On Monday, March 28, 2022 at 4:42:15 PM UTC-6, RichA wrote:
> About a $3300 loss on this scope. I've seen people selling the six inch
> Chinese Esprit scopes and being hit with $4000 losses. TeleVue scopes don't hold value and neither in most cases do the Chinese "high-end" scopes.
> The American and European and Takahashi high-end refractors fare better on resale in most cases.

I _was_ about to ask if the TeleVue scopes at least, and possibly even the Chinese ones,
were a good value _after_ their previous owners took such a loss on them.

But then I realized that to utter "value" in the same breath with "apochromatic
refractor" is to speak an oxymoron. If you want a telescope that is a good
value, you want a reflecting telescope. Or, if you insist on the convenience
of a sealed tube and compact size, get a Schmidt-Cassegrain.

But even high-quality Schmidt-Cassegrain telescopes used to be categorized
as not having the greatest optical quality. Since the halcyon days of the 1960s,
however, both Meade and Celestron have come out with coma-corrected designs;
even if they're a bit more expensive than their regular Schmidt-Cassegrains.

Of course, if one wants a "high quality" catadioptric telescope, the
traditional choice has been a Gabor-Penning telescope, particularly the
Gregory-Gabor-Penning. Or the Gregory-Bouwers-Gabor-Penning. (This
telescope used to be known by another name* before the invasion of
Ukraine.)

And there are other exotic designs. In doing the web search that turned
up the work of Gabor and Penning (I had heard of _Bouwers_ before,
and was looking to be reminded of _his_ name) I learned of an interesting
design by Hamilton from 1814.

This telescope had a thin crown objective, and a flint Mangin mirror.

While spherical aberration was corrected, it suffered from lateral color. A
web site mentioning it shows that a significant improvement can be
achieved with a convex correcting lens, and it is mentioned that an
even better correction can be achieved with a three-lens corrector.

John Savard

*Actually, I'd be willing to settle for just renaming it to the Maksutoff
telescope. This would promote pronouncing Dimitri Maksutoff's name
correctly, and would dissociate him from the anti-Western era of
Russian history.

One would probably have to go back to transliterating his name from
Old Church Slavonic, though, to go back before the era during which
Russia engaged in hegemonic actions towards Ukraine, since _that_
dates back to Peter the Great, _at least_.

On Thursday, March 31, 2022 at 1:19:46 PM UTC-4, Quadibloc wrote:
> On Monday, March 28, 2022 at 4:42:15 PM UTC-6, RichA wrote:
> > About a $3300 loss on this scope. I've seen people selling the six inch
> > Chinese Esprit scopes and being hit with $4000 losses. TeleVue scopes don't hold value and neither in most cases do the Chinese "high-end" scopes.
> > The American and European and Takahashi high-end refractors fare better on resale in most cases.
> I _was_ about to ask if the TeleVue scopes at least, and possibly even the Chinese ones,
> were a good value _after_ their previous owners took such a loss on them.
>
> But then I realized that to utter "value" in the same breath with "apochromatic
> refractor" is to speak an oxymoron. If you want a telescope that is a good
> value, you want a reflecting telescope. Or, if you insist on the convenience
> of a sealed tube and compact size, get a Schmidt-Cassegrain.
>
> But even high-quality Schmidt-Cassegrain telescopes used to be categorized
> as not having the greatest optical quality. Since the halcyon days of the 1960s,
> however, both Meade and Celestron have come out with coma-corrected designs;
> even if they're a bit more expensive than their regular Schmidt-Cassegrains.
>
> Of course, if one wants a "high quality" catadioptric telescope, the
> traditional choice has been a Gabor-Penning telescope, particularly the
> Gregory-Gabor-Penning. Or the Gregory-Bouwers-Gabor-Penning. (This
> telescope used to be known by another name* before the invasion of
> Ukraine.)
>
> And there are other exotic designs. In doing the web search that turned
> up the work of Gabor and Penning (I had heard of _Bouwers_ before,
> and was looking to be reminded of _his_ name) I learned of an interesting
> design by Hamilton from 1814.
>
> This telescope had a thin crown objective, and a flint Mangin mirror.
>
> While spherical aberration was corrected, it suffered from lateral color. A
> web site mentioning it shows that a significant improvement can be
> achieved with a convex correcting lens, and it is mentioned that an
> even better correction can be achieved with a three-lens corrector.
>
> John Savard
>
> *Actually, I'd be willing to settle for just renaming it to the Maksutoff
> telescope. This would promote pronouncing Dimitri Maksutoff's name
> correctly, and would dissociate him from the anti-Western era of
> Russian history.
>
> One would probably have to go back to transliterating his name from
> Old Church Slavonic, though, to go back before the era during which
> Russia engaged in hegemonic actions towards Ukraine, since _that_
> dates back to Peter the Great, _at least_.

