used AF-S 70-300 1:4.5-5.6 G VR hunting and rattling autofocus

dieselnutjob

Senior Member
I bought a 70-300 AF-S VR on ebay a few days ago and today it arrived.
It was described by the seller as "Used - but in excellent condition." which is one of the reasons I bought this particular one.
I just tried is on my brand new D750 (which works perfectly with my 24-120 F4) and when I try to focus on something at the other end of the garden (so 20ft away) or any other distance it hunts backwards and forwards rapidly and rattles as it does so. Red squares in the view finder flash on and off as it briefly goes "through" the focus but it just hunts for a couple of seconds and gives up, focusing on nothing.
If I use the manual focus ring then it's fine.
I had a quick go at cleaning the contacts but it doesn't seem to make any difference.
Is there anything I can do before complaining to the seller?
 

dieselnutjob

Senior Member
I put it down and did other stuff for a an hour or two.
When I had another go it worked perfect, but only for a couple of minutes and then it started hunting again.
Put it down again for a few minutes, seemed to work a bit longer.
It's almost as if it is trying to fix itself. Moisture inside? Drying out now that I unpacked it?
 

Texas

Senior Member
About all you can try is cycle the lense's switches back and forth a bunch of times. Cleans the corrosion off.
 

dieselnutjob

Senior Member
further update
it seems more reliable in the mid range of zoom
between say 135 and 200mm it's pretty good
at the far near or far distance it starts hunting
I am guessing that one of the ribbon cables that moves as it it zoomed has been flexed too many time and is only happy in the middle, or something
 

dieselnutjob

Senior Member
The more I use this lens, the better is seems to get.
I just played with it for about ten minutes at varying focal lengths and it was fine.
Now the camera battery is on charge.
I am wondering it it could just be lack of use?
Maybe there are contact areas inside that slide about and just needed some use to wipe oxidisation off of the contacts.
Will keep experimenting.
Next test is to verify that the VR works.
 

Fred Kingston

Senior Member
[FONT=&quot]Technically, Nikon says f/5.6 is the limit (f/8 on the most recent cameras), but it's a bit beyond that, and has a lot of subtle issues. A zoom lens is typically not t/5.6 [/FONT]

Nikon's AF struggles if you exceed the above parameters... IOW, if your F-stop is greater than the F5.6 to F8, the lens will not AF very well... Add a polarizing filter of lens converter and you'll definitely be too dark to AF...
 

dieselnutjob

Senior Member
I think that I have resolved this. I found a youtube video on this exact lens describing how to dismantle and re-assemble it, so got the screwdrivers out.

It looks to me like someone has been there before me as a I found red blobs of paint on some of the screws inside and some handwriting on one part.

Also I found that one of the ribbon cables did not have the locking tab properly and fully pushed home. This is one of the ribbon cables that flexes as the lens is zoomed which is why it was more reliable at some focal lengths than others.

I pushed in the locking tab fully and re-assembled the lens and it appears to be working well now. I will have to wait for daylight tomorrow to verify though.
 
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