Orion or Skyliner Dob, or Dob at all?

[joshy2]

Hi all,

I've tried searching for answers to these questions as I don't want to ask something that's been answered lots before, but couldn't turn up anything. Forgive me if I've missed the threads!

Having done a fair bit of reading around (I know I also need to try and get to a Star Party, which I will do soon) I've reached the conclusion that a 12" Dobsonian is likely the telescope for me. Because GoTo and tracking abilities are important to me, I believe the best choices are either an Orion SkyQuest xx12g GoTo Truss Tube or a Skyliner 300p. I don't think Meade's Lightbridge models have GoTo or motorised tracking.

For background:

- My main viewing interests are the planets/solar system rather than deep space objects, although I would definitely be interested in those too. I know that Dobs are more used for deep space objects but I like the thought of having a large aperture view of the planets as well.

- I'm not interested in astrophotography.

- My budget would be £1000ish max, though I'd be happy to buy second hand. Yes, I will go to a Star Party (or few) before spending this kind of money on a 'scope, but I wanted to ask advice here to enhance my knowledge first. 

My questions are:

1. What are the pros & cons of an Orion vs Sky-watcher? Is one better than the other? The Orion is a few £hundred more but don't know if the extra cost is justified.

2. I live in NW London and with a young family and other commitments, for the foreseeable future, I'm unlikely to travel out to the countryside with my 'scope. Most of the viewing will be done in my back garden. I've read that in an area of high light pollution, this could negate the benefits of having a large aperture 'scope. My maximum power would be limited anyway. Is this true? Would I be better off with a different type of scope and certain lens selections?

3. My thinking behind getting a Dob is that based on my understanding (please correct me if I'm wrong) I have a wider field of view for a given aperature (say 12") than with a refractor or SCT, assuming the lenses are the same - but that I'd have the ability to use higher power lenses to 'zoom in' and really get the detail if I wanted to. It might not work so well the other way, with a narrower field-of-view 'scope and wider field lenses. Is that sound thinking? I don't want to sound like I've got newbie 'aperature fever' but it seems to make sense to get the biggest 'scope one can afford and practically use (I'm happy that a 12" Dob is portable enough for me).

Thanks very much in advance for all your help! Sorry there's a bit of an essay to read through but I wanted to try and provide as many details as I could to help.

Josh

[joshy2]

Edit, I've just seen in this thread (having said I couldn't see anything that answered my questions!) that Orion and Sky-watcher are owned by the same company. Does this mean the two models above area really the same scope? http://stargazerslounge.com/topic/259757-best-8-dobsonian-for-around-%C2%A3500/

P.S. How do I edit a post? I'd rather have put this in my OP than make a reply but couldn't see an edit button.

[Cornelius Varley]

You need 50 posts before you can start editing. Most of Orion's products are sourced from Synta (manufacturers of Celestron and Skywatcher) . They might not be identical though, and some are unique to Orion (the 4.5" Skyquest and the big truss dobs).

Orion (US) telescopes tend to cost a bit more than their Skywatcher counterparts because they are imported from the US. Skywatcher (Synta) telescopes have a larger distribution network and are imported straight from the country of origin.

[DevonSkies]

I have a Skywatcher 10" Dob. I live in East Devon, where there is some light pollution, but I imagine much less than in the London area. However, I feel I'm not getting the full benefit of my 10" aperture simply because the light pollution is limiting my ability to see faint objects. Also, bear in mind that a 12" Dob is a large, heavy instrument to have to carry in and out of the garden. If your main interest is solar system objects I wonder whether you might be better served by a smaller Maksutov-Cassegrain or Schmidt-Cassegrain telescope? You won't need the light gathering power of a 12" for planets, although the larger aperture does give higher resolution (atmospheric conditions permitting). You are right that with a Mak or SCT you will lose the ability to get really wide-field views, but if this isn't your primary interest then maybe you could supplement it with a wide-field scope at a later date?

Just a couple of thoughts!

[Tinker1947]

I have the 12" SW Goto, i built a small Dob Shed on the back of the Obby, the 300P sits on a base that slides in and out of the shed then gets transported on a sack barrow to its levelled slab, its not to heavy if done in 2 moves, Base then the scope....The scope its self is extremely accurate once set-up and tracks very well.

Picture taken before the sliding base had been installed.....

[jetstream]

I wonder how much magnification London's seeing will allow for lunar/planetary? An 8" something would be not too seeing sensitive, give great resolution on the moon/planets seeing considered and still have the ability to go deep when at dark sites. Possibly a C8 on a GoTo mount?