--

The big problem with most of these exotic designs is that that are generally limited to modest apertures, either because of the expense or impracticality.

When all is said and done, the plain-old 6-inch f/6 or f/8 Newtonian starts to look rather good.

On Friday, April 1, 2022 at 11:06:54 AM UTC-6, W wrote:

> The big problem with most of these exotic designs is that that are generally limited to modest apertures, either because of the expense or impracticality.
>
> When all is said and done, the plain-old 6-inch f/6 or f/8 Newtonian starts to look rather good.

True enough, but a Mak or a Schmidt-Cassegrain are considerably
_less_ expensive per inch of aperture than an apo... so, if for
some reason, an amateur wishes to go for the convenience of a
sealed-tube design, choosing one of those is at least a _step_ in
the direction of sanity, even if the plain old Newtonian would have
been even better.

But the 6-inch f/8 and the 8-inch f/6 of yore are _also_ limited in
aperture, to 6 inches and 8 inches respectively. You can buy a
C14 if your pockets are deep enough.

So if we're talking about removing the constraints of aperture with
a Newtonian, we're talking about an f/5 or faster Dobsonian,
not about the old faithful sentimental favorites. And we don't have
Coulter Optical to order from any more...

John Savard

On Friday, April 1, 2022 at 11:50:19 AM UTC-6, Quadibloc wrote:

> So if we're talking about removing the constraints of aperture with
> a Newtonian, we're talking about an f/5 or faster Dobsonian,
> not about the old faithful sentimental favorites. And we don't have
> Coulter Optical to order from any more...

*That* brought back memories.

A web search turned up old advertisements from Coulter Optical.

Odyssey Compact, 10.1", $299.50
Odyssey 1, 13.1", $499.50
Odyssey 2, 17.5", $1,195.00
Odyssey 29", $3,495.00

Compare that to what I saw in Dobsonians today on the web site
of one astronomy retailer...

6" Tabletop Dobsonian - $390
6" Dobsonian - $580
8" Dobsonian - $820
10" Dobsonian - $1,140

and 10" is where it *ends* rather than where it *begins*.

However, looking around a bit more, I found another site
that was less bad...

10" Dobsonian - $850
12" Go-To Dobsonian - $2,560
14" Go-To Dobsonian - $3,615
16" Go-To Dobsonian - $4,680

so 10" isn't the ultimate limit these days on the aperture
available to the amateur, as I had feared at first.

John Savard

On Friday, April 1, 2022 at 12:19:58 PM UTC-6, Quadibloc wrote:

> However, looking around a bit more, I found another site
> that was less bad...
>
> 10" Dobsonian - $850
> 12" Go-To Dobsonian - $2,560
> 14" Go-To Dobsonian - $3,615
> 16" Go-To Dobsonian - $4,680
>
> so 10" isn't the ultimate limit these days on the aperture
> available to the amateur, as I had feared at first.

Looking still further, I found another site
sellling a 12" Dobsonian for $1,550, so if one
perseveres it is possible to get closer to an
inexpensive telescope (considering the aperture)
of this type.

John Savard

On Friday, April 1, 2022 at 1:50:19 PM UTC-4, Quadibloc wrote:
> On Friday, April 1, 2022 at 11:06:54 AM UTC-6, W wrote:
>
> > The big problem with most of these exotic designs is that that are generally limited to modest apertures, either because of the expense or impracticality.
> >
> > When all is said and done, the plain-old 6-inch f/6 or f/8 Newtonian starts to look rather good.
> True enough, but a Mak or a Schmidt-Cassegrain are considerably
> _less_ expensive per inch of aperture than an apo... so, if for
> some reason, an amateur wishes to go for the convenience of a
> sealed-tube design, choosing one of those is at least a _step_ in
> the direction of sanity, even if the plain old Newtonian would have
> been even better.
>
> But the 6-inch f/8 and the 8-inch f/6 of yore are _also_ limited in
> aperture, to 6 inches and 8 inches respectively. You can buy a
> C14 if your pockets are deep enough.
>
> So if we're talking about removing the constraints of aperture with
> a Newtonian, we're talking about an f/5 or faster Dobsonian,
> not about the old faithful sentimental favorites. And we don't have
> Coulter Optical to order from any more...
>
> John Savard
Twisting my words a bit!

