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05-07-2017, 03:23 PM   #1
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K mount Adapter won't lock with Pentax FA 80-200

Hi,

I recently received a K-mount adapter (New PK-M4/3 Adapter Ring for Pentax PK/K Lens To Micro 4/3 Olympus Panasonic M43 | eBay) and it works with most of my Pentax and K-mount lenses, except for a Pentax FA 80-200mm lens. That lens will not lock onto the mount.

I was looking at the lens, which has a plastic mount, and there is a small hole for the locking, so I'm not quite sure why this is a problem. Is this a known problem with this lens, or with FA mount in general?

Is there a way to get it to work? I've ordered another, different adapter to try, but it'll be awhile before it gets here.

Thanks,
Jim

EDIT: Here are pictures of the lens mount and the adapter:

This is the mound end of the Pentax lens. The hole where the locking pin is supposed to fall into is circled in red:




This is the adapter mount end. The locking pin is circled in red:




Last edited by ohaya; 05-07-2017 at 04:18 PM. Reason: Add pictures
05-07-2017, 08:44 PM   #2
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I suspect the issue is the adapter was not built to Pentax specifications; I'm not sure that Pentax publishes that type of information for third-party equipment manufacturers. And the manufacturer probably didn't try it with all Pentax lenses.
05-07-2017, 10:53 PM   #3
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I've taking a more detailed look at the adapter, and I have a guess about what might be wrong.

When I try to mount the lens and turn it, at one point, I can see that silver knob move, very slightly. I think that is when the lock pin on the mount is entering the lock hole on the lens mount.

But then I can keep on turning the lens and I can see the know move slightly again.

I think that what is happening at that point is that the lock pin is coming out of the hole.

Looking at the pin more closely, the way that it is designed is that at the tip, it is slightly tapered, so I think that what is happening is that the pin is entering the hole on the lens mount (the tapered part of the pin), but the diameter of the body of the pin is (I am guessing) too large, so the pin cannot enter the hole completely.

Either that, or the tapered area of the pin is too long (i.e., it should be a smaller taper), so no non-tapered part of the pin "catches" on the hole, so it doesn't lock the lens.

---------- Post added 05-07-17 at 11:18 PM ----------

QuoteOriginally posted by ohaya Quote
I've taking a more detailed look at the adapter, and I have a guess about what might be wrong.

When I try to mount the lens and turn it, at one point, I can see that silver knob move, very slightly. I think that is when the lock pin on the mount is entering the lock hole on the lens mount.

But then I can keep on turning the lens and I can see the know move slightly again.

I think that what is happening at that point is that the lock pin is coming out of the hole.

Looking at the pin more closely, the way that it is designed is that at the tip, it is slightly tapered, so I think that what is happening is that the pin is entering the hole on the lens mount (the tapered part of the pin), but the diameter of the body of the pin is (I am guessing) too large, so the pin cannot enter the hole completely.

Either that, or the tapered area of the pin is too long (i.e., it should be a smaller taper), so no non-tapered part of the pin "catches" on the hole, so it doesn't lock the lens.

I just found I had another brand adapter, a Fotodiox, and I tried it with the same lens and it locks perfectly.

I checked the lock pin on the Fotodiox adapter and it is NOT tapered, so I think that that (the tapering) is the problem with the other adapter I have.
05-07-2017, 11:23 PM   #4
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QuoteOriginally posted by ohaya Quote
When I try to mount the lens and turn it, at one point, I can see that silver knob move, very slightly. I think that is when the lock pin on the mount is entering the lock hole on the lens mount.

But then I can keep on turning the lens and I can see the know move slightly again.

I think that what is happening at that point is that the lock pin is coming out of the hole.
...
I just found I had another brand adapter, a Fotodiox, and I tried it with the same lens and it locks perfectly.

I checked the lock pin on the Fotodiox adapter and it is NOT tapered, so I think that that (the tapering) is the problem with the other adapter I have.
Yes, I think you found the problem. Looking at the original adapter, it doesn't seem like that tapered pin comes far enough out of its hole. Also, I'd be wary of using it with a plastic mount lens, as it's likely to cause wear around the edges of the lens' locking-pin hole.

Glad to hear the Fotodiox adapter works OK

05-07-2017, 11:39 PM   #5
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QuoteOriginally posted by leekil Quote
And the manufacturer probably didn't try it with all Pentax lenses.
Since allegedly there are some 20 million Pentax lenses out there testing them all is a bit out of the question.

The tolerances are off either in the bayonet - preventing the lens from rotating far enough or the placement of the pin. The tolerances on the lens side can be off too. Add the errors together and the parts don't mesh.

If jiggling the lens doesn't get it to lock replace the adapter.

I have two Minolta to K-mount (glassless) adapters. With one adapter and one lens in particular I have to hold in lens release to get the tab to clear and lock. The same lens on the other adapter will clear the lock tab without having to hold it in the release position.
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