Since all kinds of digital effects are available in the edit bay, glass lens filters might seem old fashioned. Who needs a star filter when you can just dial one in? True, but digital magic takes time, skill and often the budget for plug-in programs. Sometimes it’s quicker and simpler to create effects right in the camera with lens filters. And sometimes it even looks better than the electronic equivalent.
The most common lens filters are used to control five aspects of video: brightness, color, light quality, focus and resolution. We’ll take ’em one at a time, and show you what they do in this photo essay.
Let’s start with polarizers – filters so versatile that they straddle three out of five of these areas: brightness, color and light quality. A polarizer is made of two rings: the back one screws onto the front of the lens, but the front one rotates freely. A polarizer reduces overall brightness by about 1.5 aperture (f-) stops (for instance, from f16 to f9.5). We’ll explain why this might be desirable when we get to neutral density filters, below. A polarizer can also change colors somewhat, especially darkening blue skies or water, for dramatic effect (Figure 1).
Finally, a polarizer can alter light quality by suppressing reflections on glass and water (Figure 2) and by reducing specular highlights, which are small, bright reflections from water, shiny metal or glass (Figure 3).
Neutral density filters limit the amount of light entering the lens, allowing camcorder’s aperture to open by one or more f-stops. For example, an ND3 opens one stop and an ND6 two stops. Opening the aperture reduces depth of field, throwing backgrounds out of focus for portraits, flower close-ups and similar shots. For instance, an ND9 filter can force your lens open three stops, from f11 to f5.6., throwing the background out of focus (Figure 4).
When parts of an image are just too bright for even your smallest f-stop, they flare out to blank, ugly white. In this case, a neutral density filter may not widen the aperture, but it will reduce the overall light enough to prevent this unpleasant effect (Figure 5). This can be a common occurrence where the sky is visible in a shot on a sunny day.
For even better control, a graduated neutral density filter starts clear at one side and darkens progressively. By positioning it with the dark side up, you can control over-bright skies in scenic shots (Figure 6).
Overall color tints are easy to add and fine-tune in post production, so you might not need actual glass in the field. Still, graduated color filters can create some great effects. A graduated colored filter can turn a noon sky into a sunset, without giving foreground subjects a sudden sunburn (Figure 7). A graduated blue or green filter (with the color on the bottom) can jazz up dull lake or ocean water colors.
Light Quality Control
We said that a polarizer can reduce sparkles off water, glass, or bright metal – but what if you want to enhance them? Star filters and similar filters are great for gee-whiz treatments of lights (Figure 8).
Camcorders focus so closely that close-up lenses (diopters) are rarely needed. But what if you need to shoot one subject six inches away and another other 100 feet away while keeping both of them sharp? The answer is a split-field diopter. This sneaky device will focus one half of your lens very close, even though the focus setting on the camcorder is distant or even at infinity.
A diffusion filter can reduce the natural resolution of your lens, to create smoke, fog or steam effects. For an el-cheapo alternative, try stretching a clear baggy over the lens. Experiment with multiple thicknesses until you get the effect you want (Figure 9). Another trick can be to smear petroleum jelly around the edge of an inexpensive clear-glass lens (not on your camera’s lens!) for a romantic soft-focus look on your leading lady. Diffusion can also be used to soften wrinkles and blemishes in portrait shots. Be careful, however, when intercutting closeups when only one is diffused. The change in sharpness from shot to shot will give the trick away.
[Sidebar: Where to Get Filters]
Most large camera stores and mail order houses carry a wide range of filters. Motion picture supply companies, however, tend to have square, unmounted filters intended for the large matte boxes of cine cameras. To find more about what filters can do and what’s available, the Tiffen Web site (www.tiffen.com) is a good place to start.