A C-14 has a very long focal length and will not compete very well with an 18-inch f5 Newt, except maybe in a college observatory somewhere, where the agenda are a bit different anyway.

A major astro magazine wasted several pages on an overly-complicated homemade telescope that was impractical and stupid to an extent beyond all belief. I stopped the subscription after a while.

On Sat, 2 Apr 2022 10:15:18 -0700 (PDT), W <wsnell01@hotmail.com>
wrote:

>On Friday, April 1, 2022 at 1:50:19 PM UTC-4, Quadibloc wrote:
>> On Friday, April 1, 2022 at 11:06:54 AM UTC-6, W wrote:
>>
>> > The big problem with most of these exotic designs is that that are generally limited to modest apertures, either because of the expense or impracticality.
>> >
>> > When all is said and done, the plain-old 6-inch f/6 or f/8 Newtonian starts to look rather good.
>> True enough, but a Mak or a Schmidt-Cassegrain are considerably
>> _less_ expensive per inch of aperture than an apo... so, if for
>> some reason, an amateur wishes to go for the convenience of a
>> sealed-tube design, choosing one of those is at least a _step_ in
>> the direction of sanity, even if the plain old Newtonian would have
>> been even better.
>>
>> But the 6-inch f/8 and the 8-inch f/6 of yore are _also_ limited in
>> aperture, to 6 inches and 8 inches respectively. You can buy a
>> C14 if your pockets are deep enough.
>>
>> So if we're talking about removing the constraints of aperture with
>> a Newtonian, we're talking about an f/5 or faster Dobsonian,
>> not about the old faithful sentimental favorites. And we don't have
>> Coulter Optical to order from any more...
>>
>> John Savard
>
>Twisting my words a bit!
>
>A C-14 has a very long focal length and will not compete very well with an 18-inch f5 Newt, except maybe in a college observatory somewhere, where the agenda are a bit different anyway.

Aperture is everything for imaging. But for visual? You're never going
to get anything brighter than it appears without a telescope. What
aperture buys you is the ability to operate at a higher magnification
before you start losing light. Which is important... if the targets
you're interested in require high magnification. Otherwise, aperture
is wasted.

On Saturday, April 2, 2022 at 6:02:55 PM UTC-4, Chris L Peterson wrote:

> Aperture is everything for imaging. But for visual? You're never going
> to get anything brighter than it appears without a telescope. What
> aperture buys you is the ability to operate at a higher magnification
> before you start losing light. Which is important... if the targets
> you're interested in require high magnification. Otherwise, aperture
> is wasted.

No.
Compare an 18-inch at 100x with a 2.4-inch at 100x, side by side, same type of eyepiece, same object, both used visually.

On Sat, 2 Apr 2022 15:37:01 -0700 (PDT), W <wsnell01@hotmail.com>
wrote:

>On Saturday, April 2, 2022 at 6:02:55 PM UTC-4, Chris L Peterson wrote:
>
>> Aperture is everything for imaging. But for visual? You're never going
>> to get anything brighter than it appears without a telescope. What
>> aperture buys you is the ability to operate at a higher magnification
>> before you start losing light. Which is important... if the targets
>> you're interested in require high magnification. Otherwise, aperture
>> is wasted.
>
>No.
>Compare an 18-inch at 100x with a 2.4-inch at 100x, side by side, same type of eyepiece, same object, both used visually.

Your test is meaningless without specifying the focal length of the
telescope and the eyepiece.

On Saturday, April 2, 2022 at 10:39:24 PM UTC-4, Chris L Peterson wrote:
> On Sat, 2 Apr 2022 15:37:01 -0700 (PDT), W <wsne...@hotmail.com>
> wrote:
> >On Saturday, April 2, 2022 at 6:02:55 PM UTC-4, Chris L Peterson wrote:
> >
> >> Aperture is everything for imaging. But for visual? You're never going
> >> to get anything brighter than it appears without a telescope. What
> >> aperture buys you is the ability to operate at a higher magnification
> >> before you start losing light. Which is important... if the targets
> >> you're interested in require high magnification. Otherwise, aperture
> >> is wasted.
> >
> >No.
> >Compare an 18-inch at 100x with a 2.4-inch at 100x, side by side, same type of eyepiece, same object, both used visually.
> Your test is meaningless without specifying the focal length of the
> telescope and the eyepiece.

