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I have a Sigma 12-24mm f/4.5-5.6 which I am very happy with.

I have a Canon 5D MkIII body.

The lens will focus normally, then after a certain amount of time will stop focusing. To force it to start focusing again, one must remove the lens and attach it again - then will work normally until it stops autofocusing again (maybe 30secs - 1 minute.

On other Canon bodies (not 5D MkIII) the lens works normally and I have no problem with other lenses on the body.

Any advice would be appreciated.

  • What specific 'other bodies' does the lens work with properly? Do any other lenses demonstrate this same issue on your 5DIII? – Michael C Sep 7 '17 at 3:19
  • Canon rebel t3i or t6i, I forget. No other lenses demonstrate the same problem. – Tomi Sep 7 '17 at 3:42
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Unless the contacts are dirty, that sounds like a lens firmware bug. You should contact Sigma and see if there's a newer version of the firmware for that lens.

If it's a current lens that's compatible with the Sigma Dock, you might even be able to upgrade the firmware yourself.

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    The lens is not one of Sigma's Global Vision line of lenses, which are the ones compatible with the dock. If it's the HSM II lens, it was introduced in 2011. If not, it's even older. Either way, this lens predates the dock. – scottbb Sep 6 '17 at 12:47
  • In that case, it would be a mail-in upgrade, if there's a newer firmware version available. I would assume that if it's the HSM II, they would have firmware compatible with the 5D Mark III by now. If it isn't, then who knows.... – dgatwood Sep 6 '17 at 16:12

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