[Stu]

A couple of things to straighten out first Josh [emoji6]

Light pollution is very different from atmospheric seeing conditions.

LP is a problem when trying to view DSOs because the bright sky tends to wash out or completely hide them.

For lunar and planetary work, LP is much less of a problem because the targets are bright, but you need the atmosphere to be stable in order to reach the higher powers necessary to see detail (ie x150 and above)

Poor seeing can be caused by a number of factors, but simply let's say there are two basic problems.

High level turbulence in the atmosphere, often caused by the Jetstream running overhead or just the weather conditions. Nothing much you can do about that, just try another night.

The second cause is low level turbulence caused by heat rising off surrounding buildings, Tarmac surfaces, central heating flues etc. Your views will depend upon how clear of these things you can get. If you are surrounded by houses it will be trickier than if you have a garden overlooking a park for instance. Even the gaps between houses can offer windows of good seeing at certain times.

Next thing is about fields of view. Your understanding is not quite right in that a dob can have a long focal ratio/focal length, just like other scope types.

The thing that determines the field of view (and magnification) is the focal length. If you want as short a focal length as possible in a given aperture then you want a relatively short focal ratio such as f4 perhaps. Trouble with this is, faster scopes tend to be more demanding on eyepieces, needing a paracorr and/or expensive eyepieces to get the best out of them. I think some of the Skywatcher f4.7 scopes are a good compromise.

A larger scope (or larger aperture) can, under good conditions, give better planetary images than a smaller one because of the additional resolution they offer. The detail is easier to pick out. Problem is, they are also more affected by seeing conditions (as Jetstream mentions) so if your local seeing is poor, you are less likely to get the best out of it.

I'm not saying a 12" scope is not worth getting, it's just worth considering these factors in your decision. I had a very nice Orion Optics (not US Orion) 10" f6.3 scope which gave lovely planetary images but was as tall as a 12" so probably not compact enough. The Skywatcher truss dobs do make sense from that perspective. On this note, I think Orion and Skywatcher are very similar, but as said before, Skywatcher is much better established in Europe so their pricing tends to be lower.

[NGC 1502]

You have some great advice already given, especially post # 7.

I do think it's best if you could see a 12" Dob in the flesh, at a dealers or star party, to see the size and feel the weight. Please check the weight of the tube assembly and also the base, the particle board Dob mounts are surprisingly large and heavy.   Not so much an issue if you can store the scope very  close to where it will be used.

I think it's a myth that a large aperture is more affected by light pollution than a small one.  All scopes work better away from LP, but good astronomy can be done from town as well.

Regards, Ed.

[Alan64]

This combination would make for an ideal kit for lunar, planetary and stellar(double and variable stars) observations beneath an illuminated dome...

http://www.firstlightoptics.com/reflectors/skywatcher-explorer-150pl-ota.html

http://www.firstlightoptics.com/skywatcher-mounts/skywatcher-eq5-pro-synscan-goto.html

Later, an 200m f/5 or a 250mm f/4 might be swapped out, on the same mounting, and for improved wide-field, deep-sky performance...

http://www.firstlightoptics.com/reflectors/skywatcher-explorer-200p-ds-ota.html

http://www.firstlightoptics.com/reflectors/skywatcher-quattro-f4-imaging-newtonian.html

...however, with the 250mm f/4 for darker sites; also, a coma-corrector would definitely be required.

[joshy2]

Thanks very much everyone for your informative replies. Especially Stu.

So it seems that to be on the safe side with regard to concerns about good seeing (assuming that it won't be good a fair amount of the time where I am) I should go for a lower aperture scope? Perhaps around 8".

Alan, thanks for your suggestions. For longevity's sake, would I  not want to go for the 200mm scope you linked to rather than the 150mm one? It's not much more expensive. Or does it not offer as good performance under an illuminated dome?

To help me understand by comparison, if I'm now looking at an 8" 'scope on a GoTo mount, what then of Meade's LX90 8" ACF? The focal ratio is f/10 which seems a fair bit higher than the Explorer 200p (f/5) - so does this mean it's not as powerful and would have a narrower field of view? If so, what makes it better than the Explorer 200p + Eq5 mount? It is a fair bit more expensive. Is one just paying for the greater compactness and cost of the SCT design or does it have a better optical quality too?


