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Best scope for planetary / star cluster observing?

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#1 chalmene

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Posted 09 August 2018 - 06:55 PM

I have used mostly Newtonian telescopes up till now. I have 6" f/6 and 16" f4.4 Newts as I enjoy DSO observing. As far as planetary and star observing, I have read here and there that long-f/l cats and refractors excel in this aspect, but have yet to own one aside from a small ST80 which I have found not to be an exceptional best observing tool. Having had an interest in trying a decent-sized refractor or Cat for quite some time, would either provide an observing advantage to my Newtonians?

 

Thank you, and clear skies



#2 ShaulaB

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Posted 09 August 2018 - 07:12 PM

An eight inch SCT is considered a "do it all" scope, for many DSO's and planets. Collimation is key to getting a good sharp image. Yes, SCT's need collimation. A Maksutov Cassegrain might be considered also.

 

Have you ever thought about a larger Newtonian? I have seen some fabulous high magnification planet images in 14 and 16 inch Zambuto mirrored Dobsonians that track. A quality mirror and good collimation will provide dynamite planet views.


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#3 havasman

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Posted 09 August 2018 - 07:27 PM

In my experience the best planetary scope is a premium 32" f3.3 Dob located in the -34o latitudes of the southern hemisphere in a very dark outback location. Same as observing everything else - aperture, optics, location and careful attention to details pays off big. It is likely a similarly located, configured, and well executed Dob of larger aperture would be better.

 

Star clusters? Same thing. Individual stars, nebulae, galaxies, etc? Same thing.

 

It's difficult to answer the "What's BEST?" question when it's unqualified.

 

Your 16" Dob should provide extremely satisfying planetary and other observing if collimated and cooled in a dark location when conditions supported good observing. Mine sure does. I've had owners of large and very fine Stellarvue APO refractors take a look at Jupiter and immediately decide they need a medium-large Dob for planetary.


Edited by havasman, 09 August 2018 - 07:29 PM.

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#4 Cajundaddy

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Posted 09 August 2018 - 07:47 PM

Yes, the 16" Dob would be my first choice for planets.  Aperture is king providing you have decent optics.  If you want another scope we will need more details as to your desires and budget.  Lots of smaller more portable scopes reveal nice planetary views but given a blank sheet of paper, I'll take the 16" you own.


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#5 chalmene

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Posted 09 August 2018 - 08:12 PM

Sorry, I guess "best scope" did sound rather elementary. I am aware aperture is king in a lot of circumstances, but for now my 16" is the largest scope I can practically utilize. Mainly curious if a refractor of cat would be a worthwhile addition to my collection for observation.


Edited by chalmene, 09 August 2018 - 08:12 PM.

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#6 Augustus

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Posted 09 August 2018 - 08:18 PM

Why doesn't your 16" work for planetary/globulars?

 

If it's cooled down properly, collimated, and has a good mirror, it should perform far better than literally anything else besides a bigger Dob.


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#7 OleCuss

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Posted 09 August 2018 - 09:25 PM

Sorry, I guess "best scope" did sound rather elementary. I am aware aperture is king in a lot of circumstances, but for now my 16" is the largest scope I can practically utilize. Mainly curious if a refractor of cat would be a worthwhile addition to my collection for observation.

You can actually make a case that a really large (maybe 6"?), premium apochromatic refractor with a great eyepiece might beat what that 16" Dobsonian will do for you.  Even if the view is not necessarily better you just might find the experience more pleasurable.

 

But the price would be shocking for most of us and you might find that you actually like what the 16" Dob does either as well or better.  A 6" refractor also generally starts getting rather long and that often means less-than optimal ergonomics on some targets.

 

If I had a 16" Dobsonian and was thinking about getting better views I'd probably consider retro-fitting a GoTo system to the Dobsonian rather buying a big refractor or Mak-Cass.  The tracking reduces the distraction of having to nudge the Dobsonian along and that means you will actually see a bit better.

 

If your intent were to do planetary AP then I'd be looking for something like a 14" SCT and Barlow the thing.  It's actually a great instrument for visually observing planets as well and might compete fairly well with your 16" Dobsonian in part due to the long "natural" focal length and the relatively good ergonomics for most targets.  But especially if you got a 14" SCT with a fork mount - not fun to try to move around/set up.


