Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

What would be the characteristics of a planet focused scope?

  • Please log in to reply
86 replies to this topic

#1 aeajr

aeajr

    Voyager 1

  • *****
  • topic starter
  • Posts: 13,799
  • Joined: 26 Jun 2015
  • Loc: Long Island, New York, USA

Posted 24 May 2020 - 08:59 PM

I have a variety of telescopes in my signature, but I consider them all general purpose.  The 12" Dob gets the most use simply because it has the largest aperture.  

 

I am thinking of getting a scope that would be optimized for observing planets.  What would be the characteristics of a planet optimized scope?  What would be the most important features?

  • Large aperture?
  • Refractor?
  • Newtonian?
  • SCT?
  • Mak?
  • Long focal length?
  • high focal ratio?
  • 2" focuser?
  • Special lens glass?
  • Special mirror glass?

What should I consider important and what is less important?

 

Or, is my Dob the best planetary telescope simply because of its large aperture?

 

Or, is my 5" Mak better for planets because of its F15 FR and longer FL?

 

Or would a 4" refractor be better?

 

Any thoughts are welcome. 

 

I am not ready to buy anything but if you want to name a particular scope and tell me why that would be better for planets than my Dob, I would love to hear your thoughts. 

 

Let's put a $3000 cap on the OTA, just to set a target.


Edited by aeajr, 24 May 2020 - 09:20 PM.


#2 Augustus

Augustus

    Fly Me To The Moon

  • *****
  • Posts: 9,488
  • Joined: 26 Dec 2015
  • Loc: Stamford, Connecticut

Posted 24 May 2020 - 09:05 PM

If you are willing to do some work yourself, a homemade/custom 8" or 10" Newtonian with the longest possible focal ratio that you can handle (f/7-f/8?), minimal central obstruction and a low-profile focuser would probably be best. 

 

Alternatively the only thing I'd say would really be worth your time would be a C9.25, and even that's a gamble. A C8 or Mak would be beaten by your Dob (and you've already got an ETX-125), as would most refractors in your price range (I guess you could get a 3" Tak, but as nice as those are your ETX or Dob is probably going to be just as good).


Edited by Augustus, 24 May 2020 - 09:06 PM.

  • ShaulaB, areyoukiddingme and aeajr like this

#3 aeajr

aeajr

    Voyager 1

  • *****
  • topic starter
  • Posts: 13,799
  • Joined: 26 Jun 2015
  • Loc: Long Island, New York, USA

Posted 24 May 2020 - 09:08 PM

Augustus,

 

You seem to be focused on longer focal length and higher FR.  Is that right?   

 

Seems you find aperture a secondary consideration.

 

Thanks!


  • Augustus likes this

#4 luxo II

luxo II

    Vanguard

  • -----
  • Posts: 2,004
  • Joined: 13 Jan 2017
  • Loc: Sydney, Australia

Posted 24 May 2020 - 09:09 PM

You're leaping to solutions without thinking about what makes a good planetary scope:

 

1. aperture - 250mm or more to take advantage of nights with excellent seeing;

2. focal length, ideally 3m or more so that you can achieve high magnification without Barlows or similar;

3. small central obstruction, ideally 26% or less,

4. exquisite optics.

 

Your $1200 cap rules out most of the real solutions, however.


Edited by luxo II, 24 May 2020 - 09:16 PM.

  • aeajr and Augustus like this

#5 Augustus

Augustus

    Fly Me To The Moon

  • *****
  • Posts: 9,488
  • Joined: 26 Dec 2015
  • Loc: Stamford, Connecticut

Posted 24 May 2020 - 09:13 PM

Augustus,

 

You seem to be focused on longer focal length and higher FR.  Is that right?   

 

Seems you find aperture a secondary consideration.

 

Thanks!

I mean, a 12" long focus scope isn't that practical, and the average size of air cells (usually under 10") means a scope over 10 inches is way more easily affected by bad seeing from my experience. Not that there's anything wrong with more aperture than that, but if you are using anything over 10" you should probably disregard optimizing it for "planetary". After a while it's not necessary anyway; a 20" f/5 for example needs all of a 15.5% central obstruction for full illumination of a 2" eyepiece.

 

C9.25s are usually very good optically and allow you to get high power easily, though the large CO isn't the best. 

