First Telescope - Finally asking for Advice and Experiences!

All,

If you have been following my adventures (or misadventures), you know
that I have been trying to spec out a new telescope. Thanks to a
great many people, I have it narrowed down to 4. Before we get to the
actual telescopes, a bit of review:

1. Sky watcher for years with 10x50 binoculars.

2. Want something that will "Grow with me".

3. Want something that I can eventually marry to my cameras (2-3
years down the road).

4. Somewhat limited transport space (Honda Insight).

5. Have access to, and will eventually own, a 3 inch refractor.

6. Want something on a GEM.

7. Need to be able to set it up solo.

After looking through a bunch of telescopes and talking to many
people, I have narrowed my choices down to 4 telescopes. All are the
Celestron Advanced Series. All are available in a GoTo version but
I'm not sure I'm interested in that (I'll proabably get it if it fits
the final budget). They a

a. 8 inch Newtonian Reflector.

b. 8 inch SCT

c. 9 1/4 inch SCT.

d. 10 inch Newtonian Reflector.


All of the above fit into my budget and I am going to do a fit test on
the 10 inch refractor (the 45 inch length is going to be close).
Without starting a firstorm on SCT vs. Reflector, I would appreciate
experiences/opinions on the following:

1. Optical Problems with these. I'm especially worried about coma
with the reflectors (should I be?).

2. Ability to set up solo.

3. Dewing problems with the SCT vs. Collimation (sp?) issues with the
Reflectors.

4. Overall suitability for eventually trying to take pictures with
them.

5. Any experience or general advice related to them (and please, no
more "why don't you get a dob?" I really want something that will
track.)

Thank you all for your help. If any of you are SDAA members, I'm
planning on going to your star party this weekend so I can get some
more eyepiece time with some of these telescopes.

Mark

Hi Mark,

a. 8 inch Newtonian Reflector.

b. 8 inch SCT

c. 9 1/4 inch SCT.

d. 10 inch Newtonian Reflector.

Good candidates.

All of the above fit into my budget and I am going to do a fit test on
the 10 inch refractor (the 45 inch length is going to be close).
Without starting a firstorm on SCT vs. Reflector,

Too late! ;-)

1. Optical Problems with these. I'm especially worried about coma
with the reflectors (should I be?).

8" f/5 and 10" f/4.7? Yes, you will have some coma. You mentioned it being
able to grow with you. You can add a coma corrector later. I the meantime,
I'd suggest seeing if someone local has a fast dob you can look through and
see how much it bothers you. It depends on what you want to look at. With
the drives, you can keep planets etc in the sweet spot.

2. Ability to set up solo.

How big are you?

3. Dewing problems with the SCT vs. Collimation (sp?) issues with the
Reflectors.

Get a dew shield. If it is still a problem, get a dew control system.
Kendrick has been the standard, but Dew Buster looks real good. And an SCT
needs to be collimated. But you can learn how to collimate both the newt and
the SCT.

4. Overall suitability for eventually trying to take pictures with
them.

I don't photograph, so I'll keep quiet here.

5. Any experience or general advice related to them (and please, no
more "why don't you get a dob?" I really want something that will
track.)

Gee Mark, why don't you get a dob?

Either way (newt or SCT) go for the biggest you know you will use regularly.
The best scope is the one that gets used the most. But if you're just as
likely to set up a 10" newt as an 8", get the 10" if you go newt. Same with
the 9.25 over the 8" SCT.

Also, many people really prefer the 9.25" SCTs. The focal ratio of the
primary is a little longer, so the magnification of the secondary is less.
Some people swear they are consistenly better optics than the other sizes as
a result.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/

************************************

Thank you all for your help. If any of you are SDAA members, I'm
planning on going to your star party this weekend so I can get some
more eyepiece time with some of these telescopes.

Mark

All of the above fit into my budget and I am going to do a fit test on
the 10 inch refractor (the 45 inch length is going to be close).
Without starting a firstorm on SCT vs. Reflector,

Too late! ;-)

I will admit to reading every thread that has some kind of comparison
bewteen the two. Not that I understand all of the discussion points,
but I didn't want that to start all over again.


1. Optical Problems with these. I'm especially worried about coma
with the reflectors (should I be?).

8" f/5 and 10" f/4.7? Yes, you will have some coma. You mentioned it being
able to grow with you. You can add a coma corrector later. I the meantime,
I'd suggest seeing if someone local has a fast dob you can look through and
see how much it bothers you. It depends on what you want to look at. With
the drives, you can keep planets etc in the sweet spot.

There is somebody here in San Diego that has made just such an offer.


2. Ability to set up solo.

How big are you?

