Optics > Geometric Optics > Lenses

DCS#  6A65.40

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SPHERICAL ABERRATION

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APPARATUS

object light source	113-01-C1
lens, 90 mm dia. 76 mm FL	202-21-E
aspherical lens, 80 mm dia., 66 mm FL	202-21-E
ground glass screen	113-01-A
aluminum masks	202-21-E
optical bench	113-01-D
video camera	202-09-D

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DESCRIPTION

Focus the image of the light source on the ground glass screen.  Place the circular aperture next to the lens to mask off all but the rays near the center of the lens, and refocus.  Replace aperture with a mask that passes only the rays near the outside of the lens and show that it is necessary to reposition the lens to obtain a sharply focused image.  Repeat with the aspheric lens to show that there is no need to refocus.