Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Refractors

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | (show all)
saemark30
Pooh-Bah


Reged: 02/21/12

Re: Using refractors for Deep Space Observing new [Re: Alan French]
      #5268257 - 06/12/12 03:11 PM

M31 looks awesome in 15x70 binoculars under a dark sky.
Look at how many 70mm Prontos Al sold.


Post Extras: Print Post   Remind Me!   Notify Moderator  
ckwastro
Pooh-Bah


Reged: 11/23/05

Loc: Tempe, AZ
Re: Using refractors for Deep Space Observing new [Re: JoeM101]
      #5268263 - 06/12/12 03:15 PM

Quote:

Quote:

(Apo-)Refractors smaller than 150 mm are very suitable for DSO astrophotography but I don't know how M31 would look like in a 70 mm refractor for visual observing




not very good if anything






Well, that's a matter of perspective. Let's assume the visual observing is under dark skies, of course. If you are looking to see the dust lanes, study structure, and hunt for extra-galactic GC's, then no, a 70mm instrument is not the correct tool for the job. However, if you are looking to frame M31, 32, and 110 with a nice background then a 70mm - 90mm instrument can deliver a very nice view. It all depends what you are looking to accomplish with your observing.

Edited by ckwastro (06/12/12 03:16 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
JimP
Pooh-Bah


Reged: 04/22/03

Loc: South Carolina
Re: Using refractors for Deep Space Observing new [Re: hfjacinto]
      #5268380 - 06/12/12 04:33 PM


Jav nailed it, I never called anyone stupid, what is stupid is the argument that refractors are the best scope. All scopes do things well, don't demean other scopes because they are not refractors.




OK, no problem. But, #1)I don't think you should say that we or I "should" say anything in particular because this is a refractors forum.
And, #2 I have been observing since 1965. I have owned all types of scopes including a 20" Obsession and an 18" Zambuto Starmaster. Both are gone. They were both in a roll-off roof observatory with my 10" TMB F/9 apo, first the 20" then later the 18", and almost never got used. I DO believe a Refractor is the best scope there is. And I am not demeaning any other scope or what anyone else believes. Just speaking for myself.

best,

JimP


Post Extras: Print Post   Remind Me!   Notify Moderator  
saemark30
Pooh-Bah


Reged: 02/21/12

Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5268411 - 06/12/12 05:08 PM

I like to see a comparison with a 12.5" Zambuto Starmaster. Some if not most of these bigger mirrors have zones and turn downed edges.

Post Extras: Print Post   Remind Me!   Notify Moderator  
mikey cee
Postmaster
*****

Reged: 01/18/07

Loc: bellevue ne.
Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5268414 - 06/12/12 05:12 PM

Right on Jimbo! I agree that all scopes are good for certain things. It's just that larger refractors are more "gooder" at doing more things. I still say that because we have looked thru more large mirrored scopes than reflector or SCT owners have looked thru large refractors we have "banked" the more knowhow to judge. That shouldn't be construed to somehow put down that aperture rules or that achromats don't show some minimal amount of CA etc. Mike

Post Extras: Print Post   Remind Me!   Notify Moderator  
JoeM101
scholastic sledgehammer


Reged: 04/09/12

Loc: 45.66086, -73.54702
Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5268422 - 06/12/12 05:19 PM

sorry, should have mentioned the light pollution is moderate in my viewing area... under dark skies or not, i still love using my 72. Don't get me wrong, it has become my handy grab n' go and my preferred scope also. When the neighbors bother to put out their flood lights, viewing with this scope is an utter joy, else i usually head down to the river bank where it gets pretty darn dark... comfort is key here, A1 as i just sit in my chair and look down into the diagonal and wonder at the amazing wide field views i get out this little bugger

Post Extras: Print Post   Remind Me!   Notify Moderator  
JimP
Pooh-Bah


Reged: 04/22/03

Loc: South Carolina
Re: Using refractors for Deep Space Observing new [Re: mikey cee]
      #5268446 - 06/12/12 05:36 PM

