CAMERA  ADJUSTMENTS.–Each  copy  camera has slightly different adjustments. You should consult the operating manual of your copy system to learn the proper operation and controls of your particular system. Only the minimum basic components of a copy system are discussed in this chapter. GROUND  GLASS  FOCUSING.–Ground glass focusing  is  essential  for  exacting  copy  work  The  image of a document viewed on the ground glass of a copy camera provides a means of monitoring all aspects of the image as it will appear in the reproduction. This includes image placement, image size, and any apparent unwanted   reflections. BELLOWS   EXTENSION.–A     copy     camera should be capable of a bellows extension of at least two, and preferably three times or more the focal length of the lens being used. With a 3-inch lens and a bellows extension of two focal lengths (6 inches) and the original is positioned four focal lengths (12 inches) from the film plane, a 1:1 ratio of the original size to reproduction size is obtained. A reproduction with a 1:1 ratio can be referred to as “life size.” A bellows extension that is less than two focal lengths cannot produce an image as large or larger than the original. A bellows that can be extended more than two focal lengths can produce an image  larger  than  the  original. LENSES  FOR  COPYING A primary requirement for a lens used for copying is that it must focus sharply across a flat plan; that is, it must produce a sharp image over its entire field of view-all the way out to the edges of the image. In copying, the original has only two dimensions, and the loss of definition at the edges of the image is much more serious  than  it  would  be  when  photographing  a three-dimensional   subject. Regular  camera  lenses  of  good  quality  can  produce fair to good copy negatives. But most lenses for general photography are designed to focus at a flat field for distances greater than eight times the focal length. Since most copy work is done at close distances, the image field is not sharp because of the curvature of the general lens. This effect can be compensated for by stopping down the lens. However, because of the high degree of diffraction at small apertures, stopping down reduces the overall sharpness of the image. For critical copy work,  such  as  when  copying  large,  detailed  originals,  a lens  designed  for  copying  should  be  used.  Such  lenses, called process lenses, produce the best image at a lens-to-subject  distance  of  about  10  feet  or  less. 8-8 Another very important aspect of a process lens is its  evenness  of  illumination  across  the  focal  plane. Evenness of illumination across the entire negative is particularly  important  when  copying  line  originals.  The high-contrast films used to copy line originals have a short exposure latitude and any falloff in illumination results in obvious variations in exposure between the edges and the center of the negative. For each lens there is an optimum aperture at which the lens produces the best image definition. For copy work, this optimum aperture should be used whenever possible. Since originals to be copied are flat or almost flat, an increase in depth of field by stopping down from the optimum aperture is not required or desired. With some lenses, especially process lenses, the optimum aperture   and   maximum   aperture   are   the   same. Generally, however, the optimum aperture is two full f/stops  smaller  than  the  maximum  f/stop. Most process lenses available today are apochro- matic. They are designed to be free of chromatic aberrations; that is, they focus sharply all three primary colors  in  the  same  plane.  Apochromatic  lenses  must  be used for critical work in color copying and duplication. Since exposure times in copy work are relatively long (i.e., seconds as compared to hundredths of a second), a lens equipped with a means of holding the shutter open is required. Your copy system must be completely free of vibration to obtain sharp images. For these long exposures, you must use the T and B settings and a cable release. The focal length of a lens used for copying should be governed primarily by the size of the negative to be produced. For example, the focal length should be about equal to the diagonal measurement of the negative to be made.  Therefore,  when  you  are  making  35mm negatives, use about a 1 3/4-inch or 45mm lens; a 4.5 x 6cm negatives, use a 3-inch or 75mm lens; and for 4 x 5 negatives, use a 6 1/4-inch or 160mm lens; and so on. In any case, you should use a lens that is longer than the film diagonal rather than a lens that is shorter. This way, you are taking advantage of the flatter field that is produced in the center area of the circle of illumination. A macro lens should be used when available because it is designed to produce sharp images at close planes. COPYBOARD Copyboards are an integral part of a copy system. The function of a copyboard is to hold the original flat and perfectly parallel to the lens and camera back When the copyboard is not parallel, distortion results, and it