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04-28-2020, 03:02 AM   #1
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Pentax FA 50mm f1.4 autofocus stuck, stiff mf

Hello,

About a year ago I bought used FA 1.4 50mm. It was working fine but suddenly it focus ring started to have some difficulties on turning and AF stopped responding on my K-r and Z1-p. I had left it in car for a while I am assuming that caused grease become sticky.

I tried to disassemble the lens to figure it out. First I unscrewed the front cover and focus helicoids was exposed. Tried to clean a bit with cotton pad but didnt help. Then I placed front cover back and dismantled the back cover. That part was a bit harder to reassemble because of the contact pins and spring. And when I got it together I left a very small ball bearing out I guess that was for aperture ring indents, now aperture ring is continuous. Any way when I exposed AF motor I saw some yellow grease around gears and not inside gears. I rubbed that grease with a small tweezer to the AF gears and when I turned focus ring it moved much more easily. When put everything back together it became sticky again. So I assume if I grease helicoids and AF gears it will work well.

My questions are:
- What kind of grease should I use? Same grease is ok for both AF gears and helicoid? (tamiya Cera-Grease HG I can buy this for instance)
- At home I have some neatsfoot oil that I got from whippeddog.com. This oil is for razor stropping leather care. Can it bu used for lens? Other than that I have WD40 and olive oil.
- What should I do with aperture ball bearing? I dont know where it came from so I dont know how to put back.


Last edited by onurz; 04-28-2020 at 04:34 AM. Reason: additional info.
04-28-2020, 09:46 PM   #2
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The ball bearing is usually trapped between the aperture ring and the lens body. The lens body will have some kind of spring putting outward pressure on it to push it against the inner surface of the aperture ring. That inner surface will have sawtooth-like indentations, usually irregularly spaced. Those make the click as you turn the ring. You can find the place where the bearing should go by noting the sawtooth location and looking on the lens body for a bearing-sized hole. There might be a brass-colored spring in the hole. If the aperture ring action is still kind of lame when you replace the bearing, the spring is missing.

Whatever grease you use should be minimal, really light and stable under temperature. The AF system isn't designed for a lot of drag. The grease shouldn't evaporate at high temperatures because it will migrate to lens surfaces and aperture blades.
04-29-2020, 01:45 PM   #3
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QuoteOriginally posted by Just1MoreDave Quote
Whatever grease you use should be minimal, really light and stable under temperature. The AF system isn't designed for a lot of drag. The grease shouldn't evaporate at high temperatures because it will migrate to lens surfaces and aperture blades.
Concerning these parameters tamiya Cera-Grease HG would be a safe choice, I presume.
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