a setting on an A50mm f/1.7

Thanks Tony-O for that reference. Good photos. Doesn't answer everything though. Where do the ball bearings go? Also question above for Clarky. The detent spring photo is interesting. I need to open lens up to see if I have that spring or whether its lost?
cheers
bb2

Yes, thanks! Those photos are significantly less scary than the diagram!

So are those tangs that we see him re-attaching in the photos actually parts X27 and 28 from the diagram?

Sorry for the late reply.
Guys I have never dismantled my 1.7A, so I can't really help you. I have been meaning to but never got around to it.

I just recommend if you do intend taking it apart, that you are vigilant with what comes off and how it goes back together.

Maybe its the spring that you can hear rattling inside :

As you move the aperture ring on a working lens you'll feel a series of "clicks" as you go from one position to the next. The underside of the ring itself (the bit you don't see when the lens is all together) has a short serrated section - where this section lines up with the inner barrel there will be a tiny hole in which is sat a very small spring and a ball bearing (usually 1mm). The spring pushes the ball bearing into the back of the aperture ring's serrated edge and that's what causes it to "click" into position.

Getting this lined up when you but the lens back together is one of the fiddliest parts of the job - I usually find several attempts and lots of swearing is required...

I've never taken one of these lenses apart and I've never had the luxury of a diagram on those I have, but from general experience once you take the back off a lens any piece that's loose / out of place is usually quite obvious. I'd be tempted to follow the pictures in the link Tony posted and not to worry too much about the exploded view.

There are 2 different type of problem mentioned in this thread.

1. If the aperture ring is not turning through its full range then the most likely reason is that one of the spring metals contacts have become detached. This is quite common due to the poor design. The repair however is quite easy.
Either remelt the plastic through the small hole in the contact, or apply a small blob of epoxy adhesive , such as Araldite.

2. If the aperture ring is turning fully to the 'A' position, it may be that the ball ended contact that protrudes through the lens mount is not making good contact with the the camera body. Using something like a ball point pen nib, check for movement. Also check that the contact is clean.
The contact is part of an assembly which includes a small spring and armature. When the aperture ring is moved to the 'A' position (minimum aperture) the armature is free to move and the spring provides the pressure on the contact. The actual locking pin X510 is not necessary for this,it merely locks the lens at minimum aperture in this case F22.

When taking the lens apart take care not to lose the 3 parts of the contact assembly as they are almost impossible to replace.

The repair should be quite simple providing all the parts are there, but if you don't fancy doing it yourself you try here http://www.cam-rep.co.uk/. Alan is recommended and very reasonable.

Steve

Thanks Steve! My problem is clearly number 2 -- good to figure out before taking the lens apart to the those infamous plastic welds and discovering that they're both still intact!

Comparing this lens to another lens with the A position (Sigma 28-200), I notice that the little button on this lens is distinctly "floppy" -- I can tap it down with no resistance at any aperture. On the Sigma, it goes down on its own and stays down through the whole range, and just pops back up again at f22. This could be a design difference between the brands, but it seems more likely that it's a problem with the 50mm.

Steve, I don't see a ball ended contact protruding through the lens mount. I was just about to ask you what you meant by this, but I actually do see it quite clearly in the first photo from the set we've been looking at on this thread -- so that may be what's come loose on mine? The hole there is just empty!

Check out this picture.
[IMG]http://i198.photobucket.com/albums/aa184/stevejcoe/SMCKALA.jpg[/IMG]

It goes back a couple of years. You can see the 3 parts of the assembly. In this case the armature on the left was broken. I was quoted £24 for a replacement armature, but managed to source a faulty 'A' series lens for around £5.

The spring is just a contact fit inside the contact itself. The ident on the contact locates on the armature. The assembly should be fitted or remove with the aperture ring in the 'A' position.

Steve

Thanks stevejcoe for still more info!
bb2

Yes, thanks!

So is it likely that there is something broken which will need replacing and not just something that has come loose? Steve's photo makes me think that maybe I'd be better off trying to get ahold of a broken A lens before even opening this one up...

My example is doing something similar. It travels freely across the whole aperture range and quite easily drops out of auto. I think there is a slight faint click as it goes into the 'A' setting, but nothing great and it quite quickly/easily moves enough for the camera to stop registering that it's in 'A' . This happens by mistake when you go to focus the shot and is very frustrating!

Is it worth disecting as described previously above?