 

180mm Maksutovs are good, but cooldown takes ages and all in all a C9.25 will probably beat one - plus the slightly brighter image of the 9.25 is nice.

 

150mm Maks have the same cooldown issue of a 180 (slightly lessened but still bad) and probably aren't enough of a gain over your 125 to notice.

 

C8s are a crap shoot. Dunno about the C6 but your ETX-125 would probably crush one. C5s have huge central obstructions and I find them unremarkable (and again obviously loses to an ETX).

 

A 6" f/15 achromat would be good, but you need an EQ6 or custom mount to carry one and the seven-foot OTA is a bit of a pain. 4" f/10 has a bit too much CA, and longer 4-inchers are hard to come by. 6" f/8 or f/10 is just too much CA.

 

Cheap apos generally aren't the greatest at high powers. I have an ES ED127 and haven't used it yet but I am not expecting amazing views of planets based on my experience with the ED102, plus one is right at the limit of your budget anyway. Have never been impressed by the cheaper Long Perng triplets either. Not sure about something like the AT102ED. But in any case a larger Newtonian or cat probably will show more anyway unless it's something like a Tak or A-P which seem to defy the laws of physics.


Edited by Augustus, 24 May 2020 - 09:19 PM.

  • aeajr and grzesznypl like this

#6 aeajr

aeajr

    Voyager 1

  • *****
  • topic starter
  • Posts: 13,799
  • Joined: 26 Jun 2015
  • Loc: Long Island, New York, USA

Posted 24 May 2020 - 09:14 PM

You're leaping to solutions without thinking about what makes a good planetary scope:

 

1. aperture - 250mm or more to take advantage of nights with excellent seeing;

2. focal length, ideally 3m or more so that you can achieve high magnification without Barlows or similar;

3. small central obstruction, ideally 26% or less,

5. exquisite optics.

I am not leaping to anything.  In fact that is the opposite of what I am doing.  I am asking what makes a good planetary scope.

 

So, if I understand  your post, the design of the scope is not important?  All designs are equal, based on your post except it look like you are leaning toward something with a mirror since you give a spec for a central obstruction and refractors don't have COs.  So Newtonian, SCT or Mak over refractor would be your guidence.

 

Thanks


Edited by aeajr, 24 May 2020 - 09:18 PM.

  • payner and Augustus like this

#7 aeajr

aeajr

    Voyager 1

  • *****
  • topic starter
  • Posts: 13,799
  • Joined: 26 Jun 2015
  • Loc: Long Island, New York, USA

Posted 24 May 2020 - 09:19 PM

I mean, a 12" long focus scope isn't that practical, and the average size of air cells (usually under 10") means a scope over 10 inches is way more easily affected by bad seeing from my experience. 

 

C9.25s are usually very good optically and allow you to get high power easily, though the large CO isn't the best. 

 

180mm Maksutovs are good, but cooldown takes ages and all in all a C9.25 will probably beat one - plus the slightly brighter image of the 9.25 is nice.

 

150mm Maks have the same cooldown issue of a 180 (slightly lessened but still bad) and probably aren't enough of a gain over your 125 to notice.

 

C8s are a crap shoot. Dunno about the C6 but your ETX-125 would probably crush one. C5s have huge central obstructions and I find them unremarkable (and again obviously loses to an ETX).

 

A 6" f/15 achromat would be good, but you need an EQ6 or custom mount to carry one and the seven-foot OTA is a bit of a pain. 4" f/10 has a bit too much CA, and longer 4-inchers are hard to come by. 6" f/8 or f/10 is just too much CA.

 

Cheap apos generally aren't the greatest at high powers. I have an ES ED127 and haven't used it yet but I am not expecting amazing views of planets based on my experience with the ED102, plus one is right at the limit of your budget anyway. Have never been impressed by the cheaper Long Perng triplets either. Not sure about something like the AT102ED. But in any case a larger Newtonian or cat probably will show more anyway unless it's something like a Tak or A-P which seem to defy the laws of physics.

Humm, I am not really focused on the cost at this point.  So I will make it $3000 if that helps.  Just don't want someone suggesting $50,000 scopes. 


