Canon EF 600mm f/4L IS III USM EF600mm f/4L IS III USM Instruction Manual - Page 25

17. Drop-In Filters A 52(WIII)-series Canon drop-in filter 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