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Waynemel
Tinkerer
Username: Waynemel
Post Number: 11
Registered: 08-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, January 15, 2011 - 03:25 pm: | 
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I am working on a 124G and the last problem I have to fix is with the focus. When focussing from infinity, the lens assembly begins to move unevenly. That is, the side closest to the focus knob begins moving before the other side. This occurs for about the first 10 degrees of rotation of the knob, at which point both sides move in unison.
Has anyone seen this before? I suspect that either one side is moving too easily, or the other is sticking. When the lens board retracts, it does so evenly, all the way back to infinity. What do I look for to correct this? |
Mareklew
Tinkerer
Username: Mareklew
Post Number: 221
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 16, 2011 - 09:13 am: |
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Bad news: this calls for a major stripdown...
On the axle of the focusing knob there are four snail-shell shaped cams. On each side there's one 'unwinding' forward and one 'unwinding' backwards. The one going forward pushes the lens plate forward when you turn the focusing knob from infinity towards close-up. The cam unwinding 'backwards' is pushing the lens plate back when you focus from close-up to infinity. The whole assembly can only work well if there is absolutely no slack. To take up the slack there are two springs installed. The cams pushing the lens plate out act directly on a cam surface attached to said plate. The cams going backwards press on piston-like elements that are spring-loaded and attached to the same cam linked to front plate. Obviously, the spring tension has to be greater than friction in the mechanics or you will be pushing springs around without moving the lens plate.
As the whole mechanism is lubricated with thick organic grease, you guess it, it jams when the grease thickens. Clean-up and adjustments of the springs is necessary (it can also be, that one spring got dislocated and you have now slack on one side). Either way, you have to take both side walls off, get the whole winding-counter mechanism off and strip the focusing down.
WATCH OUT: the axle goes through, across the whole camera, but it is not sleeved on the whole length! The center part is free and open under the viewing mirror! If you thought about packing the axle sleeve with fresh grease, this means you will pack the mirror box full :D Also, this means you have to be careful about flushing old grease out.
Good luck!
Marek |
Waynemel
Tinkerer
Username: Waynemel
Post Number: 13
Registered: 08-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, January 16, 2011 - 09:18 am: |
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Why is it never easy?
Well, it will be a learning experience and since I already have a working 124g, there is no pressure. Thanks for the information.
I will add to the post if I run into anything else. |
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