first  column  lighten  colors  next  to  them,  and  opposite filters darken colors on the print.  For example, a yellow- green No. 11 filter lightens subjects that are yellow-green or yellow and darkens subjects that are violet.  A No. 44 cyan filter lightens blue and blue-green and darkens light red and orange. USING FILTERS IN BLACK-AND-WHITE PHOTOGRAPHY Filters may be used in black and white photography for the following major reasons: To  make  the  tones  of  gray  in  the  final  product conform  more  closely  to  the  visual  effects  of colors in the original scene. To provide scenic contrast, such as darkening the sky  so  that  clouds  “stand  out.”    You  can  use  a No. 15 or a No. 25 filter for this purpose. To   lighten   or   darken    a   color   to   make   it “disappear”  or  stand  out  in  sharp  contrast.    An example  of  this  could  be  photographing  an  old document  that  is  written  in  blue  ink  and  has yellowed  with  age.    Here,  a  deep  yellow  filter would  darken  the  blue  writing,  and  at  the  same time,  lighten  and  possibly  remove  the  yellow stain. Whenever  you  use  a  filter,  you  must  change  the exposure.      The   amount   of   change   depends   on   the sensitivity of the film to the colors absorbed by the filter as  well  as  the  quantity  of  that  color  in  the  type  of  light used.    The  effects  of  the  filter  in   terms   of   exposure correction  are  given  on  the  film  data  sheet  as  a  filter factor. The  filter  factor  may  be  applied  to  the  exposure  by opening the diagram one f/stop each time the filter factor is doubled.  Thus a factor of two requires that the diagram be  opened  one  f/stop  larger  than  is  needed  for  correct exposure  without  a  filter;  a  factor  of  four  call  for  two f/stops, a factor of eight for three f/stops, and so on. An easy formula for determining exposure correction when you are using a filter is to divide the film speed by the  filter  factor  and  use  the  results  as  a  corrected  film speed on your exposure meter.  As an example, when you use a black-and-white film with an ISO of 400 and a No. 11 filter (filter factor four), divide four into  400  and  use the results, 100, as the film speed on the exposure meter. When using this method, make sure you return the meter dial to the correct film speed after using the filter. FILTER FOR COLOR PHOTOGRAPHY Problems  associated  with  color  materials  are  quite different  from  those  encountered  with  black-and-white materials.    In  color  photography,  the  main  problem  is achieving  correct  color  balance.      The   principal   factor involved is the color temperature of the light source being used  to  illuminate  the  subject.    This  provides  a  natural appearance   to   the   final   product.      Filters   for   color photography are classified as light balancing, conversion, and color compensating. Light Balancing Filters Light  balancing  filters  come  in  two  series  (not  to  be confused  with  a  series  that  indicated  physical  size):  the series  81  (yellowish  filters)  are  used  to  lower  the  color temperature  of  light  source,  and  the  series  82  (bluish filters)  are  used  to  raised  the  color  temperature  of  light from a light source.  Both series are used when a tungsten light source is used with color film. Conversion Filters Conversion   filters   are   used   in   color   photography when  a  significant  adjustment  of  an  exposing  light  is required to convert the color quality of the exposing light the color temperature for which a film is balanced. Conversion filters generally come in two series.  The 80 series of filters are blue in color and convert tungsten light  to  color  qualities  acceptable  for  use  with  daylight film.    The  85  series  are  amber  in   color  and   convert daylight to color qualities acceptable for use with tungsten film. The correct filter to use for a given situation with a given  film  can  be  determined  by  reading  filter  and  film data sheets.  If your are in doubt, seek help from your ship or base imaging facility. Color Compensating Filters Color  compensating  (CC)  filters  are  used  to  adjust the   overall   color   balance   obtained   from   color   film, particularly   slide   film.      Without   the   use   of   color compensating filters, improper color cast can result. For  cameras,  CC  filters  are  normally  used  to  color balance   the   light   from   sources,   such   as   fluorescent, tungsten, and mercury-vapor lights, and the “bounce” light reflected  from  colored  surfaces.    They  are  also  used  to balance lighting effects under unusual circumstances (such as underwater lighting).  These filters can be used 11-18