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

Ts 152mm f5.9 widefield extravaganza

  • Please log in to reply
170 replies to this topic

#126 kmparsons

kmparsons

    Mariner 2

  • -----
  • Posts: 283
  • Joined: 07 Jun 2007
  • Loc: Texas

Posted 22 May 2020 - 11:57 AM

I love my 4" scopes, but they do not have the horsepower to show me some DSO's as I really want to see them. For instance, I cannot see the full glory of globular clusters. I live far enough south  (29 degrees latitude) that M22 is conveniently located for comfortable observation. My guess is that the unobstructed view of a 6" refractor would outperform an 8" Newtonian or SCT. You would probably have to get up to a 10" aperture to see significantly more. Given that CA would be no problem on DSO's, this 6" achromat at its decent price sounds like a winner to me. 


  • daquad and j.gardavsky like this

#127 j.gardavsky

j.gardavsky

    Apollo

  • *****
  • Posts: 1,146
  • Joined: 18 Sep 2019
  • Loc: Germany

Posted 22 May 2020 - 12:18 PM

Well the 4” F11 will still be more portable!

You might consider the Baader solar continuum filter for viewing the Moon. Personally I never would have thought of using a solar filter on the Moon but looking at the filter specs, it seems like it should work very well. Someone here posted about how well it does with fast achros on the Moon so I am thinking of trying it out.

Scott

I am using the Baader Solar Continuum on the Moon, practically from the time when it came on the market, maybe just one or two years later.

The green narrow passband at about 540nm offeres the highest contrast for the visual observing.

I would have this filter for the Moon even on an APO.

 

Best,

JG


  • eros312 and SeattleScott like this

#128 SeattleScott

SeattleScott

    Cosmos

  • *****
  • Posts: 7,811
  • Joined: 14 Oct 2011

Posted 22 May 2020 - 08:47 PM

I am using the Baader Solar Continuum on the Moon, practically from the time when it came on the market, maybe just one or two years later.
The green narrow passband at about 540nm offeres the highest contrast for the visual observing.
I would have this filter for the Moon even on an APO.

Best,
JG

Good to know, so it could be useful with my other scopes too. Does it change the color of the Moon, or does it retain its usual grayscale appearance?

Scott
  • doctordub and j.gardavsky like this

#129 eros312

eros312

    Viking 1

  • *****
  • Posts: 601
  • Joined: 14 Feb 2009
  • Loc: Tampa, FL

Posted 22 May 2020 - 08:57 PM

I've never used it on the Moon, but on the sun it turns it green. 



#130 SeattleScott

SeattleScott

    Cosmos

  • *****
  • Posts: 7,811
  • Joined: 14 Oct 2011

Posted 22 May 2020 - 10:36 PM

I suppose that makes sense. Might be hard wrapping my mind around looking at a green moon, even if the view is technically sharper. Something to think about.

Scott

#131 bobhen

bobhen

    Skylab

  • *****
  • Posts: 4,006
  • Joined: 25 Jun 2005

Posted 23 May 2020 - 06:41 AM

I love my 4" scopes, but they do not have the horsepower to show me some DSO's as I really want to see them. For instance, I cannot see the full glory of globular clusters. I live far enough south  (29 degrees latitude) that M22 is conveniently located for comfortable observation. My guess is that the unobstructed view of a 6" refractor would outperform an 8" Newtonian or SCT. You would probably have to get up to a 10" aperture to see significantly more. Given that CA would be no problem on DSO's, this 6" achromat at its decent price sounds like a winner to me. 

IF your main interest is globular clusters, you want apochromatic aperture, either a large apo refractor or a mirror scope.

 

Globular clusters are high contrast objects (bright stars on a black background) and the high contrast optics of a refractor doesn’t help with these objects as much as they do with low contrast objects like nebula. And larger aperture will allow you to use high powers. And globular clusters like higher powers.

 

In addition, a fast 6” achromatic refractor when used at high powers will start to show CA and the stars will be softer when compared to apochromatic refractors and mirror scopes.

 

Not that you can’t point one of these fast refractors at gobulars – you can. But for the "best" views of globulars, you want largish aperture and color-free optics.

 

Bob


  • M44 likes this

#132 jag767

jag767

    Kinesis Custom Machining and Refinishing

  • *****
  • Vendors
  • topic starter
  • Posts: 1,177
  • Joined: 20 Jun 2013
  • Loc: Massapequa, NY

Posted 23 May 2020 - 08:27 AM

IF your main interest is globular clusters, you want apochromatic aperture, either a large apo refractor or a mirror scope.

