I believe this has little to do with lens firmware or AF motor speed. The Dual Pixel AF on the 70D isn't even compatible with all Canon lenses. The following are listed as having 'limited compatibility':


  • EF14mm f/2.8L USM
  • EF24mm f/1.4L USM
  • EF100mm f/2.8 Macro
  • EF400mm f/2.8L USM
  • EF500mm f/4.5L USM
  • EF600mm f/4L USM
  • EF1200mm f/5.6L USM
  • EF16-35mm f/2.8L USM
  • EF17-35mm f/2.8L USM
  • EF20-35mm f/2.8L
  • EF24-85mm f/3.5-4.5 USM
  • EF28-70mm f/2.8L USM
  • EF28-70mm f/3.5-4.5
  • EF28-70mm f/3.5-4.5 II
  • EF28-80mm f/2.8-4L USM
  • EF28-80mm f/3.5-5.6
  • EF28-80mm f/3.5-5.6 USM


These are older lenses (for example, the 100mm macro listed is the older non-USM version of the lens, not the current 100L or 100 non-L USM lenses). It's relevant that 3rd party lens makers reverse engineer their lenses to work with Canon AF systems by assigning them a Canon LensID code for an older lens. This issue has reared it's head in the past, such as when several Tamron lenses were discovered to activate the off-center cross type AF points of the 40D/50D/60D/7D only as single line points, and not crosses, and Canon subsequently acknowledged that the same issue affected a set of older lenses. I'm not aware that Canon ever addressed this via a firmware update for those bodies.

In the case of the lenses mentioned, the Tamron 17-50 non-VC uses LensID 161, which is Canon's code for the EF 28-70mm f/2.8L - and that lens is on the above list of lenses with limited compatibility. Likewise, the Sigma 18-125 uses LensID 6, which is Canon's code for the EF 28-70mm f/3.5-4.5, also on the above list.

To fix this issue, Canon would need to update the 70D firmware to deliver full compatibility with those old lenses.