Sigma 18-250 autofocus problems

Started 4 months ago | Discussions
Mike WW New Member • Posts: 14
Sigma 18-250 autofocus problems

I've got a Sigma DC 18-250 on a Nikon 3300.  A couple of years ago, before the pandemic, it had started to get balky about focusing.  If I gave the focus ring a little nudge it would snap into focus.  Seemed like it was getting better with the little use it's had since then.  But on vacation last week I got a blast of wind, somewhat dusty in the desert of Utah, and it stopped autofocusing.  It also has a gritty feel if I manual focus it, suggesting some grit got in between the focus ring and the barrel.

So... is there anything I can do, vacuum, try to squirt some alcohol up there while it's pointed down to try to flush it out?  Canned air like one would use on a computer?  Or is sending it in to Sigma or elsewhere the only solution?

What's even more troubling to me is I somewhat regularly go to places like that and I'd really be unhappy if I spent good money for repairs and had it happen again.  Or is it just the cost of doing business and a common problem with all or many lens makes?

OP Mike WW New Member • Posts: 14
Re: Sigma 18-250 autofocus problems

A follow up since it would appear nobody knows.

I bought a syringe off Amazon, non medical, but small and 99% rubbing alcohol.  I squirted it up by the focus ring.  It loosened up the rubber zoom band so I took it off and found I could squirt some down there.  I worked the zoom and focus ring a bit, squirted some more, worked it some more then let it dry.  Smooth as butter.  I never really saw anything get flushed out, but it made a world of difference.  It "feels" as smooth or better than new and autofocus works again.  I used 99% alcohol because I didn't want water in there which is relatively slow to evaporate, unlike the high test alcohol.

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