[ismaelg]

Hello,

My F50 f1.7 is my favorite and most used lens. I just love it. Recently, at an event I was shooting with it as usual. Typical of the theater dance performances I shoot, I was using K5II in TAv mode: 1/200s f3.2 ISO range 100-8000 when all of a sudden the viewfinder began to darken. After a few shots I noticed the ISO warning blinking at 8000 indicating not enough light. Something was wrong. I remember this happening once a few years ago using my K20 and the problem disappeared on its own with no explanation. I fiddled a bit with the lens dismounting and mounting again, reset the camera, power cycled it to no avail. I quickly switched to the DA35 f2.4 and continued. During a break, I mounted the 50 again but this time in the backup K-x. Same issue. So it is in the lens, not the body.
Back home, I took a detailed look and found the blades were opening very slowly after a shot. As if they were sticky. But that doesn't explain why the viewfinder would go dark as if the blades were closing on their own, fooling the meter. The lever looks fine. not bent or anything.
But, the next day, it was working like a champ. I took over a hundred test shots in rapid sequence and could not duplicate the problem.
Has anybody seen this? What can be causing this? Does Eric service these early AF lenses? Any ideas?

Thanks,

[Not a Number]

Oil or grease on the iris blades or linkages could make the movement "sticky". The viscosity of the oil/grease would change with temperature and could account for some of the erratic behavior. The springs could also have weakened with age.

The only way to find out if Eric would work on this lens would be to ask him.