I have two om lens 50/1.8 and 50/1.4 both lenses' aperture sluggish to return to full open aperture. how to repair it? strong spring? or lubricate or no lubrication? I clean the contact metal still sluggish to return to open. any suggestion? Dan

The problem is oil that has gotten into the diaphragm system from the focus helicals.  What you need to do is disassemble the lens and clean the oil off of the blades and operating linkage.  DO NOT lubricate, that is where the problem comes from in the

The aperture is dry no oil on them, do you think I should remove the optical system and flush wash the diaphragm? I have clean the operting linkage. it seems the fraction is high, if I only move the diaghragm, it has only little resistance and move

All that means is that there's no oil on the blades where you can see it.  It can still be there, both on the blades around the outer pivot area where you can't see it, and on the operating ring and linkage.  When I've opened these (and other) l

I bought your CD around 2005, I not not sure it includs these lense,  I will check it tonight