The magnification was specified: 100x.

One could visualize this comparison by considering two identical 18-inch Newts and eyepieces, at the same observing site, one telescope used at full aperture, the other with a 2.4-inch off-axis mask.

...or..

A 2.4-inch at ~100x could be obtained with an f/15 objective and a 9mm FL eyepiece.

An 18-inch at ~100x could be obtained with an f/4 objective and an 18mm FL eyepiece.

On Sun, 3 Apr 2022 04:42:51 -0700 (PDT), W <wsnell01@hotmail.com>
wrote:

>On Saturday, April 2, 2022 at 10:39:24 PM UTC-4, Chris L Peterson wrote:
>> On Sat, 2 Apr 2022 15:37:01 -0700 (PDT), W <wsne...@hotmail.com>
>> wrote:
>> >On Saturday, April 2, 2022 at 6:02:55 PM UTC-4, Chris L Peterson wrote:
>> >
>> >> Aperture is everything for imaging. But for visual? You're never going
>> >> to get anything brighter than it appears without a telescope. What
>> >> aperture buys you is the ability to operate at a higher magnification
>> >> before you start losing light. Which is important... if the targets
>> >> you're interested in require high magnification. Otherwise, aperture
>> >> is wasted.
>> >
>> >No.
>> >Compare an 18-inch at 100x with a 2.4-inch at 100x, side by side, same type of eyepiece, same object, both used visually.
>> Your test is meaningless without specifying the focal length of the
>> telescope and the eyepiece.
>
>The magnification was specified: 100x.

Which is the point. You can choose a scenario where the aperture
benefits you. And you can choose one where it doesn't. Which is why
you can't make any blanket statement about the value of aperture in a
telescope used visually.

On Sunday, April 3, 2022 at 9:47:41 AM UTC-4, Chris L Peterson wrote:
> On Sun, 3 Apr 2022 04:42:51 -0700 (PDT), W <wsne...@hotmail.com>
> wrote:
>
> >On Saturday, April 2, 2022 at 10:39:24 PM UTC-4, Chris L Peterson wrote:
> >> On Sat, 2 Apr 2022 15:37:01 -0700 (PDT), W <wsne...@hotmail.com>
> >> wrote:
> >> >On Saturday, April 2, 2022 at 6:02:55 PM UTC-4, Chris L Peterson wrote:
> >> >
> >> >> Aperture is everything for imaging. But for visual? You're never going
> >> >> to get anything brighter than it appears without a telescope. What
> >> >> aperture buys you is the ability to operate at a higher magnification
> >> >> before you start losing light. Which is important... if the targets
> >> >> you're interested in require high magnification. Otherwise, aperture
> >> >> is wasted.
> >> >
> >> >No.
> >> >Compare an 18-inch at 100x with a 2.4-inch at 100x, side by side, same type of eyepiece, same object, both used visually.
> >> Your test is meaningless without specifying the focal length of the
> >> telescope and the eyepiece.
> >
> >The magnification was specified: 100x.
> Which is the point. You can choose a scenario where the aperture
> benefits you. And you can choose one where it doesn't. Which is why
> you can't make any blanket statement about the value of aperture in a
> telescope used visually.

No, you missed the point. At any given magnification, the more light, the better with regard to visual astronomy, an exception being white-light solar observing.

The way that you will get more light is by using more aperture.

And we are comparing either a 14-inch with an 18-inch, or more dramatically, a 2.4-inch with an 18-inch.

On Sun, 3 Apr 2022 12:43:44 -0700 (PDT), W <wsnell01@hotmail.com>
wrote:

