Figure B-16. Virtual image produced by diverging lens .

TM 9-258

itself, as opposed to a luminous body, which is a light

diverges from, another point. If the beam converges to a

source.

point, a real image is produced (fig 2-47); if the beam

Image - A reproduction or picture of an object

diverges, a virtual image is produced at its apparent

source (fig 2-47). A real image can be thrown upon a

produced by light rays.

An image-forming optical

screen (fig 2-47); a virtual image exists only in the mind

element produces an image by collecting a beam of light

of the observer.

diverging from an object point and trans forming it into a

beam which converges toward, or

Figure B-16. Virtual image produced by diverging lens .

Figure B-17. Virtual image produced by diverging lens .

Image plane - The plane in which the image lies or is

Incidence - The act of falling upon, as light upon a

formed. It is perpendicular to the axis of the lens and is

surface.

Incident ray - A ray of light which falls upon or strikes

at the focal point. A real image formed by a converging

lens would be visible upon a screen placed in this plane

the surface of an object such as a lens or mirror. It is

said to be incident to the surface (figs 2-13 and 2-24), as

Imbalance - See Heterophoria.

contrasted with the ray leaving an optically dense

Incandescence - The state of a body in which its

medium or emergent ray.

Index (plural, indices)

temperature is so high that it gives off light.

a. An arrow or mark against which a

Examples: the sun or the filament of an electric lamp.

B-17