Large Dob advice please...

[DRT]

I own a Skywatcher Heritage 130p and over the past few months I have enjoyed fabulous views of the moon and clear, but very small, views of Jupiter, Mars and the Orion Nebula using the 25mm and 10mm Possil eyepieces supplied with the scope.

I decided to try upgrading the eyepieces so purchased 7mm and 18mm Celestron X-CEL LX's and a Seben 8-24mm FMC Zoom. All three provide sharper images than the cheaper eyepieces I already had but I am still not satisfied with what I am seeing. It needs to be bigger and more detailed to satisfy my desire.

Having researched the web and lots of threads on SGL I have decided to buy either the 250mm or 300mm Skywatcher Skyliner Dob, but I have two questions that I would appreciate assistance with before deciding what to buy…

1. Is there an appreciable difference in what I can expect to see when viewing planets through a 250mm or 300mm scope?

2. The FlexTube vesrion of these scopes are more expensive that the equivalent solid tubes. Is the principle difference the convenience of being able to collapse the scope to a small size for storage or are there optical benefits in going for the FlexTub version?

Any other advice anyone has would be greatly appreciated.

Thanks

Derek

[NGC 1502]

Hello Derek.   The Heritage 130 is a capable scope, but yes, a 250 - 300mm is a big and noticeable step up in capability.  There are many happy users of 10 - 12" scopes, but I do think that it would be best to see your intended scope up close, in a retailers or maybe a local club, to make sure the size and weight are right for you.

The advantage of the Flextube is that the tube can be contracted to make it more portable, but it's not lighter than the solid tube version. They are optically the same. You would need to make or buy a shroud for the Flextube to lessen dewing up of the mirrors, as they are more exposed than in the solid tube version.

All the best in your choice, Ed.

[DRT]

Thanks, Ed.

Just to clarify my first question (as I din't phrase it very well): I want to know whether there is a significant difference in what I will see through a 250mm v a 300mm scope? There is a significant price difference and the 300mm looks much bulkier than the 250mm so I want to know whether or not the added inconvenience in terms of £££ and lugging it around are outweighed by a materially better viewing experience.

Derek

[swamp thing]

Hi Derek

Not sure I'd be looking at mid to large Dobs if I was into planets.

As I don't often observe planets I can't really help though.

[DRT]

Hi swamp thing,

I'm intrigued by your first comment. I confess that I know just about nothing about the differences between different types of scope. My decision to go for a larger Dob was purely on the basis that I find the one I have easy to use and failry simple to understand. My expectation therefore was that a bigger scope simply means bigger and clearer images when I look through the eyepiece.

If big Dobs are not ideal for planets, what is? And what are big Dobs ideal for?

I can see already that joining the forum is going to cost me money

Derek

[NGC 1502]

Thanks, Ed.

Just to clarify my first question (as I din't phrase it very well): I want to know whether there is a significant difference in what I will see through a 250mm v a 300mm scope? There is a significant price difference and the 300mm looks much bulkier than the 250mm so I want to know whether or not the added inconvenience in terms of £££ and lugging it around are outweighed by a materially better viewing experience.

Derek

Hi again Derek.  I do think that will be a definite and noticeable difference in the views if you upgrade.  Deep sky objects especially will be much nicer.  You mention planets.  Refractors are often mentioned as good for planets, but a good refractor is expensive and likely to be far smaller than a Dob, and aperture equals resolution. However, larger scopes are more affected by turbulent atmosphere, but if you are patient, a 10 - 12" Dob will reward you with great planetary views.

The difference in the views between a 10" and a 12" is fairly close. I went for a 10" because it's more portable. But opinions as to how portable a scope is varies (quite genuinely) from person to person, hence my suggestion to perhaps see the scopes up close, and weigh this up for yourself.

My 10" F4.8 solid tube Dob fits across the back seat of my car, a 12" F5 solid tube would not. Of course a 10 or 12" Flextube would easily fit.

Dobs are definitley  "the best bang for the buck" in terms of what you can see with it, great allrounder.  Not suitable for everyone of course - so much choice out there !

