3B Scientific Light Box - Manual (Page 16)

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Spherical Aberration: Allow four parallel rays to strike a convex lens, parallel to its axis of
symmetry. The inner two and outer two rays meet at different foci. This defect is called spherical
aberration.
In the figure the parallel rays striking the lens near the edge are bent to a nearer focus, B, than those
passing through near the center, which meet at A. The magnitude of the defect, represented by AB in
the diagram, is shown greatly exaggerated.
• As for the concave mirror, plot the caustic curve for a convex lens (The curve is called a semi-
cubical parabola)
Chromatic Aberration:
Since the refractive index is different for different colors, they will have
different foci. This defect is called chromatic aberration. Chromatic aberration can be corrected by
combinations of lenses of different types of glass (combinations are chosen so as to simultaneously
reduce spherical aberration).
White
Lens
Blue
Red
Red
White
Fig. 18
Fig. 17
B A