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. 11-19