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helpwanted
Carpal Tunnel
Reged: 07/04/07
Posts: 2659
Loc: Phoenix, AZ
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in the recient Astronomy mag, page 46, the say the view of many open clusters gets worse as you increase magnification and telescope size. (they are talking about M37 not being effected by this).
i am planning on an XX12, and i always seek a 1 degree fov with any scope i own. that works out to be a 17T4 at 88x and exit pupil of 3.47 (i know, just under 1 degree at .93, but close enough).
i am wondering what others with a 12" or larger scope think of the comment in the magz?
i tend to think as long as you can get 1 degree, everything will still look nice. ...but i am wondering if a 12" or larger will loose it's appeal on open clusters?
any thoughts?
thanks,
david
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dave b
Post Laureate
Reged: 05/10/05
Posts: 3548
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thats how you end up with a whole van full of binoculars, wide view refractors, big reflectors....everything is a compromise.
if you can fit the whole cluster into the view, most likely you will enjoy it, no matter what size scope.
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dave bonandrini
30" f/5.2 Dobsonian
President of GCAC
Astromart Moderator
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gtown1
member
Reged: 11/07/08
Posts: 69
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The larger the size of the primary lens and corresponding magnification will render some more spread out objects such as open clusters not to be visible in the field of view. That is one irony where a smaller size primary will render some objects better than larger telescopes. I went from an 8 inch Celestron to a 12.5 inch Porta Ball to an 18 inch Obsession Ultra Compact. As a general rule, and in most situations, I enjoy best the views in the larger telescopes. They gather more light and render objects brighter and in more detail. At a star party, look at an object such as M13 in an 8 inch telescope, comparing the view to a 12 inch. M13 will not only be brighter, but you will be able to drill down and see many more individual stars in the cluster. However, an open cluster such as the Pleiades is widely spread out and will give pleasing views in smaller telescopes and binoculars. In your eyepiece collection make sure that you have a good quality low power, wide angle eyepiece.
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Happy owner of an Obsession, 18 inch Ultra Compact and a Mag 1, 12.5 inch Porta Ball.
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helpwanted
Carpal Tunnel
Reged: 07/04/07
Posts: 2659
Loc: Phoenix, AZ
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you reminded me to add to my question... forget about M45 or other very large clusters... my question just applies to something that will fit i a 1 degree fov, whether the scope is 3" or 12".
thanks for the replies so far!
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lightfever
Pooh-Bah
Reged: 09/27/04
Posts: 1281
Loc: Macomb Michigan
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In my experience most open clusters of approx one degree look better in my 12” scope. The reason is that the stars are brighter and I can see more of them. Wide field EPs are a big help because you can get the field of view you need and keep the mag up high enough to have a dark background.
I look at the double cluster with my AT-111 and think wow that looks nice, but with the 12” it’s more like WOW. Brighter stars, more stars, and more color. Granted the refractor can frame it a little better with the wider field but it looks good in the 12”.
I’ve also come across some clusters of very dim stars in the 12” that are not viewable in my smaller scopes.
A 22 or 26mm Nagler would do a nice job framing a one degree cluster.
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Mark
Tasco 15-TE 76mm
Sky Watcher 80mm ED
AT-111 Triplet
XT8i (with Woden re-figured mirror)
Discovery 12.5" f/5 Premium DHQ (PDHQ Split-tube Dobsonian)
12.5" f/6.3 Dob (Underconstruction)
Celestron CG-5GT EQ Mount
Celestron C4 EQ Mount
"Life is not about waiting for the storm to pass, but learning to dance in the rain" unknown
Edited by lightfever (11/03/09 08:11 PM)
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Lard Greystoke
sage
Reged: 07/27/08
Posts: 377
Loc: Ohio
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Only a handful of clusters are more than a degree. With a 12" you will more than make up for it by seeing and resolving clusters invisible in a smaller scope. For example, the huge cluster M35 in Gemini will sprawl over the FOV of most eyepieces, but the 12" will give an excellent view of nearby NGC 2158. You will get good views of hundreds of clusters in exchange for tight fits for half a dozen.
Also, a 12" really begins to show globular clusters in their full glory.
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Lard Greystoke
10" Odyssey Compact
"With Tantor, the elephant, he made friends. How? Ask me not."
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sailor70623
scholastic sledgehammer
Reged: 01/12/08
Posts: 944
Loc: Ok.
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And a 16" goes even deeper. More stars, almost to the core. You should love the 12", and a set of binos will grab those really wide views you miss with the 12". The 12" will even show the nebulosity in the Pleiades.
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Corornado PST
LB 16" & 12"
Z 10"
LX50 8"
8" CPC
ETX127
102&90mm MAKs
80mm Richfield APO
70mm refractor
ETX60
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7331Peg
professor emeritus
Reged: 09/01/08
Posts: 734
Loc: North coast of Oregon
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I think the whole idea is to match the scope to the cluster. A one degree FOV is going to rob the Double Cluster and the Pleiades of their visual impact. On the other hand, there are PLENTY of small cluster (say less than 30' in size) that come to life in a larger scope. The Wild Duck cluster is in that range; try Harvard 20 in Sagitta or Steph 1 in Lyra; and take a look at the NGC clusters in the upper arm of Orion. There are many, many more.
John
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coutleef
Carpal Tunnel
Reged: 02/21/08
Posts: 1733
Loc: Montréal and Saint-Donat, Québ...
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Buy a Stellarvue 50 or 60 mm finderscope to go with your dob. You can use your EP with that finderscope. The 9T6 gives 22x magnification and nearly 4° of FOV. The pleiades will fit nicely. For those large clusters, i use my finderscope, for the others the telescopes. A 35 Pan on the 12" would do the job for many clusters as well.
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François
Scopes: Nexstar 8 SE with Ron's rail and Denk S1 Powerswitch. EPs list is on my Bio.
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Hrundi
Pooh-Bah
Reged: 02/06/08
Posts: 1249
Loc: Estonia
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I've found tat with my 12" dob, a lot of the premier star clusters have lost their mystery. Basically, the easy catch syndrome.
With galaxies, globs and nebulae, you reveal more and more as you pump mag, but with these showpiece OCls, once you resolve them through and through, it doesn't open up new frontiers just on the edge of visibility and etc.
This doesn't mean, however, that this applies to all of em. M11 is still one of the most stunning things in the sky. It does mean the preferred target list changes though, to more exotic ones like that NGC near the coathangar, or that OCl just under m35.
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helpwanted
Carpal Tunnel
Reged: 07/04/07
Posts: 2659
Loc: Phoenix, AZ
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interesting replies, thanks all
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12230
Loc: Los Angeles
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M35, M41, M39, M44, M45, NGC884/869 and other similarly large clusters look more magnificent, in my opinion, at very low powers.
The problem with a larger scope isn't the field size (I have 1.4 degrees on my dob), but the magnification.
Bigger scopes can usually not get down to the really low powers that make these clusters "pop".
The last time I looked at M41, it almost seemed like a large collection of bright "field stars" instead of a cluster, even though the entire cluster was in the field. There was too much space between the stars.
It was spectacular through a friend's 4" refractor at 35X.
On the flip side of the coin, clusters like NGC2158, M71, NGC6603, and others, really come to life in a larger aperture and using higher powers.
I guess it's called "using the right tool for the job".
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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