Newbie questions

I've recently acquired an Orion 8" reflector w/ equatorial on tripod,
motors, and two eyepieces, all made in China (of course). I'm aware
that this setup is not the best, but better than what one gets in a
department store. But I don't know just what to expect from it in terms
of performance.

A few nights ago, I ranged Jupiter and viewed at 40x and 100x (the scope
is 1000mm, and the eyepieces are 25 and 10 respectively, or did I get
the magnifications wrong?). At 100x it seemed I was getting a hint of
banding/striping on Jupiter itself. Thing is, I don't know how to
evaluate this.

Is a hint of banding what one should expect at that magnification, or
should I be doing (much?) better than that? If so, what is mostly
likely the weak link in the chain? Is it the scope itself? Or is it
the eyepiece?

Collimation is not a problem, I think; I can see my own eye looking back
at me. I played with the focus to get the sharpest image and that was
the best I could do. Can't think of much else, except that Jupiter was
close to the horizon, and there was a fair amount of light pollution,
but the seeing was not bad (no twinkles).

Comments and/or opinions?

Thanks all,

Longfellow

Longfellow wrote:
I've recently acquired an Orion 8" reflector w/ equatorial on tripod,
motors, and two eyepieces, all made in China (of course). I'm aware
that this setup is not the best, but better than what one gets in a
department store. But I don't know just what to expect from it in terms
of performance.

A few nights ago, I ranged Jupiter and viewed at 40x and 100x (the scope
is 1000mm, and the eyepieces are 25 and 10 respectively, or did I get
the magnifications wrong?). At 100x it seemed I was getting a hint of
banding/striping on Jupiter itself. Thing is, I don't know how to
evaluate this.

Is a hint of banding what one should expect at that magnification, or
should I be doing (much?) better than that? If so, what is mostly
likely the weak link in the chain? Is it the scope itself? Or is it
the eyepiece?

Collimation is not a problem, I think; I can see my own eye looking back
at me. I played with the focus to get the sharpest image and that was
the best I could do. Can't think of much else, except that Jupiter was
close to the horizon, and there was a fair amount of light pollution,
but the seeing was not bad (no twinkles).

Comments and/or opinions?

Thanks all,

Longfellow

No, your scope isn't the best, but the difference between it and the
best is very subtle. Orion sells good scopes.
At 100x with good seeing, Jupiter's bands should be easily visible, more
than a hint. For example, my 10 year old daughter, who only
occasionally looks through an eyepiece, could clearly see them in our
2.5 inch refractor.
I suspect your collimation is close, but close isn't good enough. My
2.5" is well collimated, and is out performing your 8". Since you
didn't pay for a dinky scope like mine, don't put up with the
performance of a little scope! Reflectors will only come out of the box
perfectly collimated by accident. Normal set-up will require a little
adjustment. Once you get the hang of it (which doesn't take long), it's
quick and easy. Search around on the web, and you'll find tons of
information and tools. I like the barlowed laser for my dob, btw.
Couple places to start:
http://legault.club.fr/collim.html
http://www.collimator.com/coltext.htm

Shawn

On Fri, 18 Jul 2008 19:38:23 -0500, Longfellow
wrote:

Collimation is not a problem, I think; I can see my own eye looking back
at me. I played with the focus to get the sharpest image and that was
the best I could do. Can't think of much else, except that Jupiter was
close to the horizon, and there was a fair amount of light pollution,
but the seeing was not bad (no twinkles).

An 8" f/4.9 is sensitive to miscollimation and a small adjustment can
make a big difference. The manual has good instructions on
collimation and star testing. You need to use high power near 400x to
star test an 8" telescope.

Being close to the horizon will wipe out detail. Light pollution will
not affect Jupiter. In fact, sometimes details can be easier to see
at twilight.

Longfellow wrote:
I've recently acquired an Orion 8" reflector w/ equatorial on tripod,
motors, and two eyepieces, all made in China (of course). I'm aware
that this setup is not the best, but better than what one gets in a
department store. But I don't know just what to expect from it in terms
of performance.

A few nights ago, I ranged Jupiter and viewed at 40x and 100x (the scope
is 1000mm, and the eyepieces are 25 and 10 respectively, or did I get
the magnifications wrong?). At 100x it seemed I was getting a hint of
banding/striping on Jupiter itself. Thing is, I don't know how to
evaluate this.

