From the chemical breakdown of the lubrication grease of the focusing
helicoid and maybe the zoom mechanism. It's supposed to be about the
viscosity of wheel bearing grease but as it ages some greases (like
those used in some lenses of the 70's and 80's) break down such that the
viscosity is that of a thick oil. It then starts creeping and flowing
within the lens and eventually reaches the diaphragm blades which are
supposed to be totally dry. The blades then stick to each other and get
sluggish or get stuck altogether and just won't move. The can be stuck
partially open or fully open or closed. I don't know if there is any
lens that's completely immune but many of the Kirons I have owned
suffered from it. I've not had a Zuiko that shows the malady but some
do exhibit it. Another give away (maybe it hasn't reached the blades
yet) is that the focusing ring and zoom mechanisms may exhibit creep
from too little damping. The thick grease has turned to thick oil and
no longer has the same motion damping ability.
The correct solution is complete disassembly, cleaning and relube with
an appropriate grease. Expensive. Sometimes the diaphragm alone can be
cleaned by opening just one end of the lens and doing repeated flooding
and evaporation of a solvent like Ronsonol lighter fluid. But that's
ultimately only a temporary fix and doesn't solve the focusing and zoom
mechanisms damping problem.
This discussion of the 300/4.5 had to do with too much thread lock
cement placed on the name ring that serves as a retainer for the front
element. In order to service the lens for a sticky diaphragm the lens
needs to be disassembled and cleaned. But with too much glue on the
threads of the name ring it can't be disassembled without destroying the
name ring. And there are no more of those parts available. If you buy
one that already exhibits the problem you are (literally) "stuck".
Chuck Norcutt
Nicolas Mitchell wrote:
>
>> oil buildup
>
> Where does the oil come from?
> Curious,
> Nic
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