Let’s hear it for filters. There small, light, cheap and simple, but screw the right one onto the front of your camcorder lens and you can transform your video images. In fact, of all the accessories you can add to your videomaker’s kit, filters deliver the most dramatic- and the most cost-effective-visual improvement.

Here’s how you can use filters to make your videos more compelling.

A Short History

Filters go back nearly as far as the moving image itself. As you know, in the beginning most film was black and white. Black and white film renders every color as a shade of gray, and sometimes renders the same gray for different colors.

Take colors red and green, for instance. Shoot a black and white photograph of Santa Claus in a dense stand of Christmas trees and you’ll lose him, because his red suit records as the same shade of gray as the green pine needles.

A similar problem occurs with the color blue. Black and white cinematographers shoot deep blue skies full of glorious thunderheads, only to develop pictures of dull overcast. Why? Because the film renders the white clouds and the blue sky as equally light shades of gray.

Enter the filter, which can modify the way black and white film renders colors. For example, a heavy orange filter makes blue light record a medium-dark gray, so that skies look “normal” and white clouds stand out. A green filter renders more pleasing flesh tones-for Caucasians, that is.

For years, Hollywood used the “Hattie McDaniel” filter, named for the brilliant actress who won an Academy Award for Gone With the Wind, to lighten the appearance of African-American actors. This was partly to cope with the contrast problems of lighting dark faces but also achieved the crudely racist purpose of “improving” darker complexions.

With the invention of color film came new filters, developed to modify the way in which colors were captured. These are the same filters used by videomakers today.

What Filters Do

Camera filters alter one or more of four basic aspects of an image:

brightness, color, focus and the image itself.

Neutral Density (ND) filters alter brightness by reducing the amount of light that reaches the lens. Intended for by outdoor use in bright light, numbers 1, 2 and 3 neutral density filters-often coded ND1, ND2 and ND3-let in, respectively, one-half, one fourth or one-eighth of the light that strikes them. This, in turn, forces the camera’s exposure system to open the lens aperture by one, two or three f-stops.

Why do this? For two reasons. Say your lens offers apertures from f/1.8 to f/22. Generally, a lens performs better in the middle of its aperture range, about f/4 through f/11. But out in bright sunlight, your sensitive camcorder must shoot at apertures up to f/22. For better image quality, you can use an ND3 filter to shave off three stops and shoot at f/S.

The second reason for opening your lens wider is to reduce depth of field. Suppose, for instance, you’re documenting your spouse’s world-class petunias. Set your lens aperture at f/11, and the great depth of field will include not only the blossom, but the stems, the dirt and those three beetles just passing through as well. Use an ND3 filter to open your aperture to f/4, and you can reduce the depth of focus until only the flower remains in sharp focus.

The lower the f-stop number-like f/1.8-the wider the lens opening and the less the depth of focus. At the very high f/22, your depth of focus reaches from here to Saskatoon-unless, of course, you happen to be in Saskatoon.

Remember, some filters intended for other uses will also reduce the incoming light and widen the aperture. These include polarizers and color-changing filters.

Color-changing filters let you alter the overall color of the light, either to correct the way colors record or to create special color effects.

For example, even with your white balance set to daylight, you may get unpleasantly greenish results when taping in cool fluorescent light. Using an FLD filter-FL for fluorescent, D for daylight white balance-will improve the colors, flesh tones in particular.

You can also use color correcting filters to make colors less accurate, but more pleasing or dramatic. A pale pink or amber filter, for instance, can turn a routine sunset into a picture postcard.

Focus-changing filters affect the way your lens focuses on images, and they can do this in two ways. These “diopters” are not really filters, but single- element lenses that let you focus on extremely close subjects. You might use a diopter to immortalize your daughter’s stamp collection by filling the screen with each individual stamp. Diopters are readily available in Plus-1, Plus-2 and Plus-3 magnifications. A word of caution, though: if your zoom already has a macro setting, check to see how it works with diopters.

A second way to change lens focus is with a “split-field” diopter. This clever lens has magnification in one-half its area only. Suppose your frame contains a hand holding a flower in the bottom half and distant mountains in the top half. Ordinarily, you couldn’t keep both elements in focus. But position a split-field diopter so that it affects only the bottom half of the image and you can shoot both flower and horizon in focus.

Image-changing filters alter the eleinents of the picture by distorting them, repeating them, creating starburst high-lights and generally doing all those really neat things you see on soda, beer and blue jeans commercials.

The most useful of these image-changing filter is the polarizer. The only filter with more than one part, the polarizer consists of two polarizing lenses, one fixed and one rotating. By turning the rotating lens, you can darken or lighten blue skies and control the bright spots of light called “specular highlights” that occur on glass, bright metal and water. With a polarizing filter, you can make a cloudy sky look unnaturally deep and ominous.

Or suppose you’re shooting a lovely waterfall with a quiet pool at its base. By adjusting your polarizer you can make the pool surface 1) a dramatic explosion of sunlight sparkles, or 2) so clear that you can see the trout tantalizing you below it.

