Canon 400mm 2.8L prime - sticking AF?

[Marshallman]

Anyone experience this?? Back button focus on 1DX mk2 with 400mm prime 2.8L IS mk2.

Sometimes (probably worse than a permanent fault) it sits there and wont focus. If I turn the manual focus ring to somewhere near the focal length point it picks up again and autofocuses.

Regards

MikeM

[RobertTheFat]

That's not unusual, is it? Some very long lenses, especially if they start out far from the focus point, need a little help. What matters is whether they get it right in the end.

Am I being too easy on Canon? I don't have a lens that long, so my personal experience doesn't necessarily support my contention.

[Marshallman]

Not normally. Its worked perfectly until recently, from any stage of focus to pin sharp focus  straight off.

Regards

[diverhank]

Not sure what your camera is but check the menu for an item called "Lens Drive when AF Impossible".  Make sure the option is set so that the camera will try to focus even when it thinks AF is impossible.  The simple reason is the camera is often wrong about when it thinks AF is impossible.

This is the main reason sometimes AF seems stuck until you turn on and off the camera.  Not sure why Canon still has this stupid option.  It messes people more than it helps.

[Marshallman]

Thankyou Diver Hank!!
You have just solved my problem....this was the actual cause of my problem!!!
I really dont remember changing it in  the menu, but it was changed.

Thankyou!!

MikeM

[ebiggs1]

"...called "Lens Drive when AF Impossible"."

This is a common issue.  It happens to me, too.  The 1DX and 1DX Mk II both have this setting. I often say when things don't go as you expect and you can't find out why, reset the camera.  Even for us "experts"!