Thanks, that finally explains for me the normally open vs. normally
closed lens designs. Never had a Nikon and never had a working Pentax.
> Chuck Norcutt wrote:
>> I agree with your reasoning regarding the mirror but I would have
>> expected a solenoid actuation in an electronic camera. And, regardless
>> of how it's implemented Nikon and Pentax were both able to do it.
> I don't know about Pentax, other than the screw mount ones with the push
> pin. The Nikon diaphragm design uses a spring in the lens to close the
> diaphragm - just the opposite of OM. When the lens is mounted, the
> aperture lever on the body pushes the diaphragm open.
> Thus the auto aperture mechanism in the body only needs to yield to the
> spring in the lens to close the diaphragm as part of the exposure. The
> "power" stroke against the spring on a Nikon body occurs in reopening
> the diaphragm after the shot, when a bit of radial vibration doesn't
> The design difference, the fact that the high end mechanical bodies (at
> least the F2) have a mechanism to both lock up the mirror and stop down
> the diaphragm and the greater sheer mass of the bodies made them
> superior to the OM-1 and 2 bodies in that respect. Didn't stop me from
> switching. :-)
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