Is a hint of banding what one should expect at that magnification, or
should I be doing (much?) better than that? If so, what is mostly
likely the weak link in the chain? Is it the scope itself? Or is it
the eyepiece?

Collimation is not a problem, I think; I can see my own eye looking back
at me. I played with the focus to get the sharpest image and that was
the best I could do. Can't think of much else, except that Jupiter was
close to the horizon, and there was a fair amount of light pollution,
but the seeing was not bad (no twinkles).

Comments and/or opinions?

Thanks all,

Longfellow


Planet features are not as gaudy as you see in images, which are
processed to make faint features very apparent. Learn to use filters
which screw onto the eyepiece to increase contrast and decrease
brightness, but also learn to look, or rather stare, and you'll see
more. Learning to judge when the atmosphere is steady (stars twinkling
slowly or not at all) is also important.

--- Dave

Longfellow wrote:
A few nights ago, I ranged Jupiter and viewed at 40x and 100x (the scope
is 1000mm, and the eyepieces are 25 and 10 respectively, or did I get
the magnifications wrong?). At 100x it seemed I was getting a hint of
banding/striping on Jupiter itself. Thing is, I don't know how to
evaluate this.

I'm afraid I can't, either, because what may seem like a hint to a
beginner will likely seem glaringly obvious to someone who's been
observing a while and knows what to expect.

Chances are, the optics themselves are not at fault. Seeing, Jupiter's
low angular altitude, and collimation are the best bets.

Collimation is not a problem, I think; I can see my own eye looking back
at me.

That would only ensure the very coarsest of collimation. It could be
bad enough to net you a significantly suboptimal image, and you could
still see your eye looking back at you. In a reflector of that size,
misalignment by half a degree can cause noticeable image degradation. I
would mark the mirror and use a collimation tool of some sort, even if
it's as simple as a sight tube.

I played with the focus to get the sharpest image and that was
the best I could do. Can't think of much else, except that Jupiter was
close to the horizon, and there was a fair amount of light pollution,
but the seeing was not bad (no twinkles).

Scintillation (twinkling) is not the same thing as seeing. Both are
caused by atmospheric turbulence, but the seeing can be poor even when
the stars are not twinkling (and vice versa). See MOPFAQ for more
information on this:

http://localhost/reference/faq.html#seeing

Light pollution does not really affect the planets (except for Pluto),
and it certainly won't lose you any noticeable detail on Jupiter.

--
Brian Tung
NOTE: Below addresses changing soon...
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
My posts do not represent the views of either Aerospace of USC/ISI.

http://localhost/reference/faq.html#seeing


This should be http://astro.isi.edu/reference/faq.html#seeing

Our club has a class where folks build 6" f/8 dobs with purchased optics,
spider, focuser and Rigel Quickfinder, with the tube, wooden parts,
etc.pre-fabricated by us and ready to be assembled. A post like this
reinforces the wisdom of what we do. The design is forgiving to slight
miscollimation, and the owner/builder is comfortable working with
collimation and learning how to do it better. I can't count the number of
times I have found smaller scopes to outperform larger scopes for any number
of reasons, including collimation and questionable optical quality.

You need to seek out your local astro club, where you will find folks who
can quickly show you how to collimate your scope and where you will learn
what you can/should see. Spending an evening with a club will do more to
facilitate your enjoyment of your scope than anything else.

Dennis

On 2008-07-19, Longfellow wrote:
snip

Thanks to all who responded!

The FAQ was very helpful; having studied this stuff so long ago allows
me to recognize most of it, but now having a real application at hand
makes it real as well.

I do indeed have instructions about collimating and star testing the
instrument, and will follow them precisely in due course. After having
done due diligence, I will inevitably be back with more newbie
questions. And I will study the FAQ more thoroughly, as it gives me a
framework from which to explore various subjects and issues.

You guys are a gentlemenly lot, unlike those inhabiting other Usenet
groups, and I think that the fact that you are so is remarkable; hence
this remark. s.a.a is now on my short list and I'll be reading here
regularly.

Now... to discover acceptably clear and dark skies somewhere within
reasonable driving distance...

Thanks again,

Longfellow

Dennis Woos wrote:
http://localhost/reference/faq.html#seeing

This should be http://astro.isi.edu/reference/faq.html#seeing

Yeah, oops. Unless, of course, you've mirrored my FAQ on your own
machine.

--
Brian Tung
NOTE: Below addresses changing soon...
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
My posts do not represent the views of either Aerospace of USC/ISI.