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Long slow Newtonians

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#26 CHASLX200

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Posted 13 September 2018 - 05:39 AM

Hi Bob!

The 6" seems like a humble scope size but under the most stable skies it becomes apparent how limiting the atmosphere really is for high definition viewing. I'm more convinced than ever how important accurate figure is for the finest and detailed images. Those breathtaking nights are rare enough that most folks may never get to appreciate what can be achieved. Indeed, there are areas where seeing always limits even small scopes and I feel blessed to live where the veil is often lifted.

Best,
Mike

I sure got the seeing for super well made optics.  I know what Zambuto and OMI optics can do from 11 to 18" in my seeing 1000x+ is no problem.  So i would want the best optic made for my scope.


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#27 barbie

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Posted 13 September 2018 - 09:30 PM

I sure got the seeing for super well made optics.  I know what Zambuto and OMI optics can do from 11 to 18" in my seeing 1000x+ is no problem.  So i would want the best optic made for my scope.

Then go out and buy a Zambuto 18"!lol.gif   Heck, since you're always bragging about your seeing, why not buy two 18" scopes and make a binoscope out of it!!  You certainly have bought and sold a number of scopes so this would be something new for you to try!lol.gif lol.gif


Edited by barbie, 13 September 2018 - 09:40 PM.

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#28 CHASLX200

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Posted 14 September 2018 - 05:26 AM

Then go out and buy a Zambuto 18"!lol.gif   Heck, since you're always bragging about your seeing, why not buy two 18" scopes and make a binoscope out of it!!  You certainly have bought and sold a number of scopes so this would be something new for you to try!lol.gif lol.gif

I am done with big scopes. If i had a place to house a big Dob it would be a 20" F/6 for planets only.



#29 GShaffer

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Posted 14 September 2018 - 05:32 AM

Mike, I can fully attest to some of the most incredible planetary views and double stars with one of your 6" f/9 mirrors in a custom made telescope. IIRC, the secondary was only .75" and the views of Saturn were simply breathtaking. Thanks for having made some of the finest long focal length mirrors on the planet. Bob Schilling

 

I can 2nd this.....my 6.7" f/9.2 from Mike is 2nd to none I have seen......


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#30 25585

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Posted 14 September 2018 - 06:42 AM

I was looking for long focal length Newts the other day and the f/8 6" was about the longest I could find at most places.  Does anyone sell complete scopes of longer focal lengths or are they ATM only now days?

Orion Optics UK, who made my 10 inch F6 can do a 6 inch F11 VX6XL model https://stargazerslo...70-inches-long/  and I think an 8 inch F8 VX8XL. http://scopeviews.co...ptics200Dob.htm


Edited by 25585, 14 September 2018 - 06:46 AM.

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#31 Jon Isaacs

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Posted 15 September 2018 - 10:32 AM

Mike, I can fully attest to some of the most incredible planetary views and double stars with one of your 6" f/9 mirrors in a custom made telescope. IIRC, the secondary was only .75" and the views of Saturn were simply breathtaking. Thanks for having made some of the finest long focal length mirrors on the planet. Bob Schilling

 

Mike has a story about one of his 6 inch Dobs and the Grand Canyon Star Party.  I'll share the beginning and let Mike finish it if his inherent sense of modesty will allow it. .

 

It seems that among all the fancy scopes , Mike had one of his long focal length 6 inchers pointed a Jupiter (or maybe Saturn ).  A guy comes to take a look and spends a lot of time just looking. 

 

When he's done,  he says to Mike; 

 

Jon


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#32 PXR-5

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Posted 15 September 2018 - 04:15 PM

I once owned a Meade 6" f8 on a pier EQ, while it was heavy it was my favourite scope. But at f8 it was also my fastest scope.
It's pretty much life in the slow lane around here as you can tell by my signature LOL f10 is pretty fast for me ;)
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#33 Mike Spooner

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Posted 15 September 2018 - 04:42 PM

Mike has a story about one of his 6 inch Dobs and the Grand Canyon Star Party.  I'll share the beginning and let Mike finish it if his inherent sense of modesty will allow it. .
 
It seems that among all the fancy scopes , Mike had one of his long focal length 6 inchers pointed a Jupiter (or maybe Saturn ).  A guy comes to take a look and spends a lot of time just looking. 
 
