Negative lenses form only vertical images because light rays passing through
them spread. These lenses are also called concave, divergent, or dispersive.
Negative lenses may be used as part of a compound lens to correct aberrations,
but cannot be used individually as photographic lenses. Negative lenses, which
are concave lenses, spread light rays. These lenses are thinner in the center
than at the edge.
(1) Double-concave lenses (bi-concave) have two concave curvatures.
(2) Plano-concave
lenses
have
one
concave
surface
and
one
piano
surface.
(3) Concavo-convex lenses (diverging meniscus) have one face with a
concave surface and one face with a convex surface. The concave surface
is more strongly curved.
The convex surface of either converging or
diverging lenses of this type is often toward the light. The location of
the more pronounced curve determines whether a lens is convergent or
divergent.
NOTE: All light is shown entering lenses from left to right.
REVIEW EXERCISES
1.
What is a pinhole lens?
_______________________________________________________________________________.
2.
A small pinhole will produce a blurred image and a large pinhole will
produce a sharp image. (Circle one.)
TRUE
FALSE
3.
If you use the principle of refraction in a multiple pinhole camera, the
image will be brighter. (Circle one.)
TRUE
FALSE
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