Focus speed changes when using APS-C glass on full frame?

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90000w
90000w New Member • Posts: 9
Focus speed changes when using APS-C glass on full frame?

I'm wondering if the physical nature of covering up part of the sensor on a full frame camera necessarily will make focus less accurate and slower when using APS-C glass?

I tried out my Sigma 56mm 1.4 on an A7RII the other day and it was missing focus enough where it couldn't be trusted.

It was really only noticeable on moving objects and people, but as I was shooting someone playing basketball whose face had been saved into the camera itself, I was surprised how many shots it missed.

Is this a known issue? Or was it just an off day? I know the A7RII isn't a sports camera and it isn't the best, but the subject was very isolated on this court. I was missing shots where I had previously focused, then the subject jumped to take a shot and the camera lost focus despite the change in distance from the camera while the subject jumping was minimal.

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