Prism Diagonal Anti Chromatic Aberration Effect?

I read that in a 90 degrees prism diagonal. Chromatic aberrations
are almost cancelled. I'd like to know to what extend it is true
and what is the rule. For the entering light cone, it encounters
flat surface via the air-glass interface, and since there is an angle
of the incident light, chromatic deviation occurs from the splitting
of the white light into the different wavelength inside the glass, But
when the light cone exits on the other flat surface of the prism diagonal,
the chromatic aberrations are cancelled from the opposite
glass-to-air interface and the light cone returns to its original
unchromatic aberrated form (this is assuming of course that the
objective lens of the telescope is an apo or sct where chromatic
aberrations are a nil compared to an achromat).

Now what is the rule, like does shorter focal ratio or steeper
light cone make the prism diagonal ineffective in cancelling
the chromatic aberrations inside the prism diagonal? In long focal
ratio scope or light cone entering and exiting a prism diagonal with
parallel entry and exit surface (remembering that there is no chromatic
aberrations from the internal reflections). How many percentage
approximately of the light cone returns to its original unchromatic
aberrated form after it exits the prism diagonal.

If anyone has any site or articles about this in details. Let me
know. Thanks. (Note: Some may say that a prism diagonal is
obsolete and just buy a mirror diagonal. Well, the above inquiry is
to understand better the behavior of chromatic aberrations in
parallel entering and exiting surfaces such as a prism diagonal
and novelty item like binoviewer (which has almost zero
chromatic aberration when I observe thru one) and also to
get some idea like how some products such as the chromacorr
(which removes spherical aberrations) work.

optidud

I read that in a 90 degrees prism diagonal. Chromatic aberrations
are almost cancelled.

Do you believe everything you read on the net? What you read is not true.
Prisms do not cancel chromatic aberration, they just shift it a bit - more blue
color error with a bit less red color error.

Roland Christen

(Chris1011) wrote in message ...
I read that in a 90 degrees prism diagonal. Chromatic aberrations
are almost cancelled.

Do you believe everything you read on the net? What you read is not true.
Prisms do not cancel chromatic aberration, they just shift it a bit - more blue
color error with a bit less red color error.

Roland Christen

Maybe the term to use is "minimize" chromatic aberrations. I viewed thru
a binoviewer without any compensator and I can't detect any violet
fringing or secondary spectrum even on bright objects. A binoviewer has
more glass than an achromat yet produces unnoticeable chromatic aberrations
and I read someone sugggested that since a prism or binocular has parallel
flat surfaces on the entry and exit side, then the chromatic aberrations
may be minimized by the air to glass and (back to) glass to air interface.
Now I'd like to know to what degree and percentage is the remaining
spectrum of chromatic aberrations. Also if someone has articles about this
shifting to blue with less red. Lemme know. I just want to get
explanations why I don't see chromatic aberrations when using a binoviewer
(without any compensator) and even a prism diagonal when their glasses are
thicker than that of an achromat.

optidud

This topic reminds me of the once sold 4" triplet "semi-apo" telescope kit, which in fact originated
from recycled Chinese border patrol giant binoculars. If the scope was not used with an appropriate
optical length prism, the performance was rather mediocre.

David

While we're talking about prism diagonals, I have a question. With a commercial
prism diagonal (Celestron, for example)about how much light throughput is there
to the eyepiece? Are these diagonals FMC or MC? Just wondering. I'm
contemplating the purchase of a dielectric diagonal for use with my 8"SCT and
4"APO. Wondering if the extra bucks are worth it, aside from the durability
factor that the dielectric diag. provides,

Thanks in advance,

Jeff

On 14 Jul 2003 00:02:11 GMT, (JMcad94630) ...reflected:

While we're talking about prism diagonals, I have a question. With a commercial
prism diagonal (Celestron, for example)about how much light throughput is there
to the eyepiece? Are these diagonals FMC or MC? Just wondering. I'm
contemplating the purchase of a dielectric diagonal for use with my 8"SCT and
4"APO. Wondering if the extra bucks are worth it, aside from the durability
factor that the dielectric diag. provides,

Thanks in advance,

Jeff

I'm wondering about whether to purchase Takahashi's 1.25" star diagonal
(prism), or a William Optics 2" mirror diagonal to go with my FS-102.