  • Augustus likes this

#8 Augustus

Augustus

    Fly Me To The Moon

  • *****
  • Posts: 9,488
  • Joined: 26 Dec 2015
  • Loc: Stamford, Connecticut

Posted 24 May 2020 - 09:21 PM

Humm, I am not really focused on the cost at this point.  So I will make it $3000 if that helps.  Just don't want someone suggesting $50,000 scopes. 

In that case, anything I mentioned above but with the option of a 4" or 5" Tak or similar high-quality and preferably slow apo (Stellarvue? I really don't know tons about fancy refractors). Still probably wouldn't be my first pick. I only have my 5" apo because a friend covered the cost in exchange for letting him borrow it a few times a year (long story), I will probably use it occasionally but I would most likely prefer my C9.25 or a Dob for planets.

 

A 14"-17.5" Dob with a quality mirror would also be a good pick for 3k, but it's hard to say whether that would be a dedicated planetary scope.


Edited by Augustus, 24 May 2020 - 09:24 PM.


#9 gezak22

gezak22

    Gemini

  • *****
  • Posts: 3,245
  • Joined: 15 Aug 2004
  • Loc: On far side of moon. Send help.

Posted 24 May 2020 - 09:49 PM

You should try to minimize the impact of floaters. Therefore, I would want either a bino setup (binoviewer or binoscope) or a setup where 250x still yields an exit pupil of 1 mm or larger. However, you should also maximize viewing comfort while viewing for extended periods of time, therefore I would want a setup that uses both eyes (and a good chair).

 

Obviously, optics should be of a high quality and seeing (and tube currents) should be minimal.


  • CeleNoptic and Augustus like this

#10 grzesznypl

grzesznypl

    Messenger

  • *****
  • Posts: 437
  • Joined: 07 Apr 2019
  • Loc: Jackson Heights, NY ... for now

Posted 24 May 2020 - 09:58 PM

Here is solution no one yet suggested ... refigure your AD12 mirror. I know your scope its only 1 year old more or less but refigured mirror would give you much better planetary details at the fraction of the cost of premium APO. In addition it would also improve DSO viewing as well. Then getting binoviewer as gezak22 suggested would even enhance planetary experience further.


  • Jon Isaacs, CeleNoptic, Augustus and 1 other like this

#11 SeaBee1

SeaBee1

    Skylab

  • *****
  • Posts: 4,130
  • Joined: 19 Mar 2015
  • Loc: Under the DFW light barrier

Posted 24 May 2020 - 10:18 PM

Ed, my thought is that you are pretty well equipped for planet observing with your 12".

 

From my own experience, when I was using my Celestron Omni 102mm, I was able to see, on good nights, festoons in Jupiter's cloud bands, the Cassini Division in Saturn's rings, a few of Saturn's moons, shadow transits across Jupiter's surface, polar caps on Mars, etc... but when I finished building my 10 inch Dob and deployed THAT sucker on Saturn for its first light... Holy Smoke! The difference was amazing! I will remember that view forever...

 

I guess it wasn't really a fair comparison. The Omni is an off the shelf scope, though a good one, but I optimized the 10 inch in every possible way... premium primary mirror, premium secondary mirror, base optimized for easy tracking, etc... the Omni is just plain outclassed and not just because of the lesser aperture.

 

I wouldn't look any further than in your garage and bring out the 12 incher...

 

Keep looking up!

 

CB


  • JamesMStephens and Augustus like this

#12 luxo II

luxo II

    Vanguard

  • -----
  • Posts: 2,004
  • Joined: 13 Jan 2017
  • Loc: Sydney, Australia

Posted 24 May 2020 - 10:48 PM

All designs are equal, based on your post

Not at all.

But your budget knocks out the solutions I would consider, and about all that are left after that constraint are your 12” dobsonian (cheap and simple big aperture) or entry-level SCTs (maybe a C9.25 or C11).

Neither however are optimal for their aperture - the secondary obstruction is large and the optical quality is probably not exceptional.

FWIW if I were to make a 10-12” dob as a planetary scope I’d be looking for a Zambuto mirror around f/7-8.

Edited by luxo II, 24 May 2020 - 10:54 PM.


#13 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 85,049
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 24 May 2020 - 11:32 PM

My thinking:

 

- The best planetary scope depends on your seeing conditions.  

 

- Focal ratio is not important, Maks and SCTs use a magnifying mirror to turn very fast mirrors in into slow scopes. Barlows do this same thing. 

