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Lighting the Original
Determining Exposure - 14209_226

Photography (Basic) - Introduction to photography and other graphic techniques
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Figure 8-4.–Lighting large originals. Kelvin  Temperature  of  Illumination When you are producing color copies, the Kelvin temperature (color) of the light source should match the color balance of the color film being used. When a light source produces an illumination color other than that for which a color film is balanced, filters must be used to alter the Kelvin temperature of the illumination to correspond with the color balance of the film. Rises and drops in voltage also affect the color temperature  and  intensity  of  illumination.  Fluctuation  in voltage  can  be  controlled  by  using  a  voltage  regulator. Lighting  Large  Originals For  most  copy  work,  you  should  position  the  lights at  a  45-degree  angle,  about  36  inches  from  the copyboard, and aimed at the center of the original. However, there are occasions when you may have to copy a large chart, and the normal lighting setup causes uneven  illumination.  Light  from  an  artificial  source must travel farther to reach the center of the original, and the light reflected from the edges must travel farther to reach the lens. This causes the light to be less intense along the edges and may result in underexposure of these  areas.  You  can  correct  this  condition  by  adjusting the lights. Keep the lights at a 45-degree angle, but move them closer to the lens optical axis until the light beams from the lamps intersect in front of the original (fig. 8-4). Balance is generally achieved when the beams cross each other at a point approximately one third of the distance  from  the  copyboard  to  the  lens.  Check  the lighting on the ground glass or through the viewfinder to see whether it is even from the center to the outer edges. When lighting large copy, the use of portrait lights with umbrellas is a good source of illumination. The wide coverage and diffused light, produced from this light source, allows you to light the original easily and evenly. To check the evenness of the lighting, use a flash meter and take readings from the center, corners, and intermediate  points  on  the  original. Reflection  Control Unwanted reflections often affect copying. Proper placement  of  the  lights  is  generally  sufficient  to eliminate most normal reflections. The three types of unwanted  reflections  in  copy  work  are  as  follows: Reflections  from  the  light  source Reflections over the entire surface of the original or  copyboard Optical  flare Reflections from the light source are caused by light reflecting from the camera stand, lens board, cable release, or other shiny objects around the copy setup. The reflections usually occur when you are copying glass-covered  originals,  glossy  photographs,  or  other smooth-surfaced originals. The best way to eliminate this type of reflection (when changing the position of the lights does not help) is to use a black cloth or a sheet of cardboard (painted dull black) as a shield between the lens and copyboard. You can do this by cutting a hole the size of the lens in the center of the cloth or board then placing the cloth or board over or around the lens. A lens hood also helps in reducing or eliminating this type  of  reflection. Reflections over the entire surface of an original can occur  with  rough,  scratched,  crumpled  prints  or paintings  with  brush  marks,  canvas  texture,  cracks,  and so forth. These reflections are caused by high spots on the  surface  of  the  original  and  cause  small  light reflections of the light source. Such small reflections cover the surface of the original with a haze of light that results in a low-contrast copy image. Reflections of this type are more difficult to avoid than reflections of the light source. As long as the lights shine directly on the rough surface, such reflections occur no matter in what position the lights are placed. There are two lighting methods  by  which  this  type  of  reflection  can  be minimized or eliminated. These methods are bounce lighting  and  polarized  lighting. 8-15







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