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ALPO Venus section telescope recommendation: it hurts.

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#1 Magnetic Field

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Posted 22 May 2019 - 02:52 PM

And only God knows if they are also flat earthers.

 

 

It causes pain to read the following (http://www.alpo-astr...nus/ven1210.pdf):

 

"With the highest optical quality and mechanical stability assumed, the minimum recommended aperture for
useful observations of Venus and participation in all aspects of our programs is about 15.2 cm. (6.0 in.) for reflectors and 7.5 cm. (3.0 in.) for refractors."

 

 

This cannot be true (even not in 1999). How can anyone take them for full?


Edited by Magnetic Field, 22 May 2019 - 02:53 PM.

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#2 Astrojensen

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Posted 22 May 2019 - 03:07 PM

It's not been true since the invention of the silver on glass process (as long as the silver is fresh) and certainly not since the invention of aluminizing. 

 

I know the Englishmen are often a bit, um, conservative, but this is stretching it. 

 

The 3" refractor = 6" reflector rule nonsense has been repeated ad nauseam in most of Patrick Moore's books (and a lot of other english astronomy books). 

 

 

Clear skies!
Thomas, Denmark


Edited by Astrojensen, 22 May 2019 - 03:09 PM.

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#3 Jeff Morgan

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Posted 22 May 2019 - 07:45 PM

Maybe you can build a 3" reflector and demonstrate equality to the 3" refractor?



#4 Magnetic Field

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Posted 23 May 2019 - 01:13 AM

Maybe you can build a 3" reflector and demonstrate equality to the 3" refractor?

To answer your first question: do you know how hard it is to argue with moon landing conspirasists?***

 

The ALPO Venus section guideline (my guess) uses the generic term "reflector" for catadioptrics as well.

 

People may disagree with me: but ALPO Venus completely disqualified themselves with such guidelines.

 

I saw this ALPO Venus guideline 20 years ago and I couldn't believe it then. It was quite of a shocker to read the same unsubstantiated myth after 20 years again (hey we now live in a modern world).

 

 

***Tell me about science and evidence (yesterday I just peer reviewed a paper  in physics for a journal).



#5 Magnetic Field

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Posted 23 May 2019 - 02:24 AM

It's not been true since the invention of the silver on glass process (as long as the silver is fresh) and certainly not since the invention of aluminizing. 

 

I know the Englishmen are often a bit, um, conservative, but this is stretching it. 

 

The 3" refractor = 6" reflector rule nonsense has been repeated ad nauseam in most of Patrick Moore's books (and a lot of other english astronomy books). 

 

 

Clear skies!
Thomas, Denmark

It is just mind blowing stupid to rule out a-priori a whole class of observations and telescopes.

 

Okay, Meade doesn't produce the ETX-105 any more and Intes with their top-class Russian 5" Makustovs ceased trading. But there are good 130mm and 114mm Newtonians  out there. Also the 5" Maksutovs and 5" SCT are not to dismiss.

 

And yes it is better to observe Venus in a tiny Micky Mouse 3" apochromat that even may show a slight blue fringe around Venus and at the same time dismissing all observations from the 130mm Newtonian.



#6 Jon Isaacs

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Posted 23 May 2019 - 02:53 AM

Maybe you can build a 3" reflector and demonstrate equality to the 3" refractor?

One would only need to build a reflector under 6 inches and demonstrate it's equality (superiority) to the 3 inch refractor, 

 

"With the highest optical quality and mechanical stability assumed, the minimum recommended aperture for
useful observations of Venus and participation in all aspects of our programs is about 15.2 cm. (6.0 in.) for reflectors and 7.5 cm. (3.0 in.) for refractors."

 

That does not seem like much of a challenge.. 

