Don Holbrook wrote:
> Long time, quiet (till now), digest reader. Have a 24-48/3.8 lens that the
> diaphragm will not stop down. f-stop ring & rear tab move ok, stopdown
> button moves rear tab ok Assume either stuck or linkage problem. Can anyone
> point out what to look for if I pull the center ring off the rear mount that
> the tabs come thru, or lead me to a parts diagram that will show the linkage.
> Thanks in advance. Off-list OK.
>
I don't know specifically about this lens, but there are a lot of
similarities in those of various brands that I've had apart. Since the
lens elements move as it is focused and/or zoomed, the mechanism that
stops it down is generally some sort of long metal thingie that sticks
deep down into the lens from the aperture stop down ring on the back and
engages with some sort of tab on the diaphragm mechanism. Sometimes it
is like a two pronged fork that engages the tab, sometimes ust a lever
that pushes against the tab from one side.
I've dealt with a few lenses where this mechanism has come uncoupled,
with the lever/fork slipping off/past the tab. Usually, well, every time
so far, it has been possible to get it right easily. Not a bad idea to
see if it needs a small amount of judicious bending towards the center
so it will stay on in the future. The mechanism that controls the tab
that conveys aperture setting to the camera body is similar, but so far
always a fork, since it must positively locate the tab against pressure
in both directions.
Take a close look at how the ring assembly is assembled before pulling
out. You need to be able to get all the bits in the right places with
the connections down into the lens body connected correctly all at once.
On some lenses, it's easy, others are more challenging, easier perhaps
with more hands. :-)
Moose
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