In the old days film photographers always carried a little wallet full of filters. You had an 81A for a warm up that made photos in full daylight a bit warmer, and an 80A, FLD, and 85C for correcting different types of artificial lighting. If you’d been in the business for a while, you may have had one of those boxy filter holders more common on movie cameras and a set of the square glass filters that might have included gradient filters for making the sky more dramatic when the foreground was lighter colored.
Digital cameras have done away with most types of filters. White balance on pictures in RAW format can be made after the fact and there’s little need for filters to correct lighting. Gradients and other effects are now easier in post-processing and few photographers bother with gradient filters anymore.
Yet, even in the digital age, there are still a few filters that are nice to have.
When is a filter not really a filter? When it’s a sky filter. A skylight or Sky 1A is really just a clear piece of glass, yet it’s one of the most important investments you can make. A sky filter isn’t on the lens for your photos, which it doesn’t change at all, it’s there for the lens. Specifically to protect the front glass of your lens from dust, dirt, sand, scratches and forward impacts. It’s not just a good idea, it’s the cheapest insurance you can buy for a lens.
Polarizing filters are a big help getting the sky colors more saturated on a sunny day with haze. It also helps saturate other colors and cuts reflections from glass and metal.
Polarizing filters come in two flavors: Circular and linear. A linear polarizer is a rotating element that lets light aligned along a single axis into your lens. A circular polarizer has a polarizing element, just like a linear polarizer, but behind that is a quarter-wave scrambler that depolarizes the light.
The circular polarizer is the most common, but I use them both. The circular polarizer is supposed to be more consistent for beam splitting cameras, but really it helps the auto-focus more than the exposure. I use a linear polarizer when I don’t care about predictable results, when I want to shake things up and get a different perspective on a scene.
A polarizer can also function similarly to a neutral density filter on sunny days, cutting the exposure up to two stops.
A Neutral Density (ND) filter is very handy to have, particularly on bright days. It will cut the available light and let you select a wider aperture on a sunny day. ND filters come in multiples that provide a predictable reduction in the amount of light staringt at 0.3 (one stop),
and go in steps like 0.6 (two stops), 0.9 (three stops) and 1.2 (four stops). ND filters go all the way up to specialty filters like the 3.6, which is a whopping 12 stop reduction. You need a really bright scene for a 3.6. Think white cat on a snow field in broad daylight using an arc welder as a fill.
Those of you using your DSLRs for video, this is not an optional investment. You’re limited in your selection of shutter speeds and the only way you’ll get the f-stop you want in some shots is with a neutral density filter. Very seldom have I needed more than a 0.9 shooting video and, if that situation arose, you can stack ND filters for even more light reduction. Most of the video shooters I know carry a 0.3, 0.6, and 0.9.
So, there are still places for filters in modern digital photography, just not as many as the old days and the filters serve a different purpose.