5' 10". Not in great shape but I have no problem with 5 mile hikes in
the hills and lifting the occasional bag of fertilizer or concrete.


3. Dewing problems with the SCT vs. Collimation (sp?) issues with the
Reflectors.

Get a dew shield. If it is still a problem, get a dew control system.
Kendrick has been the standard, but Dew Buster looks real good. And an SCT
needs to be collimated. But you can learn how to collimate both the newt and
the SCT.

From what I understand, the Reflectors need to be collimated regularly
(maybe even before every viewing) and you need to work on both the
primary and secondary (although just the primary regularly). What I
read made it sound like the SCT's needed collimation occasionally.
I'm sure experience will teach me the truth.

Edward Smith schrieb in im Newsbeitrag:
...

snipped

From what I understand, the Reflectors need to be collimated regularly
(maybe even before every viewing) and you need to work on both the
primary and secondary (although just the primary regularly). What I
read made it sound like the SCT's needed collimation occasionally.
I'm sure experience will teach me the truth.

If handled carefully, the reflector should not need to be collimated very
often. Collimating an SCT is more difficult than performing the same on a
reflector. The advantage, imo, of an sct over the relector is the length of
the tube (transportation) and the fact that it is a good compromise between
a refractor and a reflector. As far as goto options are concerned, I prefer
using star charts and star-hopping. I feel that I am more at "one" with the
universe and it improves one's ability to locate faint object through
practice. Goto features are excellent if you live in an area where light
pollution is a concern, though, since you definitely need to be able to
discern faint objects if using the starhopping method. You will be
surprised at how efficient you get with the starhopping method.

Having said all of this, I am also in the market for a telescope and will
be leaning toward a good-sized reflector, due to cost considerations and the
fact that I really want a light bucket :-)

David

On Tue, 27 Jan 2004 05:17:23 GMT, Edward Smith wrote:

3. Want something that I can eventually marry to my cameras (2-3
years down the road).

a. 8 inch Newtonian Reflector.

b. 8 inch SCT

c. 9 1/4 inch SCT.

d. 10 inch Newtonian Reflector.


All of the above fit into my budget and I am going to do a fit test on
the 10 inch refractor (the 45 inch length is going to be close).
Without starting a firstorm on SCT vs. Reflector, I would appreciate
experiences/opinions on the following:

1. Optical Problems with these. I'm especially worried about coma
with the reflectors (should I be?).

Depends on the focal ratio. Anything around f/4 or f/5, definitely.
There are coma correctors on the market, however.

2. Ability to set up solo.

That depends on you. If at all possible, find someone with the sizes
you're considering, and see how easy it is to lift the OTA's onto the
mounts.

3. Dewing problems with the SCT vs. Collimation (sp?) issues with the
Reflectors.

SCTs need to be collimated, too. The severity of image problems is
typically less than with Newtonians, but proper collimation is important
nonetheless. Unless you live in a desert, dew is definitely an issue with
SCTs. You will want minimally a dew shield (ranging from a couple dollars
for a home-made one, to $100+ for an aluminum premade one). That will
only delay the onset of dew, so it's a good bet you'll also want a dew
heater system.

4. Overall suitability for eventually trying to take pictures with
them.

It's likely you'd have trouble with the Newtonians, due to a lack of
backfocus. SCTs have all the backfocus in the world.

You should check out the amount of backfocus on the specific models you're
considering.

5. Any experience or general advice related to them (and please, no
more "why don't you get a dob?" I really want something that will
track.)

Your choices might be a bit touchy on that GEM mount. If going with an
SCT, I think fork + wedge would be far more stable than a CG-5. Just an
educated guess.

In any case, I don't think I'd trust that mount with a 10" Newtonian OTA.


--
- Mike

Remove 'spambegone.net' and reverse to send e-mail.

"David Goldstein" wrote in message ...
Collimating an SCT is more difficult than performing the same on a
reflector.

This is _so_ NOT true

David Goldstein wrote:

Collimating an SCT is more difficult than performing the same on a
reflector.

Well, maybe yes and maybe no. In a Newtonian, both primary and secondary need
to be adjusted for proper alignment. The first step is centering the middle
of the secondary in the focuser, and the second step is adjusting the tilt.
The third step is adjusting the primary mirror for gross alignment and the
final step is the star alignment. This amounts to 4 processes which must be
properly executed for good collimation. With an SCT, there is only one thing
which can be easily adjusted: the tilt of the secondary mirror. Usually, a
star test alignment can be easily performed for the SCT, so that is only one
step needed vs. the four which the Newtonian requires. Once a person becomes
familiar with the SCT alignment proceedure (which isn't really all that hard),
it can often be done faster than possible on a fully mis-aligned Newtonian
telescope. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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