Tamron 24-70mm Vi USD partial dismantling

Question

I am aware of the relative wisdom of pulling lenses apart. Specific warnings based on knowledge of this lens or closely related ones are welcome. Generic ones are unlikely to be helpful.

• I have a **Tamron 24-70mm Di USD lens whose lock switch is stuck on so that the lens is 'stuck' in the 24mm position.(Happened rapidly but progressively over a short period. Turning lens to 24mm position engaged lock and disengagement got progressively harder and now can not be done).

• I urgently 'need' to use the lens and the (lens-repair-)cavalry is too far away in space and time. So ...

• I wish to investigate dismantling the lens far enough to unstick or to remove the lens lock.

• Other lenses that I have dismantled and assembled have sometimes had means of dismantly access from both ends of the lens and it may be "safe" and "simple" to do what I want to achieve. How to do this is not obvious and I'd rather avoid prying up random rubber pieces to no avail.

• Is anyone able to advise how or if 'simple & safe" access to the lens lock mechanism may be achieved? (I am not afraid of performing sensible mechanical operations and am aware there are risks. Knowing which operations may be sensible would be helpful).

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Notes / longer:

I have a Tamron 24-70mm Di USD with Sony A-mount.
(This version has "VC" with Nikon and Canon mounts)

The lens lock slider is stuck in the locked position - so it's a 24mm sub-prime { :-) ] lens.

The lens is out of warranty by a few months.
I wish to use it for an event in 3 days time.
The sole authorised repairer is too far away for safety in space and time.

Every time the lens was turned to 24mm position with barrel horizontal the lock engaged. The slider would not disengage the lock. Initially, pointing the lens front downwards and gently tapping the lens allowed lock disengagement. Required tapping vigour increased each time and is now not effective at 'tapping' levels that I do not wish to exceed.

I may return the lens for professional attention in due course but for now 'need to use it'. Unsticking the lock would be enough. Removing the lock would be acceptable.

I'm aware that interfering with the lens assembly proper may lead to misalignment which would probably need professional attention and which may not be repairable. I have pulled various lenses apart in the part - never with bad consequences. I'm aware that past results do not guarantee future ones :-).

Thoughts?

Answer 1

Don't know exactly how useful this might be but Roger Cicala's lensrentals blog has comparison teardowns of the Canon, Nikon, and Tamron 24-70/2.8 lenses with lots of pictures.

Quoting the Tamron relevant text from that article:

Front Group

One thing that all 3 of these lenses have in common is a large front group at the end of an extending barrel. They all disassemble the same way – a makeup ring is removed exposing the screws that let us remove the front group from the lens.

...

Opening up the Back

For all 3 lenses, opening up the back involves removing the screws that hold the bayonet mount and electrical connections in place. ...

... We dissected a Canon-mount Tamron, so it doesn’t have a mechanical aperture lever. Had we done a Nikon-mount version then the bayonet mount would have had an aperture control lever, like the Nikon. Like Nikon, however, the Tamron (and most third-party lenses) use shims under the bayonet mount to achieve proper spacing.

I'd assume the A-mount is closer to the Canon in this regard.

... Under the shim, however, the Tamron has a PCB like the Canon. Older third-party lenses generally didn’t have PCBs, but in recent years most are using them. I particularly like Tamron’s because they are a very cool black color. I assume the plug with green marks on it is a computer connection for factory adjustments....

Removing the Rear Zoom Components

Once [its] PCB is removed, the Tamron shows some traits similar to both the Nikon and the Canon lenses. It doesn’t come apart modularly like a Canon, but it is a bit more organized inside than the Nikon. The aperture key ... need to be removed, along with 4 mounting screws, then the mid barrel comes off. ... The mid-barrel contains the Tamron’s GMR unit.

He also has a final section on how to make optical adjustments for the Tamron.

I'm guessing that once you can get the optical assemblies out of the barrel, you can access the back of the switch to see what might be physically broken, and hopefully find a way to jury-rig up a fix. But I'm not the type of girl who pulls her lenses apart. Her fountain pens, yes. But not her lenses. I took the back ring off my Oly OM 50/1.2 and quietly put it back on again after I saw what I would be dealing with inside, and called a local CLA guy up instead to fix the aperture ring sticking. :)