Six-inch apo for $2990? Lunt get hold of some FPL-51?

On Sat, 3 Oct 2015 04:48:35 -0700 (PDT), Quadibloc
wrote:

It's simple and obvious to say that an SCT beats a refractor; whether a
Newtonian beats an SCT is a question of judgment that doesn't have a simple and
obvious answer, which is why there are many different kinds of telescope.

Of course, a Newtonian has the worst optics of any popular design.
SCTs of good quality outperform Newts. So if you're doing something
critical with your scope (particularly imaging), you typically need to
have corrected optics of some kind- whether an SCT or a Newt. And such
correction is available are reasonable cost and is commonly used. So
the analysis needs to consider more than just the capabilities of the
basic scope design.

On Saturday, 3 October 2015 16:23:40 UTC+2, Chris L Peterson wrote:
On Sat, 3 Oct 2015 04:48:35 -0700 (PDT), Quadibloc
wrote:

It's simple and obvious to say that an SCT beats a refractor; whether a
Newtonian beats an SCT is a question of judgment that doesn't have a simple and
obvious answer, which is why there are many different kinds of telescope..

Of course, a Newtonian has the worst optics of any popular design.
SCTs of good quality outperform Newts. So if you're doing something
critical with your scope (particularly imaging), you typically need to
have corrected optics of some kind- whether an SCT or a Newt. And such
correction is available are reasonable cost and is commonly used. So
the analysis needs to consider more than just the capabilities of the
basic scope design.

Large, central obstruction, long cool down times from heated storage and [historically] indifferent optical quality have made the SCT the least desirable design? Perhaps somebody should have told that to the people taking excellent images with the xxxxxx things despite its ridiculously long focal lengths?

The refractor performs well above its aperture, has no central obstruction, nor serious thermal problems? So a 6" refractor is arguably equivalent to a 10" Newtonian under most conditions?

The APO triplet suffers from long cool down times when brought out from heated storage? The fast APO has a very short depth of focus and requires specialized and very expensive eyepieces, motor driven focusers and field curvature correction for imaging making it even more ridiculously expensive to own? It has to be refocused for imaging each colour despite the claimed apochramatism?

Aperture wins regardless of local seeing? Yet smaller, classical refractor owners claim they cut through seeing and CA has no effect on planetary detail? If aperture wins how can a modern amateur, with a modestly-sized instrument trash the images of the world's great observatories? Large apertures make large instruments and the telescope which gets used most is the best telescope?

The Newt suffers from hopeless coma unless optically corrected? Adding to the cost and making the Newt less competitive on retail pricing? The faster it is the more which has to be spent on eyepieces? A slow, optimized Newt trashes everything else by having a tiny secondary and perfect achromatism? The lightweight, premium quality primary can be fan cooled to speed its readiness for splitting close doubles and providing the finest planetary detail seen in any instrument totally regardless of size or cost?

Can all these "facts" be simultaneously true?

On Sat, 3 Oct 2015 10:25:47 -0700 (PDT), "Chris.B"
wrote:

Can all these "facts" be simultaneously true?

This just supports the view that you can't fully consider the
qualities of a scope without considering the intended usage.

On Saturday, 3 October 2015 10:23:40 UTC-4, Chris L Peterson wrote:
On Sat, 3 Oct 2015 04:48:35 -0700 (PDT), Quadibloc
wrote:

It's simple and obvious to say that an SCT beats a refractor; whether a
Newtonian beats an SCT is a question of judgment that doesn't have a simple and
obvious answer, which is why there are many different kinds of telescope..

Of course, a Newtonian has the worst optics of any popular design.
SCTs of good quality outperform Newts. So if you're doing something
critical with your scope (particularly imaging), you typically need to
have corrected optics of some kind- whether an SCT or a Newt. And such
correction is available are reasonable cost and is commonly used. So
the analysis needs to consider more than just the capabilities of the
basic scope design.

It's very hard to take coma from a Newtonian if you've used SCT's for years, even the uncorrected edge designs are better than a Newtonian. The only thing the Newtonian can have an edge in (and it's less than it used to be owing to modern coatings) is contrast.

On Sat, 3 Oct 2015 14:27:28 -0700 (PDT), RichA
wrote:

On Saturday, 3 October 2015 10:23:40 UTC-4, Chris L Peterson wrote:
On Sat, 3 Oct 2015 04:48:35 -0700 (PDT), Quadibloc
wrote:

It's simple and obvious to say that an SCT beats a refractor; whether a
Newtonian beats an SCT is a question of judgment that doesn't have a simple and
obvious answer, which is why there are many different kinds of telescope.

Of course, a Newtonian has the worst optics of any popular design.
SCTs of good quality outperform Newts. So if you're doing something
critical with your scope (particularly imaging), you typically need to
have corrected optics of some kind- whether an SCT or a Newt. And such
correction is available are reasonable cost and is commonly used. So
the analysis needs to consider more than just the capabilities of the
basic scope design.

It's very hard to take coma from a Newtonian if you've used SCT's for years, even the uncorrected edge designs are better than a Newtonian. The only thing the Newtonian can have an edge in (and it's less than it used to be owing to modern coatings) is contrast.

SCTs are commonly used with field flatteners, and Newts are commonly
(although less so) used with coma correctors. Many classical designs
have been tweaked in recent years to reduce or eliminate the
aberrations associated with them.

