Distortion - Pincushion And Barrel

Purpose

To show pincushion and barrel distortion.

Equipment

Bright point source with condenser lens, 10 cm focal length plano-convex lens, iris, wire mesh,and 23 cm focal length convex lens in baffle, all on moving optical table, component positioning strip.

Suggestions

To facilitate efficient changing from one demonstration to the other a component positioning template is◙included (the meter stick lying in front of the optical rail).

Setup Time

5 min.

Images

l6-40

Description

The optical system in the photograph includes the following: bright point source with condenser lens, 10cm focal length plano-convex lens with flat side toward light source, iris, fine wire screen, large diameter 23 cm focal length convex lens, and screen at about 12 foot distance (not shown in photograph). This arrangement produces barrel distortion as shown in the photograph at the right. To produce pincushion distortion it is only necessary to move the iris from before the lens to after it and to◙slightly refocus by moving the 23 cm lens. ◙This demonstration also shows "curvature of field,"

References

Lecture Demonstrations References: Hecht-Zajac, Optics, 184-186, (1973); Pohl, Optik and Und Atomphysik, 40-41, (1967);Sears, Optics 125-127, (1958); Francon, Experiences de Physique, 139-140, (1958). Lecture Demonstrations Information Sheets.