Does prism introduce chromatic aberration?

My other thread called "Prism Diagonal Anti Chromatic Aberration Effect"
has such bad choice of words that some readers may misunderstood what I
mean. Of course I didn't mean that a prism diagonal can cancel the chromatic
aberrations of an achromat. What I mean to say is. Given a light cone
with zero chromatic aberration (just for the sake of example since many
will agree no objective lens has zero chromatic aberration). Does the prism
diagonal introduce chromatic aberrations to the light cone and to what
degree. Again I'm asking this because I don't notice any chromatic
aberrations when viewing thru a prism diagonal and a binoviewer but
wondering if the amount is so small that only the image overall color is
lessen which doesn't make the violent fringe noticeable. And also what
really do compensators (such as AP Glaspath Compensator) actually do to the
light cone to remove what little chromatic aberrations is produced in
the prism and binoviewer (which is not noticeable to sight).

optidud

And also what
really do compensators (such as AP Glaspath Compensator) actually do to the
light cone to remove what little chromatic aberrations is produced in
the prism and binoviewer (which is not noticeable to sight).

Prisms introduce primary color (not the same as the secondary spectrum of an
achromat) plus spherical aberration. The amount of these errors is proportional
to the prism optical path length. In Binoviewers this optical path length can
approach 4 inches, so the errors are not trivial. The glaspath compensator in
the Baader Binocular Viewer was designed to cancel both primary spectrum and
correct the spherical aberration. Another way to minimize these errors is to
use very long focal ratio scopes with the binoviewer. The way it is done is to
add a 3x barlow ahead of the prism set, so that the Binoviewer "sees" a long
focal length beam. If you prefer to use a Binoviewer without that much
magnification, you will have to limit yourself to low powers where these errors
are not so noticeable.

Roland Christen

(Chris1011) wrote in message ...
And also what
really do compensators (such as AP Glaspath Compensator) actually do to the
light cone to remove what little chromatic aberrations is produced in
the prism and binoviewer (which is not noticeable to sight).

Prisms introduce primary color (not the same as the secondary spectrum of an
achromat) plus spherical aberration. The amount of these errors is proportional
to the prism optical path length. In Binoviewers this optical path length can
approach 4 inches, so the errors are not trivial. The glaspath compensator in
the Baader Binocular Viewer was designed to cancel both primary spectrum and
correct the spherical aberration. Another way to minimize these errors is to
use very long focal ratio scopes with the binoviewer. The way it is done is to
add a 3x barlow ahead of the prism set, so that the Binoviewer "sees" a long
focal length beam. If you prefer to use a Binoviewer without that much
magnification, you will have to limit yourself to low powers where these errors
are not so noticeable.

Roland Christen

I know secondary spectrum means the difference between the blue/red
and green colors, and is 1/2000 of the focal length in achromat and
1/16,000 in flourite. Now if anyone knows what is the primary color
Roland is talking about and what is the color of the fringe. Let me
know. I'd like to have an idea how a binoviewer chromatic rendering
would be improved with a compensator. Right now. I can't detect any
fringe of any color in a binoviewer when used in an f/8 apo scope.
I'd like to be able to see this primary color shift without a compensator
so I'd know what improvement in the image to expect with a compensator.

optidud

Right now. I can't detect any
fringe of any color in a binoviewer when used in an f/8 apo scope.

What Binoviewer are you using? Does it have a built-in 3x Barlow? If it does
not have this Barlow, then it will disperse the light slightly - well known law
of optics. Whether you can see it or not depends on your local observing
conditions and how well your eyes respond to the visual spectrum. Some people
cannot see color fringing, even in short tube achromats. For other people, the
same scope will show screaming purple color fringing.

Roland Christen

I bought the Televue Binoviewer but didn't get the 2X corrector. And
I was wondering whether to get it. When used in a 4" f/8 apo, I can't
detect any color fringing at 53X even at bright daytime tests. Also do
you or anyone knows how to connect the AP 1.25X glaspath compensator to
the televue nosepiece via some kind of adapter? I don't need the 2X
capability of the TV corrector, just the 1.25X magnification of the AP
Glaspath compensator.

btw.. what are the primary color that can get affected, you mean all colors
such as green, blue and red, all of them will be dispersed? How can one
detect the dispersion. I'd like to know what image quality improvement
to expect if I get the 1.25X glaspath compensator.

optidud

(Chris1011) wrote in message ...
Right now. I can't detect any
fringe of any color in a binoviewer when used in an f/8 apo scope.

What Binoviewer are you using? Does it have a built-in 3x Barlow? If it does
not have this Barlow, then it will disperse the light slightly - well known law
of optics. Whether you can see it or not depends on your local observing
conditions and how well your eyes respond to the visual spectrum. Some people
cannot see color fringing, even in short tube achromats. For other people, the
same scope will show screaming purple color fringing.

Roland Christen

I bought the Televue Binoviewer but didn't get the 2X corrector. And
I was wondering whether to get it. When used in a 4" f/8 apo, I can't
detect any color fringing at 53X even at bright daytime tests.

That does not surprise me. You won't see color at that low magnification.

Also doyou or anyone knows how to connect the AP 1.25X glaspath compensator
tothe televue nosepiece via some kind of adapter?

The Televue unit was not made for this device. It was made to be used with its
own Barlow.

Roland Christen

(Chris1011) wrote in message

Also doyou or anyone knows how to connect the AP 1.25X glaspath compensator
tothe televue nosepiece via some kind of adapter?

The Televue unit was not made for this device. It was made to be used with its
own Barlow.

Roland Christen


I wonder if you are talking of the adapter simply not fitting or the
optical design themselves. But the Baader Bino optical light length
is very near the light length of other manufacturers such as Televue,
Denkmeier, Lumicon, etc. Isn't it. So the 1.25X glaspath compensator
which corrects for primary color should also work for other
manufacturer's binoviewers (if a matching adapter can be made to fit
them).

Note that other brands such as Lumicon doesn't have a matching
compensator. What they have is such as focal extender/reducer
lens to make it focus at say 1.5X or lower, but this design doesn't
necessarity correct automatically for primary color introduced in
the bino prisms, right?

So for those who own Lumicon or other manufacturers binos. They must
have options to use the Televue 2X corrector for example to correct
for the primary color error introduced in the bino prism. I wonder
if a compensator such as the Glaspath compensator can work for a
range of given binoviewer glass light length of say 4.5"-5". Or does
it work at exact optical light length of say 4.5" only (or whatever
is the light length of the Baader binoviewer) for the primary error
correction to work?

optidud