P.S. Why do I think refractors are the best scopes (for me)? Because I consider myself, in spite of imaging in recent years, a visual observer with a primary interest in the Moon, Planets and, Double Stars (Deep Sky). I also concluded, based on personal observations, that a refractor, inch for inch, was the best scope to use for my interests. And, I concluded that 7-8" of aperture was enough to see the kind of detail I was interested in observing. Do I use my refractors for other Deep Sky objects (besides doubles)? Of course! Are there some things I cannot see because my biggest aperture refractor is a 10"? Well, of course! But that does not bother me in the least. I am told that globular clusters are fantastic in the big aperture scopes. I am certain they are. When I want to see more stars in a globular cluster or detect fainter globular clusters, using my small aperture refractors, I just use my Collins I3 eyepiece... :^)

best,

JimP


Post Extras: Print Post   Remind Me!   Notify Moderator  
ckwastro
Pooh-Bah


Reged: 11/23/05

Loc: Tempe, AZ
Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5268484 - 06/12/12 05:55 PM

Quote:

I like to see a comparison with a 12.5" Zambuto Starmaster. Some if not most of these bigger mirrors have zones and turn downed edges.




Just curious why you think this? I might be misinterpreting here, but it appears you are saying most of Carl's mirrors have these issues. If that's the case then I must completely disagree. If not, then I apologize for misunderstanding.

I owned one of Carl's mirrors for almost 7 years, and used another half-dozen on a regular basis and not one had any zone, TDE, rough surface, or astigmatism, that could be detected in a star test. I can also say the same thing about Royce & Spooner mirrors. Unfortunately I've never used a Lockwood or Kennedy mirror so can't speak to those.

I think most of the "premium" mirror makers don't have these issues, and if they do, don't release the product from their shop. They rigorously test for these beforehand.


Post Extras: Print Post   Remind Me!   Notify Moderator  
saemark30
Pooh-Bah


Reged: 02/21/12

Re: Using refractors for Deep Space Observing new [Re: ckwastro]
      #5268562 - 06/12/12 06:46 PM

Not saying any Z mirrors have issues.
But curious as to why you cannot detect any aberrations in the star test in any large mirror?
If you have read Suiter's Star Testing book, it will reveal methods of testing for the various aberrations. And collimation would have to be perfect in a sub f/4 system.

I'm not sure there is a way to denote a mirror is perfect without use of an autocollimation setup and interferometry.
Some refractor manufacturers are using that, but I can't speak for the makers you listed.
Making a large 40" mirror would require at least a 40" optical flat.


Post Extras: Print Post   Remind Me!   Notify Moderator  
ckwastro
Pooh-Bah


Reged: 11/23/05

Loc: Tempe, AZ
Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5268603 - 06/12/12 07:10 PM

Quote:

But curious as to why you cannot detect any aberrations in the star test in any large mirror?





Not saying that. I was merely saying the large mirrors I have used from the makers I listed did not have any zones or TDE that you mentioned. I also didn't notice rough surface (dog biscuit) or astigmatism in any of the star tests, or at least detectable by me. None of the mirrors were sub f/4. I have noticed slight under-correction on some. No mirror is perfect but these guys come ridiculously close.

Edited by ckwastro (06/12/12 07:11 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
buddyjesus
Carpal Tunnel
*****

Reged: 07/07/10

Loc: Davison, Michigan
Re: Using refractors for Deep Space Observing new [Re: ckwastro]
      #5268714 - 06/12/12 08:45 PM

Peanut butter jelly. peanut butter jelly time!





I look forward to the next blow up and the lock. At least I am not too late for this one.

I happen to think the scope you would use the most would be the best for whatever you look at.


Post Extras: Print Post   Remind Me!   Notify Moderator  
ckwastro
Pooh-Bah


Reged: 11/23/05

Loc: Tempe, AZ
Re: Using refractors for Deep Space Observing new [Re: buddyjesus]
      #5268904 - 06/13/12 12:45 AM

Quote:

Peanut butter jelly. peanut butter jelly time!


