The K mount lens coupler holds the aperture open. It is closed by
default. I'm sure that theres a specification on the maximum travel
allowed and to work properly the lever in the camera body must travel
that distance.
Steve Jolly wrote:
Collin Brendemuehl wrote:
It doesn't make mechanical sense
If two 50mm (K & FA, for the sake of argument) lenses have the
indicator set to f "8" and f "2" is the same diameter, for the body
to close the mechanism down to f "8" would not the distance be
identical?
On the original K-mount, moving the stop-down coupler closed the
aperture until it reached a mechanical stop, set by turning the
aperture ring. You could continue to move the coupler beyond this
point but it had no further effect on the aperture. Hence the
relationship between absolute coupler position and lens aperture could
be undefined, because all the body had to do was move the coupler
through its full range to ensure that the lens was set to the correct
aperture.
With later K-mount versions (for A, F, FA and D-FA lenses), this mode
of aperture setting was maintained, but in addition, the aperture
could be controlled from the body by moving the mechanical stop out of
the way (by setting the lens to its smallest aperture) and only moving
the stop-down coupler part-way. In this scenario the relationship
between coupler position and lens aperture must be strictly defined,
since that's how the aperture is actually set.
FAJ and DA lenses lack the aperture ring and its mechanical stop
entirely and their aperture can only be controlled from the body.
Make sense?
S
--
A man's only as old as the woman he feels.
--Groucho Marx
