Download Lens Types

INtroduction to Optical
Lenses
BY: Maggie Castle
Overview
Lenses used for visible light wavelengths are usually
made from glass
They are transparent at the wavelengths your
looking for
GOAL IN IMAGING: to collect rays and bring them to
a common point so you can use a sensor and record
the light to make an image
each lens has a different dispersion of light and
different focal length (see picture examples)
Basic Types of Lenses
Convex (mag > 1, image is larger)(one side is curved
out)
Concave (mag <1 image is smaller)(one side is
curved in)
Bi-Convex (gets larger faster )(two sides are curved
out)
Bi-Concave (gets smaller faster)(two sides are
curved in)
Focal Length is next to lens
The Ray Model and
Finding the Focal Length
Rays Model is a simpler model then the Wave model
the equation to find focal length is , (1/z1) + (1/z2) = (1/f), where z1 is the length
from the object to the lens, z2 is the length from the lens to the focal point, and f
is the focal length
the equation to find the magnification is , M=-(z2/z1)
You would place a sensor at the focal point to get a focused image
Convex have a + focal length (image is on the other side of light)
Concave has a - focal length ( image is on the same side as the light source)
Since the what you are imaging is on the same side as the image with a
concave lens, they are not used in imaging systems. They are used in things
such as eye glasses because the image is on the same side as the eye.
Advantages and
Disadvantages to Lenses
Advantage- glass lenses are used in visible light so
we are able to see them and the images they create.
Lenses are also able to combine with other lenses to
increase focus
One Problem is that different wavelengths in the
visible light spectrum focus at different focal points
so it is extremely difficult to get all in focus.
Your Turn!
These lenses are called tombstone lenses due to the
shape
If you hold the concave (- focal length) and the larger
convex (+ focal length) the image is right side up and
smaller
If you hold the convex (+ focal length) with the larger
convex (+focal length) the image is upside down and
larger