Canon 100-400 L II Manual Focus Disable.

[bento2]

Can the manual focus be disabled in AF mode as with Canon Electronic Manual Focus on some other EF Lenses?

It shows up in the AF Menu of my 7D2, but selecting "Disable MF in AF mode" appears to have no effect.

[cicopo]

There is a switch on the lens that you use for AF or MF. It's not done by using the menues.

[RobertTheFat · Accepted solution]

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@bento2 wrote:

Can the manual focus be disabled in AF mode as with Canon Electronic Manual Focus on some other EF Lenses?

It shows up in the AF Menu of my 7D2, but selecting "Disable MF in AF mode" appears to have no effect.

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I'm not familiar with that option, but I would expect it to have an effect only on the recent series of STM lenses, i.e. those lenses whose "manual" focus is electrical, not mechanical.

[bento2]

Thanks to Cicopo, Robert and Diverhank for your assistance.
Must revise my left hand position on the lens.!

[diverhank]

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@bento2 wrote:

Can the manual focus be disabled in AF mode as with Canon Electronic Manual Focus on some other EF Lenses?

It shows up in the AF Menu of my 7D2, but selecting "Disable MF in AF mode" appears to have no effect.

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That option is for the lenses that has electronic MF (focus by wire, not physically) - one lens I can think of is the EF 85mm f/1.2L II.  You disable it if the focus ring moves on you during shooting (the focus ring can be very light and might move if you jostle it enough).  There is no effect for lenses with physical MF which I believe the 100-400 II is.

[TCampbell]

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@bento2 wrote:

Can the manual focus be disabled in AF mode as with Canon Electronic Manual Focus on some other EF Lenses?

It shows up in the AF Menu of my 7D2, but selecting "Disable MF in AF mode" appears to have no effect.

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Correct.... it will not have an effect with THIS lens.  This option is something that ONLY applies to lenses with Canon's "stepper motor" focusing (these lenses all have the "STM" suffix in the lens model... e.g. "EF 50mm f/1.8 STM")

The 100-400 has USM focus motors.  The focus ring on the lens has a mechanical link to the focusing elements within the lens -- except since it's a USM lens, there is a bit of a "clutch" which is designed to deliberately allow for the focus to slip.  This gives you full-time manual focus override without fear of damaging anything (becuase if the motors try to force the lens one direction and you try to force focus in the opposite direction then the clutch is designed to slip -- avoiding any damage.)  

The STM lenses have no mechanical linkage in the focus system between the focus rings and the focusing elements in the lens.  It's strictly a "focus by wire" system where the computer notices you turning the ring and it tells the focus motors in the lens to move.  If you were to snip the correct wires, then you wouldn't be able to manually focus the lens.  

On an STM lens, you can't focus the lens if the lens isn't powered up.  On a USM lens, you can focus the lens at anytime (it doesn't need power for manual focus.).