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 ----------
Originally posted by ohaya 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.