Again, usage is important. A corrected SCT is an excellent imaging
scope, since the size of the obstruction isn't very important. Coma is
not so serious in a scope intended for visual use, because the
observer can dynamically move around to keep the interesting bits
centered.

On Saturday, October 3, 2015 at 10:23:40 AM UTC-4, Chris L Peterson wrote:
On Sat, 3 Oct 2015 04:48:35 -0700 (PDT), Quadibloc
wrote:

It's simple and obvious to say that an SCT beats a refractor; whether a
Newtonian beats an SCT is a question of judgment that doesn't have a simple and
obvious answer, which is why there are many different kinds of telescope.

Of course, a Newtonian has the worst optics of any popular design.

Incorrect.


SCTs of good quality outperform Newts.

Incorrect.

On Saturday, October 3, 2015 at 1:25:52 PM UTC-4, Chris.B wrote:
On Saturday, 3 October 2015 16:23:40 UTC+2, Chris L Peterson wrote:
On Sat, 3 Oct 2015 04:48:35 -0700 (PDT), Quadibloc
wrote:

It's simple and obvious to say that an SCT beats a refractor; whether a
Newtonian beats an SCT is a question of judgment that doesn't have a simple and
obvious answer, which is why there are many different kinds of telescope.

Of course, a Newtonian has the worst optics of any popular design.
SCTs of good quality outperform Newts. So if you're doing something
critical with your scope (particularly imaging), you typically need to
have corrected optics of some kind- whether an SCT or a Newt. And such
correction is available are reasonable cost and is commonly used. So
the analysis needs to consider more than just the capabilities of the
basic scope design.

Large, central obstruction, long cool down times from heated storage and [historically] indifferent optical quality have made the SCT the least
desirable design? Perhaps somebody should have told that to the people taking
excellent images with the xxxxxx things despite its ridiculously long focal
lengths?

For imaging the obstruction doesn't matter much. Precautions can be taken WRT cool down time. Optical quality might or might not be "indifferent."


The refractor performs well above its aperture, has no central obstruction,
nor serious thermal problems? So a 6" refractor is arguably equivalent to a
10" Newtonian under most conditions?

The Newt has nearly three times the light gathering power and almost twice the resolution. Configure and use the Newt properly and it should beat the 6" refractor, in many/most cases. It can certainly be obtained at a much lower cost and is likely to be easier to set up, transport and store.

The APO triplet suffers from long cool down times when brought out from heated storage? The fast APO has a very short depth of focus and requires specialized and very expensive eyepieces, motor driven focusers and field curvature correction for imaging making it even more ridiculously expensive to own? It has to be refocused for imaging each colour despite the claimed apochramatism?

Aperture wins regardless of local seeing? Yet smaller, classical refractor owners claim they cut through seeing and CA has no effect on planetary detail? If aperture wins how can a modern amateur, with a modestly-sized instrument trash the images of the world's great observatories? Large apertures make large instruments and the telescope which gets used most is the best telescope?

The Newt suffers from hopeless coma unless optically corrected? Adding to the cost and making the Newt less competitive on retail pricing? The faster it is the more which has to be spent on eyepieces? A slow, optimized Newt trashes everything else by having a tiny secondary and perfect achromatism? The lightweight, premium quality primary can be fan cooled to speed its readiness for splitting close doubles and providing the finest planetary detail seen in any instrument totally regardless of size or cost?

Can all these "facts" be simultaneously true?

On Wed, 7 Oct 2015 07:02:54 -0700 (PDT), wrote:

On Saturday, October 3, 2015 at 10:23:40 AM UTC-4, Chris L Peterson wrote:
On Sat, 3 Oct 2015 04:48:35 -0700 (PDT), Quadibloc
wrote:

It's simple and obvious to say that an SCT beats a refractor; whether a
Newtonian beats an SCT is a question of judgment that doesn't have a simple and
obvious answer, which is why there are many different kinds of telescope.

Of course, a Newtonian has the worst optics of any popular design.

Incorrect.


SCTs of good quality outperform Newts.

Incorrect.

We'll add optics to the ever growing list of things you are ignorant
about.

On Wednesday, October 7, 2015 at 10:12:08 AM UTC-4, Chris L Peterson wrote:
On Wed, 7 Oct 2015 07:02:54 -0700 (PDT), wsnell01 wrote:

On Saturday, October 3, 2015 at 10:23:40 AM UTC-4, Chris L Peterson wrote:

Of course, a Newtonian has the worst optics of any popular design.

Incorrect.


SCTs of good quality outperform Newts.

Incorrect.

We'll add optics to the ever growing list of things you are ignorant
about.

("We" being you and your tapeworm, peterson?)

Newtonians of good quality outperform SCTs.

On Wednesday, October 7, 2015 at 2:27:59 PM UTC-6, wrote:

Newtonians of good quality outperform SCTs.

That's certainly what I believed, based on what I read in the amateur
astronomical literature in the past.

However, now that I think of it, there could be a simple cause for this
confusion.

A typical f/8 Newtonian will have better optical quality than a typical Schmidt-
Cassegrain (8", f/10, spherical primary and secondary, not a modern coma-free
design)...

but perhaps an f/5 Newtonian would indeed have worse optical quality.

So you and I are thinking of the traditional ranking of telescopes, back when
the typical Newtonian had a 6" aperture and an equatorial mount... and he's
thinking of Dobs when he thinks of a Newtonian.

Hence, you can both be right.

John Savard