First Scopes - Round 2

First, thank you very much to everybody who responded to my "First
Scopes - Any experience with these?" post. I got a ton of answers and
valuable advice (althoug I'm a little disappointed Starlord didn't
tell me to read his FAQ ;-) ].

Based on what I have learned and the advice I was given, I have
broadened my horizons a bit and have taken some measurements of my
primary vehicle. While before I was looking at 2 different 5 inch
Mak's, I now realize that, for roughly the same price, I could have an
8 inch scope on a nice equatorial mount. I am looking at two
different telescopes. So you won't have to look up the specifics,
they a

1. Celestron C8-S
Type: Schmidt-Cass
Aperatu 8 inches
Mount: CG-5 Equatorial
Focal Length: 2052mm
Focal Ratio: f10

2. Celestron C8-N
Type: Newtonian Reflector
Aperatu 8 inches
Mount: CG-5 Equatorial
Focal Length: 1000mm
Focal Ratio: f5

The resolving power on the two is the same, the Newtonian is about 13
pounds heavier and 20 inches longer, and the photographic resolution
on the Newtonian is double the Schmidt-Cass.

So, aside from the portability concerns, I would like to make sure I
understand the tradeoffs between these two telescopes. Please jump in
and correct/add as you can:

a. Because it has a longer Focal Length, the Schmidt-Cass will have a
greater eye relief for a given magnification because the eyepiece
focal length for a given magnificaion will be about 2.5 times that of
the Newtonian.

b. The Newtonian will reach Thermal Equilibrium faster.

c. The Newtonian will have a greater field of view.

d. The Newtonian will be better for most astrophotography (thinking
about the future).

e. The Schmidt-Cass would be better for any terrestrial photography
attempts.

f. The Newtonian will require more maintenance (not positive about
this one).

Is there anything else?

Also, I'm wondering if these telescopes can be set up by one person.

Thank you for your help.

Mark

"Edward Smith" wrote in message
...
First, thank you very much to everybody who responded to my "First
Scopes - Any experience with these?" post. I got a ton of answers and
valuable advice (althoug I'm a little disappointed Starlord didn't
tell me to read his FAQ ;-) ].

Based on what I have learned and the advice I was given, I have
broadened my horizons a bit and have taken some measurements of my
primary vehicle. While before I was looking at 2 different 5 inch
Mak's, I now realize that, for roughly the same price, I could have an
8 inch scope on a nice equatorial mount. I am looking at two
different telescopes. So you won't have to look up the specifics,
they a

1. Celestron C8-S
Type: Schmidt-Cass
Aperatu 8 inches
Mount: CG-5 Equatorial
Focal Length: 2052mm
Focal Ratio: f10

2. Celestron C8-N
Type: Newtonian Reflector
Aperatu 8 inches
Mount: CG-5 Equatorial
Focal Length: 1000mm
Focal Ratio: f5

The resolving power on the two is the same, the Newtonian is about 13
pounds heavier and 20 inches longer, and the photographic resolution
on the Newtonian is double the Schmidt-Cass.
This is only because the focal length is half. The 'angular' resolution
remains basically the same.

So, aside from the portability concerns, I would like to make sure I
understand the tradeoffs between these two telescopes. Please jump in
and correct/add as you can:

a. Because it has a longer Focal Length, the Schmidt-Cass will have a
greater eye relief for a given magnification because the eyepiece
focal length for a given magnificaion will be about 2.5 times that of
the Newtonian.

b. The Newtonian will reach Thermal Equilibrium faster.

c. The Newtonian will have a greater field of view.

d. The Newtonian will be better for most astrophotography (thinking
about the future).

e. The Schmidt-Cass would be better for any terrestrial photography
attempts.
These two, contradict one another. See below.

f. The Newtonian will require more maintenance (not positive about
this one).

Is there anything else?

Also, I'm wondering if these telescopes can be set up by one person.

Thank you for your help.
If you want to image, then the SCT, may well be the best choice. The
'problem' with the Newtonian, in this regard, is 'back focus'. Basically,
you can only use the Newtonian to image, if you can place the film/CCD,
exactly where the eyepiece normally sits. The range of adjustment available
is tiny. The Newtonian is 'better', in terms of having a shorter focal
length (which may well give a better 'match' to a typical CCD), but can be
very difficult to use with many imagers, especially if other acessories are
needed in the light path (filter wheel, or OAG for instance). The different
'resolutions', are simply related to the focal length, so you can make the
SCT, give the same film resolution, by using a focal compressor to bring
it's focal length down to match that of the Newtonian. The huge range
available from the SCT focusser, is probably the single biggest 'plus' for
the design. It comes at the cost of inreasing optical aberration, as you
move away from the design focus point, but this is normally entirely
acceptable over the ranges involved.
I'd not worry about 'magnification' very much at all. Basically the 'best'
deep sky views, are often at very low magnifications, and the Newtonian,
then wins (though on wider views, a coma corrector may be necessary).
However use of a focal compressor/field flattener on the SCT, allows it to
give similar results.
Seperately there is the issue of 'comfort'. The two scopes have very
different eyepiece positions, and some people quite strongly prefer one to
the other. Worth actually trying looking at some positions in the 'sky',
using both scopes in a shop, to see what is involved. Also worth looking
through a fork mounted scope (like the Nexstar 8), as another 'reference'
point. Generally, many people would consider this design (alt/az mount using
a fork), as the 'nicest' for visual eyepiece position across a lot of the
sky, but then you have the downside of needing a wedge to avoid field
rotation, for imaging...