 

- Optical quality is important.

 

- Enough aperture to be seeing limited on very good night's is important. Do not think that the Dawes limit is a measure of planetary contrast and resolution.. in 2 arc-second seeing, an 8 inch is superior to a 4 inch.  

 

- Thermal equilibrium and thermal behavior are critical, particularly for larger scope.

 

- A smaller secondary is desirable.

 

- Preparation is important.  Collimation.. The surface the scope rests on.. grass is good, pavement not good..

 

-----

 

My backyard generally south of the jet streams in one of mildest climates in the world. It's  about 5 miles from the Pacific Ocean and often gentle evening breezes flow in off the ocean. It's sheltered from the afternoon sun.

 

Seeing under 1 arc-second is pretty common, half arc-second happens..

 

For me a good quality scope in the neighborhood of 12.5 inches is good fit for my conditions. If I want to get the best planetary views, split the closest double stars, I'll use my 13.1 inch F/5.5. It has a Royce mirror, a 20% CO. Mechanically it's nicely made and has a Feathertouch focuser..

 

6446676-Birthday Dob CN.jpg
 
For Ed, for Zane, for you, this might not be the optimal scope. Sometimes a planetary scope is about making the best of a bad situation rather than taking advantage of good opportunities. 
 
The biggest factor is the observer, the skills of the observer, the hours at the eyepiece. 
 
Jon

  • payner, DHEB, SeaBee1 and 2 others like this

#14 luxo II

luxo II

    Vanguard

  • -----
  • Posts: 2,004
  • Joined: 13 Jan 2017
  • Loc: Sydney, Australia

Posted 25 May 2020 - 12:13 AM

There’s another need missing - portability.

If I had an backyard obs in an ideal location I’d probably have a 16” f/7 or a 12” trischiefspiegler, but portability dictates otherwise.

Hence my 10” mak which imho is the next best thing.

Edited by luxo II, 25 May 2020 - 01:49 AM.

  • Jon Isaacs likes this

#15 Epox75

Epox75

    Ranger 4

  • -----
  • Posts: 356
  • Joined: 19 Apr 2017
  • Loc: Netherlands

Posted 25 May 2020 - 06:28 AM

I started with planetary imaging and observing by buying a C11 seven years ago, i'll never regret that decision and if i'll ever think about getting a new scope for planetary that would be probably a C14.

 

The pros are the ease of collimation (only one mirror to play with), excellent optics, resolution, the enclosed optics keep everything clean and that it's compact. The cons are that is heavy, it takes time to cool down and at it's very seeing sensitive, I often had to renounce imaging with a 2x barlow and go at it's native focal length  



#16 aeajr

aeajr

    Voyager 1

  • *****
  • topic starter
  • Posts: 13,799
  • Joined: 26 Jun 2015
  • Loc: Long Island, New York, USA

Posted 25 May 2020 - 07:02 AM

Thanks for the posts friends.

 

RESTATING THE QUESTION

 

Let me make some clarifications as I don't think I did a good job of explaining what I am looking for.  This is NOT a shopping trip and I am not really looking for specific scopes.  I should not have mentioned price or asked for specific models as that is not really what I am looking for. 

 

I am trying to understand the decision points.

 

If I wanted to design a scope specifically for planetary visual observing, no AP, what would be the parameters I would want to optimize?

 

If I was shopping for a scope specifically for planetary visual observing, no AP, what would be the parameters I would want to look for?

 

 

For Example:

Would higher or lower focal ratios be better?  Why? 

 

Are refractors preferable over Newtonian reflectors?  Why? 

 

Are catadioptrics the best because they combine lenses and mirrors with high focal ratios? 

 

 

Portability, price, brand, optics quality are not in play here.  I am trying to understand what I would need to consider if I were looking for a scope optimized for planetary observing.  I am not looking for brand, price, or model. 

 

Things I have read but don't understand.

 

I have read that Maks are great planet scopes but I never hear why Maks are considered Planet scopes.

 

I have heard that long focal ratio refractors are great planetary scopes, but no one says why?  CA?  Resolution? ???

 

I have read that Newtonians lose sharpness due to the central obstruction.  But does their typical lower FR make them less optimized for planets even though they are more affordable for larger apertures? 

 

Hopefully I am making my request clearer.   I should never have mentioned price as this is not about buying anything, at least not now.  I am trying to learn before I even consider shopping for something.

