I don’t tend to work with modern lenses, but I got this one anyway just to work on something newer.
It was described as having a problem with the focusing. It could be used manually, but the auto focus had problems … I made a guess it was something stuck in the focus gears.
Should either be an easy fix … or something that I would need to replace part(s).
It turns out that it is was both ??
First is to remove the inner ring
Remove the two screws holding the contact pin pcb
Remove the three screws on the black ring
When pulling out the black ring you will have to maneuver around the pcb
Now you can remove the mounting ring.
Remove the four screws
Be careful will pulling off the ring as there are shims underneath it.
… also the screw drive pin may come off with the ring.
Gently take the shims out.
Do not bend the shims and keep them right side up.
Pull out the focus drive pin
The outer cover (the one with the orange ring) is held on by three screws. You will first need to pull off the rubber zoom grip. This should just slide off with a little work. It is held on by tension … there should be no adhesive.
Now you will see an area that has a metal plate
Underneath there is another place with mutliple contacts.
You really do not need to remove these … though you need to be aware of them as the thin metal can be bent easily when you put this back together.
Remove the three screws.
Pull off the outer cover.
Remove the three screws
There is one more thing that needs to be done in order to take this layer off.
On the sides of the lens you will see three long screws within slots. These are coupled to the inner zoom ring.
Unscrew and remove them.
You can now pull the assembly off gently as there is some metal contacts within.
Take the piece that you just removed … sadly, I am missing the picture I took of the inside … Look inside and you will find a ring that looks like this.
You can gently pull it out … note the contacts that are attached, try not to bend them too much.
As you can see from this image this ring is broken. This is called the focus differential ring.
The screw drive from the camera turns this ring. The protruding part couples with the focus cam, which moves the lens element group.
When the AF mechanism is engaged this ring will jam … which is why it was described that manual focusing worked.
OK. Now I just need to figure out how to fix it.
I tried a number of adhesive ideas, but they all failed … you can’t just plop a bunch of epoxy on it as it needs to fit back into the lens assembly … though it could also be because I am not the most knowledgeable person about using adhesives.
I gave up after a couple of weeks and ordered a $20 replacement part.
Getting back to the rest of the lens … you should now be left with this.
Since I was here, I decided to clean out the back to the lens assembly.
You can unscrew the rear element with a spanner wrench.
When putting the lens back together, remember that some of these components have metal contact arms … these do not like to be bent too much, and some have very thin fingers.
You will need to position the aperture arm and focus arm so that they fit the levers below.
When putting the lens mount ring back on you will need to use another screwdriver to align the holes in the shims.