$3000 and which scope???

"Alan W. Craft" wrote in message
...

These are decisions based on personal choice. Certainly an 8 inch F5
Newtonian
can provide some nice images, but then so can an 8 inch F10 SCT.

Which of the two, and without Paracorrs or focal reducers, or even
barlows,
would be best for general observing, from wide-field vistas to the serious
long-term
study of Galilean transits?

That's all I'm asking.


Are you sure you want to ask that ..., now?

The 8" F10 SCT will give you a native range of 1.3 degrees of field with a
5.5mm exit pupil at 37x in a 2" 55mm Plossl, up to 400x with a 5mm eyepiece
of your choice. And although you excluded it from the comparison, with the
F6.3 R/C the focal length drops to 1280mm. (This pushes the primary mirror
up closer to the secondary and causes the primary baffle to cut more deeply
into the light cone. So, for eyepieces with a field stop greater than
roughly 36mm, you will get vignetting, setting the practical limit on a
fully illuminated field to around 1.5 degrees with the R/C.)

I suggest you spend some time with an eyepiece calculator and figure in a
paracorr for the F5. If you expect to be wide field lover, you're going to
need one. Not only, but you will be buying some expensive eyepieces. And, to
avoid turning to Mr. Nagler yet again, you will also need a barlow to
maintain useful eye relief at magnifications above 200x.

Fast Newts ain't cheap, unless you limit your field of view to the center of
the primary.

-Stephen

"Stephen Paul" wrote in message
...


I suggest you spend some time with an eyepiece calculator and figure in a
paracorr for the F5. If you expect to be wide field lover, you're going
to
need one. Not only, but you will be buying some expensive eyepieces. And,
to
avoid turning to Mr. Nagler yet again, you will also need a barlow to
maintain useful eye relief at magnifications above 200x.

Fast Newts ain't cheap, unless you limit your field of view to the center
of
the primary.

-Stephen



Don't need no steenking paracorr for an f/5 newt. My f/4.7 is solid without
one and I would never consider buying a paracorr for it.

Clear skies,

Tom

Someone who owns a Synta 8" f/5 posted within and stated that he detected
only a negligible amount of coma, to which I replied that that was good to
hear, so
I'm not scared, mister.

The point is that there is coma in an F5 Newtonian, no way around it. It may
not bother you but it's there. Personly, I just use a Paracorr because I have
one, but it is not necessary to achive reasonable views.


Yes, an...

...f/4.1...

Yeah and the same thing happens with my F5 scopes too.

Which of the two, and without Paracorrs or focal reducers, or even barlows,
would be best for general observing, from wide-field vistas to the serious
long-term
study of Galilean transits?

The fact is that focal reducers and Paracorrs do exist so there is no need to
answer your hypothetical question. Both improve the view of their respective
scopes so it is quite clear (pun intended) that adding optical elements can
improve the view.

Still, by just how much would the effective aperture be reduced with, say,
even a
50mm ocular, and for someone in their advancing years with a maximum 5mm
dark-adapted pupil?

It would be cut in half to 4 inches. The exit pupil is the focal length of the
eyepiece divided by the Focal ratio of the scope. So a 50mm eyepiece will have
a 10 mm exit pupil of which only the inner half will be seen by the observer.
If you have a 5mm exit pupil then a 25mm eyepiece is the largest you can go
without losing effective aperture. Sometimes it is worth it, certainly when
searching the skies for a faint target that added FOV can help.

Oh, and then there's another little tiresome aspect of catadioptrics...

...dew...

...with its consequent wires and strips and shields and such.


No doubt there are drawbacks to SCTs, and dew is one of the reasons why I
prefer Newtonians.

But there are trade offs here if you are looking for a 10+ inch scope that is
reasonably portable, has decent drives and even has GOTO, then one is stuck
with an SCT in this price range.

Personally I like Dobsonians. But I have been hanging around this group long
enough to know that there are plenty of good alternatives with good optics that
make sense for other people.

jon isaacs

Don't need no steenking paracorr for an f/5 newt. My f/4.7 is solid without
one and I would never consider buying a paracorr for it.

Clear skies,

There is no way around coma in a fast Newtonian except with a paracorr and/or
highly corrected eyepieces (read expensive.)

Ever tried a Paracorr in your scope?

jon

Alan W. Craft wrote in message . ..
On 13 Oct 2003 05:44:38 -0700, (Rod Mollise) ...reflected:
But it's best not to introduce those extra elements into the optical train,
especially when one considers that the Schmidt-Cassegrain design is optically
inferior to that of a classical Newtonian, and that a Schmidt is more difficult
to manufacture than a Maksutov-Cassegrain, so I once read.

I ask you, why throw caution to the wind?



