Law of relative size of object and image

TM 9-258

its path is deviated away from the normal (fig 2-24).The

lens, convexo-concave lens, corrected lens, cylindrical

amount of deviation is determined by means of the

lens, dialyte, diverging lens, double-concave lens,

equation for the index of refraction for the two media

double-convex lens, doublet erector eyelens, field lens,

involved. See index of refraction.

meniscus-converging lens, meniscus diverging lens,

Law of relative size of object and image - The size of

minus lens, objective, orthoscopic lens, plano-concave

lens, planoconvex lens, plus lens, and triplet.

the image is to the size of the object as the image

Lens cell - A number of lenses mounted as a unit in

distance from the lens or mirror is to the object distance.

Law of reversibility - If the direction of light is

a tubular mounting frame.

Lens diopter - See diopter.

reversed, it will travel in the opposite direction over the

Lens equation, elementary - The equation giving the

same path despite the number of times it is reflected or

refracted.

relation between the distances from the optical center of

Lens (plural, lenses) - A transparent object, usually a

the lens of the object (Do), the image (Di), and the

piece of optical glass, having two polished surfaces of'

principal focus (F). These values are related as

which at least one is curved, usually with a spherical

plus

equals

curvature. It is shaped so that rays of light, on passing

through it, are made to converge or diverge. The fact

that lenses either converge or diverge rays provides one

Lens erecting system - See erecting system.

means of classification, the type of curvature provides

Lens retaining ring - See retaining ring.

another (fig 4-1), the corrections made in the lens

provides still another. The term lens may be employed

Lens system - Two or more lenses arranged to work in

to mean a compound lens which can consist of two or

conjunction with one another (fig B-19). When in proper

more elements.

See achromatic lens, anastigmat,

alinement, the principal axes will be coincident and the

aplanatic lens, apochromatic lens, astigmatizer,

system can be referred to as a "centered lens system."

collective lens, compound lens, concavo-convex lens,

converging

Figure B-19. Optical system of erecting telescope .

Lenses of the eye - The refractive elements of the

Limiting angle of resolution - The angle subtended by

eye. See cornea and crystalline lens.

two points which are just far enough apart to permit them

Light-adapter - A term applied to the adjustment of

to be distinguished as separate points. It is commonly

used as a measure of resolving power.

the visual cells of the retina of the-eye for the clearest

Limits of accommodation The distances of the

and most distinct 'sight under good lighting conditions. It

nearest and farthest points which can be focused clearly

applies to the process whereby the cones of the retina

by the eyes of an individual. Usually varies from 4 to 5

take over the major portion of the act of seeing.

Light ray - The term applied to the radii of waves of

inches to infinity. See accommodation.

Line of elevation In artillery, the line of the axis of the

light to indicate the direction of travel of the light. Light

bore of a gun when it is in firing position (fig B-3).

rays are indicated by arrows and lines (fig 2-5).

B-19