> If your lens resembles this:
>
> http://www.epinions.com/Sigma_AF_28_200mm_f_3_5_5_6_DL_Aspherical_Hyperzoom_Macro_for_Canon_EOS__Camera_Lenses_787101
>
> then it is likely not worth fixing, except as a hobby/learning 
> process. Getting
> parts will be interesting, usually one special orders the parts from 
> the after
> market service unit of the manufacturer. Many times this can only be 
> done when
> one has a special relationship with said unit (as in, approved 
> service lab, a
> status usually achieved after at least one tech takes a course with 
> the
> manufacturer).

The more I know the less I know - as always.
It appears that there has been a whole line of Sigma 28-200mm lenses.
Mine isn't the above one and isn't the latest one and ...

The lens AFTER the above DL is well spoken of here

        http://shutterbug.com/equipmentreviews/lenses/0103sb_sigma/

and variably so elsewhere.

An approximate lineage seems to be

f/3.8-5.6    68?mm filter
f/3.5-5.6    72mm filter
"                    DL Hyperzoom 67mm filter
"                    Compact Hyperzoom 67mm filter
"                    DG ... 62mm filter

It may be that some are not available for all brands of cameras, 
although this seems unlikely.
Once they get to "digital" lenses with cameras with 'different crop 
factors' then they may decide to build lenses that only suit some 
cameras, but at full frame 35mm all should be compatible.


The Sigma agents here were very cooperative once I managed to contact 
them.
I can get a complete autofocus outer shell for about $US70 - albeit in 
grey wheras mine is black :-(.

Re your later comment on back-focusing problems. Reports on nominally 
identical lenses vary vastly. This seems to depend on specific lens, 
camera model, specific camera, user experience, user expectations and 
more. Having lenses which appear to be the same model but aren't 9as 
above) adds to the joy. What I do know is that the lens I bought 
focuses as well as anything else I've got on my 7D and produces photos 
which are I consider to be very acceptable for a cheap 28-300mm lens.



        RM 

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