I look forward to the next blow up and the lock.





Wow, I guess people are just itching for flame wars these days. I took absolutely no offense to saemark30's posts, and hope he didn't with mine. From my perspective, we were both just looking for some clarification on our comments, and I even apologized in advance if I had misinterpreted his post. I'd hardly call that a blowup, let alone worthy of a thread lock. Sheesh.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5269112 - 06/13/12 07:27 AM

Quote:

I DO believe a Refractor is the best scope there is.




I find that there is no one best scope...

A 10 inch f/9 likely ok tor some objects in some situations but the 90 inch focal length makes for a narrow maximum field of view as well as a scope and mount that is difficult to transport and setup. Now if one is lucky enough to live in a black zone with excellent seeing, the manageability is not so important but for those of us who do transport our scopes to darker or more stable skies, there are scopes that are more practical.

As refractors grow in size they inherently become longer because color correction scales with focal ratio/aperture so that while a 10 inch f/5 Newtonian is a reasonable scope to build, a 10 inch f/5 refractor is not...

The best scope, the one I happen to be looking through at the moment.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
JJK
Carpal Tunnel


Reged: 04/28/08

Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5269204 - 06/13/12 09:06 AM

Quote:

OK, no problem. But, #1)I don't think you should say that we or I "should" say anything in particular because this is a refractors forum.
And, #2 I have been observing since 1965. I have owned all types of scopes including a 20" Obsession and an 18" Zambuto Starmaster. Both are gone. They were both in a roll-off roof observatory with my 10" TMB F/9 apo, first the 20" then later the 18", and almost never got used. I DO believe a Refractor is the best scope there is. And I am not demeaning any other scope or what anyone else believes. Just speaking for myself.

best,

JimP




Hi Jim,

What was it about the Obsession 20" that you didn't like, compare to the 10" f/9 refractor? My largest aperture refractor is an A-P 180 f/9 EDT (great scope, but I can see the virtue in getting an even larger apo), and my A-P 10" Mak-Cass is as close to a refractor as I could imagine, but I used to have a 20" Obsession (Galaxy Optics premium primary) and it provided stunning views of many DSOs.

I recall vividly studying the NA nebula for over 45 minutes one night (it appeared to have puffy cumulus clouds across it), M20 had pastel colors in it (beyond the standard blue and green), M42 was more detailed and had more color than I see with my A-P Mak-Cass (and the number of jewel-like stars in the heart of the nebula below the Trapezium more numerous) globs were tight and bright, etc.

I replaced the 20" with an Obsession 25" f/4.5, but that scope really deserves to be at a much darker sky site.


Post Extras: Print Post   Remind Me!   Notify Moderator  
ckwastro
Pooh-Bah


Reged: 11/23/05

Loc: Tempe, AZ
Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5269318 - 06/13/12 10:39 AM

Quote:

I find that there is no one best scope...




Jon, you nailed it here.

I enjoy whichever one I'm using a the time, which all depends on what I want to accomplish on that particular observing session. If I'm hunting Hickson Groups and Abell PNs, I want a big dob. I would always choose a large mirrored scope over any other design for the serious deep-sky work I like to do. Lunar / planetary is usually my Mewlon or my refractor, although the 92mm is a bit small for any serious work in that category. Wide-field vistas under dark skies is where the 92 really shines.

I understand the "je ne sais quoi" with refractors. Whenever I use the AP, it gets me thinking about buying the TEC 160 or 180, or the TOA 150. There is just something about refractors that appeals to my aesthetic side. It's usually the mount size required for these bigger refractors that holds me back because it's not very practical for me.

This is why I usually try to have three scopes in my arsenal. I'm currently working on a replacement for the 14.5 I sold a couple years ago, but have not decided which way I want to go on that one yet.


