that older lenses aren't capable, read this:
Nikon's 'Worst' and 'Best' Zoom Lenses Compared
The key is that there may be sharper lenses - the DFA 50 is s razor blade - but the lenses you have should be acceptably sharp with the right techniques. (stop down a little, use one of the enhanced focus options listed in the thread, avoid super high contrast to limit purple fringing, etc.)
To sum this up, your lenses could be damaged, a filter could be softening results, wide open performance could be erratic due to difficulty of obtaining focus accurately, pdaf sensor could needed cleaning, fine focus adjustment may be needed, etc. Most people have found these steps to make most older lenses results sharp enough to be quite usable.