Does Canon R6 Mark II work with Canon EF 100-400mm f/4.5-5.6L IS II via EF-EOS R Adapter?

What works & limitations

• Full Dual Pixel CMOS AF II subject recognition including real-time animal, bird, and vehicle tracking — Canon's own EF-EOS R adapter provides direct EF motor control integration that third-party adapters cannot replicate
• AF speed via Canon's EF-EOS R adapter with EF lenses is substantially faster than with any third-party adapter — Canon's proprietary communication optimizes the EF USM motor drive protocol for the R-series DIGIC X processor
• Full IS operation of the 100-400mm L IS II — Canon's IS Mode 1 (Normal) and Mode 2 (Panning) both communicate correctly with R6 Mark II IBIS for coordinated stabilization at 400mm
• Complete EXIF data pass-through including zoom position — Lightroom reads focal length accurately at any zoom position from 100mm to 400mm for lens profile corrections and metadata search
• Compatible with Canon EF Extender 1.4x III and 2x III — mount order is: R6 Mark II body → EF-EOS R adapter → Extender 1.4x III → 100-400mm lens; this gives 140-560mm at f/6.3 max aperture with full AF retained
• Aperture range f/4.5 at 100mm to f/5.6 at 400mm — variable but expected; the R6 Mark II's metering system handles the aperture shift automatically in Av, P, and Auto modes
• Continuous tracking at very high burst rates (40fps electronic) may drop subject lock more frequently than native RF lenses — Canon recommends 20fps (Hi+) for best tracking reliability with EF lenses via adapter; 10fps Hi gives the most stable tracking
• The EF-EOS R Control Ring Adapter (adds a control ring) is a more expensive variant — not necessary for this lens; the standard EF-EOS R adapter (drop-in filter version also available for ND/PL filtration at the adapter level) is sufficient
• The EF 100-400mm f/4.5-5.6L IS II weighs 1570g; the EF-EOS R adapter adds 115g and 26.7mm to the total lens length; with the R6 Mark II (670g) the total handheld system is approximately 2355g — a monopod or lens support (Wimberley P-5 gimbal head) is strongly recommended for sustained shooting sessions above 30 minutes
• Canon EF-EOS R adapter firmware updates are applied via the R6 Mark II camera menu under Setup 3 > Lens Firmware Update; mount the adapter without a lens attached, then select the adapter in the menu — as of 2025, Canon has released 4 firmware updates for the EF-EOS R adapter, each improving compatibility with specific EF lens+extender combinations
• Canon EF Extender stacking configuration: body → EF-EOS R adapter → EF Extender → lens — not body → adapter → lens → extender; incorrect mounting order causes the extender to bind against the EF-EOS R adapter's inner optics and can damage both components
• For users transitioning from EF to RF: this adapter+lens combination costs approximately $250 (adapter) + $2,300 (lens used) = $2,550 total; the native Canon RF 100-500mm f/4.5-7.1L IS USM costs approximately $2,800 new and provides native AF performance with full subject tracking at the R6 Mark II's 40fps burst rate