 

Jon



#7 Starman1

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Posted 23 May 2019 - 06:11 AM

It depends what you want to see.
Phases? Any decent 50mm scope should do fine.
Cloud features with a #47 violet filter at 500x to 600x ? You'd better have at least a superb 12-15" reflector or 10-12" refractor and excellent seeing.
And if you want to observe features in daylight, tracking is important.
One cannot generalize, therefore, on a minimum aperture for Venus.
I have no clue how they came up with those aperture recommendations.

Edited by Starman1, 23 May 2019 - 06:11 AM.

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#8 Magnetic Field

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Posted 23 May 2019 - 06:54 AM

It depends what you want to see.
Phases? Any decent 50mm scope should do fine.
Cloud features with a #47 violet filter at 500x to 600x ? You'd better have at least a superb 12-15" reflector or 10-12" refractor and excellent seeing.
And if you want to observe features in daylight, tracking is important.
One cannot generalize, therefore, on a minimum aperture for Venus.
I have no clue how they came up with those aperture recommendations.

This myth and lore of refractor aperture equals 2 times reflector aperture gets me going.

 

 

If there were a "junk status" like what we often see for credit ratings or bonds on the global financial market the ALPO Venus guideline would qualify for it.

 

 

Btw: I was so impressed by this fellas Venus drawings (post #85):

 

https://www.cloudyni...ochromat/page-4

 

One of the best Venus drawings I have ever seen (unbelievable what a 40cm Dall-Kirkham can deliver)

 

So I started searching the internet for similar drawings and came across that nonsense ALPO Venus watch programe section guideline. You would think ALPO (Association of Lunar and Planetary Observers) is a respectable organisation of enthusiasts.


Edited by Magnetic Field, 23 May 2019 - 06:59 AM.


#9 David Gray

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Posted 23 May 2019 - 07:06 AM

For what is used visually for Venus cloud features – scopes used etc.: consulting this might clarify –

 

https://britastro.or...imJBAA118-5.pdf

 

Such reports are refereed by the professional community before acceptance/publication....

 

More on the site...... https://britastro.org/node/4937



#10 Eddgie

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Posted 23 May 2019 - 07:25 AM

I had an MN56 for a brief while. It was easily better for viewing pretty much anything expect very large targets than any 80mm refractor I have ever owned.

 

Some people simply don't upgrade their web pages.  As a matter of fact, I still sometimes get questions from friends about the Mars close approach that occurred a decade ago.  Articles saying it is coming are still out there on the web.

 

It is just the nature of the beast.   Some huge quantity of data on the web is out of date.



#11 Magnetic Field

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Posted 23 May 2019 - 08:41 AM

I had an MN56 for a brief while. It was easily better for viewing pretty much anything expect very large targets than any 80mm refractor I have ever owned.

 

Some people simply don't upgrade their web pages.  As a matter of fact, I still sometimes get questions from friends about the Mars close approach that occurred a decade ago.  Articles saying it is coming are still out there on the web.

 

It is just the nature of the beast.   Some huge quantity of data on the web is out of date.

(I don't think it was an oversight. People deeply believe in that myth. Is there any (former) flat earther out there who has ever converted?)

 

 

Your experience is not uncommon:

 

https://neilenglish....f-newtonianism/

 

 

Although, I admit one could probably compile a list similar to the link above of  anecdotes in favour of the refractor.


Edited by Magnetic Field, 23 May 2019 - 08:41 AM.

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#12 stanislas-jean

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Posted 24 May 2019 - 02:19 AM

Why this question?

Recommendations are just recommendations only.

This is depending on the scope in use indeed but not only depending more on your own vision ability during visual observation.

The third step consists in the seeing parameter that degrade the perfect.

Perfect being the couple scope-own eyes, different from a guy to an other with or without experience.

About the above posts something is quite absent this the strehl of the opics in cause, any design.

An aperture, a design of opics and the opical acuracy allow to reach some contrast levels considering the size of the feature observed.