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#8 havasman

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Posted 09 August 2018 - 10:05 PM

Sorry, I guess "best scope" did sound rather elementary. I am aware aperture is king in a lot of circumstances, but for now my 16" is the largest scope I can practically utilize. Mainly curious if a refractor of cat would be a worthwhile addition to my collection for observation.

Very good Q!

An example - last Monday I took my 16" f4.49 Dob and a 4.5" f7 triplet refractor to the dark site for a long session. The big scope showed globular cluster clusters in a galaxy >22Mn LY away, clearly curled ansae on NGC7009 and other treats. The refractor + O-III filter showed the entire veil nebula complex in a field and the N American/Pelican complex very clearly as well as extremely satisfying widefield scans in Sagittarius and Aquila. Both the big E dark nebula near Tarazed and the dark Barnard 168 running away from the Cocoon Nebula were just swell.

I have found a medium-short focal ratio refractor to be a great complementary scope to my 16". The big Dob can produce high mag when called for and that is what an SCT brings to the party so I think it less complementary. The refractor also comes in a smaller package than the Dob and brings widefield capability for which there is no substitute.

My friend with the 32" was talking about aperture. He said that folks buying scopes > about 18-20" with the intent of hauling them out to a dark site regularly are probably overloading themselves. It would be a special case that would make that not so. Your 16" aperture is mighty!


Edited by havasman, 09 August 2018 - 10:06 PM.

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#9 gnowellsct

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Posted 09 August 2018 - 11:36 PM

Sorry, I guess "best scope" did sound rather elementary. I am aware aperture is king in a lot of circumstances, but for now my 16" is the largest scope I can practically utilize. Mainly curious if a refractor of cat would be a worthwhile addition to my collection for observation.

Well there's no answer to "cluster" because something like NGC 7788/90 is one kind of cluster (suitable for a 14" or bigger) and the Perseid Double Cluster is quite another, suitable for small refractors.

 

Furthermore, even though you're an experienced observer, you may not know what you're doing, in the sense that maybe you've never really had a gorgeous view of M57 at 16x.  You take in the whole bottom of Lyra.  You may not in that sense know that such a view is worth having.   And maybe your viewing sophistication has gotten to the point that you need a bit more quality than an ST80 offers, in order to have fun with low power views....and also to appreciate small aperture views at higher powers with no CA, etc.

 

So the question is how to put together something where the whole is greater than the sum of the parts.  If you want to talk about configurations like this

 

c14 and ap900 cloudynights size.JPG

 

or this

 

c8 with Vixen 102mm 4 inch.jpg

 

you get into a very different style of observing.  A tracking mount, machined precision, the ability to switch between a larger aperture and a smaller one, and the ability to see M57 as a tiny bubble at 16x or a true ring at 200x and greater in a larger instrument.  (And longer set up and break down times.)

 

I would think you would find it very different.  Whether it's for you or not, I can't say.  Whether the views will be *better* than what you have is hard to say too, since it depends not just on what you have (and how well you take care of it) but what you will get (and how well you take care of it).  

 

The best thing to do of course is set up next to people who have the kinds of rigs you might be interested in and see how they go about their viewing and how much you do or do not like the views.  

 

In other words from one point of view maybe you just want to mess around with different telescopes and see what they offer.  Or alternatively you might be looking to get out of the introductory and mid level optics and get into various rigs that have some pizzazz, however you choose to define that.  Some people say no no no SCTs they're not classy well OK maybe you need a double apo:

 

GT 130 and 81s Landis May 8 2018 - smaller.jpg

 

So, looking to branch out but not do so by getting a 25 inch dob, trying to emphasize different aspects of the gear.  Can be pricey, can be fun.  You sort of have to wander around at star parties or look through the groups till something clicks and you think: Yes!  I want to try that!  Because the "which view is better" is a dead end.  Some people rave about the views of M57 in their 80 mm and you don't know why.  So maybe that's what you need to do.   But you're interested in SCTs.  I get that!  Me too.  But don't go for an SCT expecting wide field clusters.  Don't expect an 8" SCT to keep up with your 16" on globulars.  But *maybe* an 8" SCT with an apo up top would be different *experience* that you'd enjoy trying it for a while. 

