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"The foci of concave mirrors may be in front of the mirror, in which case they are real; or they may be behind teh mirror, in which case they are virtual." -Avery 1895

Foci of Concave Mirror

"The foci of concave mirrors may be in front of the mirror, in which case they are real; or they may…

"When the rays diverge form a point at a distance from the mirror less than that of the principal focus, the reflected rays diverge as if from a point back of the mirrir. This point, b, is a virtual focus." -Avery 1895

Rays Diverging from Beyond the Center of Curvature on a Concave Mirror

"When the rays diverge form a point at a distance from the mirror less than that of the principal focus,…

"A convex mirror is generally a part of the other surface of a spherical shell. It increases the divergence, or decreases the convergence of light that falls upon it. The foci are virtual; the principal focus is midway between the center of the mirror and the center of curvature. The foci may be located and the images determined by processes closely similar to those used for concave mirrors, as illustrated." -Avery 1895

Convex Mirror

"A convex mirror is generally a part of the other surface of a spherical shell. It increases the divergence,…

"Parallel rays strike the convex mirror, reflect, and diverge as if they had originated from a virtual focus inside the mirror. Focus F is located between the surface of the mirror and the mirror's center if it were a full body sphere." —Quackenbos 1859

Reflection by Convex Mirrors

"Parallel rays strike the convex mirror, reflect, and diverge as if they had originated from a virtual…