>On Sunday, April 3, 2022 at 9:47:41 AM UTC-4, Chris L Peterson wrote:
>> On Sun, 3 Apr 2022 04:42:51 -0700 (PDT), W <wsne...@hotmail.com>
>> wrote:
>>
>> >On Saturday, April 2, 2022 at 10:39:24 PM UTC-4, Chris L Peterson wrote:
>> >> On Sat, 2 Apr 2022 15:37:01 -0700 (PDT), W <wsne...@hotmail.com>
>> >> wrote:
>> >> >On Saturday, April 2, 2022 at 6:02:55 PM UTC-4, Chris L Peterson wrote:
>> >> >
>> >> >> Aperture is everything for imaging. But for visual? You're never going
>> >> >> to get anything brighter than it appears without a telescope. What
>> >> >> aperture buys you is the ability to operate at a higher magnification
>> >> >> before you start losing light. Which is important... if the targets
>> >> >> you're interested in require high magnification. Otherwise, aperture
>> >> >> is wasted.
>> >> >
>> >> >No.
>> >> >Compare an 18-inch at 100x with a 2.4-inch at 100x, side by side, same type of eyepiece, same object, both used visually.
>> >> Your test is meaningless without specifying the focal length of the
>> >> telescope and the eyepiece.
>> >
>> >The magnification was specified: 100x.
>> Which is the point. You can choose a scenario where the aperture
>> benefits you. And you can choose one where it doesn't. Which is why
>> you can't make any blanket statement about the value of aperture in a
>> telescope used visually.
>
>No, you missed the point. At any given magnification, the more light, the better with regard to visual astronomy, an exception being white-light solar observing.
>
>The way that you will get more light is by using more aperture.
>
>And we are comparing either a 14-inch with an 18-inch, or more dramatically, a 2.4-inch with an 18-inch.

A larger aperture will not necessarily place more light in your eye.

Consider, for instance, a 1000mm FL telescope used with a 25mm EP (so,
40X magnification). A typical observer will certainly get a brighter
image with a 200mm aperture than a 100mm aperture. But going to 300mm
or 400mm will make no difference.

There's a reason people don't make 8X100 binoculars!

On Sunday, April 3, 2022 at 5:43:27 PM UTC-4, Chris L Peterson wrote:
> On Sun, 3 Apr 2022 12:43:44 -0700 (PDT), W <wsne...@hotmail.com>
> wrote:
>
> >On Sunday, April 3, 2022 at 9:47:41 AM UTC-4, Chris L Peterson wrote:
> >> On Sun, 3 Apr 2022 04:42:51 -0700 (PDT), W <wsne...@hotmail.com>
> >> wrote:
> >>
> >> >On Saturday, April 2, 2022 at 10:39:24 PM UTC-4, Chris L Peterson wrote:
> >> >> On Sat, 2 Apr 2022 15:37:01 -0700 (PDT), W <wsne...@hotmail.com>
> >> >> wrote:
> >> >> >On Saturday, April 2, 2022 at 6:02:55 PM UTC-4, Chris L Peterson wrote:
> >> >> >
> >> >> >> Aperture is everything for imaging. But for visual? You're never going
> >> >> >> to get anything brighter than it appears without a telescope. What
> >> >> >> aperture buys you is the ability to operate at a higher magnification
> >> >> >> before you start losing light. Which is important... if the targets
> >> >> >> you're interested in require high magnification. Otherwise, aperture
> >> >> >> is wasted.
> >> >> >
> >> >> >No.
> >> >> >Compare an 18-inch at 100x with a 2.4-inch at 100x, side by side, same type of eyepiece, same object, both used visually.
> >> >> Your test is meaningless without specifying the focal length of the
> >> >> telescope and the eyepiece.
> >> >
> >> >The magnification was specified: 100x.
> >> Which is the point. You can choose a scenario where the aperture
> >> benefits you. And you can choose one where it doesn't. Which is why
> >> you can't make any blanket statement about the value of aperture in a
> >> telescope used visually.
> >
> >No, you missed the point. At any given magnification, the more light, the better with regard to visual astronomy, an exception being white-light solar observing.
> >
> >The way that you will get more light is by using more aperture.
> >
> >And we are comparing either a 14-inch with an 18-inch, or more dramatically, a 2.4-inch with an 18-inch.
> A larger aperture will not necessarily place more light in your eye.
>
> Consider, for instance, a 1000mm FL telescope used with a 25mm EP (so,
> 40X magnification). A typical observer will certainly get a brighter
> image with a 200mm aperture than a 100mm aperture. But going to 300mm
> or 400mm will make no difference.
>
> There's a reason people don't make 8X100 binoculars!

You are disagreeing with something that I didn't even say!

Your statement about the 300mm is clearly in error.

The global average of the maximum pupil diameter is around 6.5 mm.

So using 40x will result in an effective aperture of 260mm for that average person.

Clearly, that is an improvement in light-gathering power over a 200mm!

And there are some people who exceed a 7 mm pupil by a fair margin.

