Many thanks, that was jolly interesting.
N
On 5 Jun 2009, at 15:16, Chuck Norcutt wrote:
> 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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