I just got a C100 mark ii a month ago and I have had the same lens on for a couple weeks but just now noticed the EF-S yellow indicator on my viewfinder/LED screen. What does it mean? I wasn't sure if I accidentally enabled something.
Some EF-S lenses can have some light fall off at the edges so this setting crops in on the sensor to eliminate it. With the Canon EF-S 18-135mm IS STM lens on my C100 mk2, I haven't noticed any darkening of the edges of the frame so I keep the EF-S setting off.
The sensor size on the C100 Mark II is 24.6 x 13.8 mm. An APS-C sensor should be 25.1 x 16.7mm. So the C100's sensor is a tad smaller. Thus, any vingnetting wouldn't be any worse (should actually be a tiny amount better) than if using that same lens on an APS-C photo camera. So would also leave that setting off.
If instead, the C100's sensor was wider like the EOS C70 (26.2mm), then I could then see the need to have that feature enabled.
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.