Useless to speak the merit of the apo against the newton, mak, CC, etc... To be sure watch the ftm curves of each, contrasts are better for low frequencies in an apo, for high frequencies absolutly not and contrasts may be washed in presence of average apo optics. Stunning ! but obvious, fpl 51, 53, XX etc nothing to see as main parameter.

And we must on aware with control bulletin with given data sometimes optimistic.

Writing this, for me enoughly evident now, remains the initial question of this forum, access to venusian features.

Venusian features are low contrast level, say 1-2% depending also on the color of observation, but on all the light spectra, features are there.

How it is possible to reach such levels?

1- with high proven strehl optics that not degrade high frequencies,

2- good training with visual observations,

3- find solutions in order to adjust the light level of the disk proper to reveal features when cancelling the light glare,

4- get images 7/10 and better,

5- a recall have a perfect aligned and collimated optic, not approximative, any design.

Now it is said, 3" refractor 6" reflector.

On the 80ies I started on venus with a 3" polarex unitron (you now an achromat making violeted images) and a simple 4.5" newtonian tube fully open. This allow me me to follow on an elongation day to day a correlation between high altitude formations on venus and some white bright spots occuring in the atmosphere.

More recently, still on venus a simple 2" refractor revealed banding structure of the atmosphere, ashen light also but this is an other topic and controversial.

What I can conclude a 2" refractor can do, a little but can do, a 4" reflector can do also, but with high strehl optics.

With such seeing parameters is almost negligeable.

We could speak about uranus also a substantial more difficult target, this is more crucial to get something but with high strehl optics, adequate seeing and good viewing abilities.

I did some tests on the ground in order to verify all these abilities/assessments when viewing long distance targets with very low contrasted banding features with the help of a vc200L, high strehl and 42%CO.

This is changing to the always theorical considerations developped into forums .

Observing planets even an uranus depends on mesopic vision, not photopic, this is a strange field that is variable between observers.

Keep in mind also that the observation is a match between the scope in use and an eye through a filter and an eyepiece, that adjust the light level and that must properly be set to reach an optimum, for reaching the potential resolution limit of the image at the focus plan of your scope.

Always 3 stages to consider, adding the seeing filter, but globally improved by the training and experience of you.

No need to push a 20" for the exercise.

Good skies

Stanislas-Jean


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#13 Magnetic Field

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Posted 24 May 2019 - 12:03 PM

Why this question?

Recommendations are just recommendations only.

This is depending on the scope in use indeed but not only depending more on your own vision ability during visual observation.

The third step consists in the seeing parameter that degrade the perfect.

Perfect being the couple scope-own eyes, different from a guy to an other with or without experience.

About the above posts something is quite absent this the strehl of the opics in cause, any design.

An aperture, a design of opics and the opical acuracy allow to reach some contrast levels considering the size of the feature observed.

Useless to speak the merit of the apo against the newton, mak, CC, etc... To be sure watch the ftm curves of each, contrasts are better for low frequencies in an apo, for high frequencies absolutly not and contrasts may be washed in presence of average apo optics. Stunning ! but obvious, fpl 51, 53, XX etc nothing to see as main parameter.

And we must on aware with control bulletin with given data sometimes optimistic.

Writing this, for me enoughly evident now, remains the initial question of this forum, access to venusian features.

Venusian features are low contrast level, say 1-2% depending also on the color of observation, but on all the light spectra, features are there.

How it is possible to reach such levels?

1- with high proven strehl optics that not degrade high frequencies,

2- good training with visual observations,

3- find solutions in order to adjust the light level of the disk proper to reveal features when cancelling the light glare,

4- get images 7/10 and better,

5- a recall have a perfect aligned and collimated optic, not approximative, any design.

Now it is said, 3" refractor 6" reflector.

On the 80ies I started on venus with a 3" polarex unitron (you now an achromat making violeted images) and a simple 4.5" newtonian tube fully open. This allow me me to follow on an elongation day to day a correlation between high altitude formations on venus and some white bright spots occuring in the atmosphere.

