How to use a gel filter on Canon wide-angle lenses
A select group of Canon wide-angle lenses have a gel filter holder at the rear of the lens. The gel filter holder is designed to accept square cut gel filters.
Wide-angle lenses show significant vignetting when using filters on the front of the lens due to the large size front elements and wide-angle of view. With such a wide-angle of view the lens actually sees the edges of the filter or filter holder.
In some cases a filter on the front of the lens reflects writing found around the front of some wide-angle lenses; the extreme depth of field can make the writing appear in pictures.
A select group of Canon EF lenses support a rear gel filter
Only a few lenses have gel filter slots in the rear, they are typically the extreme wide-angle lenses. Recently launched lenses like the EF 16-35mm f/2.8L II USM use a large 82mm filter thread instead of a gel filter holder in the rear.
- EF 8-15mm f/4L Fisheye Zoom USM
- EF 11-24mm f/4L USM
- EF 14mm f/2.8L USM
- EF 14mm f/2.8L II USM
- EF 15mm f/2.8 Fisheye
- EF 17-35mm f/2.8L USM
- EF 17-40mm f/4L USM
If you have another lens to add to the list please leave a comment below.
Gel filter holder practicalities
The rear gel filter holder is both useful and annoying in use. Neutral density filters or colour filters for black and white are great to use in the rear gel filter slot. Even colour conversion filters like a CTB or CTO work great. However in dusty or damp environments the need to remove the lens from the camera body to change the filter can present additional problems of dust or moisture in the camera or lens.
Using polarising filters is not really possible, since the small amount of rotation required to optimise the polarisation effect is almost impossible to achieve with the lens not on the camera. Similarly using graduated ND filters not practically possible.
If you want to experiment with different aperture shapes, you can put star and other shapes in the filter slot for artistic bokeh effects.
Handling the 31mm square gel filters is also challenging; it is very easy to get finger prints on the filters. Actually getting the filter in and out is awkward sometimes too.
Some of the zoom lenses that have a gel filter holder have a caution in the manual that the lens should not be set to the widest setting as the rear element of the lens moves in to contact with the gel filter in the holder. Please check your manual.
Where to get 31mm gel filters?
Rosco and Lee both produce a swatch of filter samples that are a little bigger than the 31mm slot in the rear of the lens. So for a handful of change and a sharp knife you have a huge range of colours and ND filters on tap. 🙂