Orion "clear aperture" 3.6 reflector?

The last couple of Orion catalogs have featured this "SkyView Pro 3.6CA
Reflector". I haven't seen any reviews on this scope- does anyone know of
any? And does a reflector made this way really have the additional
advantages they discuss and why haven't I seen this in larger apertures?

Thanks,
Bill

It's an off-axis Newtonian design that's been available from several
companies. In theory, you get the performance of an APO refractor
because there is no obstruction from the secondary mirror. But you also
get the coma inherent with any newtonian design and the focal ratio is
higher than most APOs these days. This makes it primarily a visual
instrument.

You haven't seen larger apertures because the mirror is literally cut
(think cookie dough) out of a parabolic blank at least twice as big. To
make the 3.6" mirror for this scope, they probably start with a 12", f/4
mirror and cut 4-6 smaller mirrors from it.

Bill Ryan wrote:

The last couple of Orion catalogs have featured this "SkyView Pro 3.6CA
Reflector". I haven't seen any reviews on this scope- does anyone know of
any? And does a reflector made this way really have the additional
advantages they discuss and why haven't I seen this in larger apertures?

Thanks,
Bill

"Tim Killian" wrote in message
...
It's an off-axis Newtonian design that's been available from several
companies. In theory, you get the performance of an APO refractor
because there is no obstruction from the secondary mirror. But you also
get the coma inherent with any newtonian design and the focal ratio is
higher than most APOs these days. This makes it primarily a visual
instrument.

That's unfortunate. I guess then it would make better sense to spend $350
more for their 100mm apo refractor ota.

Bill


You haven't seen larger apertures because the mirror is literally cut
(think cookie dough) out of a parabolic blank at least twice as big. To
make the 3.6" mirror for this scope, they probably start with a 12", f/4
mirror and cut 4-6 smaller mirrors from it.

Bill Ryan wrote:

The last couple of Orion catalogs have featured this "SkyView Pro 3.6CA
Reflector". I haven't seen any reviews on this scope- does anyone know
of
any? And does a reflector made this way really have the additional
advantages they discuss and why haven't I seen this in larger apertures?

Thanks,
Bill

Actually it's more like $999 for the 100mm APO OTA.

http://www.telescope.com/shopping/pr...roductID=54904

Hi Bill,

I originally introduced this design about 7 years ago (DGM Optics). If you
browse my site you will see that I do offer larger scopes and/or optics
sets. This type of scope is made by cutting 4 smaller off-axis paraboloids
from a larger parent mirror. In order to produce my scopes at around F/10 we
start with a 10.25" f/4 parent. The off-axis sections are cut out at a point
where they are decentered just enough for the incoming light to not obstruct
the tip of the secondary but are kept about .25" from the outside edge of
the parent mirror.
If you browse the below links to user reviews, you`ll find that, contrary to
popular mythology, coma is not a problem with these scope even using the F/4
parent mirror.

I would also mention that the Orion scopes are significantly different than
my scopes in several regards;

1. F/10 (DGM) vs F/13 (Orion)
2. Orion optics are most likely an "off the shelf" 10" f/4.8, quality
unknown.
3. DGM optics by Dodgen Optical. I`ll let the user reviews speak to quality
of the scopes.

http://users.erols.com/dgmoptics/OA-4%20review.htm
http://users.erols.com/dgmoptics/Customer.htm
http://www.scopereviews.com/page1m.html#3
http://www.scopereviews.com/page1f.html#3
http://www.cloudynights.com/reviews/oa4.htm
http://www.cloudynights.com/reviews/oa42.htm
http://www.excelsis.com/1.0/section....&findtext=&con
d=&range=d&archive=-1&range=d

Dan McShane
www.dgmoptics.com
http://groups.yahoo.com/group/offaxis/

Bill Ryan wrote in message
nk.net...
The last couple of Orion catalogs have featured this "SkyView Pro 3.6CA
Reflector". I haven't seen any reviews on this scope- does anyone know of
any? And does a reflector made this way really have the additional
advantages they discuss and why haven't I seen this in larger apertures?

Thanks,
Bill

Tim Killian wrote in message
...
It's an off-axis Newtonian design that's been available from several
companies. In theory, you get the performance of an APO refractor
because there is no obstruction from the secondary mirror. But you also
get the coma inherent with any newtonian design and the focal ratio is
higher than most APOs these days.

Tim, reports of coma being problematic are all but nil from actual
user/owners of OANs.

This makes it primarily a visual instrument.

These are fine scope imaging wise as long as you stick to lunar, planetary,
or solar.

You haven't seen larger apertures because the mirror is literally cut
(think cookie dough) out of a parabolic blank at least twice as big. To
make the 3.6" mirror for this scope, they probably start with a 12", f/4
mirror and cut 4-6 smaller mirrors from it.

For my 98mm F/10 OANs we start with a 10.25 F/4 and get 4 OA paraboloids.
Also they don`t get cut out until the "parent mirror" is fully polished and
figured.

Dan McShane

Bill Ryan wrote:

The last couple of Orion catalogs have featured this "SkyView Pro 3.6CA
Reflector". I haven't seen any reviews on this scope- does anyone know
of
any? And does a reflector made this way really have the additional
advantages they discuss and why haven't I seen this in larger apertures?

Thanks,
Bill

The coma in these OA scopes would be exactly the same as the f/4 parent
mirror. If you're in the center of the FOV, it's not a problem. Off axis
is another story.

Dan McShane wrote:

Tim Killian wrote in message
...

It's an off-axis Newtonian design that's been available from several
companies. In theory, you get the performance of an APO refractor
because there is no obstruction from the secondary mirror. But you also
get the coma inherent with any newtonian design and the focal ratio is
higher than most APOs these days.


Tim, reports of coma being problematic are all but nil from actual
user/owners of OANs.


This makes it primarily a visual instrument.


These are fine scope imaging wise as long as you stick to lunar, planetary,
or solar.

Dan,
An interesting discussion on the construction of modern OAN's but isnt this
an ancient design used at long f ratio as far back as the 1800's? I seem to
remember a picture of one with a bipod set of legs at the eyepiece end so it
could be proped up in one of the ATM books.
Bill Bambrick
41 N, 73 W, 95 ASL

You might be confusing it with the large Herschellian (e.g. Lord Rossi)
reflectors used in the 1800s. They have the eyepiece at prime focus off
to one side of the scope.


Jb2269 wrote:

Dan,
An interesting discussion on the construction of modern OAN's but isnt this
an ancient design used at long f ratio as far back as the 1800's? I seem to
remember a picture of one with a bipod set of legs at the eyepiece end so it
could be proped up in one of the ATM books.
Bill Bambrick
41 N, 73 W, 95 ASL

On Wed, 02 Feb 2005 10:47:29 -0700, Tim Killian
wrote:

It's an off-axis Newtonian design that's been available from several
companies. In theory, you get the performance of an APO refractor
because there is no obstruction from the secondary mirror.

Un, no. Any obstructed scope with an obstruction
under about 15% performs almost like it had no obstruction
but, NO reflector I've ever seen produces images like the best
apos, inch per inch, unobstructed or not. The use of a "sector"
of a larger paraboloid is interesting, but it not a perfect sub for
an apo, despite the high price.
-Rich