More recently, still on venus a simple 2" refractor revealed banding structure of the atmosphere, ashen light also but this is an other topic and controversial.

What I can conclude a 2" refractor can do, a little but can do, a 4" reflector can do also, but with high strehl optics.

With such seeing parameters is almost negligeable.

We could speak about uranus also a substantial more difficult target, this is more crucial to get something but with high strehl optics, adequate seeing and good viewing abilities.

I did some tests on the ground in order to verify all these abilities/assessments when viewing long distance targets with very low contrasted banding features with the help of a vc200L, high strehl and 42%CO.

This is changing to the always theorical considerations developped into forums .

Observing planets even an uranus depends on mesopic vision, not photopic, this is a strange field that is variable between observers.

Keep in mind also that the observation is a match between the scope in use and an eye through a filter and an eyepiece, that adjust the light level and that must properly be set to reach an optimum, for reaching the potential resolution limit of the image at the focus plan of your scope.

Always 3 stages to consider, adding the seeing filter, but globally improved by the training and experience of you.

No need to push a 20" for the exercise.

Good skies

Stanislas-Jean

Yes Stanislas

 

This is exactly my point: it should be should judged on merit and not misconception. Otherwise a bias is being introduced on the execution thereof.

 

What would happen if someone observes the Venus Ashen Light with a 130mm Newtonian? Will ALPO Venus section call in the doctors because on flat-earth  an obstructed telescope is the root of all evil and the Ashen Light is the ghost artefact of the secondary mirror. At the same time accepting all incoming reports from refractors that show Venus with a glorified blue false colour fringe.

 

Although I suffer from eye floaters, but I still want to test an apochromat either a 80mm or 90mm and is explained in post #86 in the following thread. But this is rather a personal situation I would say:

 

https://www.cloudyni...ochromat/page-4



#14 gwlee

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Posted 24 May 2019 - 01:00 PM

It's not been true since the invention of the silver on glass process (as long as the silver is fresh) and certainly not since the invention of aluminizing. 

 

I know the Englishmen are often a bit, um, conservative, but this is stretching it. 

 

The 3" refractor = 6" reflector rule nonsense has been repeated ad nauseam in most of Patrick Moore's books (and a lot of other english astronomy books). 

 

 

Clear skies!
Thomas, Denmark

Thomas, I was born in the States, but my mother’s side of the family is English, so I have lived in both both countries. I started school in England and enjoy many hobbies that are popular on both sides of the pond, astronomy being one, and found stark differences in the way Americans and Englishmen approach their hobbies as well as many other things in life. 

 

IME, Americans tend to just buy a telescope (or anything else) and learn by doing, with hit or miss results. Englishmen are more likely to come up through a formal club system and learn the “proper way” of doing things, as my mother was found of saying, so tend to be a bit hide bound about astronomy and a lot of other things. 

 

However, it’s a mystery to me how anyone who has set up a 3-inch refractor and a 6-inch newt on the same night and looked through both could conclude they are equivalent instruments.  


Edited by gwlee, 24 May 2019 - 01:04 PM.

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#15 Magnetic Field

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Posted 24 May 2019 - 01:19 PM

Thomas, I was born in the States, but my mother’s side of the family is English, so I have lived in both both countries. I started school in England and enjoy many hobbies that are popular on both sides of the pond, astronomy being one, and found stark differences in the way Americans and Englishmen approach their hobbies as well as many other things in life. 

 

IME, Americans tend to just buy a telescope (or anything else) and learn by doing, with hit or miss results. Englishmen are more likely to come up through a formal club system and learn the “proper way” of doing things, as my mother was found of saying, so tend to be a bit hide bound about astronomy and a lot of other things. 

 

However, it’s a mystery to me how anyone who has set up a 3-inch refractor and a 6-inch newt on the same night and looked through both could conclude they are equivalent instruments.  

I have been brought up in a German speaking country.