Globular clusters are high contrast objects (bright stars on a black background) and the high contrast optics of a refractor doesn’t help with these objects as much as they do with low contrast objects like nebula. And larger aperture will allow you to use high powers. And globular clusters like higher powers.

In addition, a fast 6” achromatic refractor when used at high powers will start to show CA and the stars will be softer when compared to apochromatic refractors and mirror scopes.

Not that you can’t point one of these fast refractors at gobulars – you can. But for the "best" views of globulars, you want largish aperture and color-free optics.

Bob

Sure, and that rabbit hole will cost thousands. First the price bump to a 6" f8 apo, then a 3.7" focuser, then a more robust mount, then 3" accessories, then hey lets go to a 6" triplet, bigger mount (again) and by the time I'm there I'm looking through a honda civic 😅.

If money was no object I'm confident we'd all have observatories with 10" apos.

Edited by jag767, 23 May 2020 - 08:45 AM.

  • doctordub, kmparsons and Jon_Doh like this

#133 j.gardavsky

j.gardavsky

    Apollo

  • *****
  • Posts: 1,146
  • Joined: 18 Sep 2019
  • Loc: Germany

Posted 23 May 2020 - 08:40 AM

Good to know, so it could be useful with my other scopes too. Does it change the color of the Moon, or does it retain its usual grayscale appearance?

Scott

The Moon is green like a meadow on a rainy day.

After a couple of minutes I am o.k. with the green color, as all my attention is towards the finest details, looking for the rimae, hunting the smallest craterlets, and experiencing a 3D illusion on the ejectas from the craters.

 

Even the full Moon is worth of looking through this filter.

 

Technically, the 540nm (and around) wavelength, lets the refractor and eyepiece optics operate with the highest possible Strehl. It is close to the wavelengths for which are the refractors and eyepieces optimized, and and for which the refractor lenses will be eventually hand figured.

 

Shown to a friend of mine, he has ordered this filter on the next day.

 

However, to each his/her own, just saying,

JG


  • doctordub and SeattleScott like this

#134 kmparsons

kmparsons

    Mariner 2

  • -----
  • Posts: 283
  • Joined: 07 Jun 2007
  • Loc: Texas

Posted 23 May 2020 - 09:34 AM

Thanks, Bob, but a 6" apo would be a bit rich for my blood (or bank account). Maybe the 8" SCT would be the better choice. I love globulars, but really I like to look at everything. As you say, the 6" achro would be good on nebulae, and, of course, wide-field views. I think the ideal set-up for me would be a dual mount, like the Losmandy Alt/Az, with a longer focus scope for higher magnification views on one side and this 6" achromat on the other. 



#135 jag767

jag767

    Kinesis Custom Machining and Refinishing

  • *****
  • Vendors
  • topic starter
  • Posts: 1,177
  • Joined: 20 Jun 2013
  • Loc: Massapequa, NY

Posted 23 May 2020 - 09:45 AM

At the end of the day this is my hobby, one amongst many, and I have to draw a line somewhere. As far as lines go, it's not a bad place to be. This guy handles all deep sky stuff well, fantastic views of the moon, and even the planetary views are quite nice, with Jupiter being the largest challenge. Even still, the view is good enough that I'm considering letting go of my 4"ed scope.

#136 bobhen

bobhen

    Skylab

  • *****
  • Posts: 4,006
  • Joined: 25 Jun 2005

Posted 23 May 2020 - 10:35 AM

Thanks, Bob, but a 6" apo would be a bit rich for my blood (or bank account). Maybe the 8" SCT would be the better choice. I love globulars, but really I like to look at everything. As you say, the 6" achro would be good on nebulae, and, of course, wide-field views. I think the ideal set-up for me would be a dual mount, like the Losmandy Alt/Az, with a longer focus scope for higher magnification views on one side and this 6" achromat on the other. 

Yes a lot of people do just that (even me) because different objects are best viewed with different scopes. A 6" apo is, of course, very expensive but a larger Newtonian or SCT are very reasonable, as these things go.

 

A nice twin mount setup might be: an Orion 120mm F5 achromat on one side and a Celestron 9.25 on the other. All the high power work would go to the SCT, which would have a lot more aperture than the 6" refractor. And wide field observing would be done with the 120 F5, which would have a wider field than the 6" refractor.

 

Just a suggestion but you get the idea. Good luck in selecting. 

