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05-01-2014, 12:58 PM   #1
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SMC-M 50mm f1.7 with focus ring that won't turn

I've had this lens since 1986, and it's always had buttery smooth focusing.

But this evening, I turned the focus ring to find it was getting stuck at about 8'. I can't get it any closer to infinity. It doesn't stop dead (with a metal to metal feel), but slows down pretty quickly.

Is this a common fault that I might be able to sort if I popped the 4 screws off on the back, or is it a case of sending it off for a service?

Cheers,
Graham

05-01-2014, 01:22 PM   #2
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Is the focus ring nice and round or has it perhaps been squashed? That can cause the focusing to have resistance and a stop
05-01-2014, 01:28 PM   #3
gma
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Thanks for the suggestion. It's perfectly round. The lens appears to be in tip top condition, and I have taken very good care of it.
05-01-2014, 01:33 PM   #4
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Just a guess . . . sounds like maybe there's some crud accumulation jamming up the focussing helicoil.

05-01-2014, 01:57 PM   #5
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Have you dropped the lens recently? I had butterfingers and dropped a 50/4 macro once. There was no obvious out-of-roundness, but the focus became very tight - I (gently!) squeezed the barrel in a vise and returned the focus smoothness to normal.
05-01-2014, 02:56 PM   #6
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Are you using a teleconverter? If not it may be gunked up in the back. Cleaning may cost more than a replacement, but I'm sure if you've had it for 28 years, there's some sentiment....
05-01-2014, 03:42 PM   #7
gma
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QuoteOriginally posted by manacho2005 Quote
Are you using a teleconverter? If not it may be gunked up in the back. Cleaning may cost more than a replacement, but I'm sure if you've had it for 28 years, there's some sentiment....
I think there was some crud. It hasn't been dropped recently, and I've not got a teleconverter. I've only ever really used it on a K1000.

I just put it face down on my desk and tried to undo one of the screws on the rear plate. I had to push quite hard, but it wouldn't budge.

Weirdly, pushing down on the back of the lens seems to have unblocked whatever it was! For now, at least. Thanks for the suggestions, but for the moment it seems to be back on form. :-)
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