Gel filters

Some lenses offer such a wide angle of view that there’s a risk of the edge of the filter being recorded in a picture. To get around this, a number of ultra-wides, including the EF 17-40mm f/4l USM and EF 11-24mm f/4l, have a filter holder on the rear of the lens that’s designed to hold square cut gel filters.

Obviously this isn’t exactly convenient, as you need to remove the lens each time you want to change the filter. You’re also limited in the type of filter you can use – neutral density and coloured gel filters are fine, but polarizing and graduated filters aren’t.

The dinner plate-sized front elements on super-telephoto lenses such as the EF 500mm f/4l IS II USM are also incompatible with front-mounted filters. These heavyweights typically come with a drop-in filter holder in the barrel of the lens, which can also accommodate gel filters.