Question about RF cam on 90/2 Apo Asph Summicron

[awilder]

Has anyone that owns this lens ever carefully examine the surface of the RF cam that contacts the camera's steel roller? On my sample it appears to be treated with a thin layer of black paint (?) consistant with other nearby metal portions designed to deaden reflection. With use and rubbing by the cam roller, a small portion of this treatment has flaked off leaving exposed an underlying flat section of precision machined brass. Because the thickness of this flaked off portion is now missing, it has a small effect on RF focus. Dave Elwell at Leica confirmed that the cam surface on a new 90/2 Apo Asph also appears to be black attributing it to "anodization". If it's the same as mine, why would Leica apply anything to this small critical surface that is constantly at risk for rubbing and wear? Previous lenses have used a flat polished brass surface as far back as I can remember. Any ideas?

 

[jaapv]

Bur the effect will be extremly small, well within machining tolerances. A thickness of the anodizing 0.05 mm on a sloped surface makes less than 0.01 mm difference on the movement of the roller. It is impossible that this will have any effect on focussing. The wear over the years on the soft brass of cam is certain to be a lot more.

 

[paulh]

Just checked mine. Its black all over. Maybe I havent used it enough.

 

[awilder]

The change in focus translates to under 1mm of focus ring rotation. The thickness of the black surface treatment appears to be on the order of maybe 0.02 or 0.03 mm.