 

I would say that the most conservative way to start is with a classy 3 to 4 inch apo, maybe a Vixen Ed81s, maybe an SW102.  If you like it and want more then stick an SCT under it.  If not, you've got a Dob and an apo, that sounds pretty good to me.

 

Greg N


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#10 Jon Isaacs

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Posted 10 August 2018 - 09:27 AM

Well there's no answer to "cluster" because something like NGC 7788/90 is one kind of cluster (suitable for a 14" or bigger) and the Perseid Double Cluster is quite another, suitable for small refractors.

 

The double cluster is not the best example since the pair easily fit in the eyepieces of a 16 inch F/4.4. The Pleiades are a better example. 

 

Remembering that the OP has both the 16 inch and a 6 inch F/6, optically the only thing missing are the widest fields of views,  3 degrees and beyond. 

 

Jon


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#11 epee

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Posted 10 August 2018 - 09:49 AM

I’ll second the pairing of a large Dob with a fast 100mm+ refractor. I keep mine on separate mounts.
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#12 chalmene

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Posted 10 August 2018 - 10:16 AM

Why doesn't your 16" work for planetary/globulars?

 

If it's cooled down properly, collimated, and has a good mirror, it should perform far better than literally anything else besides a bigger Dob.

Oh, I love my 16", it works well for everything. And yes I collimate and cool every outing. Just asking as I have really never used any other type but Newtonians, and I know different types have their finer points. :)



#13 gnowellsct

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Posted 10 August 2018 - 02:08 PM

The double cluster is not the best example since the pair easily fit in the eyepieces of a 16 inch F/4.4. The Pleiades are a better example. 

 

Remembering that the OP has both the 16 inch and a 6 inch F/6, optically the only thing missing are the widest fields of views,  3 degrees and beyond. 

 

Jon

I think he said he has an ST80 but I agree he might be ready for something in the 3 to 4 inch range that's more apo-ish and less cost-conscious-ish.  GN



#14 Tony Flanders

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Posted 10 August 2018 - 02:36 PM

I think he said he has an ST80 but I agree he might be ready for something in the 3 to 4 inch range that's more apo-ish and less cost-conscious-ish.  GN

That's my hunch. The ST80 is a great little low-to-medium-power scope, especially for the price. But if you use top-quality equipment all the time, you can hardly help being aware of its mediocre focuser, its huge false color, field curvature, and its inability to use 2-inch eyepieces.

 

Assuming that his 6-inch f/6 has a first-class mirror and is well-collimated and cooled, it's going to equal or beat any affordable refractor on the planets and on the overwhelming majority of clusters. But a good 4-inch APO would come close on those, and beat the Newt on wide-field viewing and thermal characteristics.


Edited by Tony Flanders, 10 August 2018 - 02:36 PM.

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#15 gnowellsct

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Posted 10 August 2018 - 02:57 PM

The double cluster is not the best example since the pair easily fit in the eyepieces of a 16 inch F/4.4. The Pleiades are a better example. 

 

 

 

Jon

Y'aint really "fitting it in" if you don't have the long tail leading to Stock 2.  That's my story and I'm sticking to it.  But any one of these instruments (refractor, dob, etc.) is doing better than the humble SCTs.   In any case I think we both agreed that a three to four inch aperture and more than 3 degrees (maybe more than four) are a cure for melancholia.  He's done the achromat thing.  Time for an apo IMO.    But no need to quibble.  Let the people see 'n' choose.  Remember 14 inchers = 356 mm, 16 inch = 406 mm, 8 inch = 200 mm, and the refractors go by mm in the usual case anyhow.  The spectacular double cluster "tail" is indicated with a red streamer.  GN

 

double cluster and fovs with labels low res.jpg


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#16 gnowellsct

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Posted 10 August 2018 - 02:59 PM

No stars were injured in the making of that graphic.  I should add that the max fov is calculated using a 40mm 70 degree eyepiece and that the map is SCT flipped.  


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#17 Exnihilo

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Posted 20 August 2018 - 12:46 PM

Those are nice rigs Greg!
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#18 BillP

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Posted 22 August 2018 - 08:25 AM

Sorry, I guess "best scope" did sound rather elementary. I am aware aperture is king in a lot of circumstances, but for now my 16" is the largest scope I can practically utilize. Mainly curious if a refractor of cat would be a worthwhile addition to my collection for observation.