Regards, Ed.

[Alien 13]

Long focal length refractors or Maks tend to give better views per inch than the Dobs on planets, Dobs excell on faint fuzzies where the shorter f ratio gives you a brighter image.

[astronymonkey]

Hi Derek,

Its a slippery slope once you start going big as aperture fever soon sets in.

The surface area of a 10 in ch mirror is 78.5 sq inches, whereas a 12 inch has 113.1 sq inches, so thats over 40% bigger.

With this in mind Id choose the 12 inch but would consider the flextube option as this will make transporting much easier. An alternative is the Meade Lightbridge, which is broken into 3 sections plus the base for transporting.

As for what you can see, Ive never compared a 10 and 12 side by side but I think there would be some improvement with the larger aperture given the 40% plus increase in light gathering ,

Compared to the 130 you have both the 10 and 12 inch scope will allow for more magnification and will have better resolution  despite not being specifically designed for planetary viewing, and both will be able to handle 250x magnification which is about the max you can go to in the UK under normal seeing conditions.

cheers

[John]

On the physical size / weight of dobs, I posted this a while back, which might be of some use:

http://stargazerslounge.com/topic/172790-dobsonian-size-comparison/?p=1766685

[brantuk]

The big benefit of large aperture dobs is their ability to gather light - the bigger the better. The more light you present to the eye in astronomy, the more contrast and clarity you get with the object and the more detail you will see. This light gathering ability is particularly useful for observing very faint and distant objects like galaxies, nebulae, and clusters (faint fuzzies).

The size of the object you observe is entirely dependent on the eyepiece used - that's what magnifies the object. The telescope merely focuses the object. For planets you would either use a long focal length refractor (tend to be expensive per aperture inch) or a compound scope like a cassegraine (eg Sct or Mak) which will give you a 2m-3m focal length by folding the light between mirrors.

Big dobs still give a good account of themselves on planets though, and Mak's, Sct's can still be used on dso's - especially the bigger ones from 8" upwards. But dobs do generally have a wider field of view. The difference between 10" and 12" is appreciable but not hugely significant imho. The larger one will let you peer a bit deeper into the deep sky. The smaller of the two will be lighter, much easier to carry out to a dark sites and star parties, and a little more convenient to store. Hth

[DRT]

Thanks all, this is all great stuff and food for thought.

Something else worth mentioning is that almost all of my star gazing will be from my back garden. I live in a small town so there is a fair amount of light polution but the garden itself is quite enclosed and very dark. Does this have a bearing on the type of scope I should be choosing? (Solid v FlexTube / Dob v Refractor / etc.)

[cotterless45]

With stargazing live coming up next month there will be plenty opportunities to see scopes in action. Our local group in Derbyshire

http://www.roslistonastronomy.org.uk

Will be out performing with scopes and hot drinks and friendly advice,

Nick.

[brantuk]

Derek - if you want to see any of these scopes in the flesh and have a look through to compare them - you'd be welcome to visit East Mids Stargazers (EMS). We are a friendly local group (started here on SGL) who meet at a dark site in Belper not far from you. Click the link in my signature for further details if you fancy an evening of group observing.

[DRT]

Thanks, both, I might take you up on those invitations

[Luke]

re: dobs on planets, I can tell you that I had an absolutely jaw-droppingly good view of Jupter through a 300 flextube when conditions were perfect. It was like a photo. A very good photo! I've had three Skywatcher dobs and have been impressed by the optics in them for the price.

The dob will shine on deep sky thanks to its large aperture, but planets will be fine.

10 vs 12, it's a tricky choice.

My 10 inch (a GSO) feels vritually no effort to move, while the 12 inch flextube was a bit of effort. Nothing major, but I get very lazy at times and appreciate the lighter load

Can't go far wrong either way. One's a bit easier to move, the other has a bit more aperture.

I personally find there is enough aperture in my 10 to think I will stick with it rather than switch back to a 12. I do notice the improvement with a 12, but a 10 is still a powerful scope.

