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SMC takumar 50mm 1.4 aperture issue
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PostPosted: Thu Jul 30, 2020 9:30 am    Post subject: SMC takumar 50mm 1.4 aperture issue Reply with quote

Hello,

I just picked up an smc tak 50 1.4 in fairly good condition. I quickly tested it before buying it but I didn't notice any issues, until now.
It looks like when the lens is focused before infinity the aperture slips from f8 to to fully closed (f16).

Here is a quick video showing the issue: https://streamable.com/sy19e4

When focused to infinity the lens behave normally.
When focused closer it behaves normally until the half click after f8. After that any movement will close down the aperture to its minimum size.
Switching the auto/man switch back and forth once will set the correct aperture.
When the lens is set to auto it behaves has expected, the problem is that i'd like to use it on a mirrorless.

I had something a bit similar with a nikkor that I badly reassembled, the aperture tab was too short to reach the aperture mechanism when focused to the min distance.
I also noticed that if I gently shake the lens I can feel that something is kind of loose, not a screw or a small part but more like the whole optical block. This is my first takumar so I have no idea if this is expected.

I was going to open the lens to remove the few specs of dust that worked their way there anyway but I'd like to know if any of you had faced this issue.

Thanks


PostPosted: Thu Jul 30, 2020 12:21 pm    Post subject: Reply with quote

It does sound as if something is misaligned in the mount. Look carefully at the set screws that secure aperture indicator/DOF ring. If they look disturbed someone's been inside.


PostPosted: Thu Jul 30, 2020 1:48 pm    Post subject: Reply with quote

Gardener wrote:
It does sound as if something is misaligned in the mount. Look carefully at the set screws that secure aperture indicator/DOF ring. If they look disturbed someone's been inside.


It does look like they've been touched, the paint is very slightly worn out around the tiny screws. I just hope it's a simple bad reassembly job and not something broken.
I'm waiting for a rubber tool to remove the front ring, my usual technique didn't work with this lens, I'll post here again when I get inside, the lens design doesn't look too complex and I have experience with nikkor primes
The lens is still usable so I'm not too worried, I planned on using it for portrait and I doubt I'l lever go over f4-5.6.

What about the loose optical block (?) when I shake the lens, is it normal ?


PostPosted: Sat Aug 01, 2020 10:46 pm    Post subject: Reply with quote

I finally had time to disassemble it today. The hardest part was removing the front ring, a bit of alcohol did the trick.
I disassembled everything down to the aperture control mechanism, found out the the aperture arm (blue on the pic) was slipping over the pin supposed to keep it in place (green on the pic).
I removed the arm from its support and slightly bent it so that it doesn't slip anymore, the lens is now fully functional. It's a fairly easy lens to work with

Pic of the aperture mechanism: