Camera filters are available in different shapes, sizes, and materials including delicate gelatin filters that drop into holders or lens hoods, glass filters to screw onto your lenses and rectangular filters that fit modular holders.
Gelatin filters are made by dissolving organic dye in liquid gelatin then cutting it into square or rectangular shapes. The most popular size is 3×3 inches, although they’re available up to 14×18. Since gel filters are only .1mm thick, they offer excellent optical quality but are fragile. You can tape gel filters to the front of a lens, but they’ll last longer if you use them in a holder designed for the task. In the past, gel filters were inexpensive but now you can expect to pay up to $25. True filter hounds always check the junk boxes of photo swap meets when gel filters can often be found for a buck or less—sometimes still sealed in their original envelopes.
Some glass filters are constructed by sandwiching a gelatin filter between two sheets of glass. Over time, these materials can separate, causing bubbling and peeling. An alternative is to dye the glass in a molten state, which also means there’s no danger of color shifts as the filter ages. All polarizers are laminated because they use polarizing film to make the filter do what it’s supposed to do—reduce reflections.
How well a filter ring is made should be obvious from just picking it up, twirling it around in your fingers, and screwing it onto a lens. Heliopan and B+W mount their filters in brass rings because the material won’t bind or cross thread. Hoya uses aluminum because it absorbs shock in case of accidental impact.
In Jurassic times camera manufacturers kept the filter thread sizes on their lenses consistent but nowadays they don’t let that get in the way of a new design. That means you might need several sizes of the same filter. With modular systems you only need one filter along with a holder and adapters for different lens threads. Filters for Cokin’s “A” size measures 75x75mm while the larger “P” size is 84x84mm. An adapter lets you use “A” filters in “P” holders. The super-sized X-Pro filter measures 6.7×5.1 inches. Cokin may have popularized the modular concept but similar systems are available from lots of other companies.
Some cameras, such as the new Panasonic Lumix G5, that was used to make the photo above, have internal filters that are built into their firmware. This photograph was made with the G5’s Impressive Art Filter. ©2012 Joe Farace