 

But even in the 90s there were flat earthers in Germany, Austria and Switzerland who thought a 3" inch refractor equals a 6" reflector.



#16 David Gray

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Posted 24 May 2019 - 01:51 PM

I’m English born; well Scottish/Danish/Greek ancestry (though our sons insist: Celts/Vikings/Spartans...lol.gif ...).

 

I’m afraid that 3” refractor = 6” reflector stuff is too entrenched in some quarters (and evidently beyond these shores – ALPO........).  Also 6” = 10” reflector often mooted).  Most just ignored it – the Links I posted here (Post # 9) should bear some witness to that.

 

Being **English** (**stereotyping being another eternal entrenchment it seems**....flame.gif ..) as someone actually living here n’east England these 75-yrs I, and many others I know, found our own way.

 

In my case to firmly underline I was never a Sir Moore ‘disciple’: his books too shallow for me – I never bought any; but given by well-meaning relatives etc.  The few I still have these near 6 decades, look new/unused...... Going straight into Sidgwick, Peek (Jupiter) Alexander (Saturn) and of that ilk – those books, lived-in, look very battered – well used.

 

Beyond those Sky & Telescope 1962-2005 (stopped when the preceding 10-yrs were getting too ‘stargazy’ for my tastes - as is the BAA now).  Those Ashbrook years’ issues were an excellent supplement to those Sidgwick et al books.

 

A BAA Member: ‘club’ training: is offered but never insisted upon; the clue is in the *Association* bit.


Edited by David Gray, 24 May 2019 - 01:56 PM.

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#17 Magnetic Field

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Posted 24 May 2019 - 02:01 PM

I’m English born; well Scottish/Danish/Greek ancestry (though our sons insist: Celts/Vikings/Spartans...lol.gif ...).

 

I lived for 9 years in Edinburgh before moving to the South of England.

 

I still understand Scottish.

 

It was always windy there and when I think back: how is it ever possible there to observe anything in that windy conditions. At that time I didn't have a telescope (only recently made my way back into amateur astronomy after a hiatus of 18 years). But could see the Royal Observatory  from my office.



#18 stanislas-jean

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Posted 24 May 2019 - 02:18 PM

More than the baa booklet that I have, just recommendations, therefore to anybody for making his "rule".

More that topic, have a look on:

http://alpo-j.asahik...atest/Venus.htm

you will get several reports of several countries, different observers and annual reports issued for some.

I issued on all the reports I produced since years, only sketches.

If this is an help for you for having largely more data than this simple booklet, very limited.

You know we had the period that big guns were an absolute must, now it seems the director of the section is coming back to moderate aperture, etc... we have periods for and without. So.

Here in france, if you don't own an apo you are stupid, don't have a c14, data subject to high discussion, not a dobson (the last must) you are stupid. People never discuss about scope strehl in cause, actual seeing during obs, main parameters that affect the data results, even by imaging. Nobody is using procedure for self control of pertinence data.

It's not important.

Good skies.

Stanislas-Jean



#19 David Gray

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Posted 24 May 2019 - 02:45 PM

Sidgwick (“Observational Astronomy for Amateurs” - 1955) seems to favour that refractor over reflector notion;

as does Roth ( Handbook for Planet Observers“ – 1966).

 

But see this link to page 33 (2nd paragraph) of Peek’s “The Planet Jupiter” – 1958....I still remember the delight of

reading that when I got my copy in 1963 – the 10” f/8 Newt followed the year after....... https://archive.org/...upiter/page/n17


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#20 Jeff Morgan

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Posted 24 May 2019 - 02:48 PM

But even in the 90s there were flat earthers in Germany, Austria and Switzerland who thought a 3" inch refractor equals a 6" reflector.

 

I never took it to mean "3" refractor = 6" reflector".

 

Rather, refractors are more "efficient" than reflectors. At equal apertures it is no contest. 

