changes. The light leak causes areas of the film to become fogged. Exposure A negative that has detail in both the shadow and highlight  areas  is  exposed  properly.  However,  when evaluating  the  negative  image,  it  is  necessary  to consider the subject matter because less exposure is required for light sandy beaches and snowcovered terrain and more exposure is required for dark terrain, such as forests and industrial sites. When  you  are  viewing  a  negative  that  has  been exposed normally, patches of snow or light beach scenes appear overexposed. Inversely, patches of dark terrain or industrial sites appear underexposed. When the negative  is  completely  underexposed  or  overexposed, the  film  sensitivity  or  filter  factor  (S/C)  was  set incorrectly or the automatic exposure control (ABC) in the camera system malfunctioned. Vacuum The lack of adequate vacuum in a serial-frame camera permits the film to sag away from the focal plane, causing the image to be blurred. The most common indication of insufficient vacuum is crooked data  blocks. Miscellaneous Defects Reflections from the camera window of the aircraft, depending on the angle of the sun in relation to the window, can cause flare (nonimage-forming exposure) of the film. Condensation on a camera lens can result in a halo effect surrounding film image points. This is generally caused by rapid aircraft descent immediately before a photo  run. AERIAL DUPLICATION Two   methods   of   producing   high-quality reproductions of black-and-white aerial film are in use today. One method is the specific tone reproduction method. The second method is simpler and more feasible for shipboard use, so it is discussed in more detail  in  this  chapter.  This  method  is  called  the trigradient tone reproduction method or the 1.00 print gamma  method. The following criteria is recommended as a guide to   optimum   photographic   quality   and   product uniformity   in   producing   duplicate   positives   or negatives from original aerial negatives. The overall objective of these recommendations is to ensure that a maximum  amount  of  intelligence  information  is retained in an optimum form. Only   the   straight-line   portion   of   the characteristic curve of the duplicating or printing material must be used. For most duplicating film, the straight line lies between densities of 0.40 to 1.80. Thus the D-min should be close to 0.40 and the D-max should be no more than 1.80 in the duplicate. Normally, the contrast of the duplicate is correct when the density range between the D-max and D-min falls between 0.80 and 1.20, preferably near 1.00. The requirement for using the straight line is met when the exposure level of the printer is correct. The contrast requirement is met when the processing is correct. Specifically, the contrast of the duplicate can be increased or decreased relative to the original by increasing or decreasing gamma, respectively. To achieve these goals, you must use some form of tone control  to  guide  the  printing  and  processing  operations. The duplication of aerial reconnaissance imagery requires  that  exacting  standards  and  controls  be stressed. This helps to ensure that the imagery is of the highest  quality. SPECIFIC TONE REPRODUCTION METHOD The purpose is to match the characteristic curve and the  density  range  of  the  original  negative  to  the characteristic  curve  of  the  duplicating  material  being used. TRIGRADIENT  TONE  REPRODUCTION METHOD The  trigradient  tone  reproduction  method  of duplicating  is  an  objective  method  for  determining printing  and  processing  requirements.  This  method allows you to select one of three standardized processes. Each process produces a different contrast or gradient. The processing requirement is selected by determining whether the density range of the duplicate should be increased, maintained, or decreased. By doing so, you can alter the density range of the imagery, if necessary, in each generation. Thus the density range of the final 4-39