Service for Tokina RMC iris

Stuck iris can now be released without taking the whole lens apart.

Image above shows a preowned Tokina RMC 28 f2.8 budget wide angle lens with M42 thread mount. This lens arrived from auction site with iris stuck wide open - common problem for a common and otherwise useful wide angle.

Usually iris stops responding when enough oil has been accumulated on the iris blades. Taking the lens apart and cleaning the iris blades can be a time consuming job. Because stuck iris is a common problem for second hand Tokina RMC lenses it was necessary to try to find a solution.

Luckily the back of the lens opens rather easily and exposes the iris blades from behind. After some testing it was found that rubbing the iris blades first with kerosene removed much of the grease that had found its way to the wrong location. Even when the blades looked rather clean, they were still sticky and felt as if they were never going to move effortlessly as they should. After final rubbing of the blades was done with xylene normal feel and operation of the iris was restored. The operation is somewhat tricky because no liquid should drop inside the lens from the iris blades while they are worked on.

Oily aperture blades is not the only iris related problem on Tokina RMC 28 f2.8. Part of the problem is tension on the iris motivator spring that has weakened over years and decades. However, slightly slow iris movement is not a problem when the lens is adapted with an adapter and the iris is not coupled with camera body.

If the lens stops down from the iris ring when adapted, all is well and the Tokina is ready to take pictures.

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