On Tue, 5 Apr 2022 12:22:31 -0700 (PDT), W <wsnell01@hotmail.com>
wrote:

>On Sunday, April 3, 2022 at 5:43:27 PM UTC-4, Chris L Peterson wrote:
>> On Sun, 3 Apr 2022 12:43:44 -0700 (PDT), W <wsne...@hotmail.com>
>> wrote:
>>
>> >On Sunday, April 3, 2022 at 9:47:41 AM UTC-4, Chris L Peterson wrote:
>> >> On Sun, 3 Apr 2022 04:42:51 -0700 (PDT), W <wsne...@hotmail.com>
>> >> wrote:
>> >>
>> >> >On Saturday, April 2, 2022 at 10:39:24 PM UTC-4, Chris L Peterson wrote:
>> >> >> On Sat, 2 Apr 2022 15:37:01 -0700 (PDT), W <wsne...@hotmail.com>
>> >> >> wrote:
>> >> >> >On Saturday, April 2, 2022 at 6:02:55 PM UTC-4, Chris L Peterson wrote:
>> >> >> >
>> >> >> >> Aperture is everything for imaging. But for visual? You're never going
>> >> >> >> to get anything brighter than it appears without a telescope. What
>> >> >> >> aperture buys you is the ability to operate at a higher magnification
>> >> >> >> before you start losing light. Which is important... if the targets
>> >> >> >> you're interested in require high magnification. Otherwise, aperture
>> >> >> >> is wasted.
>> >> >> >
>> >> >> >No.
>> >> >> >Compare an 18-inch at 100x with a 2.4-inch at 100x, side by side, same type of eyepiece, same object, both used visually.
>> >> >> Your test is meaningless without specifying the focal length of the
>> >> >> telescope and the eyepiece.
>> >> >
>> >> >The magnification was specified: 100x.
>> >> Which is the point. You can choose a scenario where the aperture
>> >> benefits you. And you can choose one where it doesn't. Which is why
>> >> you can't make any blanket statement about the value of aperture in a
>> >> telescope used visually.
>> >
>> >No, you missed the point. At any given magnification, the more light, the better with regard to visual astronomy, an exception being white-light solar observing.
>> >
>> >The way that you will get more light is by using more aperture.
>> >
>> >And we are comparing either a 14-inch with an 18-inch, or more dramatically, a 2.4-inch with an 18-inch.
>> A larger aperture will not necessarily place more light in your eye.
>>
>> Consider, for instance, a 1000mm FL telescope used with a 25mm EP (so,
>> 40X magnification). A typical observer will certainly get a brighter
>> image with a 200mm aperture than a 100mm aperture. But going to 300mm
>> or 400mm will make no difference.
>>
>> There's a reason people don't make 8X100 binoculars!
>
>You are disagreeing with something that I didn't even say!
>
>Your statement about the 300mm is clearly in error.
>
>The global average of the maximum pupil diameter is around 6.5 mm.
>
>So using 40x will result in an effective aperture of 260mm for that average person.
>
>Clearly, that is an improvement in light-gathering power over a 200mm!
>
>And there are some people who exceed a 7 mm pupil by a fair margin.

I'm using 5mm, which is probably more accurate for most amateur
astronomers. But it doesn't really matter what number you use, the
principle is the same, which is that for any given magnification,
there is a point where adding aperture will have no effect.

