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TM 9-254
9-1.
Optical Terms - Continued
n.
Reflection. Light striking a surface and returning or bouncing back as shown in figure 9-5.
Figure 9-5. Reflection From a Plane Mirror
o.
Refraction. The bending of light due to a change in speed which occurs when a ray of light passes from one
medium to another of different optical density, as shown in figure 9-6.
Figure 9-6. Effects of Refraction
p.
Roll Test. A test usually performed on instruments such as telescopes or optical alignment devices which are
required to rotate on bearing surfaces. The mechanical and optical axis of the instrument must be coincident of each
other when rotated through 360 degrees.
q.
Separation. This condition results when the cement between the surface of a compound lens breaks down.
It shows up as jagged lines or streaks, yellowish in color between the two lenses.
Change 2 9-4
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