| Author |
Message |
    
Tobias_f
Tinkerer
Username: Tobias_f
Post Number: 1
Registered: 06-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, June 23, 2009 - 12:40 pm: | 
|
Hi all,
despite being a long time reader, I am a new member to the forum.
I have been slowly restoring my IIIa, which initially needed the slow speed escapement cleaned, and the RF mirror replaced. Last week I finally had the whole thing complete, re-covered, test roll shot, everything was perfect. So after a few days of it sitting in front of me, and periodically picking it up to check that what i had done a good job, the RF just changed its mind. It did not fall, and was not in the sun.
What seems to be happening is that its infinity is now at about 1m, and its closest focusing point is at about 30cm. Since I never touched the RF mechanisms, i am pretty sure that the cam has not moved, and it still has a full range of movement, it is just not focusing at the right distances.
Does anyone have any idea what could have spontaneously happened, or how to rectify this issue?
Also, on a side note, due to the time that passed between my starting the repair and completing it, i have forgotten what held the end caps on the RF tube: were they cemented in, originally?
Thanks for your input,
Tobias |
M_currie
Tinkerer
Username: M_currie
Post Number: 185
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 24, 2009 - 07:34 am: |
|
It's been ages since I had one of these open, but I seem to recall that the moving part of the RF mechanism is returned to infinity by a spring, and that the cam lever only pushes, does not pull, so the fact that the cam is returning all the way does not guarantee that the mirror is following it back. If this is so, my guess is that something is hanging up the mirror mechanism from swinging back, and that you need to get under the cover again, and see if you can free it up. Perhaps a screw too tight, or a lack of lubrication. I don't think the return spring is very strong.
One thing I'd try before anything else is to take the lens off, and see what happens if you push the cam in all the way and then let it go with a snap. If the mirror returns, then you know it's just a little binding. Perhaps if that's the case you can limber it up without opening it. |
Markus
Tinkerer
Username: Markus
Post Number: 127
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, June 25, 2009 - 03:37 pm: |
|
Sounds similar to the mechanism on the Zorki 4. I bought one with a stuck rangefinder, the spring was still in place but too weak to push the cam out. A drop of oil on on the pivot and a minute or two of exercising the mechanism by hand and it now works perfectly. |
|
