Aperture communication issues between Canon EOS R8 and sigma 150-600mm f/5-6.3 DG OS HSM C

[Patrickcm03]

Recently I have been noticing some autofocus issues with my Canon EOS R8 but only with my telephoto lens: the Sigma 150-600mm f/5-6.3 DG OS HSM Contemporary. I have been doing some troubleshooting over the past week and pinpointed that it was most likely an issue with the lens. There is an issue with the aperture communication between the sigma lens and my r8 as the autofocus works with the lens from 150mm to around 300mm but stops working above 300mm, right around where the minimum aperture changes to f/6.3, yet it shows a minimum aperture of f/5 even at 600mm. Both the lens and body firmware are up to date. I don't think the issue is the canon ef to rf adaptor, as the af worked well through the entire range of my Canon EF 75-300mm f/4-5.6 properly communicating a change in minimum aperture.

Has anyone else noticed this issue with this lens with other mirrorless cameras? What are some recommended steps for a fix?

[deebatman316]

@Waddizzle Very true but the last high end Rebel the EOS 850D/ EOS EOS Rebel T8i can AF at F/8. It uses the same AF system as the EOS-3, EOS-1V and many other EOS-1D series cameras.

[Waddizzle]

“ …Very true but the last high end Rebel the EOS 850D/ EOS EOS Rebel T8i can AF at F/8. It uses the same AF system as the EOS-3, EOS-1V and many other EOS-1D series cameras.

[deebatman316]

@Waddizzle I have an EOS 5D Mark IV. But the EOS Rebel T8i/ EOS 850D do not have the exact same AF system like the EOS 80D & EOS 90D. It’s been awhile since I’ve looked but if I remember correctly it’s the center AF Point only. For AF at F/8 and other AF points. Like the older EOS-1V, EOS-3 & EOS-1D series. Now the other cameras more than just the center point can be used for AF at F/8. But they do in deed use 45 points. But an earlier generation of it. The EOS 6D Mark II does have all of the AF points in the center. But my EOS 5D Mark IV does not. But it has a completely different AF system. But I don’t own a Rebel.

[Waddizzle]

@deebatman316

Thr 80D, 90D, and 6D2 each hsve 45 cross type af points arranged in the same pattern.  They also have the same number of F8 AF points (27) arranged in the same places. 

[deebatman316]

@Waddizzle Ok it might’ve been those older cameras then it’s been awhile.