Figure B-5. Astigmatism

TM 9-258

b. A defect of the human eye causing straight lines

Astigmatizer - A cylindrical lens which may be

in a certain direction to appear blurred and distorted

rotated into the line of sight of a range finder to cause the

while lines in another direction may be well defined. This

effect of astigmatism, to stretch a ray of light from a

defect results when rays from a point are not brought to

single point to form a line.

Axis (plural, axes) - A straight line passing through a

a single focal point on the image on the retina but a short

line is formed. It is caused by unsymmetrical surfaces of

body and indicating its center. See axis of bore, principal

the cornea and the crystalline lens of the eye (A, fig B-5).

axis, and optical axis.

Axis of bore - The center line or straight line

B-5