 

Do you use your 6" f/6 imaging Newt for visual?  If so then that instrument is certainly portable enough to serve as a quick look instrument and would give a relatively wide field view capability although the off-axis will present some coma.

 

The FOV rendition of a refractive optic is qualitatively very different from that produced by Newtonians or SCTs.  In your case I would not see an SCT of any advantage unless you wanted medium aperture with portability.  Thermally they can be quite difficult to maintain at equilibrium out of the box, depending on your local climate.  Your little ST80 achromat has a significant amount of CA given its very short focal ratio so not really recommended beyond 75x or so (I had one).

 

Adding an Apochromat to your collection would certainly provide you with a different qualitative view, and also offer more ease of use as there is little thermal management or collimation to contend with.  The views tend to visually show a view a bit better contrasted due to their more baffled light path and inherently reduced scatter from refractive vs. reflective optics.  Their view is also generally fully illuminated to the edge of the field which is not the case for Newtonians.  Star point rendition is also considered qualitatively more aesthetic by many, myself included (probably due to smaller aperture, very stable thermal behavior, lack of added diffraction from central obstructions).

 

In adding a Apo refractor to your collection, realize that you will be working at smaller apertures so your expectations should be tempered by what 4" and 5" optics can reasonably achieve.  The main compromise I find is in where you want to balance light grasp vs. portability.  I personally prefer a 4" because of its inherent portability and very stable thermal behavior, so I weight those more vs. light grasp.  For planets and star clusters I find the 4" quite nice.  And using the smaller aperture does tend to hone one's observing skills quite a bit -- so a wealth of details can be had for planetary with careful observation (actually makes it more fun for me).  They also produce quite enthralling wide field views...so they are unparalleled for scanning rich regions of the Milky Way as example.  A quality Apo can also then go from a beautiful wide field low magnification view up to 200x, 300x and more with similarly very rich FOV (unlike the small achromat you have which is limited at higher magnifications). 

 

Having myself "tasted" all the primary designs at apertures up to 20", IMO I think something like a 120mm Apo will provide you with quite a different visual experience than you are probably having from your 6" f/6 Newt, and be a better compliment to your larger Dob.  I've had 6" f/8 Newts and 5" f/5 Newts and while nice, I found them not as capable as their Apo counterparts and the views qualitatively not up to what the Apo could regularly produce.  And if you choose an Apo with a proper amount of backfocus so that binoviewers can be used without the need of an OCA or Barlow, then their wide field low magnification views through a binoviewer are simply breath taking!  My personal favorite is using the 17.5mm Morpheus in my binoviewer in my 4" and 6" Apos.  This yields 47x/1.6° TFOV/2.2mm Exit Pupil in the 4" and 69x/1.1° TFOV/2.2mm Exit Pupil in the 6" (I prefer the 2-3mm exit pupil for general scanning/observing).  On some evenings I will not change the eyepieces/magnifications the experience is that good.


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#19 Eddgie

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Posted 22 August 2018 - 09:17 AM

My simple answer is that if you can't fit a lot of larger objects into the field of your current scopes that you are just dying to see in a larger true field then you need a smaller scope.

 

Another reason for a small scope is richest field viewing but if you don't go regularly to dark skies, this kind of scope won't get used much.

 

Before I started using image intensified eyepiece I got almost zero pleasure from using small scopes and if the 80mm does not do much for you, I don't think 4" will do much better.

 

Now if you want to totally jazz your observing or burn through light pollution, consider an image intensified eyepiece with your current large scope. It will be in many ways like doubling your aperture and will open up nebula viewing like you would not believe.

 

Unless you crave a bigger field for the few dozen objects that demand it though, there is little benefit in going smaller and focal length alone should never really be a factor because Barlow lenses let you get as much scale as you need.


Edited by Eddgie, 22 August 2018 - 09:18 AM.


#20 Eddgie

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Posted 22 August 2018 - 09:36 AM

And while I agree that the 120mm ED is a beautiful scope, mine lasted about 4 months before I got bored with it.  I would look at even bright targets with the 120mm but if those targets would fit into the field of my 12" sob the were always much more pleasing to me in the bigger scope.

