new telescope

I have been watching post here for a couple of years. I took the
advice of some of you and bought a pair of binoculars and have been
star gazing for over a year now. I know a little about the sky now,
but still very green. I'm about to buy my first telescope, and so far
I've narrowed my choices to the Orion XT-8 or XT-10, but remain open
for suggestions. If I go with the XT-10, how does it perform on the
Planets and what accessories do you recommend?

"96redneck" wrote in message
...
I have been watching post here for a couple of years. I took the
advice of some of you and bought a pair of binoculars and have been
star gazing for over a year now. I know a little about the sky now,
but still very green. I'm about to buy my first telescope, and so far
I've narrowed my choices to the Orion XT-8 or XT-10, but remain open
for suggestions. If I go with the XT-10, how does it perform on the
Planets and what accessories do you recommend?

Go with the XT-10 -- more aperture, not that much heavier to move. If you
can handle the extra $$$, get the Intelliscope -- you can use the scope as a
normal Dob or you can use the Intelliscope.

Accessories:
-- order the 9X50 right-angle finder scope and install it in place of the
straight-through finder that comes on the XT-10
-- get a 2X Barlow; the Orion barlows are perfectly fine
-- don't buy any extra eyepieces until you have used the scope for a while
-- you may want to stick a Telrad on it.

Here are my experiences with my XT-8
http://www.schlatter.org/Dad/Astronomy/xt%208.htm

and my XT-12 Intelliscope
http://www.schlatter.org/Dad/Astronomy/XT%2012.htm

On Sun, 05 Mar 2006 17:09:40 -0500, 96redneck wrote:

I have been watching post here for a couple of years. I took the
advice of some of you and bought a pair of binoculars and have been
star gazing for over a year now. I know a little about the sky now,
but still very green. I'm about to buy my first telescope, and so far
I've narrowed my choices to the Orion XT-8 or XT-10, but remain open
for suggestions. If I go with the XT-10, how does it perform on the
Planets and what accessories do you recommend?

I have a friend who owns the XT-8 (Tom Wales) and he could not be happier
with it. I took a look at the Whirlpool (M51) a year or two ago through it
and was quite impressed with the image. The contrast was superb and the
spiral structure hinted at itself even in my backyards 4.8 to 5.0 magnitude
sky.


--
Martin R. Howell
"The Astro Post"
www.theastropost.com
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Starboard wrote:

Enough cannot be said for portability. I drag my scope out every clear
night and I know that I wouldn't if it was *any* bigger. Moving the
scope does not end with just moving it to the backyard, it must be
moved multiple times per night. In fact, the XT-8 is about as big as I
would go for a scope that must be transported. Not for sheer weight
reasons, but for weight x bulk. I banged the tube assembly into the
fish tank already once trying to navigate out the back door with it.


Good advice, Errol.


I would also investigate whether not there were any known disadvantage
to a scope with a shorter focal ration, as the XT-10 is (F/4.7 vs
F/5.9). Like is there added difficulty in focussing at high power?

Collimation will become more critical.



Having said that, I know that I will buy a bigger scope (probably the
XT-12) in the future, one I can dolly around and keep in the shed,
because like Joe S said, bigger is better.



Portability is key if you must transport the scope to view. I found I
was not using my 10" Dob and it is no longer here. When I bought a new
SCT in 2003, I bought an 8" vs. 11" due to mass considerations .. based
on a fork mount. Today I might reconsider, and buy an 11" on a GEM
since I'm now interested in astrophotography .. and I think the
individual pieces might be easier to move around.

Eventually I will have a bigger scope .. but only when I move to a home
with less polluted skies. For now the transportability and set up ease
of my Nexstar8GPS (now with SkyAlign) wins .. and so would an 8" Dob.

Phil

Good advice, Errol.

Well Phil, pat yourself on the back. I have a pretty good teacher(s).
(Thanks again for all your past help)

Tell me, in *badly polluted* skies, does one benefit *as much* from
more aperture? I mean doesn't it seem that at some point, additional
aperture would, along with gathering more light from the object under
observation, also gather more light from the pollution as well?

