Canon RF 400mm f/2.8 L IS USM Instructions Manual page 25

15. Drop-In Filters
The Canon Drop-In Filter 52(WIII) series can be used with the lens.
Detaching Drop-In Filters
To detach a drop-in filter, press in both lock
buttons and pull the filter holder straight out of
the slot.
Attaching Drop-In Filters
To attach a drop-in filter, push the filter holder
straight down into the slot until it clicks into
place. The filter holder can be attached facing
either forwards or backwards.
A Drop-In Screw-Type Filter Holder 52(WIII) and
Canon PROTECT filter are included with the
lens.
Before using a commercially available lens filter,
first detach the PROTECT filter. The filter size is
52 mm, and only one filter can be used.
PROTECT filter
Drop-In Screw-Type Filter
Holder
Lock buttons
ENG-24