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Jupiter 21M Repair Thread
Posted By: Helios 1984, 08-01-2015, 12:19 PM

Hi guys,

I bought lens for 55.00$ on Ebay but wasn't aware that it was defective. I couldn't find any servicing guide for this particular lens so I go blind mode. After removing the back of the housing and I noticed the abnormal shape of the M/A lever, it was quite bent. After a bit of research to know how it was supposed to look and I unbent it with pliers. I reassembled the lens but it still was defective, the Helicoid could not focus beyond 4.5m. I disassembled the lens again and found out that the tip of the M/A lever would get stuck on the Stop Down Lever, and as I kept doing a backward focusing movement the M/A lever would slowly bend.









Note: Only unscrew these if you need to remove the M/A lever. Also, the spring that hold the Auto Aperture Pin is fragile, it can easily break if the screw that holds it is fastened too tightly.


Note: Only unscrew these if you need to remove the M/A lever.

On the picture bellow, I already fixed the M/A Lever



----------------------------------------------------------------------------------------------------------------------------------------------------

Now back to the issues I had with my lens.

Issue No.1: The maximum aperture that I could use was f/11.
Cause: The M/A Lever wasn't positioned between the Stop down lever and the M/A Switch.

Issues No.2: The helicoid focus mechanism could not go beyond 4.5m.
Cause: The edge of this aluminum ring was not filed, it caused the Stop Down Lever to get stuck on it, thus preventing the helicoid from properly functioning.

When the M/A switch is set on Manual, the M/A Lever should push the Stop Down Lever all the way to the left so you can have access to all the Stops with the Aperture ring. Since the M/A Lever was bent, the Stop Down Lever was not properly positioned and only half the stops were available.




I filed the edge so it would not interfere anymore




Here's what the inside of your Jupiter-21M should look.



The only plausible explanation for this mess would be a M/A lever that was already bent on the assembly line, curved enough to get stuck on the top of the Stop Down Lever, which would cause a chain reaction the moment someone used did a backward focus movement.




Thank you for your time.

Last edited by Helios 1984; 12-31-2016 at 08:50 PM.
Views: 3,221
08-01-2015, 09:42 PM   #2
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Good work. Interesting chase and detective novel almost.
02-11-2016, 02:42 PM   #3
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Original Poster
I found these pictures on a German photography forum, same exact mechanical issues as I had with this lens.





Source: Phillipp from Digicamclub.de
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