Best Wishes

(althoug I'm a little disappointed Starlord didn't tell me to read his FAQ
-) ].

Well, as you seemed to know of better types of telescopes other than the crudie
Department store ones, I figured you had either 1. already read it, or 2. had
talked to other telescope owners, or 3. been looking at better types already.

If by some chance now of the above or anything like them apply, then yes Please
Read the Telescope Buyers FAQ and use it as a guildline to avoid the pitfalls of
telescope ownership.

There, happy now?

Oh, and while I don't to photos with my Dob, ( daylight or otherwise ) I am able
to set up and use my Babylon 8 , ( 8inch F8 Dob ) all by myself and it needs far
less care that some other telescopes.


--
"In this universe the night was falling,the shadows were lengthening
towards an east that would not know another dawn.
But elsewhere the stars were still young and the light of morning
lingered: and along the path he once had followed, man would one day go
again."

Arthur C. Clarke, The City & The Stars

SIAR
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"Edward Smith" wrote in message
...
First, thank you very much to everybody who responded to my "First
Scopes - Any experience with these?" post. I got a ton of answers and
valuable advice (althoug I'm a little disappointed Starlord didn't
tell me to read his FAQ ;-) ].

Based on what I have learned and the advice I was given, I have
broadened my horizons a bit and have taken some measurements of my
primary vehicle.


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.558 / Virus Database: 350 - Release Date: 1/2/04

Big old Snip!

Seperately there is the issue of 'comfort'. The two scopes have very
different eyepiece positions, and some people quite strongly prefer one to
the other. Worth actually trying looking at some positions in the 'sky',
using both scopes in a shop, to see what is involved. Also worth looking
through a fork mounted scope (like the Nexstar 8), as another 'reference'
point. Generally, many people would consider this design (alt/az mount using
a fork), as the 'nicest' for visual eyepiece position across a lot of the
sky, but then you have the downside of needing a wedge to avoid field
rotation, for imaging...

Best Wishes


Actually, I've been attending a lot of local star parties and outreach
events and looking through as many scopes as I can (and asking lots of
questions). Before I go on, let me issue a blanket "thank you" to all
of you who volunteer your very expensive equipment so the likes of me
can explore the space around us. My biggest reason for wanting a
telescope of my own is so I can choose what I want to look at and can
explore on my own. I do plan on giving back in the same way so many
of you do.

Back to the subject though. I have generally found that I like the
German Equatorial mounted scopes the best. They seem to give the most
room. I hadn't considered the weight and balance issue of these
mounts though. I need to ask some more questions I guess. Eyepiece
position does seem to be more of an issue for a Newtonian Reflector on
a German Equatorial mount than it does for a Schmidt/Mak-Cass on the
same mount, but I haven't found it to be uncomfortable. I'm going out
again on Friday and will look a little harder.

(althoug I'm a little disappointed Starlord didn't tell me to read his FAQ
-) ].

Well, as you seemed to know of better types of telescopes other than the crudie
Department store ones, I figured you had either 1. already read it, or 2. had
talked to other telescope owners, or 3. been looking at better types already.

Actually, I saw your replies to other people's posts and started by
reading it (I actually bookmarked it and have been back a couple of
times). I figured that I wouldn't waste people's time asking
questions for which the answers were readily available.


If by some chance now of the above or anything like them apply, then yes Please
Read the Telescope Buyers FAQ and use it as a guildline to avoid the pitfalls of
telescope ownership.

There, happy now?

Getting there. Of course, I'll be even happier when I buy the
telescope and look through it for the first time.

"Edward Smith" wrote in message
...
Big old Snip!

Seperately there is the issue of 'comfort'. The two scopes have very
different eyepiece positions, and some people quite strongly prefer one
to
the other. Worth actually trying looking at some positions in the 'sky',
using both scopes in a shop, to see what is involved. Also worth looking
through a fork mounted scope (like the Nexstar 8), as another 'reference'
point. Generally, many people would consider this design (alt/az mount
using
a fork), as the 'nicest' for visual eyepiece position across a lot of the
sky, but then you have the downside of needing a wedge to avoid field
rotation, for imaging...

Best Wishes


Actually, I've been attending a lot of local star parties and outreach
events and looking through as many scopes as I can (and asking lots of
questions). Before I go on, let me issue a blanket "thank you" to all
of you who volunteer your very expensive equipment so the likes of me
can explore the space around us. My biggest reason for wanting a
telescope of my own is so I can choose what I want to look at and can
explore on my own. I do plan on giving back in the same way so many
of you do.

Back to the subject though. I have generally found that I like the
German Equatorial mounted scopes the best. They seem to give the most
room. I hadn't considered the weight and balance issue of these
mounts though. I need to ask some more questions I guess. Eyepiece
position does seem to be more of an issue for a Newtonian Reflector on
a German Equatorial mount than it does for a Schmidt/Mak-Cass on the
same mount, but I haven't found it to be uncomfortable. I'm going out
again on Friday and will look a little harder.
Very good.
It was a 'caveat' worth making. I think it also relates to which design you
are 'used' to. There are 'solutions' for the Newtonian on a GEM (for
instance, systems that allow you to rotate the entire tube), but the cost
then goes up.
The GEM, is much easier to balance fore/aft for loads like cameras, than a
fork (with the GEM, you can just move the scope tube forward in the mount,
but with a fork, you need to start adding weight to the front of the tube).
The fork though, runs without a balance weight in the other axis (which does
increase the bearing loads a lot)...

Best Wishes