Errol

Starboard wrote:
Good advice, Errol.


Well Phil, pat yourself on the back. I have a pretty good teacher(s).
(Thanks again for all your past help)

Tell me, in *badly polluted* skies, does one benefit *as much* from
more aperture? I mean doesn't it seem that at some point, additional
aperture would, along with gathering more light from the object under
observation, also gather more light from the pollution as well?



I've read that, but don't understand it. Perhaps urban legend. Let the
more knowlegable comment.

Of course, one plus of more aperture (but not with a Dob beyond 200x or
so) is you can push the magnification higher and improve contrast .. or
so it seems to me.

Phil

Of course, one plus of more aperture (but not with a Dob beyond 200x or
so) is you can push the magnification higher and improve contrast .. or
so it seems to me.

Yep.

And I guess the additionally *gathered* pollution is not beyond a
measure of control with the range of filters available...

Errol

"Starboard" wrote in message
oups.com...
Tell me, in *badly polluted* skies, does one benefit *as much* from
more aperture? I mean doesn't it seem that at some point, additional
aperture would, along with gathering more light from the object under
observation, also gather more light from the pollution as well?


Background sky brightness is determined by exit pupil (not aperture). A 2mm
exit pupil in a 100mm aperture and a 2mm exit pupil in a 200mm aperture have
the same background brightness. However, the 100mm scope is operating at
50x, where the 200mm scope is operating at 100x.

Since the larger aperture scope provides a larger image scale (for extended
objects like planets, galaxies, nebulae) the human eye has an easier time
detecting subtle differences in contrast between adjacent features
(including seeing the object against the background sky).

Another way to state that is if you hold power constant, exit pupil changes
with aperture. So, if you start out with an 200mm aperture at 100x, and you
move up to a 300mm aperture at 100x, the exit pupil goes up from 2mm to 3mm.
So, yes, the sky background brightness does change (get brighter) with the
increase in aperture. To compensate, bump the power up to 150x in the 300mm
scope (which again, is the advantage to the larger aperture...; larger image
scale at the same exit pupil/sky background brightness!!).

-Stephen

"Starboard" wrote in message
oups.com...
Good advice, Errol.

Well Phil, pat yourself on the back. I have a pretty good teacher(s).
(Thanks again for all your past help)

Tell me, in *badly polluted* skies, does one benefit *as much* from
more aperture? I mean doesn't it seem that at some point, additional
aperture would, along with gathering more light from the object under
observation, also gather more light from the pollution as well?


By the way, in my experience under mag 5.2 skies, holding sky background
brightness in the range of a 2.4mm to 2.6mm exit pupil, the difference
between a 6" scope and a 10" scope isn't as significant with galaxies,
nebulae, and open clusters as it is with planets and globular clusters.

I just ran the Messier marathon evening list from M77 through M84/M86 using
both my 6" F5 altazimuth mounted Newtonian with Telrad, and my C9.25 on G-11
with DSCs side by side (an experiment). After getting as far as M82, I gave
up on the C9.25 and gadgetry, and continued on with just the 6" F5 and
Telrad.

Holding the exit pupil around 2.5mm (24mm eyepiece in the C9.25, 13mm
eyepiece in the 6" F5) there just isn't all that much more detail to see
with the larger aperture until you get to the globs (and finding stuff with
the Telrad takes as little time as using the DSCs).

Starboard wrote:
Tell me, in *badly polluted* skies, does one benefit *as much* from
more aperture? I mean doesn't it seem that at some point, additional
aperture would, along with gathering more light from the object under
observation, also gather more light from the pollution as well?

Obviously, at some point, the benefit from aperture must drop to zero:
for instance, for overcast skies. (Though they really have to be
overcast. I have been able to see Jupiter through the telescope at a
time when I couldn't see it with the unaided eye, and I think it would
have been invisible through a very small telescope, too.)

--
Brian Tung
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
(Location of these pages soon to change. Stay tuned for updates.)