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11-08-2009, 04:49 AM   #1
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stu49's Avatar

Join Date: Oct 2009
Location: Norfolk, England
Posts: 19
M50f1.7 dismantle ??

The above lens has fungus and a sticking iris. Can I dismantle this from the back only, or do I need a lens spanner to get into the front ?

Any help appreciated

11-08-2009, 12:58 PM   #2
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Join Date: Oct 2009
Posts: 283
I've dealt with one of these that had dust inside and wasn't properly reassembled.

Assuming the fungus isn't inside the sealed groups of elements then it's easiest to go in through the front. There are no small parts to lose or components that need to be set up during reassembly. Simply unscrew the finishing ring (the bit that has "Pentax M 50mm 1:1.7" on) then unscrew the front element group - they're screwed into the filter threads and undo just as a filter would.

I'm not sure about the sticking iris. It really depends on where the problem lies - with the iris blades themselves or the mechanism that stops them down.

Last edited by Dangermouse; 11-08-2009 at 01:03 PM. Reason: Re-read original post and added detail
11-08-2009, 05:11 PM   #3
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Join Date: Dec 2008
Location: Brisbane
Posts: 58
Hey Stu,

as Dangermouse has said you can open the lens from the front by unscrewing the ring with the writing on. I got one of these from a local rubber supply store that makes turning that ring real easy. See this post in this thread.

I've cleaned my M50 f1.7 a while ago so I can't remember if I only opened it from the front or from the back as well. I actually had the whole apperture assembly fall out whilst I was doing this which freaked me out at first but I was able to work out how it all went back together easy enough.

Just make sure your working on a nice big clean well lit space so you don't loose any of the little screws from the inside. You should be able to find some more info here about cleaning the iris'.

They are pretty simple and relatively easy to work on though. Good Luck!

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