 

Bob



#137 bobhen

bobhen

    Skylab

  • *****
  • Posts: 4,006
  • Joined: 25 Jun 2005

Posted 23 May 2020 - 10:41 AM

Sure, and that rabbit hole will cost thousands. First the price bump to a 6" f8 apo, then a 3.7" focuser, then a more robust mount, then 3" accessories, then hey lets go to a 6" triplet, bigger mount (again) and by the time I'm there I'm looking through a honda civic .

If money was no object I'm confident we'd all have observatories with 10" apos.

You don't need an apo refractor to have apochromatic optics. A Newtonian will do that and they can be both larger AND cost less than a fast 6" achromatic refractor.

 

Bob


Edited by bobhen, 23 May 2020 - 10:41 AM.


#138 SeattleScott

SeattleScott

    Cosmos

  • *****
  • Posts: 7,811
  • Joined: 14 Oct 2011

Posted 23 May 2020 - 05:03 PM

You don't need an apo refractor to have apochromatic optics. A Newtonian will do that and they can be both larger AND cost less than a fast 6" achromatic refractor.

Bob

True, but in my experience an 8” reflector doesn’t provide views as aesthetically pleasing as a 6” achro. The 6” achro is more work to get out, but when I am in the mood for those perfect pinpoint stars, it is worth it.

Scott
  • jag767 likes this

#139 jag767

jag767

    Kinesis Custom Machining and Refinishing

  • *****
  • Vendors
  • topic starter
  • Posts: 1,177
  • Joined: 20 Jun 2013
  • Loc: Massapequa, NY

Posted 24 May 2020 - 04:51 AM

True, but in my experience an 8” reflector doesn’t provide views as aesthetically pleasing as a 6” achro. The 6” achro is more work to get out, but when I am in the mood for those perfect pinpoint stars, it is worth it.

Scott


My sentiments exactly. I dont do reflectors, despite having tried several times. The view just doesnt do it for me. This 6" on the other hand just hits the spot.
  • Bomber Bob and j.gardavsky like this

#140 bobhen

bobhen

    Skylab

  • *****
  • Posts: 4,006
  • Joined: 25 Jun 2005

Posted 24 May 2020 - 06:27 AM

Well there is something to be said for aesthetics. But aesthetics are in the eye of the beholder. There are many who find the diffraction spikes produced by a Newtonian aesthetically pleasing, so much so that they ADD them to their deep sky images.

 

"an 8” reflector doesn’t provide views as aesthetically pleasing as a (fast) 6” achro"

 

The above statement just doesn’t apply to all objects; certainly not to solar system objects or in any object that requires high magnification. 

 

In any event, let’s not forget the reason we get telescopes in the first place. The “primary” reason for a telescope is not aesthetics but because telescopes allow us to “see more” of what is out there than we can with just our eyes alone. If that is the “main” objective, then there are other choices other than the fast achromat that will meet that objective “on more objects” and can even “cost less”.

 

Don’t get me wrong I love refractors and own more refractors than reflectors. I even own a fast F5 achromat but that scope is much more specialized, or limited, if you will, than other designs. 

 

Certainly, for low power, deep sky viewing fast achromats can be a fine choice but that is their specialty. Once you move away from that speciality you start making compromises. And that's fine for many. But that 8” Newtonian is far and away the better “general use” telescope.

 

Aesthetics are subjective. On the other hand, performance can be quantified.

 

Bob


  • daquad and howardcano like this

#141 jag767

jag767

    Kinesis Custom Machining and Refinishing

  • *****
  • Vendors
  • topic starter
  • Posts: 1,177
  • Joined: 20 Jun 2013
  • Loc: Massapequa, NY

Posted 24 May 2020 - 06:48 AM

Well there is something to be said for aesthetics. But aesthetics are in the eye of the beholder. There are many who find the diffraction spikes produced by a Newtonian aesthetically pleasing, so much so that they ADD them to their deep sky images.

"an 8” reflector doesn’t provide views as aesthetically pleasing as a (fast) 6” achro"

The above statement just doesn’t apply to all objects; certainly not to solar system objects or in any object that requires high magnification.

In any event, let’s not forget the reason we get telescopes in the first place. The “primary” reason for a telescope is not aesthetics but because telescopes allow us to “see more” of what is out there than we can with just our eyes alone. If that is the “main” objective, then there are other choices other than the fast achromat that will meet that objective “on more objects” and can even “cost less”.

