A page from the "Causes of Color" exhibit...
How else does dispersive refraction affect the colors we see?
Dispersive refraction effects in crystals
Crystals have their own colors (see emeralds and rubies), but dispersive refraction can enhance the appeal of a well-cut jewel.
"Double refraction" can be observed using crossed polarizers. Because of the asymmetrical geometry of the crystal, polarized light is separated into ordinary and extraordinary rays moving at different velocities through the crystal. The second polarizer recombines these rays to produce color by interference.
Getting rid of dispersive refraction: chromatic aberration
Light is dispersed into the colors of the spectrum by refraction. When we are using a refractive lens to enlarge an image, this becomes a problem; we don’t want to see the image with distorted colors at the edges of objects. This problem is known as chromatic aberration.
Chromatic aberration is a problem for any devices relying on lenses, such as telescopes, microscopes, and cameras. Digital cameras include software to compensate for this effect.
The magnifying lenses of early telescopes were simple convex lenses. At high magnification, refraction by these lenses dispersed the light into its component colors, haloing the stars and planets in rainbow colors and distorting the image seen.
Newton was the first to solve this problem, enlarging the image by reflection instead of refraction.
The essence of a reflecting telescope is that the refractive lens is eliminated and a parabolic mirror reflects the image.
There are applications that still use a refracting lens, so other methods of reducing chromatic aberration are employed. One method uses lenses of glass with different refractive indices. Joining a flint glass negative lens, which has a higher refractive index, to a crown glass positive lens, with a lower refractive index, forms a doublet lens corrected for dispersive refraction haloes.