 

Cloudy Nights has been one of my key learning resources and all of you are my teachers.   But sometimes I don't ask the right questions in the right way.   Perhaps this will help.


Edited by aeajr, 25 May 2020 - 10:21 AM.

  • rdmarco, DHEB and vdog like this

#17 Epox75

Epox75

    Ranger 4

  • -----
  • Posts: 356
  • Joined: 19 Apr 2017
  • Loc: Netherlands

Posted 25 May 2020 - 07:43 AM

 

 

If I was shopping for a scope specifically for planetary visual observing, no AP, what would be the paramaters I would want to look for?

 

For Example:

 

Would higher or lower focal ratios be better?  Why? 

 

In my opinion aperture first of all and a focal ratio between f/8 and f/10. Aperture is for details and it's nice to see as much details as possible.

 

Most of the planets are bright compared to other objects so even at a higher focal ratio (if you consider f/8 to f/10 high) and high magnification you will still see them bright...if you have a large enough aperture. 

 

I say between f/8 and f/10 also because at this focal ratio I've never had the feeling it was too much while observing, even with average seeing. I once tried to observe Jupiter with the focal reducer at f/6.3 and it was a way less pleasant experience compared to the native f/10 of my scope. 

I am not an expert, that's my opinion developed while observing, I hope it helps. 


Edited by Epox75, 25 May 2020 - 07:49 AM.

  • aeajr likes this

#18 luxo II

luxo II

    Vanguard

  • -----
  • Posts: 2,004
  • Joined: 13 Jan 2017
  • Loc: Sydney, Australia

Posted 25 May 2020 - 07:53 AM

I’ll suggest enjoy what your gear shows.

Go visit some star parties and see what other people’s scopes can do. And keep an eye out for someone with a big mak (intes, AP, TEC, Santel or APM) and try that, ideally side by side near some dobs or SCTs of similar aperture.

Then consider the tradeoffs Involved.

Put it this way:

A 10” APO refractor is neither affordable nor portable. You had better win Lotto to afford one of these.

The next best is a 10” Tri-schiefspiegler, also not portable and no-one makes these hence strictly a DIY scope.

After that ... maybe a 12”-16” f/7 Newtonian with a Zambuto primary, small secondary, not small and also a DIY effort. Probably the most cost effective solution but there are little issues Ike encoders or making it track so this is also a DIY affair.

Then the commercial SCTs... at least a C11 or 12” Meade, but to be honest they are both limited by mediocre optics.

Then there are the unicorns - the exotic big maks from AP, TEC, Santel, Intes and APM - more compact than a 10” LZOS refractor but that kind of compact size, and while they were commercially made they are strictly a low-volume premium quality product made by artisans hence do not come cheaply.

Edited by luxo II, 25 May 2020 - 08:15 AM.


#19 sanbai

sanbai

    Messenger

  • *****
  • Posts: 453
  • Joined: 18 May 2019
  • Loc: Baton Rouge, LA

Posted 25 May 2020 - 08:13 AM

This is going to be always a compromise.

 

Longer focal ratios would be better. It minimizes aberrations and allows using longer FL eyepieces. Classical eyepieces have eye relief proportional to the focal length. If you want to use an ortho or a plossl because the "minimal glass", then long focal lengths will make observations more comfortable, and with less. On the other hand, very long scopes aren't practical. Cassegrain-like designs make that easier, though.

 

Refractors are preferable to reflectors when comparing apertures. Better contrast and resolution. Lack of obstructions helps in that regard. However, they quickly become monsters. Large refractors (>6") would need a tripled to avoid CA. Thermal equilibrium starts to be a big issue, not to say price and comfort. Usually aperture rules, so they cannot be "ultimate" planetary scopes.

 

If seeing allows, you want bigger apertures. As said, a good 12" dob is much better than a 6" refractor. If you are in an area of poor seeing, then go back to refractors. With reflectors CA is removed, which is the main enemy for planetary views (not coma, not astigmatism, not curvature...). Newtonians are good because they have smaller obstruction. That minimizes diffraction and its effects. A large f-ratio newtonian could also be made with an spherical mirror, easier than parabolic. They could also be with a lighter mirror, which helps thermal equilibrium. But they quickly become too long. Think of a 16" f/10... Well, a dob with that mirror, now that planets are low, isn't that bad.

