$3000 and which scope???

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"Jan Owen" wrote in message
news:2eZib.64967$vj2.38245@fed1read06...


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"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!

To be more clear, in the last paragraph above, I should have said: "this
Parks f/5 mirror is going to have just as much coma as any other Newtonian
f/5 paraboloidal mirror..."

On 14 Oct 2003 06:50:58 -0700, (Rod Mollise) ...reflected:

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_...

So, one has to add an extra element to IMPROVE an image at an
f/10 ratio?

More's the pity.

...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...

Me! Me! Me!

...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.

There was a time, and not too long ago, when a Meade and a
Celestron were not so "good, old." However, the fact that they've
improved is leading me to consider purchasing one of my own;
perhaps next year.

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

Alan

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

What makes it catadioptric, then? Is there one of those Barlow-type
"correctors" at the focuser? That would make it like one of those
Celestron short Newts.

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.txt

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?

Most likely.

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...

Jan, aren't you the guy who uses a Paracorr with an F6 mirror? I have never
tried it, though my 8 inch scope is F6. Is it worth it?

jon

On Tue, 14 Oct 2003 20:15:32 +0000, Steve Taylor ...reflected:

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

It's almost just as I expected: an extender and a field-flattener,
but separate, and in separate locations within the optical train.

Am I close?

They say it's quite heavy for an 8" f/3(f/6), and with the optical
window being a dew magnet. Of course, that's no surprise.

Alan

On Tue, 14 Oct 2003 13:41:44 -0700, "Jan Owen" ...reflected:

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?

No.

Or are you thinking that you just won't see the coma that's there?

Rather, as I explained to Mr. Issacs, someone who has a Synta or
other of identical aperture and focal ratio stated that they noticed very
little coma within theirs, to which I replied that that was good to hear.

As promised, I will give a full unbiased report once the Parks arrives.

Bottom line is that this Parks f/5 mirror is going to have just as much
coma as any other f/5 mirror.

Yes, a law of optics, I realise, or whatever.

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...

Precisely upon what I'm basing all of my hopes and dreams.

Incidentally, thank you for virtually addressing me face-to-face, Mr. Owens.

Alan

On 14 Oct 2003 22:18:37 GMT, (Jon Isaacs) ...reflected:

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?

Most likely.

Do you mean to say, Jon, that you wouldn't see the coma that's there,
either?

blows raspberry

snip

Alan

--
To reply, remove the "z" if one appears in my address
"Jon Isaacs" wrote in message
...
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?

Most likely.

Most likely, what?

A lot of folks are insensitive to coma. So they won't CARE that there is
coma in the outer field. That's great for them. Personally, I prefer
pinpoints edge to edge, and you just can't get there with an f/5
Newtonian. Even with a Paracorr. In fact, you can't get there with an
f/6 without a Paracorr.


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...

Jan, aren't you the guy who uses a Paracorr with an F6 mirror? I have
never
tried it, though my 8 inch scope is F6. Is it worth it?

That's me, all right. With an f/6 paraboloid AND a Paracorr, there is
still coma, but it has been reduced so much that the comatic blur circle
is smaller than the airy disc, so while coma is still there, you really
won't see it. Of course, if you aren't sensitive to coma, you might not
see it any way. But I would, and that's why I use a Paracorr, even at
f/6.


jon

Now let me say one more thing.

Above, I said some folks aren't sensitive to coma. Frankly, folks who can
look at a comatic image and see a pinpoint, are folks I don't want
evaluating optics... At least not ones I may be considering buying. When
they say the images are pristine, and I know they aren't, that puts
everything they say about off-axis images into limbo, doesn't it?

Someone recently asked if I trusted scope/optics reviews from other
members of SAA.

The answer is, only a few whose evaluation skills I understand and am
calibrated with...

Others mean well, but their observations are suspect.

Further, very few folks have access to test equipment capable of
delivering a meaningful evaluation of most optics. Star tests are nice,
and can reveal a lot in capable hands. In capable hands. But that does
not replace green light interferometry, for instance.

The Japanese test telescope optics. Here, we kinda' discuss them from a
qualitative perspective, but we don't do in-depth optical testing... For
the most part, no one can afford it. So the results are only worthy of
discussion at a relatively low level... And for the most part, that's
what we see on SAA.

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...

Precisely upon what I'm basing all of my hopes and dreams.


Alan:

If I look for it, I do notice the Coma in my F5 Newts (one GS, one Synta).
However I do not find it that it is distracting. Some people do.

If you are looking for perfection, then it is likely you will be disappointed.
But if your expectations are that realistic (and they seem to be) and you are
willing to live with some amount of edge aberation, then you ought to be happy
with your F5 scope. And of course, there is nothing that keeps you from
deciding to buy a Paracorr if you decide that you might prefer one.

I most often use my Paracorr at F5 but I find the views more than acceptable
without it. At F4.1, I always use it.

Jon

On 14 Oct 2003 23:55:47 GMT, (Jon Isaacs) ...reflected:

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...

Precisely upon what I'm basing all of my hopes and dreams.


Alan:

If I look for it, I do notice the Coma in my F5 Newts (one GS, one Synta).
However I do not find it that it is distracting. Some people do.

If you are looking for perfection, then it is likely you will be disappointed.

I'm afraid I can't afford an 8" Takahashi refractor, and all that it would
entail, so no, I'm not looking for nor expecting utter perfection in the Parks.


I chose the largest Newtonian that would ride atop a Vixen GP-DX;
with every other consideration necessarily taking second place, including
coma.

The only reason that I didn't go with an f/4 is because of the problems
involved, that is, the need for ultra-critical collimations and pronounced
coma.

An 8" f/6 would've been the ideal all-around, but the tube's too long.

But if your expectations are that realistic (and they seem to be) and you are
willing to live with some amount of edge aberation, then you ought to be happy
with your F5 scope. And of course, there is nothing that keeps you from
deciding to buy a Paracorr if you decide that you might prefer one.

Well, as Mr. Owen pointed out, some notice it, some don't. I wonder
if that's dependent upon the seeing ability of one's eyes. If so, then I may
not be too terribly bothered by it.

I most often use my Paracorr at F5 but I find the views more than acceptable
without it.

Now I have your assurance in addition to the other gentleman's.

Thank you.

At F4.1, I always use it.

Oh, I knew from the get-go that had I chose the f/4 a Paracorr would've
been a necessity rather than an option. But then, how well the f/4 would've
balanced atop the GP-DX...

Alan