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04-05-2012, 02:58 PM   #1
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using Sigma tele extenders with other brand lenses

I have 3 lenses two pentax and one tamron 17-50 2.8 and have found a nice deal on two sigma tele extenders one a 2x ex dg apo and the other a 1.4 ex dg apo
are the tele extenders compatable with any pentax mount or only with sigma lenses. any input would be appreciated.

04-05-2012, 03:10 PM   #2
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They'll work I believe, but you won't get AF.

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04-05-2012, 04:13 PM   #3
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The Sigma TCs protrude forward, so if the Pentax lens has depth between the mount and the rear lens element they will work, but otherwise they will not. You will have autofocus for screwdrive autofocus lenses but not for SDM drive. The Sigma TCs definitely work on the Pentax 300mm DA*. There isn't much reason to use a TC or shorter lenses. They are designed to extend the reach of long glass.
04-05-2012, 05:08 PM   #4
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I understood that the current sigma TCs protruded into the space of the lens it was attached to. When the glass of some lenses zoom or focus they can crunch into the protruding TC. Sigma has a chart showing which of their lenses can be used with it, but not for other makes. Are we talking about the same TCs?

04-05-2012, 06:20 PM   #5
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I have the DA300 and tried my brother's 2x Sigma TC on it. It fits and has the 7 electrical contacts, but has no Pz contacts so cannot do SDM or Sigma's hsm. The electrical contacts allow one to change apertures on lenses like the modern 300 which have no aperture ring. But AF will not work on sdm lenses. AF might work on FA and F AF lenses (my guess-haven't tried it) and other 3rd party screw drive lenses like Tamron's 28-75 f2.8.
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