Filters and Lens
In the same way we shade our eyes from strong lighting to see clearly, the videographer must shield the camera lens from direct light.
Even if strong light striking the lens does not create the obvious evidence of lens flare shown here, it may reduce the contrast of the image.
Assuming you can't easily change your camera position, you'll need to block the light in some way by using either a lens shade or lens hood, or by blocking the interposing light in some way.
Since most lens flare problems are apparent in the video viewfinder, you can observe and check the effects of lens shades.
The lens shade shown on the left is often used with prime or fixed focal length lenses. Things get a bit more complicated with zoom lenses because their angle of view changes and you can easily end up seeing the edges of the lens hood in a picture.
You can improvise a lens shade "on the fly" by using dull black paper and masking tape -- or even simply shielding the lens with your hand by zooming the lens to the desired point and shading the lens as you would your eyes.
Just be sure to check the edges of he image in the viewfinder to make sure you can't see your hand!
In addition to lens shades, a number of other attachments, such as filters, fit over the front of a camera lens.
Two classifications of filters are used in television production: glass or gel filters and post-production or electronic filters.
Glass filters consist of a transparent, colored gel sandwiched between two precisely ground and sometimes coated pieces of glass.
The filter can be the type that screws over the end of the camera lens (as shown here) or is inserted into a filter wheel behind the camera lens.
A type of filter that's much
cheaper than glass is the gel, which is a
small square or rectangular sheet of optic plastic used in front of the
lens in conjunction with a matte
box. (See below.)
The use of post-production filters (post filtration) takes place during editing.
Although these electronic filters typically have the same names as the familiar glass or gelatin filters, they often have a slightly different effect.
Tiffen's Dfx 2.0 software and special effect filters -- some 1,000 of them -- represent one example of post-production filters. They are used as plug-ins for programs, such as Apple's Final Cut Pro, Aperture, Avid, Adobe's After Effects, and Photoshop.
Post filtration not only provides a greater range of effects, but, unlike optical filtration, the effects can be readily reversed and modified during editing.
At the same time, there are certain effects that are better achieved with glass and gelatin filters.
News photographers often put an ultraviolet filter (UV filter) over the camera lens to protect it from adverse conditions encountered in ENG (electronic newsgathering) work.
It's considerably cheaper to replace a damaged filter than a lens.
Protection of this type is particularly important when the camera is used in high winds where dirt or sleet can be blown against the lens.
Video cameras tend to be sensitive to ultraviolet light, which can add a kind of haze to some scenes. Because UV filters screen out ultraviolet light while not appreciably affecting colors, many videographers keep an ultraviolet filter permanently over the lens to protect it. (Camera lenses are often more expensive than the camera itself.)
Using Filters to Create Major Color Shifts
Although optical and electronic camera adjustments are responsible for general color correction in a video camera, you may sometimes want to introduce a strong, dominant color into a scene.
For example, when one scene called for a segment shot in a ¥ photographic darkroom, the camera operator simulated a red darkroom safelight by placing a dark red glass filter over the camera lens. (A safelight is a lamp with a filter that screens out rays that will expose photographic paper. Darkrooms switched to yellow-green filters decades ago, but since audiences still associate red filters with darkrooms, directors feel they must continue to support the myth.)
If the camera has an internal white balance sensor, a video camera must be white balanced before placing the filter over the lens. If not, the white balance system will try to cancel out the effect of the colored filter.
Neutral Density Filters
Under some bright conditions you may want to reduce the amount of light passing through a lens without stopping down the iris.
As we've noted, keeping the iris at a low number (opened up to a large degree) makes selective focus possible.
Although using a higher shutter speed is normally the best solution in these cases (we'll get to that later), using a neutral density or ND filter will achieve the same result.
A neutral density filter is a gray filter that reduces light by one or more f-stops without affecting color.
Professional video cameras normally have one or more neutral density filters included in their internal filter wheels. To select a filter, you simply rotate it into position behind the lens.
The table below shows ND filter grades and the amount of light they subtract.
(Click on "more" for the second half of this section.)
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