A solid tube tends to be slightly less hassle than a flextube, though the flextube of course compacts more for storage and is more portable.

[DRT]

Thanks, Luke.

[RikM]

I compared a 10" to a 12" from light polluted Gloucester and Cheltenham and the difference to my eyes was not that great. The 12" solid tube was much bigger than I could manage and the 12" flex-tube was so much more expensive that I decided it wasn't worth it to me. I went for a solid tube 10" as that gave me 90% of the view for 50% of the cost compared to the flex-tube 12".

[DRT]

Thanks, RikM, that is really useful first-hand experience.

[Bart]

Here's a pic of my 10" and the 16" for comparison purposes

Barry

[Luke]

It would seem a shame if you don't need the compactness/portability of a flextube to pay the extra for that superb feature. My preference is solid tube if it is practical - less prone to dew, needs collimating less often (though that only takes a few mins - but I am very lazy at times! ), does not need a shroud.

SW used to do a solid 12 (I had one, as well as the 12 flextube at the same time for a period - there was absolutely nothing between them optically)

Edit: I collimate my solid tube dob about every 6 months, versus every session for my flextube, though some people seem to have the knack of not having to do that - mine is always off though.

[baggywrinkle]

/\ Nice photo, that extra 6'' certainly adds to the size.

Great thread as I am being sucked down the dob route for my retrunr to the UK and I see some great advice (as usual on SGL) coming from lots of folk.

[John]

If you can find an Orion Optics dobsonian you will find that they weigh somewhat less than the chinese equivalents which, for me at least, makes owning a 12" much more practical. I need to be able to move my scopes around reasonably easily to dodge trees, neighboring houses etc. My 12" F/5.3 solid tube Orion Optics dob weighs around the same as a Skywatcher 10" dob.The 12" Meade Lightbridge I used to own was around 25 lbs heavier overall and turned out not to be a practical proposition for me.

The Orion Optics dobs are expensive to buy new but much more reasonable to buy secondhand. They tend to have better optics in them than the chinese equivalents too.

[RikM]

Yes, John's right as usual. I would consider an OO. Probably a 12" f/4 since it would still fit in my car easily where the f/5.3 would be too long for me.

[AlexB67]

an OO flex tube 10 inch f/6 or so  of OO 12 inch at f5.3 would be a dream, alas a flextube like design does not exist with OO.  I must say I find the SW flextube 10 inch very easy to carry around the garden, my main limitation was the car size which why I stuck to that. If it wasn't for that I had almost bought a 12 inch GSO. I can relocate that 10 inch easily around the garden during a night observing and I feel very confident doing so having had it a few months now. 

If as John says in an ideal world you could get a 12 OO scope, since it is pretty much as light as the skywatcher 10 inch, it would be a very nice sweet spot scope to have. Also, that f/5.3 ratio doesn't suck either :0)   

If money was not an object and I could transport it easily by car, and a scope that is still easy to carry around the garden, for me it would probably have been a toss up between the VX10L or the VX12L.  The former a really sweet f ratio on eyepieces versus the latter with  a bit more aperture.

I could see myself getting one of these in time to come in x years time, after a slightly bigger car .

[nicks90]

I have a 12" SW flextube and when i recently bought another car, I had to limit my choice based on getting the dob base in the boot. It is BIG.

The 'problem' with the flextube is that there is a lot more weight higher up the tube due to the design, therefore the pivot point has to be higher up the tube, therefore the dob base needs to be taller. This means it is large and awkward and only just fits into the back of my audi a6 estate.

as for the tube, most 12" scopes are about F5, so the tube will be about 60" long - 5 feet - give or take a few inches. So unless you have a narrow car, it should fit across the back seat. But it is definitely worth checking if you want to go for a solid tube with subsequently smaller dob base! Otherwise you are stuck with flextube only and living with a taller/heavier base.

Having lived with my 12" dob for a while now, I am seriously glad I have it. Its a proper weapon!!! But if I was to do it all over again and was buying new instead of buying this on a whim from a club member, I would have gone for a 10" solid tube.

I;ve not made it any easier have it... sorry.