>>4520009>how much of autofocus performance is related to lens and how much to the bodyThere are some exceptions but for the most part:
>The bodyHandles actual target aquisition, so its responsible for tracking setting the desired position, figuring out exactly where the AF should be.
>The lensContains the focusing motor (usually, some older DSLRs have it in the body) so the lens is responsible for recieving the focusing information from the camera body and using the motor to set the commanded focus distance as quickly as possible.
The lens can hamper focusing speed if the focusing motor is slow, bottlenecking the process. For example if you use an old stepper motor lens on a brand new mirrorless camera, the camera will be able to aquire the correct focus point instantly, no different from any other lens, but the lens will take longer to actually set that focus. Beyond that, the kind of motor used in the lens, the lens won't make much difference to autofocus speed. Pretty much all first party lenses with ultrasonice motors will be fast focusing, and won't have much difference between them. Sometimes third party lenses, even with ultrasonic motors can be a little slower as lens firmware doesn't mesh as cleanly with the camera, but this was more an issue for the DSLR era, its less noticable with mirrorless.
To answer your question about the focus accuracy, usually focus accuracy is an issue of the camera dialing in the wrong focus point and sending that to the camera. However, since you're using a third party lens, you may just have to go into your cameras settings and mess around with per lens focus adjustment. This is likely the answer if you're missing focus by the same amount every time. Third party lenses often need some kind of calibration. ISO and aperture value won't affect autofocus in stills. Aperture will a bit if you're shooting video, with wider apertures being more accurate.