Thanks again,

Josh

 

[Stu]

Josh,

This is where you get into the delights of too many choices [emoji3][emoji16]

I think probably an 8" or 10" scope would do you fine. You can still stick with a goto dobsonian in those sizes, within your budget. I've never used one but they have good reputations.

http://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-250px-flextube-goto.html

http://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-200p-flextube-goto.html

These are very quick to setup and relatively easy to transport as they collapse down. Perhaps quite heavy though.

Personally I would not get into the complication of an EQ mount, I don't think you need to, plus I would stick with Skywatcher for dobs or Celestron for SCTs just because their distribution and pricing is better in Europe.

If you really wanted to go for a goto SCT then I guess something along the lines of a Nexstar would be worth a look

http://www.firstlightoptics.com/nexstar-evolution-telescopes/celestron-nexstar-evolution-8-telescope.html

In general, I think you get more aperture for your money with a dob. The optics on the SCT are similar quality but much longer focal length so field of view is much narrow. They tend to excel on planets and the moon but are very capable on the majority of DSOs too as they are not that big. Cool down time can be significantly longer from a warm house as the tube is closed, an hour is not unusual, sometimes more. Finally you will need dew protection in the form of a dew shield and preferably a few heater strip to keep the front plate clear.

Try to get a look at and through the different types, but I think the dob is probably the best bang for buck and simplest to use.

Stu

[Alan64]

Thanks very much everyone for your informative replies. Especially Stu.

So it seems that to be on the safe side with regard to concerns about good seeing (assuming that it won't be good a fair amount of the time where I am) I should go for a lower aperture scope? Perhaps around 8".

Alan, thanks for your suggestions. For longevity's sake, would I  not want to go for the 200mm scope you linked to rather than the 150mm one? It's not much more expensive. Or does it not offer as good performance under an illuminated dome?

To help me understand by comparison, if I'm now looking at an 8" 'scope on a GoTo mount, what then of Meade's LX90 8" ACF? The focal ratio is f/10 which seems a fair bit higher than the Explorer 200p (f/5) - so does this mean it's not as powerful and would have a narrower field of view? If so, what makes it better than the Explorer 200p + Eq5 mount? It is a fair bit more expensive. Is one just paying for the greater compactness and cost of the SCT design or does it have a better optical quality too?

Thanks again,

Josh

The 6" f/8 Newtonian would be more of a specialty instrument; again, for lunar, planetary and stellar, and some deep-sky, observations.  It would be a near-simulation of a 120mm f/10 apochromatic refractor.   Less-expensive eyepieces, along with the natural and artificial atmospheric effects, would be more "forgiving" of its nature.  If, on one night, the 8" f/5 proved to be uncooperative, the 6" f/8 could be used instead.  Granted, the longer optical tube might prove unwieldy at times, especially on an equatorial, but its optical performance would perhaps compensate for the trouble.  The 6" f/8 was very popular in the 1950s, '60s and '70s, and when amateurs observed within the solar system rather than deep space.  They were quite expensive for the time, and for good reason, per this advertisement from 1960...

http://www.company7.com/library/graphics/criterion_rv6-1960_733964.jpg

In said age, it was as though it was forbidden to observe beyond the solar system, lest one encountered the "Medusa".

It has its adherents, and to this day, but mostly in the form of a "Dobsonian".

That said, by all means go with an 8" f/5.  I have one myself, but I've yet to observe with it.  I've had it since 2003; odd, that, eh?  I would recommend flocking the tube throughout, and perhaps even adding an extension to the front of the tube, and to keep stray light out; oh, say, 8" to 10" beyond the edge of the opening.    One can be made with most any material.  I'd make mine of aluminum sheeting, riveted and lined with flocking....

http://s110.photobucket.com/user/tinker3480/media/Deepspace/DSC_9561.jpg.html

Both suggestions would increase contrast, noticeably, and effect blacker sky backgrounds around and about the objects observed.

An 8" Schmidt-Cassegrain would be an option as well; more ergonomic and easier to handle.  It would favour lunar, planetary and stellar, and just as the 6" f/8; more so in fact, with its 2032mm focal-length.  The faster Newtonians would favour deep-sky, and ideal for darker sites.

The most important thing of all: don't be in a hurry in deciding.  Research, for weeks if not months, and most certainly do not rush out and get one eyepiece after another, especially sets, afterwards.  It's best to get one at a time, tailored to the individual and the telescope, and of better quality.  The sky isn't going anywhere.

[joshy2]

Thanks again guys, I really appreciate all that info - it's made things a lot clearer.

I will try to get to some star parties now - there are some near me I've found. Thanks to your help, I'll have a clearer idea of what I'm looking at now and will be able to look out for the differences in 'scopes with a bit of an educated background.

Josh