Lama, I've never had a lens as bad as you describe, although it is
clearly what can eventually happen with oily blades if the also get dirty.
Before that, slow blades can have an opposite effect of giving
underexposure. When not yet stuck, the stop down mechanism is easily
able to stop the lens down quickly enough, but the blades are slow to
return to open, as this action is only driven by a modest spring. In its
early stages, this may cause no problem at all unless using a winder,
MD, or winding and firing quickly and changing aperture significantly
between shots, as the aperture does finally open up. Eventually, the
opening delay can become minutes, hours, days...forever.
By far the most common problem with Zuikos is the 50/1.8 MC lens. I have
acquired several such as body caps with various bodies and most have at
least slightly slow diaphrams. The problem also can occur with the later
'miJ' version, but it is less common (perhaps only relatively early
examples, as that's all I have.). Cleaning out the oil in 50/1.8s is
fairly easy for anyone reasonablly adept and with tools to work on small
mechanisms. However, since the problem is deterioration of the helicoid
grease so that a low viscosity component can migrate about in the lens,
a long term solution requires replacing the helicoid grease as well.
Moose
Lama-Jim L'Hommedieu wrote:
Tim,
Oily blades eventually cause unpredictable overexposure. Over time, the oil
picks up dust which makes the blades slow to respond.
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