SMC PENTAX-M 1:2.8 28mm version 1 disassembly.

A frequent problem with this lens is the slow aperture, even when no oil is on the aperture blades. So, here how I disassembled and cleaned this lens.

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Front

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remove the lens text ring.

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remove the front group.

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Detailed view with removed front group.

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The back, and the bayonet must be removed.

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Done.

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Also the next ring which controls the aperture setting must go, as well as the small part with screws acessable from the front.

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Remove the aperture ring, but don't let the small spring loaded ball fly through the room.

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Remove the next ring (3 screws).

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Remove the spring at the arrow, before it drops out unnoticed, and the aperture lever mechanism.

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This should come out.

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Now the aperture blade assembly can be removed, the red marked area should be free from grease and oil, if not, clean it !

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The aperture blade parts, and in this sample, the blades are clean from oil.

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But these parts are not free from oil/grease, so clean them !

Assembly.

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Put in the aperture blades.

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Then the first part.

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And the next ring (you will need patience, the positioning of the rings and blades is tricky), and fix them with the three screws.

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Then slide in, and fix this small part.

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And here it is mounted again.

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Mount the aperture pin mechanism with its spring.

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Make sure the inside looks like this again.

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Mount the small spring and the next rings, it probably won't stay put, but that can be fixed later .

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Here the next ring, with the three screws, is mounted .

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Make sure the aperture setting mechanism looks like this again.

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Time to put back the aperture ring, but do not forget the springloaded ball.

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And now the back only needs the bayonet part.

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Blow away any dust, before putting the front group back in.

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Lens text ring back in, and now the aperture is as snappy as it should be.