EF400mm f/2.8L IS II USM stops working

[miles_photo]

Weird Problem with a canon EF 400 / 2.8

Hey there,

i got a weird one here, i mainly use my 400/2.8 L II with the 1Dx, but the behaviour is reproducable on my 5D Mark III, and it only happens with the 400.

After a short time of normal function the display and autofocus stop working. Shutter still works and the cam still recognizes the lens, reset to normal function only works by detaching the lens or removing the battery. Turning the cam off and on wont help.

Anybody heard of a similar problem or has an idea how to locate the problem, before i give it to canon service?

thanks

[Peter]

One of the four focus stop buttons maybe. Call Canon and ask.

[wq9nsc]

As Peter noted, this is what happens when one of the AF stop buttons malfunctions.  I have had this happen once with my EF 400 f2.8 IS II.  Pressing and releasing each AF stop button several times cleared the fault and it could not be duplicated.

Rodger

[miles_photo]

I forgot these even existed, you just pressed them and the problem went away?

[miles_photo]

Thanks for the replies guys, will try this.