This, incidentally, is why canny fisherpeople often wear polarized sunglasses. Another popular type of image-changing filter is the soft-focus or diffusion filter. This filter makes everything look softer, as if a fine mist blew between your camcorder and your subject. These filters can add a glamorous, dreamy look to a portrait or landscape. Diffusion filters also smooth over flaws in faces or other surfaces by decreasing detail. They come in different degrees of diffusion, from barely noticeable to heavy fog.

Your Basic Kit

If you like, you can acquire no end of filters-one popular brand offers well over 100-but a good starting kit includes four: a clear filter, an ND3 neutral density filter, an FLD fluorescent filter and a polarizer. These are the filters I use most.

The clear filter. Also called a skylight or 1A filter, this is your most important filter, despite the fact that it does little or nothing to filter the light passing through it. Instead, it filters water, dust and general gunk. Think of it as a transparent len cap that protects the front surface of your delicate, expensive zoom lens.

A clear filter also bars access to that demon lens-killer, the fingerprint. Fingerprints are lethal because manufacturers improve lens performance by coating the lens surface with microscopic layers of chemicals. The oil from your fingers contains acid, which can permanently etch these delicate lens coatings and degrade their performance.

In addition, simply cleaning a lens can harm its coating, so the best plan is to protect your lens with a filter. In fact, even if you never use any other filter, spring for a 1A or skylight filter and leave it on your lens. Then, if you mess up the filter with fingerprints or an overly-aggressive cleaning, you’re only out maybe $20 and you’ve saved your camcorder lens. An ultraviolet (UV) filler works just as well as a clear filter, though a video camera does no really need to block out ultra-violet light.

The ND3 neutral density filter. When I’m shooting outdoors in bright light, I use this filter to improve the quality of my image. It works by improving both the apparent sharpness and color rendition of the image.

To see if a neutral density filter will do the same for your particular rig, take your camcorder to a photo store and ask to try one out. Outside the store, tape the passersby both with and without the filter. Back in the store or at home, review your footage and decide whether a neutral density filter is for you. Keep in mind its ability to throw unwanted backgrounds out of focus by lowering lens aperture and decreasing depth of field.

The FLD fluorescent filter. I often shoot in high school classrooms lit by cool fluorescent fixtures, so I find this filter essential. Setting white balance to daylight eliminates some of the fluorescent green ghoulies, but I also like the filter’s extra measure of skin tone correction.

The polarizing filter. For dramatic blue skies, there’s nothing like a polarizer. This kind of filter also controls reflected highlights, like reflections on store windows.

The trick to using a polarizer is to remember that you adjust its effect by rotating it. But the front of your lens may also rotate when focusing, zooming or both. So always fine-tune your polarizer after you have framed and focused your shot. Be sure and use manual focus to avoid this unwanted spinning filter effect.


Care and Feeding

Once you’ve decided on the filters for your personal kit, you need to know some facts about them.

Filters cost anywhere from just a few clams to $30 or more, depending on complexity, popularity and above all, size. To find out what size filter your lens needs, simply stare intently into it, at very close range. Eventually you will see its filter size, printed on the ring that holds the front element. Filter sizes are expressed in millimeters: 55mm, 62mm, 72mm and so forth.

Warning: filter threads are very, very fine. Screw filters on and off gently; be careful to not cross-thread them. If a filter does hang up; don’t clamp it between your thumb and index finger and twist. That will only distort the metal ring and freeze things up even worse.

Instead, drape the filter with a tissue to keep your sweat off the glass, then press your whole palm against the filter ring, contacting as much of it as possible. Twist gently but persistently; the filter will unscrew nine times out of ten. (The tenth time is what repair shops live for.)

To store your filters you can leave them in the plastic cases they come in.

Or you can stack them-possible because all filters have threads on both sides. Here’s how to do it: buy a set of metal caps, one that fits the rear threads of your filters and a second that fits the front threads. One such pair of caps is sold under the “Stack Cap” brand name.

Screw the back cap to the rear of one filter, and screw a second filter to the first. Repeat with additional filters. Then screw the second metal cap to the front of the top filter in the stack. The result: a compact, easily handled drum of filters, all protected from dust and fingers. To take out any filter, simply unscrew it from the filters above and below and remove it. Then screw the two halves of the stack back together.

Stacking filters is a great way to store them, but don’t stack them up on your lens. Even the finest filters degrade lens performance and reduce sensitivity slightly. Multiplying fitters multiplies this quality loss. So when you want to use your polarizer, don’t be lazy and screw it onto your skylight filter. Replace the clear filter with the polarizer instead.

Finally, where do you buy filters? Don’t go to an electronics supermarket. Ask them about filters and they might refer you to the percolator display. Your best bet is a camera store. Camera stores know and stock filters, and nowadays most of them sell a full line of video equipment too. They’ll understand what you need and probably have what you want.

More Filter Fun

Once you feel comfortable using filEters, you may find yourself returning to the camera store for more nifty hunks of glass, ones that create fog effects, turn pinpoint highlights into starbursts, erase middle-aged wrinkles from portraits and more.

Filters can solve problems, extend possibilities and, most important, enhance your creativity.

Check ’em out.

Jim Stinson makes industrial videos and teaches courses in professional video production.

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