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Skylight Filters
Filters for Color Printing

Photography (Basic) - Introduction to photography and other graphic techniques
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Table 3-6.–Filter Factor Equivalent Exposure Table Example:  The  unfiltered  exposure  calls  for  l/60  second, and the filter factor is 3. The correct exposure is 1/20 second (1/60 x 3 = 1/20 second). However, most cameras do not have a 1/20 second shutter speed; therefore, use 1/15 second or the next slowest shutter speed. 3.  When  you  are  using  an  SLR  camera  with through the lens (TTL) metering, put the filter on the camera lens and adjust the exposure in the normal manner. However, certain dark blue, red, and orange filters may give faulty readings if used with TTL metering systems because the meter reads 18 percent gray. The camera light meter may not be sensitive to the color of light passed by the filter. 4.   Consult a filter factor equivalent exposure table. (See table 3-6.) DARKROOM   FILTERS No types of filters are used almost exclusively in the  photographic  darkroom.  They  are  safelight  filters and  printing  filters.  The  printing  filters  include  variable contrast  filters  for  printing  black-and-white  materials and  color  printing  filters  for  printing  color  materials. SAFELIGHT   FILTERS The word  safelight  in  photography  is  used  to describe  filtered  tungsten  illumination  or  direct illumination from a sodium-vapor lamp. The color of a sodium-vapor   lamp   does   not   affect   (expose) light-sensitive  materials  under  prescribed  darkroom conditions. The word  safe  is misleading since light- sensitive materials are never completely safe from safelight  illumination.  The  use  of  a  safelight  with  some types of light- sensitive materials is not recommended Compatible  safelight  filters  for  use  with  certain light-sensitive  materials  should  be  selected  on  the  basis of  color  sensitivity  and  emulsion  speed  of  the  material. The  best  method  of  selecting  a  darkroom  safelight  filter is to use the filter recommended by the manufacturer of the light-sensitive material. Safelight filters absorb that portion of the visible spectrum produced by a tungsten lamp that would affect the light-sensitive material being handled. Sodium-vapor lamp safelights use sodium gas to provide  safelight  illumination.  Incandescent  sodium  gas produces a very narrow band of visible light in the yellow-orange  portion  of  the  spectrum.  Colorblind printing  papers  are  not  sensitive  to  this  monochromatic (one color) band of light, whereas the human eye is very sensitive to it. Therefore, a brighter print room is possible without the light affecting the printing paper. By using specially designed filters that further reduce the narrow band of sodium-vapor light, black-and-white materials sensitive to green and red light can be handled under this illumination. Table 3-7 provides some examples  for  the  application  of  safelight  filters.  Always consult the Photo-Lab-Index to determine the best safelight  for  use  with  various  light-sensitive  materials. VARIABLE  CONTRAST  PAPER PRINTING  FILTERS To obtain various degrees of contrast using variable contrast printing papers, use a series of magenta and yellow filters. The magenta filters are used to print black-and-white  negatives  that  are  low  in  contrast. 3-10







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