Large lens shows chromatic aberration on screen using arc lamp.

Large lens shows chromatic aberration on screen using arc lamp. A diverging beam of white light from a carbon arc passes through a large diameter, poor quality converging lens (f.l. 14", 7" diam.) and the cross-section of the focused beam is displayed on a translucent screen. There is a definite dispersion of the colors called chromatic aberration: blues can be seen focusing closer to the lens than the reds. Red or blue filters can be placed in the beam to illustrate where the colors are focusing. Chromatic aberration mainly takes place at the outer edge of the lens, just as white light is dispersed by a prism. Circular apertures can be placed in front of the large lens so that light passes mostly through the central portion of the lens, causing less dispersion of colors (the resulting beam is mostly white). Circular disks can be placed in front of the large lens so that light passes mostly through the outer portion of the lens, causing the dispersed colors to be more clearly defined. Also, the demonstration can be repeated with a high quality achromatic lens: there is virtually no color dispersion.