 

If you feel that you absolutely gotta have a small scope though and can't stand the thought of not trying it, I too would recommend the 120ED.  Coming from where you are though, my bet is that it would not prove to be better than what you already have.  It would only cost you maybe $1200 to $1500 to find out.  120ED was to me personally the best overall compromise in a refractor.  I have owned everything from an 80mm achromat to a 6' Astro-Physics and if you made me choose one scope 5" or smaller for conventional visual observing this would be it, but unless I lived under dark skies, I would just pass.

 

If I lived under very dark skies, it would be a Televue 101 or Genesis SDF.



#21 Adun

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Posted 22 August 2018 - 10:54 AM

Having had an interest in trying a decent-sized refractor or Cat for quite some time, would either provide an observing advantage to my Newtonians?

 

Most likely not unless aperture is the same. Maks and apos do have better star tests, with much better looking stars and no diffraction spikes, but without resolution (aperture) it won't be enough to surpass a larger newtonian.

 

My F13 90mm Mak does blow away my 114mm F4 reflector when it comes to planetary performance, but their unobstructed apertures are very similar.

Also consider atmospheric seeing: On an average night, my 6" SCT provides I'd say ~65% of the planetary detail my 10" dob would on the same night, but there are rare spectacular nights of steady seeing when my 10" dob leaves the SCT in the dust.

 

 

Oh, I love my 16", it works well for everything. And yes I collimate and cool every outing. Just asking as I have really never used any other type but Newtonians, and I know different types have their finer points. smile.gif

 

The "observing advantage" will revolve more around factors like (much) faster cooldown, much better ergonomics on your Bresser EQ mount  (less need to keep rotating the newtonian tube to avoid uncomfortable eyepiece positions, fewer vibrations thanks to a shorter Mak/SCT tube), or a much wider FOV (in the case of an ED refractor), but still in terms of pure resolution and detail for planets, aperture rules.

 

That said, last saturday I noticed the sky was very clear, stars weren't twinkling as much. Mars was very high in the sky (20º from zenith, I'm at the equator), but I had to get up early next day. I didn't have much time (only 20 minutes). Still, I felt I wanted the resolution of my "big" 10" dob for Mars so I set it out, collimated it, gave it 10 minutes to cool down, and observed. 20 minutes total.
 
It was alright, but frankly, the Mars view I got 3 weeks ago with my 90mm Mak was better. Of course, for longer sessions, with enough cooling time the 10" dob leaves the 90m mak in the dust, but for very quick sessions, when thermals come into play, the C90 has already showed me the martian polar cap and hellas by the time I'd barely be finished setting up and collimating the dob.  My C6 strikes a middle balance with somewhat quick thermals, more resolution than the Mak, and splendid ergonomics.
 
Optics are not everything. If you only consider the optics then you'll always arrive at the conclusion that aperture is king and you want the most possible for the budget, which means a dob.
 
But then again, optics are not everything. Thermals, ergonomics, time shortage (either because clouds will carpet the sky 40 minutes after dusk, or because I have to work next day), setup complexity, vibrations, health (my bad back) and portability, do matter as well, all this while atmospheric seeing limits what larger optics can do. 
 
Final note:  You found your ST80 not to be an exceptional best observing tool. Indeed it is not, but when I had a chance to vacation on a bortle 2 remote beach with sight of the south pole, I was so glad I could pack the little thing in my luggage. My best sights to date of Carina nebula, Andromeda, the Southern Pleiades, the Jewel Box, NGC3532 and the double cluster. I'd rather use that little scope from a bortle 0 sky than my 10" dob from my city home (bortle 8)


Edited by Adun, 22 August 2018 - 03:36 PM.

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#22 Jon Isaacs

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Posted 22 August 2018 - 11:32 AM

That's my hunch. The ST80 is a great little low-to-medium-power scope, especially for the price. But if you use top-quality equipment all the time, you can hardly help being aware of its mediocre focuser, its huge false color, field curvature, and its inability to use 2-inch eyepieces.

 

Well yes and no.  Stock , the ST-80 has a decent focuser once it's been adjusted but there's field curvature and at higher magnifications there's chromatic aberration to be sure. 