The reason I prefer refractors is that I like the idea of looking directly at an
object rather than at a reflection of it. I would be defeating that preference
if I went with that reportedly superb mirror diagonal, but would be risking
the introduction of spurious color, however small, with a prism.

Of course, I could bypass both via a straight-through observance, but we
are all well aware of its disadvantages, too.

Opinions? Experiences?

Alan

Alan W. Craft wrote:

I'm wondering about whether to purchase Takahashi's 1.25" star diagonal
(prism), or a William Optics 2" mirror diagonal to go with my FS-102.

The reason I prefer refractors is that I like the idea of looking directly at an
object rather than at a reflection of it.

Hi Alan,

The prism diagonal also uses reflection - looking is in no way more
"direct" than when using a flat mirror. The back side of the diagonal
is the mirror.

- Alex

I would be defeating that preference
if I went with that reportedly superb mirror diagonal, but would be risking
the introduction of spurious color, however small, with a prism.

Of course, I could bypass both via a straight-through observance, but we
are all well aware of its disadvantages, too.

Opinions? Experiences?

Alan

I'm looking for shareware optical software in the net and there are many
of them, like Modas, Optalix, Atmos, Oslo, etc. Which of them has the easiest
user interface that a novice can operate? I'd like to see ray trace of
chromatic effects of light cone when it passes thru the Takahashi 1.25"
prism diagonal, for example. I still can't visualize how the light cone behave
from the dispersing lateral chromatic effects of a prism diagonal. Or
if anyone can capture the screen and share the jpeg illustration. Pls. do.
Thanks.

optidud


Alexander Avtanski wrote in message ...
Alan W. Craft wrote:

I'm wondering about whether to purchase Takahashi's 1.25" star diagonal
(prism), or a William Optics 2" mirror diagonal to go with my FS-102.

The reason I prefer refractors is that I like the idea of looking directly at an
object rather than at a reflection of it.

Hi Alan,

The prism diagonal also uses reflection - looking is in no way more
"direct" than when using a flat mirror. The back side of the diagonal
is the mirror.

- Alex

I would be defeating that preference
if I went with that reportedly superb mirror diagonal, but would be risking
the introduction of spurious color, however small, with a prism.

Of course, I could bypass both via a straight-through observance, but we
are all well aware of its disadvantages, too.

Opinions? Experiences?

Alan

On Mon, 14 Jul 2003 14:57:44 -0700, Alexander Avtanski ...reflected:

Alan W. Craft wrote:

I'm wondering about whether to purchase Takahashi's 1.25" star diagonal
(prism), or a William Optics 2" mirror diagonal to go with my FS-102.

The reason I prefer refractors is that I like the idea of looking directly at an
object rather than at a reflection of it.

Hi Alan,

The prism diagonal also uses reflection - looking is in no way more
"direct" than when using a flat mirror. The back side of the diagonal
is the mirror.

- Alex

I was waiting for someone to tell me that!

Okay, so now I'm relegated to a straight-through observance!

What a purist!

I would be defeating that preference
if I went with that reportedly superb mirror diagonal, but would be risking
the introduction of spurious color, however small, with a prism.

Of course, I could bypass both via a straight-through observance, but we
are all well aware of its disadvantages, too.

Opinions? Experiences?

Alan

Alan

The reason I prefer refractors is that I like the idea of looking directly at an
object rather than at a reflection of it.



What's so wrong about looking at a 'reflection'....or actually 2
reflections when you count a secondary mirror...as compared to
a severely 'bended cone of converging light'? (Which actually has a
higher probability of introducing chromatic and spherical aberrations).

Do you believe that a double reflected image is somehow not giving you
reliable information?? Do you dis-believe your own reflected image in a
mirror??
Just wondering if we, who use Newtonian reflector telescopes, are
somehow missing something.
Clear Skies,
Tom W.