On Tuesday, April 5, 2022 at 4:47:55 PM UTC-4, Chris L Peterson wrote:
> On Tue, 5 Apr 2022 12:22:31 -0700 (PDT), W <wsne...@hotmail.com>
> wrote:
>
> >On Sunday, April 3, 2022 at 5:43:27 PM UTC-4, Chris L Peterson wrote:
> >> On Sun, 3 Apr 2022 12:43:44 -0700 (PDT), W <wsne...@hotmail.com>
> >> wrote:
> >>
> >> >On Sunday, April 3, 2022 at 9:47:41 AM UTC-4, Chris L Peterson wrote:
> >> >> On Sun, 3 Apr 2022 04:42:51 -0700 (PDT), W <wsne...@hotmail.com>
> >> >> wrote:
> >> >>
> >> >> >On Saturday, April 2, 2022 at 10:39:24 PM UTC-4, Chris L Peterson wrote:
> >> >> >> On Sat, 2 Apr 2022 15:37:01 -0700 (PDT), W <wsne...@hotmail.com>
> >> >> >> wrote:
> >> >> >> >On Saturday, April 2, 2022 at 6:02:55 PM UTC-4, Chris L Peterson wrote:
> >> >> >> >
> >> >> >> >> Aperture is everything for imaging. But for visual? You're never going
> >> >> >> >> to get anything brighter than it appears without a telescope. What
> >> >> >> >> aperture buys you is the ability to operate at a higher magnification
> >> >> >> >> before you start losing light. Which is important... if the targets
> >> >> >> >> you're interested in require high magnification. Otherwise, aperture
> >> >> >> >> is wasted.
> >> >> >> >
> >> >> >> >No.
> >> >> >> >Compare an 18-inch at 100x with a 2.4-inch at 100x, side by side, same type of eyepiece, same object, both used visually.
> >> >> >> Your test is meaningless without specifying the focal length of the
> >> >> >> telescope and the eyepiece.
> >> >> >
> >> >> >The magnification was specified: 100x.
> >> >> Which is the point. You can choose a scenario where the aperture
> >> >> benefits you. And you can choose one where it doesn't. Which is why
> >> >> you can't make any blanket statement about the value of aperture in a
> >> >> telescope used visually.
> >> >
> >> >No, you missed the point. At any given magnification, the more light, the better with regard to visual astronomy, an exception being white-light solar observing.
> >> >
> >> >The way that you will get more light is by using more aperture.
> >> >
> >> >And we are comparing either a 14-inch with an 18-inch, or more dramatically, a 2.4-inch with an 18-inch.
> >> A larger aperture will not necessarily place more light in your eye.
> >>
> >> Consider, for instance, a 1000mm FL telescope used with a 25mm EP (so,
> >> 40X magnification). A typical observer will certainly get a brighter
> >> image with a 200mm aperture than a 100mm aperture. But going to 300mm
> >> or 400mm will make no difference.
> >>
> >> There's a reason people don't make 8X100 binoculars!
> >
> >You are disagreeing with something that I didn't even say!
> >
> >Your statement about the 300mm is clearly in error.
> >
> >The global average of the maximum pupil diameter is around 6.5 mm.
> >
> >So using 40x will result in an effective aperture of 260mm for that average person.
> >
> >Clearly, that is an improvement in light-gathering power over a 200mm!
> >
> >And there are some people who exceed a 7 mm pupil by a fair margin.
> I'm using 5mm, which is probably more accurate for most amateur
> astronomers. But it doesn't really matter what number you use, the
> principle is the same, which is that for any given magnification,
> there is a point where adding aperture will have no effect.

The number that I used is the correct one.

Since there is no viable reason to stick to 40x magnification, your argument is meaningless and your earlier assertion unsupported (that is to say, it's wrong.)

On Tuesday, April 5, 2022 at 2:47:55 PM UTC-6, Chris L Peterson wrote:

> I'm using 5mm, which is probably more accurate for most amateur
> astronomers. But it doesn't really matter what number you use, the
> principle is the same, which is that for any given magnification,
> there is a point where adding aperture will have no effect.

That's true, but is that the same as saying that adding aperture will
have no effect, period?

When looking at extended objects like the Moon or Mars, there is a
maximum reasonable magnification, where all available detail is
easily visible.

But while the brightness of extended objects can't be increased lby
adding aperture, *point objects* like stars _can_ be made brighter by
adding aperture precisely because doing so makes greater magnification
possible.

John Savard

On Wed, 6 Apr 2022 08:26:01 -0700 (PDT), Quadibloc <jsavard@ecn.ab.ca>
wrote:

>On Tuesday, April 5, 2022 at 2:47:55 PM UTC-6, Chris L Peterson wrote:
>
>> I'm using 5mm, which is probably more accurate for most amateur
>> astronomers. But it doesn't really matter what number you use, the
>> principle is the same, which is that for any given magnification,
>> there is a point where adding aperture will have no effect.
>
>That's true, but is that the same as saying that adding aperture will
>have no effect, period?
>
>When looking at extended objects like the Moon or Mars, there is a
>maximum reasonable magnification, where all available detail is
>easily visible.
>
>But while the brightness of extended objects can't be increased lby
>adding aperture, *point objects* like stars _can_ be made brighter by
>adding aperture precisely because doing so makes greater magnification
>possible.

Sure. But my point is the same. For any object type at all, and any
given magnification, there is a point at which adding aperture will
provide no difference. This is in response to W's blanket claim that
more aperture always benefits a visual observer. That is patently
false.