When he's done,  he says to Mike; 
 
Jon


Okay Jon, since you put me on the spot. smile.gif

It was Jupiter ... He basically said they were good optics - dirty! But good. They were pretty dusty. The seeing was great that night so that helped a lot. To be honest it was the 1st decent mirror I'd made and really opened my eyes to what a good scope could perform like. After that it was hard to be satisfied with anything less. A really slippery slope to get involved with. I really like all kinds of scopes but that one no doubt biased my liking for long focus Newts.

Mike
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#34 CHASLX200

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Posted 15 September 2018 - 06:16 PM

If someone could make a nice 8" F/10 Newt OTA with a Parks tube i would buy it now.  Just seems no one makes real tubes anymore for a do it yourself.



#35 25585

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Posted 16 September 2018 - 04:39 AM

If someone could make a nice 8" F/10 Newt OTA with a Parks tube i would buy it now.  Just seems no one makes real tubes anymore for a do it yourself.

I know what you mean. The old plastic pipes suited me. You could bump them, drill holes for adding attachments, and they were tough.

 

Nowadays it's delicate aluminium or expensive carbon fibre. Back to wooden boxes or cardboard tubes for DIY.  



#36 NinePlanets

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Posted 16 September 2018 - 07:32 AM

Hey, Guys. F/8 is NOT slow. F/8 is normal for a Newt. F/6 is fast.

It wasn't until this plywood-and-pipes-pushalong revolution came about that F/4's were even considered as a normal telescope (other than the odd 4-1/4" RFT). The hand-grenade eyepiece market developed only because of the big F/4's.

 

I have a 10" F/6 but my 8" F/8 gets used more.


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#37 25585

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Posted 16 September 2018 - 10:09 AM

In the days of home or domestic mirror making, before the far eastern products swamped the market, F6 was considered fast, F8 normal.

 

Before the SCTs took over F10, only slow Newts were there (and achro refractors). But Moon and planets, + bright stars and objects were the usual viewing menu. However small cats give small FOV as restricted mainly to 1.25 eyepiece views. Newts can have huge focusers and eyepieces by comparison. 

 

Big fast mirrors gave the amateur views only observatories once had. But for me the appeal of long FL is using longer FL eyepieces, with longer eye relief and comfort. 



#38 barbie

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Posted 16 September 2018 - 11:43 AM

My 6" F8 continues to be my most used scope.  If I were stranded on a desert island and could only have one scope, it would be a 6"F8 Newtonian.


Edited by barbie, 16 September 2018 - 11:45 AM.

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#39 Jon Isaacs

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Posted 16 September 2018 - 12:06 PM

Okay Jon, since you put me on the spot. smile.gif

It was Jupiter ... He basically said they were good optics - dirty! But good. They were pretty dusty. The seeing was great that night so that helped a lot. To be honest it was the 1st decent mirror I'd made and really opened my eyes to what a good scope could perform like. After that it was hard to be satisfied with anything less. A really slippery slope to get involved with. I really like all kinds of scopes but that one no doubt biased my liking for long focus Newts.

Mike

Ok Mike..

 

Now for the other story...

Jon



#40 Jon Isaacs

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Posted 16 September 2018 - 12:25 PM

Hey, Guys. F/8 is NOT slow. F/8 is normal for a Newt. F/6 is fast.

It wasn't until this plywood-and-pipes-pushalong revolution came about that F/4's were even considered as a normal telescope (other than the odd 4-1/4" RFT). The hand-grenade eyepiece market developed only because of the big F/4's.

 

I have a 10" F/6 but my 8" F/8 gets used more.

 

I think it worked the other way.. Because the good eyepieces and coma correctors were available F/4 Newtonians came into their own.  The market for TeleVue eyepieces was and is for CATs, refractors and reflectors.

Large aperture scopes were impractical before the Dobsonian.. This photo tells the story:

 

3825418-Meade + Discovery 1.jpg

 

Two 12.5 inch scopes. Old style and one more modern.

One of these two scopes never left the driveway. One of these two scopes has been all over the southwest and in it's current truss form just got back from a week under the dark skies of the Navajo reservation.  And yes, the F/4.06 has been the better planetary scope.  Something about being stuck in the garage limits the image sharpness.

It was a nice old F/6, I had it out a few times a year. Not often for someone who gets out about 180 nights a year. Impressive but impractical in today's world where I can setup my 22 inch by myself but the 12.5 inch F/6 was a two person scope.

