The fact that it moves freely and feels right doesn't matter. On an OM
mount lens there is no physical link between aperture lever and
diaphragm except for pushing the aperture back open. On stop down the
lever just gets out of the way to allow the blades to close and a very
weak little spring pulls the blades closed.
When you activate the stop down lever you're still feeling normal spring
tension for the stop down lever itself... whether the diaphragm follows
along behind or not.
The simplest analogy I can draw is of a pinball machine with it spring
loaded ball release and the ball. In the analogy the spring loaded ball
release is the stop down lever inside the lens. The ball is the
diaphragm and gravity in combination with the slope of the table is the
lightweight diaphragm spring. When you pull back the ball release you
expect the ball to follow along behind due to gravity. If it doesn't
maybe there's some sticky substance under the ball preventing free
movement. That's oil on the blades.
Chuck Norcutt
Tom Fenwick wrote:
> I don't think that's what it is - everything moves freely, the spring
> tension feels right etc, but the iris just doesn't stop down! It was
> working fine last time I tried it, about a month ago...
>
> Tom
>
> On 28/02/07, Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx> wrote:
>> What's the probability that this thing has oil on the blades and is
>> stuck wide open?
>>
>> Chuck Norcutt
>>
>> Tom Fenwick wrote:
>>> Hi,
>>>
>>> I've got a 24/2.8 which has stopped stopping down.
>>>
>>> I've removed the easy part of the back of the mount, and everything in
>>> that section is working ok; ie the lever on the main part of the lens
>>> is being operated but it's not doing anything.
>>>
>>> I guess something has come unhooked.
>>>
>>> Is it likely to be something I can get at and re-hook fairly easily?
>>>
>>> Thanks,
>>>
>>> Tom
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