Don’t get me wrong I love refractors and own more refractors than reflectors. I even own a fast F5 achromat but that scope is much more specialized, or limited, if you will, than other designs.

Certainly, for low power, deep sky viewing fast achromats can be a fine choice but that is their specialty. Once you move away from that speciality you start making compromises. And that's fine for many. But that 8” Newtonian is far and away the better “general use” telescope.

Aesthetics are subjective. On the other hand, performance can be quantified.

Bob


Bob I've read the tak threads, performance is 100% subjective as well. 😂

#142 bobhen

bobhen

    Skylab

  • *****
  • Posts: 4,006
  • Joined: 25 Jun 2005

Posted 24 May 2020 - 08:06 AM

Bob I've read the tak threads, performance is 100% subjective as well.

No. The observers “interpretations” are subjective. The performance is not.

 

Most observing reports are just not done under controlled situations. That is why you see variations. With more rigorous controlled tests/comparisons differences would be as expected based on the specs.

 

Without a controlled test, the specs and optical bench test reports tell the story. Optics is a science. 

 

I don’t even have to have observed with (although I have) a 6” fast achormat to know that it will not perform better than a 6” apochomat. The specs tell me that.

 

Just as I don’t have to drive a Ferrari and Chevy Malibu to know which is faster – the specs tell me all I need to know.

 

Bob 



#143 Jon_Doh

Jon_Doh

    Vanguard

  • -----
  • Posts: 2,399
  • Joined: 16 Sep 2011
  • Loc: Just South of Pluto

Posted 24 May 2020 - 10:03 AM

Thanks, Bob, but a 6" apo would be a bit rich for my blood (or bank account). Maybe the 8" SCT would be the better choice. I love globulars, but really I like to look at everything. As you say, the 6" achro would be good on nebulae, and, of course, wide-field views. I think the ideal set-up for me would be a dual mount, like the Losmandy Alt/Az, with a longer focus scope for higher magnification views on one side and this 6" achromat on the other. 

Globular clusters do look good in an 8" SCT, but I did own an AR152 achro refractor and globs looked just as good as they did in the SCT, just a bit dimmer.  There was no CA or softness at higher powers that I could see.  I've often said I felt I had one that was better than average so never having looked through any other achros I can't comment on how other achros might do on the same targets.



#144 jag767

jag767

    Kinesis Custom Machining and Refinishing

  • *****
  • Vendors
  • topic starter
  • Posts: 1,177
  • Joined: 20 Jun 2013
  • Loc: Massapequa, NY

Posted 24 May 2020 - 10:47 AM

Globular clusters do look good in an 8" SCT, but I did own an AR152 achro refractor and globs looked just as good as they did in the SCT, just a bit dimmer. There was no CA or softness at higher powers that I could see. I've often said I felt I had one that was better than average so never having looked through any other achros I can't comment on how other achros might do on the same targets.


CA is there, up to a 1mm exit pupil Its passable. My 9mm is perfect for the highest mag I like with it.

Edited by jag767, 24 May 2020 - 10:51 AM.


#145 bobhen

bobhen

    Skylab

  • *****
  • Posts: 4,006
  • Joined: 25 Jun 2005

Posted 24 May 2020 - 11:00 AM

Globular clusters do look good in an 8" SCT, but I did own an AR152 achro refractor and globs looked just as good as they did in the SCT, just a bit dimmer.  There was no CA or softness at higher powers that I could see.  I've often said I felt I had one that was better than average so never having looked through any other achros I can't comment on how other achros might do on the same targets.

1. If the cluster looked dimmer then by definition it didn’t look as good. Larger color-free aperture equals more light.

 

2. Whether you see CA or not is irrelevant. It is in the design of the optic. You can’t see CA when used at low powers but that doesn’t mean it goes away, it just means that at low powers the aberration is too small to see. Of course, at low powers fine details are also too small to see.  CA is always there. A better-figured lens will not change the amount of CA present, only a design change can do that. 

 

3. The differences will manifest themselves when compared side-by-side and at higher powers.

 

The above does not mean that the fast achromat did not produce a pleasing view – they can and do.

 

Bob


  • daquad likes this

#146 SeattleScott

SeattleScott

    Cosmos

  • *****
  • Posts: 7,811
  • Joined: 14 Oct 2011

Posted 24 May 2020 - 01:40 PM

To me the achro really comes to life in winter with those showcase open clusters. The fast cooling doesn’t hurt either, although not a huge deal since open clusters aren’t really high power targets. For galaxies and globs I would just as soon use a mirrored scope.

