to compensate for a known color deficiency of an
unexposed color film. They also can be sandwiched
(layered) when mounting a color transparency to
compensate for an off-color hue.
SPECIAL-PURPOSE FILTERS
Some of the special-purpose falters you will work
with include the following:
. Neutral density
l Haze
l Polarizing
l Skylight
Neutral Density Filters
Neutral density (ND) filters reduce the amount of
light passing through a camera lens without changing
the reproduction of colors in the scene. These filters are
nonselective in their absorption of colors of light and
therefore uniformly reduce the various colors of light in
the spectrum. Thus white light and colored light are
transmitted through a ND filter with only the intensity
of the light being affected. These filters can be used with
both black-and-white and color film.
ND falters are gray in appearance. These falters may
be needed for pictures of a brilliant subject in bright
sunlight. When you have set the fastest shutter speed and
the smallest f/stop and still cannot take the picture
without overexposing the film, you can use a ND filter
to further reduce the exposure.
Haze Filters
Suspended in the earth’s atmosphere are minute
particles of vapor and dust that cause a veil-like
appearance called haze. This haze is most apparent in
distant scenes. Haze is the result of sunlight being
scattered by minute particles of matter that are present
in the air. The amount of haze can vary due to
atmospheric conditions. Haze should not be confused
with mist, fog, smog, smoke or clouds. These conditions
also can produce a veil-like appearance but falters have
no effect.
When sunlight is scattered, green and red light also
are scattered by the ever-present haze, but not nearly as
much as ultraviolet radiation, violet and blue light.
Penetration of the haze is possible when filters are
used to absorb scattered sunlight. A haze filter is any
filter that absorbs atmospherically scattered sunlight.
This includes contrast and correction filters. When
contrast and correction filters are used for haze
penetration, they may be considered special-purpose
falters. Although contrast filters can be used for cutting
haze, these filters affect the gray tone rendering of
colored objects. The contrast and correction filters that
absorb the shorter wavelengths are the most effective.
The recommended contrast and correction filter colors,
in the order of greatest to least effective, for haze
penetration are as follows:
l Red
l Orange
l Yellow
l Green
The use of an infrared sensitive black-and-white
film with an infrared filter provides the greatest haze
penetration of all.
Polarizing Filters
Polarizing filters look like gray neutral density
filters. However, their effect becomes apparent when
you look at the blue sky through a polarizing filter while
rotating it. As you rotate the falter, the sky appears to get
darker, then lighter.
Polarizing filters are used in black-and-white and
color photography for the following reasons:
l
l
l
l
l
To reduce or eliminate unwanted reflections
(glare) from nonmetallic surfaces, such as glass
and water
To effect exposure control (similar to ND filters)
To reduce the effects of haze
To darken the blue-sky image in both
black-and-white and color photography
To increase color saturation in a color photograph
without altering the hues of image colors
There are a number of different polarizing filters.
However, there are only two main types: one type fits
over the camera lens, and the other is designed to be used
over a light source. Since they do not affect color,
polarizing filters and screens may be used for both
black-and-white and color photography.
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