 

If I could chose something, I would go for a Cassegrain or Ritchey-Chrétien 16-22" f/20. At that large aperture you are probably seeing limited and obstruction would not be a problem. The issue is you would need a monster mount to be able to put your head below the mirror. Alternatively, a Dobson-like mount with Nasmyth focus. In any way, you need a third mirror for visual.

 

I think Maks are "planetary" because they allow high magnification in a very compact design and using longer FL eyepieces. But this is only in the small scopes area.

 

Luckily, many scopes today can offer great views (aperture and seeing limited) despite their focal ratio, lens or mirror.


  • DHEB and aeajr like this

#20 aeajr

aeajr

    Voyager 1

  • *****
  • topic starter
  • Posts: 13,799
  • Joined: 26 Jun 2015
  • Loc: Long Island, New York, USA

Posted 25 May 2020 - 08:21 AM

This is going to be always a compromise.

 

Longer focal ratios would be better. It minimizes aberrations and allows using longer FL eyepieces. Classical eyepieces have eye relief proportional to the focal length. If you want to use an ortho or a plossl because the "minimal glass", then long focal lengths will make observations more comfortable, and with less. On the other hand, very long scopes aren't practical. Cassegrain-like designs make that easier, though.

 

Refractors are preferable to reflectors when comparing apertures. Better contrast and resolution. Lack of obstructions helps in that regard. However, they quickly become monsters. Large refractors (>6") would need a tripled to avoid CA. Thermal equilibrium starts to be a big issue, not to say price and comfort. Usually aperture rules, so they cannot be "ultimate" planetary scopes.

 

If seeing allows, you want bigger apertures. As said, a good 12" dob is much better than a 6" refractor. If you are in an area of poor seeing, then go back to refractors. With reflectors CA is removed, which is the main enemy for planetary views (not coma, not astigmatism, not curvature...). Newtonians are good because they have smaller obstruction. That minimizes diffraction and its effects. A large f-ratio newtonian could also be made with an spherical mirror, easier than parabolic. They could also be with a lighter mirror, which helps thermal equilibrium. But they quickly become too long. Think of a 16" f/10... Well, a dob with that mirror, now that planets are low, isn't that bad.

 

If I could chose something, I would go for a Cassegrain or Ritchey-Chrétien 16-22" f/20. At that large aperture you are probably seeing limited and obstruction would not be a problem. The issue is you would need a monster mount to be able to put your head below the mirror. Alternatively, a Dobson-like mount with Nasmyth focus. In any way, you need a third mirror for visual.

 

I think Maks are "planetary" because they allow high magnification in a very compact design and using longer FL eyepieces. But this is only in the small scopes area.

 

Luckily, many scopes today can offer great views (aperture and seeing limited) despite their focal ratio, lens or mirror.

This is a great post.  This really starts to address what I am trying to understand.  

 

In many cases, I am aware of the key points you are making, but am looking to confirm.   Sometimes I think I know something, then someone like you makes a point and I go, hummm, maybe I don't know as much as I thought.

 

I really appreaciate the time you took to lay this out.

 

Please guys, keep it coming. 



#21 Epox75

Epox75

    Ranger 4

  • -----
  • Posts: 356
  • Joined: 19 Apr 2017
  • Loc: Netherlands

Posted 25 May 2020 - 08:25 AM

Then the commercial SCTs... at least a C11 or 12” Meade, but to be honest they are both limited by mediocre optics.
 

Defining the optics of Meade and Celestron SCT as mediocre it's a bit harsh. You say that because they are not niche products or you have some fact to prove this statement?


Edited by Epox75, 25 May 2020 - 08:28 AM.

  • Jon Isaacs and payner like this

#22 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 85,049
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 25 May 2020 - 08:41 AM

Uncle Rod Mollise once wrote:

 

"When it comes to planetary viewing, seeing is not the most important thing, it's the only thing."

 

That and the observer... 

 

For the telescope, optical quality and sufficient aperture are at the top of the list. 

