A7RII + MC-11 + Sigma 100-400 focusing issues

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Stigg Regular Member • Posts: 459
A7RII + MC-11 + Sigma 100-400 focusing issues

I bought the MC-11 adapter and Sigma 100-400mm lens new about two months ago. Focusing was slow but stable and accurate. It seems that as outdoor light has improved AF became worse.

At this point in time, focusing is slow and travels the full range of focus. The camera indicates focus point has been found though the actual focus point could be anywhere from closest to infinity. Another half press of the shutter button may refocus on the selected plane but with the camera indicating it has found focus before that actually occurs. Its necessary to wait for the actual focus to be found before fully pressing the shutter button. This creates a very awkward, unpredictable situation. With focus found, another half-press of the shutter button to refocus on a nearby point may result in this entire cycle repeating, or with luck the small change in focal distance may be found with no issue.

When I used the 100-400 with a Canon M50 AF was of medium speed but always stable and accurate with none of the issues described above. I have set the limit switch to the appropriate setting while using the 100-400 with the A7RII and this results in the same cycle as described in the previous paragraph, though the range of travel is shorter naturally.

I find that the Sigma 100-400 is a fine lens except for the adapter-related issues. At most times I have the A7R11 set to single AF with a small, moveable, single AF point. With continuous AF the problem seems to worsen.

Any suggestions or recommendations to achieve moderately usable AF with this combination are greatly appreciated.

Canon EOS M50 (EOS Kiss M)
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