Jon

 


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#41 CHASLX200

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Posted 16 September 2018 - 02:31 PM

I think it worked the other way.. Because the good eyepieces and coma correctors were available F/4 Newtonians came into their own.  The market for TeleVue eyepieces was and is for CATs, refractors and reflectors.

Large aperture scopes were impractical before the Dobsonian.. This photo tells the story:

 

 

 

Two 12.5 inch scopes. Old style and one more modern.

One of these two scopes never left the driveway. One of these two scopes has been all over the southwest and in it's current truss form just got back from a week under the dark skies of the Navajo reservation.  And yes, the F/4.06 has been the better planetary scope.  Something about being stuck in the garage limits the image sharpness.

It was a nice old F/6, I had it out a few times a year. Not often for someone who gets out about 180 nights a year. Impressive but impractical in today's world where I can setup my 22 inch by myself but the 12.5 inch F/6 was a two person scope.

Jon

 

I would take the old style if my back were up to it.


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#42 RobertMaples

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Posted 16 September 2018 - 09:05 PM

How does a short tube reflector with a barlow lens compare to a long tube reflector?  I've heard that a short tube with a barlow performs like a longer tube, but is that true in every aspect or are there still advantages to a true long tube reflector?



#43 izar187

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Posted 16 September 2018 - 09:47 PM

Frequently the longer slower newt will have a smaller secondary.

Planetary contrast will be improved.

The long slow newt will have significantly less coma. More improvement.

It will also focus sharp much easier. More improvement. 

Although a fine adjusting focuser will help this in a fast newt. 

 

You can get to the same magnification in both scopes. 

With a barlow(s) or ep's with built-in barlow, you will reach equal magnification.

 

Plus the barlow or ep's with built-in barrows will clean up off axis astigmatism.

Correcting maybe half of the fast newts inherent aberrations in the ep.

 

If you use a coma corrector, and multi-element astigmatism correcting ep's, in a fast newt, then you can get really, really close to a long slow newt, on planets.

 

But the fast newts larger secondary robs some contrast.

Many folks maintain that the multi-element ep's that work best in fast newts, those rob some contrast too.

 

The long slow newt, with modest design ep's, delivers a great planet. 

A fast newt of the same size, at the same magnification, needs better ep's and coma correction to even come close to equaling it. IME

 

On deep sky targets, at equal aperture and magnification... they're qual. IME

 

End ramble.



#44 Jon Isaacs

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Posted 16 September 2018 - 10:01 PM

The long slow newt, with modest design ep's, delivers a great planet.

 

 

My own thinking/experience is that a long, fast Newtonian will provide the better planetary views. One has to step back from the aperture paradigm and do some outside the box thinking.

 

Consider two scopes,  both with a 1500 mm focal length: a 150 mm F/10 and a 300 mm F/5. I think there's little doubt the 300 mm F/5 will provide the better planetary views. 

 

Sure , I'm comparing a 6 inch with a 12 inch, ergonomically that's the right comparison.  

 

Jon



#45 LFORLEESEE

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Posted 16 September 2018 - 10:09 PM

Orion Optics UK, who made my 10 inch F6 can do a 6 inch F11 VX6XL model https://stargazerslo...70-inches-long/  and I think an 8 inch F8 VX8XL. http://scopeviews.co...ptics200Dob.htm

Had this little project sitting around for a few years...12 inch F/20.

 

Orion Optics UK ground this and another one for the BBC for a Herschel Telescope doco  they were making.

 

I'm going to start the mirror box soon as per image from the Smithsonian Museum with the same mirror holder and access panel.

 

Three 7foot sections....1/ .Mirror box...2/ .carbon fibre rods....3/.carbon fibre rods with secondary holder.

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#46 CHASLX200

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Posted 17 September 2018 - 05:22 AM

How does a short tube reflector with a barlow lens compare to a long tube reflector?  I've heard that a short tube with a barlow performs like a longer tube, but is that true in every aspect or are there still advantages to a true long tube reflector?

Not even close. A slower scope is much better with much less coma. Less shallow focus as well.  Last fast scope i had i could not even use it as shallow focus drove me nuts.  Gottta have a Paracorr for the faster scope.



#47 NinePlanets

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Posted 17 September 2018 - 07:17 AM

Chicken or the Egg?  The Chicken!  :)

 

Jon Isaacs:  I worked in telescope retail in the late 1970's - early 1980's. At that time there were no commercially-produced F/4 Newtonians other than Edmund's Astroscan and Coulter's little collapsible 4-1/4" CT-100. (You might come across the odd Cave Astrola or Telescopics Newt/Cass convertible but those were not common.) One exception: Edmund's big red 8" F/5 on the fork mount that showed up about 1982.)

