Ah, but there is more than one way to skin a cat. I hope that Rick
discovers that his problem with the (must be) 200/5 is that there is
some sticky linkage or spring problem or something simple that means no
total disassembly as you describe.
However, if it is a sticky diaphragm due to broken down and migrating
helical grease there is often a simpler solution. So that I don't sound
daft for suggesting it I should say that I have applied this simpler
solution on several lenses of my own with good success.
On some lenses it is possible to easily remove the rear lens group as a
complete assembly by simply unscrewing it. On others it may be
necessary to remove individual elements by unscrewing retaining rings.
(note carefully the front side of each element for reassembly). If you
find that you can do this you may also be able to reach and clean the
diaphragm of oil without any further disassembly.
The repair technique is to carefully flood the diaphragm blades with a
volatile solvent such as Ronsonol cigarette lighter fluid. Ronsonol (as
a brand) is recommended since it's pure naptha** and leaves no residue
of its own. It also has a convenient pour spout which makes it easy to
drip the fluid onto the diaphragm. Holding the lens at an angle (so as
not to drip fluid through onto the back of the front lens elements)
place a few drops at the edge of the diaphragm cage if the diaphragm is
stuck open or directly onto the blades if the diaphragm is stuck partly
or fully closed. Rotate the lens around its optical axis to distribute
the fluid. Try to activate the blades by repeatedly pressing the DoF
preview button. Probably nothing will happen at first but the fluid
will eventually evaporate after mixing with and diluting the oil.
During evaporation it also carries bits of the oil with it. Repeat the
fluid application and attempt to operate the diaphragm. You may have to
do this *many* times with waits for evaporation in between. But
eventually it will work and the diaphragm will start to move. Keep at
it until everything works smoothly with no drag.
Reassemble the lens and enjoy it. Understand that you have not cleaned
off any oil from the internal parts of the lens barrel. That means the
problem will eventually reoccur. But it might take several years for
that to happen. If it does, rinse and repeat. :-)
**naptha may mean something different in countries other then the US.
Chuck Norcutt
On 11/29/2014 4:35 PM, Moose wrote:
On 11/29/2014 9:20 AM, Rick Beckrich wrote:
Help!
All this 180/200 conversation just reminded me that I have an OMZ
200/4.5
languishing with a non-working diaphragm (stuck wide open).
Any simple cure?
Depends where the problem is. First thing is to take off the mount. The
aperture stop down mechanism there has the auto mechanism tab from the
camera and manual button activating a spring loaded ring with a long
finger that reaches down into the innards to link with the actual
aperture mechanism. Various things may go wrong there, sticky ring,
activation 'finger' jumped out of linkage with aperture, spring jumped
of its anchors, broken pivot post, etc. Most of those may be pretty
easily repaired/reset.
I have successfully repaired several such problems on both Oly and other
brand lenses.
OTOH, if the problem is oil on the aperture blades, one must disassemble
to the point of taking the aperture mechanism out and thoroughly
cleaning it with a solvent to dissolve the grease/oil.
I have cleaned out a very few sticky and/or gritty apertures in 50 mm OM
lenses. Sometimes, it comes back. As I recall from now ancient posts,
the problem is thought to be focusing helical grease that breaks down
with age and an oily component that migrates about. The only sure cure
is then complete dis-assembly, cleaning of all oil/grease, then
re-greasing. Not worth the trouble for any but exotic lenses, I'm afraid.
But if one LIKES taking things apart ...
Tinkerer Moose
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