Hi Alan:

Caution is not involved. Frankly, images in SCTs are _better_ with the
r/c in place than _without_...at least at the field edge, which is
what many people worry/obsess about. Next time you're at a star party,
see if you can get your local CAT lover to throw an r/c on...you'll be
impressed, I guar-ron-tee. ;-)

A lot of people go on about the advantages of Newts...and there are
some, no denying that. But honestly the differences are very minor and
are, IMHO, far outweighed by the many advantages of a good, old Meade
or Celestron.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

This scope has been creating a lot of traffic in uk.sci.astro, with
Stephen Tonkin giving it a very solid review.
http://www.capenewise.co.uk

Steve

On Tue, 14 Oct 2003 17:43:17 +0000, Steve Taylor ...reflected:

This scope has been creating a lot of traffic in uk.sci.astro, with
Stephen Tonkin giving it a very solid review.
http://www.capenewise.co.uk

Steve

It's a Schmidt-Newtonian.

The Meades have been somewhat favorably reviewed
in their own right.

Alan

Alan W. Craft wrote:
On Tue, 14 Oct 2003 17:43:17 +0000, Steve Taylor ...reflected:


This scope has been creating a lot of traffic in uk.sci.astro, with
Stephen Tonkin giving it a very solid review.
http://www.capenewise.co.uk

Steve


It's a Schmidt-Newtonian.

The Meades have been somewhat favorably reviewed
in their own right.

Alan

It is emphatically NOT a Schmidt Newt - the front "plate" is flat. You
should try and retrieve the whole thread and see the comments.

Steve

On Tue, 14 Oct 2003 02:03:04 -0400, "Stephen Paul" ...reflected:


"Alan W. Craft" wrote in message
.. .

These are decisions based on personal choice. Certainly an 8 inch F5
Newtonian
can provide some nice images, but then so can an 8 inch F10 SCT.

Which of the two, and without Paracorrs or focal reducers, or even
barlows,
would be best for general observing, from wide-field vistas to the serious
long-term
study of Galilean transits?

That's all I'm asking.


Are you sure you want to ask that ..., now?

I thought I...might...

The 8" F10 SCT will give you a native range of 1.3 degrees of field with a
5.5mm exit pupil at 37x in a 2" 55mm Plossl...

No extreme oculars, thank you; and what, with the other extreme being
a 0.5mm?

Asidedly, did you not figure the average dark-adapted pupil of the 40-and-over
crowd into your equation?

...up to 400x with a 5mm eyepiece...

Yes, the Cassegrain family excels at higher magnifications.

of your choice. And although you excluded it from the comparison...
snip

You're quite right; I did.

I suggest you spend some time with an eyepiece calculator and figure in a
paracorr for the F5. If you expect to be wide field lover, you're going to
need one.

What if I am only...slightly enamored with said vistas?

Actually, I expect most deep-sky observing will be conducted within a
moderate range of magnifications, but if and when the wide-field bug
hits, I'll have an instrument ready and most capable; and with only
negligible coma, I'm betting.

Not only, but you will be buying some expensive eyepieces.

I think $300 and under's reasonable, but only for a real goodie,
and not necessarily a TeleVue product...

The eye relief of that 11mm TeleVue Plossl was horrendous; though
the field was sharp, for what I could see of it.

And, to avoid turning to Mr. Nagler yet again...

I shan't be turning to him 'tall.

...you will also need a barlow to
maintain useful eye relief at magnifications above 200x.

stamps foot as ice cream plops out of cone and onto the walk

'ZAT SO?! Hmmm, lemme see...

1016mm / 4mm = 254x...

....as my 4mm UO orthoscopic has extraordinary eye relief in proportion
to its focal length. I may easily and comfortably observe the entire
field of view, and without the sensation of the eye being too close
to the lens.

So...there.

Of course, not that I'm going to eliminate the introduction of a barlow...

Fast Newts ain't cheap...

I'll say, and $1099 for my yet-to-arrive Parks 8" f/5 o.t.a.

Though the Syntas, and the like, are going for $300 and under and
are rather promising, but heavier than the Parks if I'm not mistaken.

Alan

--
To reply, remove the "z" if one appears in my address
"Alan W. Craft" wrote in message
...
On Tue, 14 Oct 2003 02:03:04 -0400, "Stephen Paul"
...reflected:


"Alan W. Craft" wrote in message
.. .

SNIP!

Actually, I expect most deep-sky observing will be conducted within a
moderate range of magnifications, but if and when the wide-field bug
hits, I'll have an instrument ready and most capable; and with only
negligible coma, I'm betting.
******************
Are you thinking that somehow this Parks f/5 mirror is going to have less
coma than someone else's f/5 mirror? Or are you thinking that you just
won't see the coma that's there?

Bottom line is that this Parks f/5 mirror is going to have just as much
coma as any other f/5 mirror. And while some folks are less sensitive to
coma than others, there is more than enough to be easily visible in an f/5
mirror. That doesn't necessarily mean YOU will see it, or be bothered by
it, but it will be there...
*******************
SNIP!


I'll say, and $1099 for my yet-to-arrive Parks 8" f/5 o.t.a.

Though the Syntas, and the like, are going for $300 and under and
are rather promising, but heavier than the Parks if I'm not mistaken.

Alan