pentaxpete
I was testing my 'Gift' X-700 with the MD Zoom 35-70mm f3.5 made 1981 and when I processed film all the 'distance' shots were way out of focus but nearer ones were all sharp -- well, there is a bit of 'play' in the lens barrel and the chrome mount ring at rear -- so I put lens onto my 'older' SR T100X with the pure mechanical shutter ( thus saving Battery Power !) and opened it on 'B' with a locking cable release then put a ground glass microscope slide onto the film plane and had a look with a x6 magnifier -- well, the 'infinity' focus was way out then as I brought it back it 'snapped in' at 30 feet !! So now I know NOT to use the camera focus screen for 'infinity' photos but to set it to 30 feet manually. Just as another test I put the MD 50mm f1.7 lens onto the SR-T100X and had a look and 'infinity' was sharp at f1.7 OK .