Scott

#147 kmparsons

kmparsons

    Mariner 2

  • -----
  • Posts: 283
  • Joined: 07 Jun 2007
  • Loc: Texas

Posted 24 May 2020 - 03:54 PM

Actually, Bob, I have to respectfully disagree about the importance of aesthetics. The point is not just seeing, but seeing with delight. I am in the bobby because I love to see beautiful things in the sky, and judgments of beauty are notoriously variable. So, there is inevitably a high degree of subjectivity in our choice of instruments. For instance, I love long-focus achromats because, to my eye, the views are very satisfying. True, you can find some residual CA if you look for it, but, to me, the image in my f/10 and higher achros has pinpoint stars and a flat field. Now, here at CN I have been told by well-meaning (I think) people that I really should not be enjoying my views through these scopes as much as I do because [insert technical data here]. What makes technical data useful (unless one just enjoys it for its own sake) is that it is a helpful guide to alert me as to the probable quality of my visual experience. A 6" aperture f/5.9 achromat is unquestionably a niche instrument and not for everyone, but if it is a niche that is important for you, then this could be the scope for you! 


  • daquad, Jon_Doh, jag767 and 2 others like this

#148 SeattleScott

SeattleScott

    Cosmos

  • *****
  • Posts: 7,811
  • Joined: 14 Oct 2011

Posted 24 May 2020 - 04:10 PM

Well said. After all not many of us are scientists. We are doing it as a hobby so if an aesthetically pleasing view brings more pleasure than a more detailed view, then go with the aesthetically pleasing view. That’s a good way to look at it. Although Bob has a point that it is more open clusters and nebulae that benefit from a more aesthetically pleasing view, and other targets will likely look better in a slightly larger mirrored scope. So a lot depends on the intended targets.

Scott
  • jag767 and j.gardavsky like this

#149 jag767

jag767

    Kinesis Custom Machining and Refinishing

  • *****
  • Vendors
  • topic starter
  • Posts: 1,177
  • Joined: 20 Jun 2013
  • Loc: Massapequa, NY

Posted 25 May 2020 - 03:48 AM

1. If the cluster looked dimmer then by definition it didn’t look as good. Larger color-free aperture equals more light.

2. Whether you see CA or not is irrelevant. It is in the design of the optic. You can’t see CA when used at low powers but that doesn’t mean it goes away, it just means that at low powers the aberration is too small to see. Of course, at low powers fine details are also too small to see. CA is always there. A better-figured lens will not change the amount of CA present, only a design change can do that.

3. The differences will manifest themselves when compared side-by-side and at higher powers.

The above does not mean that the fast achromat did not produce a pleasing view – they can and do.

Bob


Have to disagree with you. You're one of those guys that presents his opinion as facts aren't ya? I get you prefer a 8" reflector to this and thats cool, so go have fun with an 8" reflector. I, and several others it seems, completely disagree with your opinions. And thats cool too, we'll keep our 6" achros, however inferior you think they may be.

#150 bobhen

bobhen

    Skylab

  • *****
  • Posts: 4,006
  • Joined: 25 Jun 2005

Posted 25 May 2020 - 06:17 AM

Have to disagree with you. You're one of those guys that presents his opinion as facts aren't ya? I get you prefer a 8" reflector to this and thats cool, so go have fun with an 8" reflector. I, and several others it seems, completely disagree with your opinions. And thats cool too, we'll keep our 6" achros, however inferior you think they may be.

1. If the cluster looked dimmer then by definition it didn’t look as good. Larger color-free aperture equals more light.

2. Whether you see CA or not is irrelevant. It is in the design of the optic. You can’t see CA when used at low powers but that doesn’t mean it goes away, it just means that at low powers the aberration is too small to see. Of course, at low powers fine details are also too small to see. CA is always there. A better-figured lens will not change the amount of CA present, only a design change can do that.

3. The differences will manifest themselves when compared side-by-side and at higher powers.

 

Which point above are you disagreeing with?
Which point above is opinion and not fact?
Where did I say I “prefer” anything?
Where did I say these 6” refractors were inferior in "all" areas?

 

If you read my earlier post you would know I also own a fast achromat and love it for what it does. 

 

No telescope is perfect. If you think these are then you are mistaken.

 

And BTW, you don’t have a clue about me so stop posting derogatory personal comments.

 

Bob


Edited by bobhen, 25 May 2020 - 06:19 AM.

  • daquad likes 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