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Sigma 400mm Lens Goes Haywire.

Started Jun 12, 2021 | Discussions thread
SQLGuy
SQLGuy Forum Pro • Posts: 12,664
Re: Sigma 400mm Lens Goes Haywire.

You should be able to check whether there's a stripped gear.

If you turn the focus ring with the lens detached from the camera, you should see the screw drive head in the breech turning. If it's not turning when the focus ring is turned, then something is certainly damaged in the AF drive mechanism. If it is turning, you can put a small screwdriver in the slot and put LIGHT resistance on it while turning the focus ring. If you that the screwdriver starts slipping or things feel really gritty, that would probably indicate a broken or stripped tooth.

I didn't see anyone selling this repair part, and Sigma seems to be pretty bad about parts availability for their older lenses... but it would probably be something that could be 3D printed.

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A7R2 with SEL2470Z and a number of adapted lenses (Canon FD, Minolta AF, Canon EF, Leica, Nikon...); A7R converted to IR.

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