Astroscan for planet viewing

Recognizing that the Astroscan is not best suited for view planets,
what can I expect to get from one?

I have read that its design limits it to about 100x magnification.
Why? Does this include the effect of a Barlow lens? What could I
expect from a 4-8mm eyepiece, alone and in combination with the
Barlow?

I am not looking for someone to tell me that my child's Astroscan
won't do the job- I already know that it does what it is supposed to.
What I am looking for is someone who can give me an explanation of the
telescope's limitations, the design compromises that cause the
limitations and what happens when you push the design limits.

Thanks,
JP

There are some reviews. I think I read one that said the images got
poor above 60x or so. See:

http://members.tripod.com/irwincur/edmund_astroscan.htm

http://home.freeuk.com/m.gavin/astroscan.htm

http://www.cloudynights.com/reviews/astroscan.htm

The latter seems most detailed on what you can see with it.

I had one for about 10 years and then gave it away to a fellow with
children (I still have more scopes and binos than I can justify!).

Phil

JP wrote:
Recognizing that the Astroscan is not best suited for view planets,
what can I expect to get from one?

I have read that its design limits it to about 100x magnification.
Why? Does this include the effect of a Barlow lens? What could I
expect from a 4-8mm eyepiece, alone and in combination with the
Barlow?

I am not looking for someone to tell me that my child's Astroscan
won't do the job- I already know that it does what it is supposed to.
What I am looking for is someone who can give me an explanation of the
telescope's limitations, the design compromises that cause the
limitations and what happens when you push the design limits.

Thanks,
JP

There are some reviews. I think I read one that said the images got
poor above 60x or so. See:

http://members.tripod.com/irwincur/edmund_astroscan.htm

http://home.freeuk.com/m.gavin/astroscan.htm

http://www.cloudynights.com/reviews/astroscan.htm

The latter seems most detailed on what you can see with it.

I had one for about 10 years and then gave it away to a fellow with
children (I still have more scopes and binos than I can justify!).

Phil

JP wrote:
Recognizing that the Astroscan is not best suited for view planets,
what can I expect to get from one?

I have read that its design limits it to about 100x magnification.
Why? Does this include the effect of a Barlow lens? What could I
expect from a 4-8mm eyepiece, alone and in combination with the
Barlow?

I am not looking for someone to tell me that my child's Astroscan
won't do the job- I already know that it does what it is supposed to.
What I am looking for is someone who can give me an explanation of the
telescope's limitations, the design compromises that cause the
limitations and what happens when you push the design limits.

Thanks,
JP

I am not looking for someone to tell me that my child's Astroscan
won't do the job- I already know that it does what it is supposed to.
What I am looking for is someone who can give me an explanation of the

Hi:

Depends on your expectations. Yes, you can get to 100x. At this magnification,
you should be able to detect Mars South Polar Cap (much smaller now than it was
earlier) and some hints of markings.

Why doesn't the Ascan do well with high power? Several reasons. This is a short
focal length f/4 primary mirror. This is more difficult to make well than a
higher focal ratio one. In my experience, most Astroscans have optics that
range in quality from poor to fair. Also, at this focal ratio, collimation is
critical. Unfortunately, the Astroscan's collimation can't be adjusted by the
user. I don't believe that I've EVER seen one that's been exactly in
collimation. Finally, the focuser on the Astroscan is poor and rather
frustrating to use at high powers.

But, hey!--if you don't expect too much, you can have some fun with this scope
on Mars, though it's far better in its role as a wide-angle rich-field
instrument. By way of comparison, the ubiquitous 80mm f/5 refractors do
considerably better on the planets than the Ascan...


Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

I am not looking for someone to tell me that my child's Astroscan
won't do the job- I already know that it does what it is supposed to.
What I am looking for is someone who can give me an explanation of the

Hi:

Depends on your expectations. Yes, you can get to 100x. At this magnification,
you should be able to detect Mars South Polar Cap (much smaller now than it was
earlier) and some hints of markings.

Why doesn't the Ascan do well with high power? Several reasons. This is a short
focal length f/4 primary mirror. This is more difficult to make well than a
higher focal ratio one. In my experience, most Astroscans have optics that
range in quality from poor to fair. Also, at this focal ratio, collimation is
critical. Unfortunately, the Astroscan's collimation can't be adjusted by the
user. I don't believe that I've EVER seen one that's been exactly in
collimation. Finally, the focuser on the Astroscan is poor and rather
frustrating to use at high powers.

But, hey!--if you don't expect too much, you can have some fun with this scope
on Mars, though it's far better in its role as a wide-angle rich-field
instrument. By way of comparison, the ubiquitous 80mm f/5 refractors do
considerably better on the planets than the Ascan...


Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

Recognizing that the Astroscan is not best suited for view planets,
what can I expect to get from one? ........snip.....an explanation of the
telescope's limitations, the design compromises that cause the
limitations and what happens when you push the design limits.

Thanks,
JP

OK
The ball mount is not that good for high power magnification and tracking. It
is not really that smooth.

The focuser is less than it should be. Particularly in cold weather.

If the scope is a "table top" type of scope, then it is only as stable as the
object it is sitting on. Higher magnification requires a stable mount. So you
need something sturdy to place it on. Which sorta defeats the compact, all in
one unit concept.

At f/4, it theoretically has a larger central obstruction then longer 4"+
newts. So theoretically a smidgen less contrast. Theoretically.

The RKE 2.5x barlow is optically good. But it is very heavy, due to it's
length. This is a problem on dewy nights, where heavy ep/barlow combinations
turn this scope in it's ball mount.

Yet all that aside, I've been able to easily identify where Mars' central
meridian lay, each time I've used it. Good views at 140x to 150x, on a heavy
homemade tripod. Within the expectations of an obstructed, 4" scope. Jerky
hand tracking, sticky focuser and all. YMMV.

A Klee 2.8x barlow is a good planetary viewing accessory for this scope.

john

Recognizing that the Astroscan is not best suited for view planets,
what can I expect to get from one? ........snip.....an explanation of the
telescope's limitations, the design compromises that cause the
limitations and what happens when you push the design limits.

Thanks,
JP

OK
The ball mount is not that good for high power magnification and tracking. It
is not really that smooth.

The focuser is less than it should be. Particularly in cold weather.

If the scope is a "table top" type of scope, then it is only as stable as the
object it is sitting on. Higher magnification requires a stable mount. So you
need something sturdy to place it on. Which sorta defeats the compact, all in
one unit concept.

At f/4, it theoretically has a larger central obstruction then longer 4"+
newts. So theoretically a smidgen less contrast. Theoretically.

The RKE 2.5x barlow is optically good. But it is very heavy, due to it's
length. This is a problem on dewy nights, where heavy ep/barlow combinations
turn this scope in it's ball mount.

Yet all that aside, I've been able to easily identify where Mars' central
meridian lay, each time I've used it. Good views at 140x to 150x, on a heavy
homemade tripod. Within the expectations of an obstructed, 4" scope. Jerky
hand tracking, sticky focuser and all. YMMV.

A Klee 2.8x barlow is a good planetary viewing accessory for this scope.

john