Post Extras: Print Post   Remind Me!   Notify Moderator  
JimP
Pooh-Bah


Reged: 04/22/03

Loc: South Carolina
Re: Using refractors for Deep Space Observing new [Re: Jon Isaacs]
      #5269400 - 06/13/12 11:45 AM

Quote:

Quote:

I DO believe a Refractor is the best scope there is.




I find that there is no one best scope.A 10 inch f/9 likely ok tor some objects in some situations but the 90 inch focal length makes for a narrow maximum field of view as well as a scope and mount that is difficult to transport and setup. Now if one is lucky enough to live in a black zone with excellent seeing, the manageability is not so important but for those of us who do transport our scopes to darker or more stable skies, there are
scopes that are more practical.

As refractors grow in size they inherently become longer because color correction scales with focal ratio/aperture so that while a 10 inchNewtonian is a reasonable scope to build, a 10 inch f/5 refractor is not
The best scope, the one I happen to be looking through at the moment.

Jon [/quote

Hi Jon,
I believe I answered in detail in my following post why I feel an apo is the very best scope (for me). You may not agree but then you are not me. :^)
The objects I view do not need a wider FOV than it provides. It is a Fantastic telescope and I would not trade it for any other telescope. Period.

Jimp


Post Extras: Print Post   Remind Me!   Notify Moderator  
JimP
Pooh-Bah


Reged: 04/22/03

Loc: South Carolina
Re: Using refractors for Deep Space Observing new [Re: JJK]
      #5269410 - 06/13/12 11:58 AM

"Hi Jim,What was it about the Obsession 20" that you didn't like, compare to the 10" f/9 refractor? "


One of the problems with these forums is that we often speak from our own personal POV and people then try to apply it to their situation which may not apply.
My 10" F/9 TMB is in a roll off roof observatory which is large enough for additional scopes. It is at my Farm which I get to less often than I would like. The sky is dark compared to where I live but not very dark compared to what the committed Deep Sky observer would want. When I get there and the sky is clear I find myself having to choose between the 10" refractor and, say, a 20" reflector. In spite of plans I Always used the 10" refractor. Later, I tried again with an 18" with the exact same result. I Never chose the reflector.

best,

JimP


Post Extras: Print Post   Remind Me!   Notify Moderator  
Rich N
Postmaster
*****

Reged: 09/22/04

Loc: San Francisco Bay Area, Calif...
Re: Using refractors for Deep Space Observing new [Re: JimP]
      #5269416 - 06/13/12 12:03 PM

My most frequently used scope is my AP 155mm f/7 EDFS on an AP 900GTO mount. It's fun to use visually. I can see lots of DSOs with it. But, for more detailed views of DSOs aperture, aperture, aperture.

Post Extras: Print Post   Remind Me!   Notify Moderator  
saemark30
Pooh-Bah


Reged: 02/21/12

Re: Using refractors for Deep Space Observing new [Re: Rich N]
      #5269494 - 06/13/12 12:52 PM

Even for deep sky observing optical quality matters unless we are viewing wide angle objects at 30x.
Proper baffling is important and that is why refractors have an advantage over truss systems or reflective tubes.
But large dobs make up for that with lots of aperture.
Its amazing what a 10" or larger scope shows.
Even in the city Planetary Nebulas look good and OIII and UHC filters can work magic.
It would take a world class site to get the full resolution out of a 20" mirror.


Post Extras: Print Post   Remind Me!   Notify Moderator  
saemark30
Pooh-Bah


Reged: 02/21/12

Re: Using refractors for Deep Space Observing new [Re: saemark30]
      #5269601 - 06/13/12 01:45 PM

To put things in perspective what I meant is stars look sharper in refractors than large dobs and likely to have a better/smoother figure over the exposed surfaces than a large mirror.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | (show all)


Extra information
27 registered and 36 anonymous users are browsing this forum.

Moderator:  Scott in NC, FirstSight, panhard, star drop 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 14638

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics