Lenses
Lenses
Simple lenses which are used in a
microscope can be described.
All lenses have an imaginary line that
goes through the center called an axis.
• While there are different kinds of lenses,
light traveling along the axis of any lens is
not bent.
Convex Lenses
• Light rays that enter a convex lens parallel
to its axis, refract and meet at a point
called the focal point.
• Convex lenses are sometimes called
converging lenses.
• A lens is an object
that is designed to
refract light in a
specific way.
• Many devices you
use contain lenses.
Convex & Concave Lenses
• There are two basic kinds of lenses:
– convex
– concave
To get higher magnification,
microscopes and telescopes use more
than one lens.
• A refracting telescope
has two convex lenses
with different focal
lengths.
• The lens with the
shorter focal length is
nearer to the eye.
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Refracting Telescope
Concave Lenses
• Light rays that enter a concave lens parallel
to its axis refract and spread out, diverging
as they exit the lens.
• Concave lenses are sometimes called
diverging lenses.
The focal point of a concave lens is located on
the same side of the lens as the light source.
• Imaginary lines are drawn backward in the
opposite direction of the diverging rays.
• The focal point is where the imaginary lines meet.
• The
T distance from
f
the focal
f
point to the center off
the lens is its focal length.
Because large lenses are nearly
impossible to make, most modern
telescopes use a concave mirror
instead of one lens.
The diagram shows a reflecting telescope,
much like the one used by the Hubble Space
Telescope and almost all astronomical
observatories.
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