EF 100mm 2.8 macro - strange manual focus behavior!

[jvanides]

I am currently learning about my R8 and am using it with an EF adapter so I can take macro shots with my trusty old EF 100mm f2.8 macro lens. Today, it did something weird in Manual Focus mode: It would not let me focus! The focus ring turned, but the internal elements did not keep turning. When I switched to AF, it found the focus - and then the MF mode worked!

Has anyone seen this behavior? Is there something I'm missing that's causing this?

Thanks in advance for any suggestions...

Jim V

[MikeSowsun]

Which version of the EF 100mm f/2.8 Macro do you have?

Original (non USM) 

USM                          

“L” version with IS      

[jvanides]

Mike - Ooops! Yes, I should have included that it’s an L series lens… 

Jim

[ebiggs1]

"...using it with an EF adapter ..."

Also which adapter. It can make a big difference.

[MikeSowsun]

Like other USM L lenses, the focus ring is Full Time Manual Focus, and should always be directly connected to the focus mechanism. Using an adapter should have no effect on Manual Focus. If the problem re-appears, you might need to service the lens. 

[jvanides]

The adapter is the “Canon Mount Adapter EF-EOS R” product 2971C002.

Jim

[jvanides]

Mike - When you say “…the focus ring is Full Time Manual Focus…”, may I assume you mean that even if the focus switch on the lens is set to Autofocus, turning the ring still changes the focus?

[jvanides]

Gah!! Adding to the mystery, I tried to repeat the “stuck manual focus” problem and now it works just fine. Swell.

Any thoughts? Has anyone seen this before?

[MikeSowsun]

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@jvanides wrote:

Mike - When you say “…the focus ring is Full Time Manual Focus…”, may I assume you mean that even if the focus switch on the lens is set to Autofocus, turning the ring still changes the focus?

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Yes, even when set to Autofocus, the focus ring will always be directly connected to the focus mechanism with “Ring Type” USM lenses.  Micro USM and Nano USM are 2 exceptions.