The autofocus is something that is internal to the camera. We tell it to focus and it says it did it. The focus is pulled a the top of the climb so if you are taking off in an area that has a lot of motion or isn't particularly contrast this can be an issue. You can pause the mission and refocus at any time.
Read more about the focus controls here:
If you generally always fly at the same height you could figure out what manual focus value works for you and use that.