 

While a 3" refractor may be effective for a Venus observing program, no one builds 3" reflectors. No profit is probably the main reason, but they don't scale down very well either. Hence my suggestion that you build a 3" reflector.

 

So the question shifts to "how large a reflector for a beginning astronomer to undertake a Venus observing program". 

 

Sure, Edmund Scientific and a few others made 4" reflectors. And small Maks. Moving into Maks, 5" apertures start becoming common. And maybe even a beginners instrument. But the smallest Newtonians of decent quality and commonly available would probably be ... 6".

 

I wouldn't be so quick to impugn ALPO's motives without thinking about what the beginning planetary enthusiast may have available for purchase. They exist to promote observing, not telescope types.


Edited by Jeff Morgan, 24 May 2019 - 02:49 PM.

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#21 gwlee

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Posted 24 May 2019 - 03:00 PM

I’m English born; well Scottish/Danish/Greek ancestry (though our sons insist: Celts/Vikings/Spartans...lol.gif ...).

 

I’m afraid that 3” refractor = 6” reflector stuff is too entrenched in some quarters (and evidently beyond these shores – ALPO........).  Also 6” = 10” reflector often mooted).  Most just ignored it – the Links I posted here (Post # 9) should bear some witness to that.

 

Being **English** (**stereotyping being another eternal entrenchment it seems**....flame.gif ..) as someone actually living here n’east England these 75-yrs I, and many others I know, found our own way.

 

In my case to firmly underline I was never a Sir Moore ‘disciple’: his books too shallow for me – I never bought any; but given by well-meaning relatives etc.  The few I still have these near 6 decades, look new/unused...... Going straight into Sidgwick, Peek (Jupiter) Alexander (Saturn) and of that ilk – those books, lived-in, look very battered – well used.

 

Beyond those Sky & Telescope 1962-2005 (stopped when the preceding 10-yrs were getting too ‘stargazy’ for my tastes - as is the BAA now).  Those Ashbrook years’ issues were an excellent supplement to those Sidgwick et al books.

 

A BAA Member: ‘club’ training: is offered but never insisted upon; the clue is in the *Association* bit.

My mother’s family started dispersing  immediately following WWII with some remaining in England and the rest migrating to the US, Canada, Australia, and New Zealand, which led to me living in the US, England, and Australia and visiting most of the English speaking countries. Each place has its own subtlety unique culture that gives rise to stereotypes. As a “brash” American, I have always enjoyed poking fun at my “hide bound” English cousins. 

 

There’s a lot to be said for the structured learning approach of the club system, and I learned a lot from Sir More’s books, but found some of it needed to be taken with a grain of salt.


Edited by gwlee, 24 May 2019 - 03:05 PM.


#22 David Gray

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Posted 24 May 2019 - 03:20 PM

Trouble is whenever the English (>200 dialects) are mimicked it’s usually Cockney London accent or Upper Class 'chinless-twit' stuff– I’m Northumberland born (living in Durham now): my Location (below Avatar here) is local dialect Ower Yonder - means Over There.

 

An episode of Family Guy once featured Daily Mirror comic strip’s  Andy Capp speaking broad Cockney – the character was based in West Hartlepool.......10 miles north of me.......!!

 

Can’t offer any insight on clubs; being a lone-furrow ‘loner’; not readily a ‘joiner’.


Edited by David Gray, 24 May 2019 - 03:55 PM.


#23 Michael Covington

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Posted 24 May 2019 - 06:57 PM

It's not been true since the invention of the silver on glass process (as long as the silver is fresh) and certainly not since the invention of aluminizing. 

 

I know the Englishmen are often a bit, um, conservative, but this is stretching it. 

 

The 3" refractor = 6" reflector rule nonsense has been repeated ad nauseam in most of Patrick Moore's books (and a lot of other english astronomy books). 

 

 

Clear skies!
Thomas, Denmark

I believe it came from T. W. Webb and may have been close to true at the time he wrote it (1850s).  Maybe someone can track it down.




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