Home

Please support mflenses.com if you need any graphic related work order it from us, click on above banner to order!
SearchSearch MemberlistMemberlist RegisterRegister ProfileProfile Log in to check your private messagesLog in to check your private messages Log inLog in

Chinon 50/1.7 M42 mount, stuck helicoid, how to fix?
Post new topic   Reply to topic
Home   Equipment Care and Repairs
View previous topic :: View next topic  


PostPosted: Wed Mar 12, 2014 2:07 pm    Post subject: Chinon 50/1.7 M42 mount, stuck helicoid, how to fix? Reply with quote
Hello. I have almost mint M42 Chinon 50/1.7 on which focus distance adjustment is not working - the adjustment barrel rotates freely, but lens does not extend/collapse. Any dismantle/fix guides for this lens?


PostPosted: Wed Mar 12, 2014 10:19 pm    Post subject: Re: Chinon 50/1.7 M42 mount, stuck helicoid, how to fix? Reply with quote
CuriousOne wrote:
Hello. I have almost mint M42 Chinon 50/1.7 on which focus distance adjustment is not working - the adjustment barrel rotates freely, but lens does not extend/collapse. Any dismantle/fix guides for this lens?


Sorry unable to provide requested guide. Once you dismantle lens, however:

There are three things which spring quickly to mind that can cause a frozen helicoid. First there is dirt or grit. IMHO dirt is less likely to freeze the lens 100%. Second is corrosion owing to environment and/or galvanic action. Third is a situation where the helicoid was incorrectly assembled.

Since your lens is pristine, my guess would be the second cause. I'm facing a lens myself, with frozen helicoid owing I'm certain to galvanic action. The lens is dismantled. So far I've been chicken to execute the heat cycling I hope will free the helicoid. It's a brand new lens and I'm intimidated by the ease with which I could destroy it . . . . . . permanently. So I'll be following closely your own efforts to free up your Chinon. Good luck!


PostPosted: Wed Mar 12, 2014 10:41 pm    Post subject: Reply with quote
In all likelihood it does not have stuck helicoid, what happened is the screws that hold focusing ring in place got loose. You need to remove filter ring (I don't remember off hand how, but most likely by unscrewing the name plate and three screws under) then tighten the screws and reset infinity. Of course at that point you may very well find out that helicoid is indeed stuck.


PostPosted: Thu Mar 13, 2014 4:09 am    Post subject: Reply with quote
The camera was dropped, but luckily dropped on back, so no direct damage to lens, but inertia moment caused helicoid to stuck.

Regarding the dismantle process, I've unscrewed the front plastic besel - no screws under it. Even removed front glass assembly - again no screws under it. So no idea how to reach helicoid part. Technically, from rear side it might be possible, but this requires complete disassembly of aperture part, which works flawlessly now, and no guarantee that will work again after I touch it Smile


PostPosted: Thu Mar 13, 2014 2:09 pm    Post subject: Reply with quote
If there are no screws under the front plate then the front piece serves as one big retainer nut. Check if there any set screws first, then just grab it and unscrew. If it was dropped, and helicoids are indeed stuck, you may need to go from both sides - unless the glass comes out as a single block. Glass does need to come out because mechanical damage of this sort often means hammer time.


PostPosted: Thu Mar 13, 2014 2:45 pm    Post subject: Reply with quote
CuriousOne wrote:
The camera was dropped, but luckily dropped on back, so no direct damage to lens, but inertia moment caused helicoid to stuck.



Oh, my!! I didn't think of that one when I posted earlier. But helicoids are a precision fit, so clearly any deformation could lead to sticking.

Make no mistake, I hope you are able to get your helicoid operating once again. Your ability to do so will depend on the amount of deformation and your ability to reverse it. Good luck! I think you're gonna need it!


PostPosted: Thu Mar 13, 2014 7:27 pm    Post subject: Reply with quote
There's large ring screwed in below the front lens element, but since it is below lens assembly and also glued, I believe, it is for offseting the front lens element. There's no screws under the rubber ring, also, nothing in aperture control department, so as it seems, I need to completely remove the aperture control part, to reach the helicoid assembly.


PostPosted: Fri Mar 14, 2014 5:05 am    Post subject: Reply with quote
No! Don't take it apart element by element. In lenses like this glass is either split in two groups, and comes out in two blocks (that's the most common way), or comprises a single assembly that could be pulled out of focusing assembly in one piece, aperture and all.

PS. If you sell it for parts and buy a new one it will likely be at most $20-25 in replacement costs, may be much less.


PostPosted: Fri Mar 14, 2014 9:25 am    Post subject: Reply with quote
I'm going to use it as CCTV lens, so non-working helicoid is not a much problem, just I'd like to get things sorted out, for future knowledge.


PostPosted: Fri Apr 04, 2014 3:43 pm    Post subject: Reply with quote
Finally, took it apart. Needed to use lathe for this.

But now can't screw in helicoid parts Smile
Post new topic   Reply to topic
Home   Equipment Care and Repairs
Page 1 of 1