> >I'd be interested in hearing from anyone who had
>>delved into such things or knows of access to parts.
>
> If you get in too deep, I'll give you the contact details for my
> Father, who lives in Wellington. He made his living repairing 
> cameras.
> He is  retired now, but will probably still have contacts for spares 
> etc in NZ.

Thanks.
I'll keep that offer in mind!

This is not an economic task by any standard ;-)
But for several reasons I want to make it work.
I wont spend 'forever' on it but if I can get my labour rate
equivalent value over $10/hr (or 5 ? ) and fix it I'll be happy
enough.

I've contacted Sigma locally but so far haven't found anyone who
answers a phone who can tell me anything, or anyone who knows anything
who will answer, nor anyone who will return generic email, nor anyone 
whose
personal email address I know who hasn't left the company a year ago.
Maybe tomorrow :-)

Lens problem is clear and very possibly repairable as is, but parts
would be much better. It's built in the area that matters like a "Made
in Japan" toy of 40 years ago. ie adequately to meet the target market
after a fashion but most unlikely to last long enough with any sort of 
vigorous treatment. There is a large plastic ring gear on the inner
diameter of the focus ring. This is acted on by a small brass gear
which is on the end of a 15mm odd long axle. The axle runs in a 
plastic
tube on the surface of a ring that the focus ring rotates within. The
end of the tunnel where the gear resides has had its roof broken away
when the gear tried to lift radially inwards and succeeded.
Lifting may have been caused by something falling into large gear 
track (should be v clean in there) or perhaps from a broken tooth part 
starting things off. A person manually over-riding the focus or an 
external shock could have started the damage. The specific damage is 
listed on the net by lens repairers so this isn't a one off.

As a result of the bearing damage the gear has some positional slop 
both circumferentially and
inner-radially. It has chewed out the track on the focus ring at one
end of its travel and has badly compressed and worried the plastic
gear through the rest of its length. On first inspection I thought the
gear was stripped throughout but after very magnified inspection I see
that the gear teeth have largely grown into the space between the
gears making it hard for the metal gear to run nicely. I have largely
cleaned this up - main tool = vvv small jewellers screwdriver used as
a chisel. I can PROBABLY rebuild the missing tooth using epoxy with
some sort of powdered metal filler for 'strength'. I can PROBABLY
repair the broken tunnel-roof/bearing by filing a shaft sized slot in
a metal band (= thick piece of wire?)(copper/stainless/brass/nichrome/ 
... ? ) and then epoxying this in place
as a bearing. All this will take little time or forever :-). It may 
quite well work.

Another approach to the gear damage is to rotate the focus ring gear 
by a part turn and
remount the metal fork thingy that is screwed to it. This would need a
new mounting extrusion on the barrel surface at the appropriate point
as the original gets thicker at the right point. This has to be
somewhat right as the fork thingy serves all sorts of tasks :-). Stop
for focus ring, mounts for  4 contact gray-code wipers, drives focus 
lever
into lens proper. The end stop is not a trivial application either -
go too far and the encoder fingers die instantly.

I bent one encoder dual-finger vvvvvvvv badly b4 i knew they existed. 
it
was remarkably resilient and responded to micro-surgery amazingly
well. Tweezers and same screwdriver blade and heaps of magnification
are main tools.

So, lots of fun. This, of course, in my 'spare' time :-(.

There are some nice new later versions of this on ebay .... :-)

FWIW there are several generations of the Sigma 28-200 zoom. They seem 
to have filter ring sizes of 68mm, 72mm, 62mm in order of arrival. 
I've got the 72mm. From reviews it seems that some people may be 
happier with it optically than the newer version?

This exercise has already taught me things about camera systems which 
I (, if not my wife,) feel to be well worth what I paid for the camera 
& lens combined. ($NZ95 = ~~ $US60ish). Now, making it work reliably 
enough to give me, say, 1 years trouble free service, is of more 
account than the $ spent.




        RM

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