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07-11-2019, 02:17 PM - 1 Like   #1
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SMC 400 f5.6 technical advice

I got the above lens off fleabay and have only just noticed that when the mounting clamp is loose a glass ring inside rotates on its axis. Is this correct or have I bought a duff lens?

07-11-2019, 02:45 PM   #2
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For a start, I think we need the full lens name - Pentax have made various iterations from M, A and FA* 400 f5.6 - maybe even a Takumar -. I've got the FA* and that's an internal focus lens, so nothing rotatesthere, but I don't know about the others, or why they might be affected by the mounting clamp
07-11-2019, 02:47 PM   #3
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This lens? SMC Pentax 400mm F5.6 Reviews - K Prime Lenses - Pentax Lens Reviews & Lens Database
07-11-2019, 03:25 PM   #4
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That's the one. It looks like a glass filter rotating on its own axis. The clamp must tighten on keep it in place. Must admit it doesn't look right


Last edited by BrianCoup; 07-11-2019 at 03:28 PM. Reason: additional info
07-11-2019, 05:21 PM   #5
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QuoteOriginally posted by BrianCoup Quote
That's the one. It looks like a glass filter rotating on its own axis. The clamp must tighten on keep it in place. Must admit it doesn't look right
I’ve just inspected my copy of the K400/5.6. No elements move inside mine. Is it near the mount end or the front end? Can you post a photo?

Last edited by monochrome; 07-11-2019 at 08:06 PM.
07-19-2019, 03:17 PM   #6
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there is a baffle inside mine that came loose. I simply re-glued it.....REMOVE IT not re-glue it.

Last edited by Ronald Oakes; 08-12-2019 at 03:18 PM.
08-12-2019, 03:16 PM   #7
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These lenses are notorious for having a glued in internal baffle come loose inside the lens between the mount and rear element. Its just a thin shim shaped like a doughnut that is larger diameter than can easily be accessed from the rear mount tube/barrel. Originally it was glued from inside before the rear element was installed.....THERE IS NO WAY TO RE-GLUE IT !
You have two choices......leave it alone and the lens is useless and cannot be used.....OR.....reach inside , bend it , and pull it out of the rear with a pair of needle nosed pliers after removing the mount.
If You look for them you will occasionally find a copy with this issue from a Japan seller on E-Bay listed as PARTS ONLY/DEFECTIVE...…..I have had one do this but I traded a $25 brass tumbler for it and I cant see any difference between my 3 copies at all......I have less than $100 total to acquire all three of mine and two had this minor issue.
Its a good way to get one of these for cheap if you can find one.
I was going to post a link for one currently on Ebay but it was snatched up a couple days ago !
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