EF 100-400 IS II USM

[CliveM]

I have not had this lens long but have an issue with the autofocus. If I extend the lens fully to 400mm it does not focus at all. Having recently been on a wildlife holiday where there were many 100-400mm lenses it appears I am the only one with this issue. If I first pre-focus on  shorter length it focuses OK then, and focuses when fully extended. This can't be right can it? Any thoughts before I return it to Canon?

[diverhank]

It doesn't sound right at all.  There is one thing to try:

On your camera menu, look for a magenta one...if there is an option called "Lens drive when AF impossible"...make sure that's set to ON which means the camera will continue focus search even when it thinks AF is not possible.  I find that the camera is not very smart it often thinks AF is impossible when it really is possible and just sits there doing nothing.

[CliveM]

Thanks Hank. It was set to off, so that is something else to try in the daylight tomorrow. Sometime it is not just the camera that is not too smart! Clive

[Waddizzle]

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@CliveM wrote:

Thanks Hank. It was set to off, so that is something else to try in the daylight tomorrow. Sometime it is not just the camera that is not too smart! Clive

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The 5D mark IV has complex focusing system.  It work just as hard for you, as it can against you.  Others have posted links to special manuals on just the AF system.

I use AI Servo mode, with all of the AF points active, on my cameras bodies.  The AF points visibly track and move with subjects.  There are a variety of tracking modes you can use.  I have it set to always begin from the center AF point, and then use surrounding AF “assist” points as needed.  

Then there are the priority settings, focus priority or shutter priority. I use Focus Priority for all of them.   And, there is more.  It’s too complicated to describe all settings here, just what it looks like in the viewfinder.

[diverhank]

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@CliveM wrote:

Thanks Hank. It was set to off, so that is something else to try in the daylight tomorrow. Sometime it is not just the camera that is not too smart! Clive

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Ha ha...it's just the camera.  Not sure if this will solve your problem but everything is worth a try.  I can tell you two things:

1. My day job is as a test engineer.  One thing I learned is that it's always the one you least expect (that would never happen) that will get you every time. Things work for one lens do not mean they will work the same for others...

2. I didn't read about this setting...I learned it the hard way.  I have a 5D3 and a 7D2 and both would occasionally and inexplicably quit focusing from time to time when I use the telephoto lenses (400mm f/5.6L, 600mm f/4L) - always at the most inopportuned time -  until I discovered this setting.  Since I set this to ON, I haven't had any problems.  I got the 100-400 II after I set this option and I've got no problems with it whatsoever so I don't know if this could be the culprit.  I can tell you that there is no downside to setting this option to ON.

[CliveM]

Tried it out this morning - did not work. Also tried it with the other suggestions about the range - this made no difference either.

Appreciate the suggestions though - it still might be operator error!!

[Waddizzle]

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@CliveM wrote:

Tried it out this morning - did not work. Also tried it with the other suggestions about the range - this made no difference either.

Appreciate the suggestions though - it still might be operator error!!

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What shooting mode are you using?  And, what exactly does "did not work" mean?  What exactly did you try to do?

[CliveM]

I tried it in P, Aperture and Speed priorities.

First I set the lens to be out of focus manually on a distant object, then extended the zoom to 400mm and tried to get it to autofocus. When I say it did not work - it did not focus at all. I have the camera set on A1 Servo, tried it on Full range and on 3m to infinity.

Putting the lens onto a 5DI it focussed everytime in the same modes as with the failures with the 5D4.

I still think it might be another setting and I will try going through all the settings on the 5D4 to see if there is something I have overlooked.

[Waddizzle]

You seem to have a direct issue with your one camera body.  Contact Canon Support.  The camera needs to be checked, and perhaps the lens, too.  But, most definitely have the camera checked by Canon, and only Canon.

[CliveM]

Many thanks - still working through the settings before contacting canon. Appreciate all the advice received so far.