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Discussion in 'Sony Chat' started by Norbert Jakab, May 24, 2020.

  1. Norbert Jakab

    Norbert Jakab New Member

    Hey all. I mostly use my Sony A7III with a Sigma 100-400mm lens. What, other than Sony, brand 1.4x teleconverter could I use with my setup? Is there one that will also have autofocus?
    Thanks in advance.
  2. Stephen Rundle

    Stephen Rundle In the Stop Bath

    You don't say what max ap your lens is, and it depends.

    When using the Sigma 150-600 sport with my D4s I have AF, with the D810 I don't

    Also I would assume as sigma made the converter to be used with lens so why chose a different make, I have the sigma 1.4 with the sigma as it was designed by the same company

    Personally I think you will lose AF
  3. PeteRob

    PeteRob Well-Known Member

    Autofocus with a teleconverter depends on the converter providing electronic connection between the body and the lens. The AF itself is done by the lens. I’d expect Sigma to make TCs that go with their lenses. I don’t know Sony cameras but historically for DSLRs, and I expect also the Sony SLT cameras, there is a minimum light requirement for AF imposed on the focussing system. Generally a maximum aperture of F8 is needed so a x1.4 converter needs a lens of at least F5.6 aperture. AF may also be limited to the central focussing point at F8. (That’s why big lenses are F4 or F2.8). The latest off-the sensor AF systems in mirrorless cameras can work with much lower light levels but I’ve never seen a specification for how low they can go.

    There can be compatibility issues with TCs. Much depends on whether the converter has an element that protrudes into the lens and whether this can touch the rear lens element. Canon’s own TCs suffer from this. I have no idea about Sony/Sigma.

    Using a TC can slow AF performance so, even if compatible, expect AF to feel sluggish.
  4. Stephen Rundle

    Stephen Rundle In the Stop Bath

    You have to use the sigma TC on the sigma lens for exactly that reason of elements touching

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