Beginner: Which to Buy? ETX-70 or 6" Newtonian Refractor?

Yeah I have a pair of 10x50 Bushnells... old but they do the trick. I
am amazed at dusk how many more stars can be seen through the
binoculars than with the naked eye.

I'm still keen on getting something... while the ETX-70 GOTO features
are neat it sounds like it is too small a scope.

OK... Same place that is selling the 6" Newtonian Reflector is also
selling this...

http://www.citiwellint.com/vu.php?pa...ng+Goods&age=+

a 90mm Maksutov-Cassegran with two 1.25" eyepieces (a 9mm and a 25mm)
for $189 CDN. It doesn't have an EQ mount or motor (nor the GOTO) but
it is larger than the ETX-70. My big concern is the mount... What
should I be looking for in a tripod/mount? I get the feeling that I
will want something with guides for setting azimuth,
elevation(altitude) and declination? or how how else does a newbie
end up finding things?







"Stephen Paul" wrote in message ...
Choices that you can possibly make, in order, as you mature in the hobby,
without losing anything on the investments. All of these are complimentary
tools of the hobby, which means you won't have to think about selling them
later.

#1 - 10x50 Binoculars and Terrence Dickensen's book, _Nigh****ch_.

If you like this hobby, and begin to have success using the charts in
_Nigh****ch_, then move up to:

#2 - Chinese 80mm F5 refractor (ST80) on an altitude-azimuth mounting with
slow motion controls, and the _Bright Star Altas_. Also pick up a good
barlow and a 9 or 10mm Plossl eyepiece to go with the typical 25mm Plossl
that comes with the ST80.

If you still like this hobby and have success using the charts in _Bright
Star Atlas_, then move up to:

#3 - 8" to 12" Dobsonian, depending on your personal limit for managing bulk
and weight, and _Sky Atlas 2000_. You already have the 10mm eyepiece and the
barlow from the ST80 purchase, but you should now add something in the 15mm
range.

If you are really hot on this hobby, and want to do some high power planet
imaging, then add:

#4 - Used 8" SCT on a good GEM, or well regarded Fork Mount and a CCD based
web cam.

Just some thoughts....

"David Jones" wrote in message
om...
Yeah I have a pair of 10x50 Bushnells... old but they do the trick. I
am amazed at dusk how many more stars can be seen through the
binoculars than with the naked eye.

I'm still keen on getting something... while the ETX-70 GOTO features
are neat it sounds like it is too small a scope.

OK... Same place that is selling the 6" Newtonian Reflector is also
selling this...


http://www.citiwellint.com/vu.php?pa...ng+Goods&age=+

a 90mm Maksutov-Cassegran with two 1.25" eyepieces (a 9mm and a 25mm)
for $189 CDN. It doesn't have an EQ mount or motor (nor the GOTO) but
it is larger than the ETX-70. My big concern is the mount... What
should I be looking for in a tripod/mount? I get the feeling that I
will want something with guides for setting azimuth,
elevation(altitude) and declination? or how how else does a newbie
end up finding things?
The big problem is that mounts that have really nice 'smooth' motions, and
reasonable rigidity, are expensive. Basically, the 'best' small mount
around, is probably the Vixen GP-DX, and it's slightly smaller brother the
GP. These mounts have been 'copied' by allmost everybody, and some of the
copies are quite good (though few have quite the gear quality shown by the
Vixen units). The Celestron copy, in it's 'latter' incarnation (with
improved RA bearings), can work quite well, but usually needs some 'tuning'
to be really good. Generally, a reasonable mount, will cost as much as the
scope on it. 80% of the aluminium tripods supplied with scopes, are too
'springy' to really work well (one option that is quite cheap, and gives
excellent results, is to replace the legs on such a tripod, with timber ones
made from a wood like ash - surveyors tripods are also suprisingly cheap,
and a lot better than 95% of the normal telescope ones).
Maksutov scopes, are often quite good, but have the disadvantage, of
relatively long focal lengths. This gives relatively high magnifications
(making them good for 'planetary' observation), but relatively small FOV's,
which can make them less useful for 'deep sky' observation.
There is a problem, because of your desire to image. Basically, imaging,
puts more demands on the mount, and the 'starting point', tends to be
higher, than for basic viewing. For simple viewing, the 'Dobsonian mounted
Newtonian', is the cheapest system, with the downside that you have to move
the scop yourself, but the plus of putting the money into the optics. The
Hardin Optical units are probably the best 'value' around at the moment,
being one of a number coming from Chinese manufacturers, with reasonable
optics. The Orion 'Intelliscope' series, are similar, but add a 'push to'
system, which tells you where the scope is pointing.
The way people find things with scopes, depends (a little) on the mount, but
the simplest way, is 'star hoping'. Basically most interesting objects, have
recognisable 'bright' stars reasonably close, or patterns that 'point' to
them. With a EQ mount, there are normally RA/Dec 'dials' on th axes, and you
can point the scope to a known object, and then adjust the dials so that the
reading corresponds to the RA/Dec of that object. Then if you move the scope
to the RA/Dec of the desired target, it will be pointing at the right spot.
I really have to support the suggestion, that you see if there is an
astronomy club nearby. It is terrifyingly easy to spend a lot of money on
astronomy equipment, and not get what you really want. Learning what
equipment does, is far cheaper, by looking at other people's kit, than by
buying it yourself!...

