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. Well. if the lens is corrected
for green light, that means the outer zones of the objective lens
are curved to get a perfect spherical aberration correction for
green light. Now how is that when red light passes thru the outer
zones of the lens, it focuses nearer the lens than in the center rays.
I'm still figuring out why this is the case. When manufacturers design
lenses. They all use green light, and not white light to grind the
lenses to correct for spherical aberrations even in cheap china
achromats, right?? This means the optical factories have a lot of
green laser or light source at the grinding site, has anyone seen
this themselves in optical factories such as Stellarvue's or Televue's
(I assume Astrophysics labs are restricted area)?

optidud

William Hamblen wrote in message arthlink.net...
In article , optidud wrote:

BTW.. The term for the above change of focal points for different
wavelengths is called Spherochromatism, right. So prism diagonal
and binoviewer introduces Spherochromatism, right?

Different focal points for light of different wavelengths produces
chromatic aberration. You have longitudinal (measured along the optical
axis) and lateral (measured across the optical axis) aberration.

Spherochromatism is change in spherical aberration with wavelength.
An ordinary doublet is corrected for spherical aberration at one color.
For other colors the spherical aberration would be greater. I have a
Celestron/Vixen 102 mm f/9.8 refractor. I can just see some spherical
aberration with a deep blue filter. With a yellow or green filter I can't
see any spherical aberration. If it was 1500 mm focal length instead
of 1000 mm you probably couldn't see SA with the blue filter either.