100-400mm MK2 focusing issue

[beastbeef]

So this is a new 100-400 MK2 on an 80D.

My settings are:

1 point manual focus, evaluating metering, back button focus, single shooting, and AI servo.

The issue is it (with full AF setting on the lens) would focus at 400mm on a far object fine, however, when I try to focus on something close >1m (above the MFD) at 400mm right after, it will not focus the AF motor will not even move, I have to manual focus a little before it would find focus.

This happens from short to long too. Does anyone have any ideas?

[Waddizzle]

The MFD does not equally apply to all focal lengths.  Also, pay attention to your Focus Limiter switch.  This lens takes a little getting used to.  There is a slight learning curve.  It is not mount and play.

[beastbeef]

But it does have an MFD of 0.98m at 400mm right? Which is below the distance I tested it on or am I reading it wrong? Also, the focus limiter switch is at "FULL".

This also doesn't really explain why it wouldn't focus at far from close. The AF meter would stay at 0.98 on the lens and will not move when I press the focus button.

*Also it focused fine in live view, but just not through the view finder.*

[Waddizzle]

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@beastbeef wrote:

But it does have an MFD of 0.98m at 400mm right? Which is below the distance I tested it on or am I reading it wrong? Also, the focus limiter switch is at "FULL".

This also doesn't really explain why it wouldn't focus at far from close. The AF meter would stay at 0.98 on the lens and will not move when I press the focus button.

*Also it focused fine in live view, but just not through the view finder.*

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Okay, I missed your initial comment about the distance switch.  Just as the maximum aperture varies from 100mm to 400mm, so does the MFD.  

Live View uses a different focusing system from the viewfinder.  While it may seem to focus on an object in the center of the frame, the images are soft.  Also, the focus drops off as you move towards the edges.  Remember,, the focus plane is not flat. It is curved like a small portion of a sphere that surrounds you.  As you focus closer and closer, the radius of the sphere gets smaller and smaller.

[beastbeef]

But why wouldn't it focus through the viewfinder?

Focus metre would be stuck at 0.98m when focusing on far object after focused on a close one and stuck at >3m vice versa. I have to progressively focus closer or further to get focus.

This doesn't seem normal.

[Waddizzle]

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@beastbeef wrote:

But why wouldn't it focus through the viewfinder?

Focus metre would be stuck at 0.98m when focusing on far object after focused on a close one and stuck at >3m vice versa. I have to progressively focus closer or further to get focus.

This doesn't seem normal.

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I had thought I had just explained it to you.  I can only speculate on the exact reason why it does not focus as closely as you want it to.  Do you understand that MFD gets longer as the focal length increases?  

What focal lengths are you working with?  I feel all of your observations are normal behavior.  Welcome to the learning curve that I waned you about.

[beastbeef · Accepted solution]

AF seems to be working flawlessly now after I changed the AF setting "Lens drive when AF impossible" from "stop focus search" to "continue focus search".

[ebiggs1]

"I feel all of your observations are normal behavior."

I also think what you are seeing is normal.  Sometimes you can get the focus so far off from where the lens is at, it doesn't know what to do but a little "help" form you makes all good.  Some lenses are better at this and some are worse. A lot of conditions affect this like lighting and contrast, FL and what FL the lens is currently at. This type lens is really not designed for MFD work.  If that is what you require a better choice lens is in order.

This lens is actually pretty easy to use so I don't think there is much of a learning curve involved but there is a need for feeling of just how it works involved.  After all a standard kit lens is a 70-300mm and most folks, thousands of them, with no photographic experience, handle them just fine.

[beastbeef]

Yea everything works fine now after I changed some AF settings. Weird...

[ebiggs1]

"Weird..."

Actually it's not.  It was/is working normally.