Best Wishes

What should I be looking for in a tripod/mount? I get the feeling that I
will want something with guides for setting azimuth, elevation(altitude) and
declination? or how how else does a newbie
end up finding things?

This is a good question.

There are several ways to find things.

1. Just start looking, wander around until you find something that is
interesting. Use a low power eyepiece to provide a wide field of view. I
enjoy doing this.

2. Starhopping: Using a star chart(paper or software) and the telescope's
finder, locate the desired target. Start with a bright, easily recognizable
star and find a path. Sky and Telescope has several monthly columns that are
a big help in this regard. I like Sue French's small telescope column, lots of
interesting stuff to see.

3. Setting circles, either analog or digital. You align your scope and then
using the dials or the controller, set it to the proper coordinates for a given
object. Takes decent alignment.

4. GOTO. A computerized telescope that once aligned, will hopefully point
itself at some target.

The choice of a telescope does depend on which of these techniques you are
likely to use.

Which technique will suit your needs really depends on you.

Myself, a big part of the enjoyment comes from learning the sky and learning to
locate the objects by myself. Each time I find something, whether it is the
first time or the 200th time, its a thrill.

As the years have tumbled past, my understanding and knowledge has grown so
that I have a pretty good knowledge of how large chunks of the night sky is put
together.

Some observers find Starhopping frustrating, they want to be looking at the
target as soon as possible. For me, I enjoy just looking at the star fields as
the pass in front of my eyes.

If learning your way around the sky is high on your list of reasons you are
interested in astronomy, then you will probably want a scope that optimized for
starhopping.

The things that are important for starhopping are a widefield of view, enough
aperture to see some real stuff and an easy to use intuitive mount.

I think that a 6-10 in DOB is the ideal scope for Starhopping. The shorter
focal length of the medium size DOBs allows for the wider field of view with a
bright image, the mount is stable and easy to setup and use. Best Bang for the
Buck,

For use with setting circles or GOTO, there are other priorities. The scope
points itself once aligned and the observer enjoys the target.

If one is on a budget, then one trades optical performance for the
electronics, not such a great trade. Small GOTO scopes by Meade and Celestron
have databases that include many objects one will never see because they are
beyond the ability of the scope.

So GOTO certainly has advantages, but the choice between having to point the
scope yourself in order to see an object and having the telescope point at
something you cannot see is an obvious one, so first comes optics...

-----------

Regarding the 90mm MAK on a photo style tripod. THis scope has a 1200mm focal
length and takes 1.25 inch eyepieces. The maximum field of view will be
something like 50degree (AFOV Eyepiece) x focal length eyepiece/focal length
scope. With the optimal 32 mm plossl, it will provide a 1.3 degree FOV, not so
bad, but the image will be dim because of the small aperture. The finder will
not be too helpful either.

This is not a good scope for starhopping.

Bottomline: Please check out your local astronomy club and get some eyepiece
time in before spending your hard earned cash. Amateur Astronomers are a
friendly lot who just love to show you their junk and talk about it..

Take advantage of this so that when you do buy a scope, you will get one that
does the job for you.

Best wishes, clear skies

jon

On 28 Apr 2004 11:02:27 GMT, (Jon Isaacs) wrote:

4. GOTO. A computerized telescope that once aligned, will hopefully point
itself at some target.

My ETX-125 works just fine in this regard, and has the sharpest
resolution of any telescope I've yet owned. Between the GOTO and
resolution, I've found and seen things I've never been able to find or
see before.



--------------
Beady's Corollary to Occam's Razor: "The likeliest explanation of any phenomenon is almost always the most boring one imaginable."


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My ETX-125 works just fine in this regard, and has the sharpest
resolution of any telescope I've yet owned. Between the GOTO and
resolution, I've found and seen things I've never been able to find or
see before.

I happen to currently own an ETX-125EC. (Its for sale.) Yes, the GOTO does
work quite well. But at F15 and using 1.25 inch eyepieces, the maximum field
of view is under 1 degree and without restrictng the FOV, the maximum exit
pupil is barely over 2mm.

I find that the sharpness/resolution of my Orion Space Probe 130ST (5 inch F5
Newt) to be comparable but I can see many more things with it because it offers
the possibility of a 3 + degree FOV with a 6+mm exit pupil.

An ETX-125 costs well over a grand by the time you are done. For this kind of
money, a 10 inch or 12 inch DOB will certainly offer better resolution and show
things in detail that are not possible in any 5 inch Scope..

Jon

Well they all look VERY big to me... and how do you set them up on a rough
surface...

As others have pointed out, inch for inch, a Dobsonian is more compact and less
cumbersome than an EQ mount.

There are several vendors in Canada that sell scopes similar to the Orion and
Hardin Optical line and seem to offer good prices. No need to pay the US duty.

When it comes to optics, well, it is nice to get by without spending a great
deal of money. The problem is that decent quality optics are expensive to make
so if one is buying a 6 inch scope for $200, it means that some corners must
have been cut. The two places where serious compromises are normally made is
in the optics and the mount. A poor scope on a shaky mount is just not fun to
use.

On the other hand, many of us here started with a poor scope on a poor mount, I
certainly did. It did not stop me from enjoying astronomy. But I soon moved
up.

So the hope I have is that you can spend your money on a scope that is capable
of providing many hours of enjoyment with out learning the hard way.....

That said, if you are determined to buy one of the two scope, the 90mm or the 6
inch, I would have to suggest the 6 inch and make sure you keep all the
packaging so that you can return it if you are dissatisfied.

jon