PASCO OS-8500 INTRODUCTORY OPTICS SYSTEM User Manual
Page 39
012-02744K
Introductory Optics System
®
33
Experiment 14: Spherical Lenses—Spherical and Chro-
matic Aberration, Aperture Size, and Depth of Field
EQUIPMENT NEEDED:
-Optics Bench
-Light Source
-75 mm Focal Length Convex Lens
-Variable Aperture
-Crossed Arrow Target
-Viewing Screen
-Component Holders (3)
Figure 14.1 Equipment Setup
Introduction
No matter how perfectly a spherical lens is formed, there will always be some degree of image distortion.
One source of distortion, spherical aberration, could be eliminated by changing the shape of the lens
(from spherical to paraboloid). As you will see in this experiment, however, there are simpler ways of
reducing, though not eliminating, spherical aberration.
Chromatic aberration arises because lens materials have slightly different indexes of refraction for
different colors (wavelengths) of light. Because of this, incident white light is separated by a lens into its
constituent colors, and different colored images are formed at slightly different locations. Chromatic
aberration can be corrected only with the use of compound lenses in which two or more lenses of
different material and shape are combined.
Procedure
Set up the equipment as shown in Figure 14.1. Begin with the Variable Aperture fully open. Vary the
distance between the Lens and Viewing Screen until an image of the Crossed Arrow Target is focused on
the screen.
Spherical Aberration
Slowly close the Variable Aperture. Be sure that the V formed by the two aperture plates remains
centered on the notch at the top of the Component Holder. Observe the image of the Crossed Arrow
Target on the screen.
➀ How is the focus of the image effected by the size of the aperture? ________________________
______________________________________________________________________________.
➁ What size aperture would give the best possible image focus? Why is this aperture size not practical?
_________________________________________________________________________.
Viewing Screen
Crossed Arrow Target
Variable Aperture
75 mm Lens