On Wednesday, April 6, 2022 at 11:35:51 AM UTC-4, Chris L Peterson wrote:
> On Wed, 6 Apr 2022 08:26:01 -0700 (PDT), Quadibloc <jsa...@ecn.ab.ca>
> wrote:
> >On Tuesday, April 5, 2022 at 2:47:55 PM UTC-6, Chris L Peterson wrote:
> >
> >> I'm using 5mm, which is probably more accurate for most amateur
> >> astronomers. But it doesn't really matter what number you use, the
> >> principle is the same, which is that for any given magnification,
> >> there is a point where adding aperture will have no effect.
> >
> >That's true, but is that the same as saying that adding aperture will
> >have no effect, period?
> >
> >When looking at extended objects like the Moon or Mars, there is a
> >maximum reasonable magnification, where all available detail is
> >easily visible.
> >
> >But while the brightness of extended objects can't be increased lby
> >adding aperture, *point objects* like stars _can_ be made brighter by
> >adding aperture precisely because doing so makes greater magnification
> >possible.
> Sure. But my point is the same. For any object type at all, and any
> given magnification, there is a point at which adding aperture will
> provide no difference. This is in response to W's blanket claim that
> more aperture always benefits a visual observer. That is patently
> false.

Where did I make a "blanket claim that
more aperture always benefits a visual observer?"

Point that out or shut up.

On Wednesday, April 6, 2022 at 11:26:02 AM UTC-4, Quadibloc wrote:
> On Tuesday, April 5, 2022 at 2:47:55 PM UTC-6, Chris L Peterson wrote:
>
> > I'm using 5mm, which is probably more accurate for most amateur
> > astronomers. But it doesn't really matter what number you use, the
> > principle is the same, which is that for any given magnification,
> > there is a point where adding aperture will have no effect.
> That's true, but is that the same as saying that adding aperture will
> have no effect, period?
>
> When looking at extended objects like the Moon or Mars, there is a
> maximum reasonable magnification, where all available detail is
> easily visible.
>
> But while the brightness of extended objects can't be increased lby
> adding aperture, *point objects* like stars _can_ be made brighter by
> adding aperture precisely because doing so makes greater magnification
> possible.
>
> John Savard

There seems to more than a little confusion on peterson's part and possibly on yours as well.

"Brightness" can mean the intensity of light coming from a defined area. But that doesn't always tell the story.

Important things are the amount of light and the contrast of an object against the background. If you don't gather the light, then these obviously suffer.

On 06/04/2022 16:35, Chris L Peterson wrote:
> On Wed, 6 Apr 2022 08:26:01 -0700 (PDT), Quadibloc <jsavard@ecn.ab.ca>
> wrote:
>
>> On Tuesday, April 5, 2022 at 2:47:55 PM UTC-6, Chris L Peterson wrote:
>>
>>> I'm using 5mm, which is probably more accurate for most amateur
>>> astronomers. But it doesn't really matter what number you use, the
>>> principle is the same, which is that for any given magnification,
>>> there is a point where adding aperture will have no effect.
>>
>> That's true, but is that the same as saying that adding aperture will
>> have no effect, period?
>>
>> When looking at extended objects like the Moon or Mars, there is a
>> maximum reasonable magnification, where all available detail is
>> easily visible.
>>
>> But while the brightness of extended objects can't be increased lby
>> adding aperture, *point objects* like stars _can_ be made brighter by
>> adding aperture precisely because doing so makes greater magnification
>> possible.
>
> Sure. But my point is the same. For any object type at all, and any
> given magnification, there is a point at which adding aperture will
> provide no difference. This is in response to W's blanket claim that

It can even make it worse. There is a sweet spot just below the length
scale of the turbulence above the telescope where you see a sharper
image jumping around rather than one that has been blurred by seeing.
Eye cadence can follow that to some extent.

CCDs and lucky imaging can exploit the very rare moments when the entire
of a much larger aperture is almost free of phase errors but the human
eye cannot (even for the best visual planetary observers).

> more aperture always benefits a visual observer. That is patently
> false.

I think he is more or less right at least in the range of apertures that
an amateur astronomer is ever likely to encounter (typically <0.5m).

The main reason why a larger aperture and so lower limiting stellar
magnitude ultimately fails is that some extended objects won't fit into
the field of view. M31 and M33 being fairly obvious examples.

--
Regards,
Martin Brown