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05-09-2011, 07:59 AM   #1
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PK-M 50/1.4 ring stuck, back-plate screws stuck

I have an almost mint PK-M 50/1.4 lens.
Suddenly and without hitting or dropping the lens the focus ring got stuck at the close end of the scale and I cannot focus past 0.5m or so.
The aperture ring also became clunky and there is a sound of something loose within the lens.
Following advice found on several threads here and in other forums I tried to open the back-plate to get access to the inside works of the lens, but alas! three of the five screws will not open (using a watchmaker Philips screwdriver), am I using the wrong screwdriver, are stuck screws a known issues in these old (>30 years) lenses? what can be done to save this great instrument?

Many thanks in advance.

05-09-2011, 09:33 AM   #2
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I'd send it to Eric Henderson for repair and CLA - Eric is well-known here as the expert for such things. His website is pentaxs dot com and he is also a member here.
05-09-2011, 11:00 AM   #3
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It sounds a lot like a problem I had with my M50mm f1.7. It was making noise like something was rattling inside and the focus got VERY hard to turn. Try tightening the inner ring where all the letting is near the front element. I used a pencil with an eraser on the end to tighten it. Other than that, it may need repair.
05-09-2011, 11:18 AM   #4
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QuoteOriginally posted by fungiman_md Quote
but alas! three of the five screws will not open (using a watchmaker Philips screwdriver), am I using the wrong screwdriver, are stuck screws a known issues in these old (>30 years) lenses? what can be done to save this great instrument?
The screws on Japanese lenses are not Phillips-head. They are JIS. Do not try to force the screw or you will strip the screw.

List of screw drives - Wikipedia, the free encyclopedia

You can buy a set of JIS drivers at micro-tools.com. You can also buy a lens ring to open the lens from the front.

05-10-2011, 12:54 AM   #5
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Many thanks - I hope I hadn't stripped the screws already.
I'll order a set of JIS screwdrivers, if it'll fail I'll send it to a local shop for repair (although Pentax specialists here are very rare).
I hope this great lens can be salvaged.
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