Originally posted by pasorro It is not the normal sound. Are you sure the focus ring is enable in af position.?
Try to change from af to manual focus on the lens some times. You Must not opérate the lens in manual mode if the camera is not in manual focus mode. It has not quick shift.
Can anybody explain it in better english?
On the FA* lenses with the AF/MF clutch if you push the focus ring one way it is AF and the ring is locked. If you push the other way it will work as MF even if the camera is set to AF and this is OK. It will not AF in this mode. As indicated above there is no QuickShift. If the ring is not fully pushed either way I'm not sure what would happen but in my only FA* lenses (80-200 f/2.8 and 300 f/4.5) the lens has not been able to get into this inbetween setting - it has clicked fully into one or the other without any play to permit hanging in this theoretical middle state.
---------- Post added 03-09-17 at 01:43 PM ----------
I just verified this on my FA* 300. If I push it back towards the body the lens clicks into manual focus mode. Clicking it forward puts it back to AF. Please note that I then needed to turn it slightly before it locked in place in the AF mode. Also note that right above the window to the lens distances it is labeled Auto Focus to show when it is in that mode.
---------- Post added 03-09-17 at 01:46 PM ----------
From your videos it isn't clear that the "auto focus" words appear clearly - are they partially covered? See this picture for how they should appear:
https://www.pentaxforums.com/lensreviews/showfull.php?product=190&bigimage=s...85mm_F1_4_.jpg
---------- Post added 03-09-17 at 01:57 PM ----------
Just put the FA* 300 on my camera. If I confuse it I can get some of the behavior like this while it hunts. Put something in the front of the lens at a distance that it can focus on and try again. If it quickly locks in and doesn't hunt it may be OK - the hunting itself sounds nutty when happening - mine has been CLA'd and is very agile when focusing normally. It was hard to find something with poor contrast to get it to fail. I am still not postive that your lens sounds right - it does seem a little odd.