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06-17-2011, 10:05 PM   #1
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Cosina 55mm f1.2 repair guidance

Bit of a disappointing day. My Cosina 55mm f1.2 has a problem.

The focus ring has started spinning freely, doesn't change focus. Something has obviously let go. I pulled back the rubber grip ring to get at the only screw I can find....and that screw is in place and tight....not the issue. Stop down metering still works fine, so doesn't appear to be any further internal failures.

Anyone experience a similar failure and know the fix? Worse case, I'll reach out to Eric, and see if he's willing to look at it. Might not be Pentax glass, but I'm sure a man of his skills can fix it up.

Thanks.

06-17-2011, 10:59 PM - 1 Like   #2
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I don't have experience with that exact lens but on many other lenses you have to unscrew the name ring around the front element to get to the screws that hold the focus ring. You need some kind of rubber tool to turn the ring. It can be a large o-ring or anything with good friction surface.

Also on some lenses the whole front end with the filter thread unscrews and there might be tiny setscrew(s) around the barrel which you have to loosen first to get it moving.

After you've removed the name ring or the whole filter thread barrel you most likely will see three screws around the front element. Tightening these will attach the focus ring to the focus helicoid again. But if you just tighten the screws you will most likely lose infinity focus so you must adust the infinity. So keep the screws loose a bit longer.

Attach the lens (partly dismantled) to your camera and find a scene where you need infinity focus. Now turn the actual focus barrel under the focus ring until the lens is properly focused. You can rotate the focus barrel from the aforementioned screws by putting a screwdriver to a screwhead and dont turn the screw but revolve the screw around the front element (this is the same thing as turning the focus ring). If you cant reach infinity you have to turn the loose focus ring back a bit to allow the focus barrel to move more.

After you've found the infinity focus line up the infinity mark on the focus ring with the index and tighten the focus ring screws and test. You should have a working focus ring all the way to infinity.

After that just screw the name ring/fliter thread barrel back on and tighten possible set screws and you're done.

Hope this makes sense and helps
06-19-2011, 11:25 AM   #3
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Appreciate the reply Ovim. I'll give it a go!

I need to track down something proper to get that front ring off. Tried a few things, but no dice. Will see if I can find a rubber cap or o-ring at the local hardware store. Until then, my 50mm f1.4 will have to suffice.

Cheers.
06-21-2011, 10:28 AM   #4
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Hi WiseOx,
I did send my Cosina 55/1.2 to Eric for C/L/A, about a year or two ago. He did say that he mostly works on Pentax lenses but he had a go at it, and did his usual fine job! Might save you some headaches instead of disassembling it yourself. Good luck!

06-21-2011, 11:02 AM   #5
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Good to know! Thanks NeverSatisfied.
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