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Forum: Pentax SLR Lens Discussion
01-30-2017, 09:25 PM
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This is an older lens that I used for some time on my MZ5 film camera. Later it was used on my ist DS, and more recently on my K30. Up until a few weeks ago, it had been operating perfectly, then suddenly all shots were over exposed, almost to the point of white-out. A check on the lens itself showed that the small lever near the rear element that controls the aperture, was locked up solid.
I removed the four screws that hold the metal mount in place, then carefully removed the mount. This has to be jiggled a bit to disengage it from the aperture mechanism. The aperture ring must be held down in place, otherwise it is easy to lose the tiny indent ball, spring and operating button.
The offending part was the small lever and its pivot ( see red arrow ) that had seized up due to some corrosion. A tiny drop of penetrating fluid was applied to the pivot with a small screw driver, and then the little arm worked back and forward until it loosened up. This small arm is normally operated by a cam effect on the plastic aperture ring, but had seized in the wide open position, hence the over exposure.
A couple of things to keep an eye on are the tiny compression spring indicated by the yellow arrow, and the aperture ring release button indicated by the green arrow.
The screws holding the mount in place actually screw into plastic, so should be done up firmly without overtightening, which would strip the plastic female thread.
All good now, so I hope that I get a few more years out of this lens.
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