Re: The diameters of EFM and RF mounts
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It's tough understanding what Canon was thinking with EF-M. The same could be said for Nikon with their CX mount, Pentax with Q, and Samsung NX.
Sony's choice is odd in a way too. Assuming the Wikipedia article is correct, E mount's diameter is 46.1mm whereas EF-M is 47mm. Does the narrow mount hinder their sensor based shake reduction on Full-Frame cameras? Maybe.
If these companies had forethought they would have simply been proactive and quickly created a mirrorless version of their mount by shrinking the flange distance and using the same diameter of their SLR era mounts once they saw Micro 4/3rds show up. Though, I do understand Nikon enlarging theirs due to F-mount being so narrow.
I don't think any of the big camera companies did a great job anticipating market direction besides the Micro 4/3rds group for what it is. Even then I don't know if their forward looking mount helped them that much in the long run now that larger formats are becoming lower priced. Maybe other companies copies them too literally with a focus on small sensors and were worse off for it.
I'm fine with how the Canon's APS-C vs. Full-Frame mount separation has been, but what I use EF-M for works with the current lens selection plus contributions by Sigma and Viltrox. Do I want more options? Sure! But I don't need fast ranged lenses like some sports and wildlife APS-C photographers probably do.
I think if EF-M gets dropped it's going to be due to internal battles at Canon. Didn't EF-M start as part of the PowerShot division? I think Magic Lantern noted some type of firmware separation from the M50 onward. Maybe the RF group isn't thrilled with how well EF-M has done lately with minimal releases and fought to end it. Who knows! Maybe we will find out soon.