Focus lock

Mom use function of the focus lock of the camera when she take the photo of I running.
focus lock:pushed half of the shutter buttons.
Photo point#1(-600mm)

Photo point#2(-300mm)

Photo point#3(just in focus)

Photo point#4(+300mm)

Photo point#5(+600mm)

Photos of #1 #5 are out of focus,Photos of #3 #5 are in focus.If it is error less than +-20% of photography distance and the focus lock distance, it is an in focus for us.
Helen Eriksen - Miles Davis