The Canon Drop-In Filter Mount Adapter EF-EOS R with Variable ND Filter lets EF and EF-S lenses be used on EOS R series cameras, and adds a drop-in variable neutral density filter in the adapter. Canon states that density can be controlled from ND3 to ND500, equivalent to 1.5 to 9 f-stops, which suits daytime long exposures. Canon also notes that once the white line on the adjustment dial is no longer visible (ND250 or above), a blue tinge or density irregularity may occur.

Canon UK lists compatibility with the EOS R, R3, R5, R5 C, R6, R6 Mark II, RP, R8, R50, R100, R1, R5 Mark II and R8 Mark II, and with the Cinema EOS C50 and C70, while Canon Europe lists the EF-EOS R Drop-In Filter Mount Adapter as an optional accessory for the EOS C80. The adapter is weather sealed against dust and moisture.