 

At that time, the best eyepieces available for these shorties were orthoscopics and the odd surplus Erfle. Meade supplied a 2" Erfle too. There were also the Clave Plossl's from France but they cost a lot of money to import and the best choices were the Meade R.G. Erfles and Orthos and the Brandon Orthoscopics. Even Edmund only supplied their 28mm RKE with the A-scan.

 

Then along came Coulter with their big blue 13.1" plywood push-along. I believe that was the first large-ish F/short produced in any numbers. It was about that time that Al Nagler came on the scene with his 1-1/4" Plossls which were the first of that design affordable by the average telescope user. Then he followed up with his 13mm Nagler design. We called it the "coffee can". Few could afford one and the kidney bean effect and its weight made it a very hard sell.

 

At least that's how my memory has it. Almost all Newtonians commercially produced at that time were F/6 - F/10. F8 was typical. Plossl's were new and all the rage. (I still use mine, but my Meade R.G's get the most use.  ;)


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#48 Jon Isaacs

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Posted 17 September 2018 - 08:09 AM

At least that's how my memory has it. Almost all Newtonians commercially produced at that time were F/6 - F/10. F8 was typical

 

 

I think it's true that fast Newtonians are pretty much a modern luxury that has made large apertures portable and practical. Back in the day,  a 12.5 inch F/6 was quite rare and few Scopes were larger.  Today,  beginners consider a 12 inch Dob as a possibility. 

 

But the question here is whether the Scopes came about because of availability of the Naglers or vice versa.  The eyepieces did become popular with people using all types of Scopes and since the first quality truss Dobs did not appear until nearly 10 years after the introduction of the Naglers, it would seem the eyepieces enabled the development of Premium quality Dobs. 

 

I don't think the Coulter crew was a big force in popularizing the Naglers.  Some years ago I purchased a 13.1 inch Blue Tube and it came with or this and Kellners. 

 

In the last 10 years,  something similar has happened.  The Ethos eyepieces and the Paracorr 2 have resulted in a move to even faster Dobs . F/3 is the new F/4. The Ethos eyepieces came about as a new design and became popular with owners of all scope types but the Paracorr 2 was designed after Al looked through one of Mike Lockwoods sub F/4 mirrors and decided it deserved a better coma corrector .

 

From what I know and I have seen , it has been the existence of high quality eyepieces and then the coma correctors that have made high quality,  fast Newtonians possible.  Obviously TeleVue has benefitted from this shift but they do OK without the Big Dob market .

 

Jon



#49 NinePlanets

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Posted 17 September 2018 - 08:10 AM

You know what? Now that my memory is jogged a bit, there were some other sawed-off Newtonians available in ~1980: Meade sold a 6"F/5 on an equatorial mount (their model 645) and there was also an outfit (Star Instruments?) in California that produced a 6" F/4 tube assembly with Meade accoutrements. Both of these were considered to be "wide field" telescopes but, naturally, coma was terrible and there were no parracor's around then.

 

I think it was 1980 that the TV Plossls  hit the market. (Coma still sucked.)

 

These fancy new hand grenade eyepieces truly do make all the difference. They DO allow F/short (under f/8) telescopes to work and big ones to be portable. Al Nagler revolutionized the telescope industry. You're right. The egg enabled the chicken!  :)


Edited by NinePlanets, 17 September 2018 - 08:13 AM.

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#50 starcanoe

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Posted 17 September 2018 - 08:15 AM

My own thinking/experience is that a long, fast Newtonian will provide the better planetary views. One has to step back from the aperture paradigm and do some outside the box thinking.

 

Consider two scopes,  both with a 1500 mm focal length: a 150 mm F/10 and a 300 mm F/5. I think there's little doubt the 300 mm F/5 will provide the better planetary views. 

 

Sure , I'm comparing a 6 inch with a 12 inch, ergonomically that's the right comparison.  

 

Jon

 

And what is a good 6 inch mirror going to cost vs a good 12 inch? And the weight of the mirrors and scope. Mirror cell complexity. Alignment tolerances. Coma corrector vs none. Eyepiece cost differences. Cool down times. Grab and go vs grab and grunt.

 

Looking at just focal length is silly.


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