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Figure 8-18.  ESD Protective Workstation (2 Operator Station shown)
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TM-9-254 Gearcase Transfer M548 M548A1 (
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Figure 9-1.  Deviation of Light Rays Through a Converging Lens
TM 9-254 CHAPTER 9 OPTICAL DATA Section I.  DEFINITION OF COMMON OPTICAL TERMS 9-1. Optical Terms. a. Aberration.  An aberration is any defect of a lens or optical system which causes the image to be imperfect. There are six general types of aberrations which are defined and listed below. (1) Chromatic aberration causes colored fringes around the borders of objects seen through the lens. (2) Coma is an aberration which causes oblique pencils of light from a point on the object to be imaged as a comet-shaped blur instead of a point. (3) Curvature of image is an aberration which causes an image to be focused in a curved plane instead of a flat plane. (4) Astigmatism is an aberration which causes the lens to have more than one focal point of the object being viewed. (5) Distortion is an aberration which causes the objects being viewed to appear misshapen or deformed. (6) Spherical aberration exists when rays of light passing through a lens near its edge are focused to a point nearer the lens than those rays passing through the lens near the center.  The effect of this aberration is poor definition of the image being viewed. b. Auto-Collimation.  Establish a line-of-sight perpendicular to a mirror with an infinity setting of the telescope. This is a process used, in the set up of test fixtures, to insure the proper alignment of the projector collimator and the test adapter being used.  Auto-collimation is accomplished by placing a front surface mirror on the mounting surface of the test adapter, in front of the objective end of the collimator.  Then while sighting through the eyepiece of the collimator, position the collimator so that its reticle is superimposed on the reflected reticle image. c. Collimation.    The  process  of  aligning  the  axis  or  center  of  an  optical  system  to  the  mechanical  axis  of  an instrument. d. Converge.    In  a  lens  this  means  to  deviate  light  rays  toward  a  common  center  or  focal  point  as  shown  in figure 9-1.  When applied to binoculars or any stereoscopic instrument, it means to align the line-of-sight of each side of the instrument to meet at a common focus to obtain a single image. e. Diopter.  A unit of optical measurement which indicates the refractive power of a lens or prism.  The shorter a len’s focal length the greater power in diopters it will have. f. Diverge.  In a lens this means to deviate the light rays outward from a common center in different directions, as shown in figure 9-2. Change 2  9-1

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