Hey, I know what is spherical aberrations and spherochromatism.
There's just something I can't figure out. Suppose an objective
lens has spherical aberrations corrected on the color green. The
author said it would be uncorrected in color red, meaning the
red outer rays would focus closer to the lens than the center. If
you will recall that in a thin lens, the red is the one farthest away
from the lens while violet is the one nearest the lens. Now if you
optimize a lens specifically the outer rays for the color green. If red
light comes from the same lens. The red outer rays should be refracted
and end up farther away from the lens, yet the author said it should
be nearer the lens. I searched all the archives here but can't find the
answer. So if anyone knows the answer to this, lemme know.
Don't make me antagonize for days figuring out why Thanks.

optidud



William Hamblen wrote in message arthlink.net...
In article , optidud wrote:
Yes, I've realized the Spherochromatism is not the same as primary
color error and I've consulted many references about this a while ago.
But there is something that eludes me and I wonder if I'd figure it
out by simply sketching on paper. They say that when spherochromatism
is corrected for green light, it is undercorrected in red light and
overcorrected in blue light, Which means that in red light, the
outer rays focus closer to the lens than the paraxial rays, and
the opposite is true in the blue.

Spherical aberration is called spherical aberration because lenses
and mirrors that have surfaces that are segments of a sphere have the
unfortunate property that rays focused by the edges of the lens don't come
to the same point as rays focused by the center of the lens. The lens
designer can minimize the amount of spherical aberration by selecting
the right curves for his lens. The lens curvatures for best correction
of spherical aberration depend on the index of refraction of the glass,
which changes with wavelength of light. With an ordinary achromatic lens
the designer can get best correction for spherical aberration at one
wavelength. At other wavelengths you get more spherical aberration.
For visual telescopes they engineer the lens so the correction for
spherical aberration is best at wavelengths where the human eye is
most sensitive.