 

Some years ago I was looking through my boxes full of junk and i realized that with a simple shim,  I could mount an old 2 inch Williams Optics focuser to an ST-80. It transformed the scope,  no longer was it an inexpensive also run, rather it was an amazing deep sky,  widefield scope that could provide a 6.0 degree TFoV with the 31 mm Nagler and 6.6 degree TFoV with the 41mm Panoptic. 

 

They're nights when it takes the forefront .

 

5543416-Ioptron Halloween Scope.jpg
 
But it is a one trick pony and makes a nice addition to a 4 inch ed/apo rather than a replacement.. .
 
Jon

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#23 Jon Isaacs

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Posted 22 August 2018 - 11:34 AM

No stars were injured in the making of that graphic.  I should add that the max fov is calculated using a 40mm 70 degree eyepiece and that the map is SCT flipped.  

 

:roflmao:

 

I am just so happy there were no stars injured . 

 

Jon



#24 Keith Rivich

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Posted 22 August 2018 - 11:56 AM

You can actually make a case that a really large (maybe 6"?), premium apochromatic refractor with a great eyepiece might beat what that 16" Dobsonian will do for you.  Even if the view is not necessarily better you just might find the experience more pleasurable.

 

But the price would be shocking for most of us and you might find that you actually like what the 16" Dob does either as well or better.  A 6" refractor also generally starts getting rather long and that often means less-than optimal ergonomics on some targets.

 

If I had a 16" Dobsonian and was thinking about getting better views I'd probably consider retro-fitting a GoTo system to the Dobsonian rather buying a big refractor or Mak-Cass.  The tracking reduces the distraction of having to nudge the Dobsonian along and that means you will actually see a bit better.

 

If your intent were to do planetary AP then I'd be looking for something like a 14" SCT and Barlow the thing.  It's actually a great instrument for visually observing planets as well and might compete fairly well with your 16" Dobsonian in part due to the long "natural" focal length and the relatively good ergonomics for most targets.  But especially if you got a 14" SCT with a fork mount - not fun to try to move around/set up.

In my opinion, nope.

 

I have access to 6" and 11" refractors of very good quality and they do not come close to equaling or surpassing my 18" Obsession. 


Edited by Keith Rivich, 22 August 2018 - 12:01 PM.

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#25 BillP

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Posted 22 August 2018 - 03:41 PM

You can actually make a case that a really large (maybe 6"?), premium apochromatic refractor with a great eyepiece might beat what that 16" Dobsonian will do for you.  Even if the view is not necessarily better you just might find the experience more pleasurable.

 

This can be very true!  Just depends on your perspective.  I was recently at a dark site in New Mexico for a week observing.  I was using substantially a 6" Apo but would wonder over to the 16", 18", and 20" Dobs that friends had there.  The larger apertures obviously could view targets showing more detail/structure and at higher magnifications.  But even so, their views were limited in terms of what we know the structures of the objects to be from ground-based and space-based imaging.  In the end some of the extra details were casually "interesting" to see, but nothing that I felt was overwhelmingly over the top.  One exception was glob cores with the 20" as this aperture had enough pull that when close up in the core there was still enough light to let all the individual star colors come through which was quite enthralling.  However, I'm sure glad I didn't have to manage the setup, acclimation, collimation and re-collimation, operation, precarious ladder observing, and breakdown of that monster.  So view was nice, but operationally I considered it a complete nightmare.  All that being so, went back to and spent the majority of my time with the 6" Apo as its views were beautiful, had greater context since generally worked at lower magnifications to keep the targets bright like the bigger apertures, and operationally it was completely easy-peasy with zero hassles over the course of each evening's observing.  I generally stopped observing with a telescope at around 2-3am each evening, then spent the last hour in a lounge chair observing the Milky Way in detail naked eye.  In many ways that end of evening observing at the dark site was the most memorable over what any telescope could provide, even the 20".  A lot of magic to observe in the sky...more when you have studied up on what you are looking at...and aperture is largely irrelevant IMO to the reward of the experience as any aperture will do.  So your best "scopes" for planetary and cluster observing are really your "brain" to know the details of what you are observing before you observe it and your "eyes" to take in all the context of the object.  Any aperture scope will due after those two grin.gif


Edited by BillP, 22 August 2018 - 03:43 PM.

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