EOS 350D Autofocus won't work with Sigma teleconverter and lens

[Owentwynne]

I have the canon eos 350d and the sigma 1401 1.4x teleconverter and I have the sigma 150-600mm lens but the auto focus won’t work. Is this a compatibility issue or is it the firmware that needs updating. 
thanks. 

[kvbarkley]

It is probably that the largest aperture is too high for AF to work. See if it works at the shortest focal length. In fact the 600mm aperture on those lenses is a little too large, so the lens lies to the camera to get it to work.

[shadowsports · Accepted solution]

Greetings,

I think kvbarkley's assessment is correct.  I have the TC-1401 and 150-600c (now retired).  Let me see what I can find out.  Do you have a Sigma USB Dock by chance?  Also what FW is your 150-600 running?

****

Update.  What kvbarkley concluded is correct.  

What I found.  Latest FW for the lens: Ver.2.03 2020.08.20

If your lens has firmware (any) v1.0.x and you intent to keep it, upgrading to FW v2.0.x is worth while.  Sigma did make various improvements to AF which would improve the resale value of the lens.  The USB Dock is cheap and a wise investment especially if you own more than one Global Vision lens (Art, Contemporary or Sport). 

Compatibility Sheet

SIGMA 150-600mm F5-6.3 DG OS HSM |
Contemporary [C015] with 1.4x

Notes:
AF *4
*4 When it is attached to cameras that are compatible with AF at F8,blurry images may result of subjects of low contrast or luminance.

Using the SIGMA TELE CONVERTER decreases the effective aperture by one F-stop (with 1.4x Tele Converter)

If you want to use the TC-1401 with the lens, its time for a newer EOS body 😃

[Owentwynne]

I have the 5d mark iii at my other house I will try that too see if it works. If so I will get a new camera body. 
many thanks. 

[kvbarkley]

Probably only a few lf the focus points will work. If you check the manual, they will tell you the ones that can focus at f/8.