Sigma EF lens with Canon R6 mkii

[prigekhas]

so I have an R6 mkii and I bought a sigma ex 24-70mm 2.8 macro wanting to use it for video/photography. photos, everything seems to work fine, but on video, the autofocus just craps the bed

ive read there can be issues on the older lenses with the newer AF tech and software. Is that what’s happening? or is it possibly a lens issue?

[shadowsports]

Greetings,

in this case, I'm quite sure It's the age of the lens.  The ex version of this lens was released in 2004 (22yrs old). The motor technology and communication standards in older lenses are not capable of keeping up with the communication standards and speeds of mirrorless body's.  It's important to use a Canon brand adapter, but that won't matter if you're using a 20 plus year old lens.  I used a Sigma EF 24-70 f2.8 Art successfully adapted to my R5 C.  If you can't afford the RF version new, shop used or refurbished.  I don't recommend the Canon EF 24-70 since one, it doesn't have IS and two, it's prone to ribbon cable failure.  Only the Mark II is still under support.  Since your body has IBIS you will get some IS but if the ribbon cable goes it's going to be expensive.  Hopefully you can return the EX lens and purchase something newer.