 

https://www.cloudyni...-telescope-r402

 

Jon


  • payner, aeajr, Epox75 and 3 others like this

#23 Jond105

Jond105

    Fly Me to the Moon

  • *****
  • Moderators
  • Posts: 5,419
  • Joined: 19 Feb 2018
  • Loc: Detroit

Posted 25 May 2020 - 09:01 AM

I’ll go ahead and say this... last night I had my achro and mak out. Mak was definitely at ambient temperature as it had been out for the first three hours while I observed with the refractor. I switch to the mak and observe some with that for about a half hour until Jupiter is up. I give Jupiter 45 minutes on the mak, and it was struggling. I put back on my 90mm achro, I got a nice crisper view. I get what Jon was saying with Rod, though Me and him don’t get along, but in bad seeing I had here last night, I could get a better view with the refractor. The red spot was more easily seen in the mak, but a lot of the view was dancing. 
 

When Saturn came around, I think Saturn isn’t as tough of an object. The mak was fine with it, though boiling, still easier of a target than Jupiter I feel as your not trying to pinpoint every single detail you can. I even wrote about it in my Facebook group. 



#24 luxo II

luxo II

    Vanguard

  • -----
  • Posts: 2,004
  • Joined: 13 Jan 2017
  • Loc: Sydney, Australia

Posted 25 May 2020 - 09:05 AM

. You say that because they are not niche products or you have some fact to prove this statement?

This has been done to death before and you can search CN for yourself.

1. F/10 imho is an ugly compromise for an SCTs as it entails a big central obstruction, and isn’t long enough - f/15 would have been a lot better choice. And it’s not ideal for imaging either (too slow).

Although Celestron and Meade could have split their products into two lines, say an f/5.6 astrograph and an f/15 for planetary, instead they’ve stuck to one configuration trying to be Jack-of-all-trades but master of none.

Celestron has certainly tried variations - hence the RASA, and the rebranding of the SW 189mm f/15 mak for the US market - which is a very sweet scope for planetary.

2. The theoretical optical performance is limited by the central obstruction and at 30-34% it hurts, plain and simple. There really is a reason my scopes CO is 26%.

3. The quality of their production is “good enough”. Neither Celestron nor Meade ever offered any real money-back guarantee of optical quality (eg 1/6 or 1/8 wave P-V) backed up with actual DPAC test - whereas Intes did. AP and TEC and Questar don’t either though their production is on a whole different quality level.

4. There is a Russian test lab that published the results of DPAC tests of hundreds of scopes including dozens of SCTs. The results are accessible and a while back I downloaded the lot and plotted the results for those from 8” up. The SCT results show a typical bell curve as expected for a mass produced item, with Celestrons median being around ⅓ wave P-V and measles a tad worse. A few good ones, some dreadful ones, and a lot of very ordinary ones. But none above strehl 0.92 and certainly nothing anywhere close to strehl 0.985.

Edited by luxo II, 25 May 2020 - 09:39 AM.


#25 grzesznypl

grzesznypl

    Messenger

  • *****
  • Posts: 437
  • Joined: 07 Apr 2019
  • Loc: Jackson Heights, NY ... for now

Posted 25 May 2020 - 09:16 AM

Uncle Rod Mollise once wrote:

 

"When it comes to planetary viewing, seeing is not the most important thing, it's the only thing."

 

That and the observer... 

 

For the telescope, optical quality and sufficient aperture are at the top of the list. 

 

https://www.cloudyni...-telescope-r402

 

Jon

From that article: 

"The most important thing is the stability of the air above. The better your seeing i.e. steadiness of the image, the larger the instrument I would install. The farther south you live, the larger the scope that will be most effective. If you can only afford a 6"or 7" instrument, don't despair that you will not see anything. I know some top planetary amateurs who regularly observe with those apertures and have seen amazing detail on the planets."

So again stability of the air and quality optics will be the key IMHO otherwise you will spend a lot of money for nominal gain over your AD12. I would not go very crazy with expenses considering where you live and where you observe. Large Apos will require large mounts, same goes for large Cassegrain or Ritchey-Chrétien and while $3000 is a lot of money for used or even new dob it is not for beforehand mention solutions.

Take under consideration one more thing. You eyepiece collection is not really optimize on high end planetary viewing. You will want to get some quality orthos (Tak Abbes), Toes, Delites or other high end planetary pieces if you want to observe the most delicate planetary details and that's not a small expense.


Edited by grzesznypl, 25 May 2020 - 09:17 AM.

  • payner and aeajr like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics