Advice before buying a dobsonian

EricB (Eric) · #1 22-01-2012, 04:42 PM

Hi there! I am new of IIS which seems to be a great forum!

A bit of background on me: I am not totally new to astronomy having practised it in my teens and 20s with a refractor (75mn, equatorial mount). My experience is mostly in the northern hemisphere. I now live in the southern Adelaide hills where I have a good night sky to the south east.

I am now very keen to return to astronomy, but I am experiencing the typical beginner's dilemma in relation to what to buy. Having done some web research, I am set on a dobsonian because it delivers decent aperture for reasonable prices. I also like its simplicity of use. I am leaning towards Sky-Watcher because of the consistent positive reviews I have seen on the web. A collapsible seems a good option as I have limited storage room in my garage. I have a budget of $1500 to $2000, including accessories.

Here are my options as I see them:

- Buy a SW 10" GOTO for $1499 (Andrews Comm.)
- Buy a SW 12" manual for $1299 (Andrews)
- Spend an extra $500 and buy a SW 12" GOTO for $1999 (Andrews)

At this stage I feel that I should get the 10 GOTO, but I am sill unsure. Here are my questions:

- Is there a very noticeable difference between a 10" and a 12" Dobs in terms of performance?
- Is GOTO a big advantage compared to manual for someone like me who is relatively unfamiliar with the southern skies but not very tech minded. In other words is GOTO straightforward in terms of set up and use?
- Does at 12" fit in a Corolla sedan?
- I am set on Sky-Watcher but should I consider other brands?

Sorry for the long post. I would be very appreciative of your help and advice.

Cheers,

Eric

Shark Bait (Stu) · #2 22-01-2012, 05:39 PM

Hi Eric,

I am fairly new to IIS as well. This is a great forum.

Quote:

Originally Posted by EricB

- Is there a very noticeable difference between a 10" and a 12" Dobs in terms of performance?
- Is GOTO a big advantage compared to manual for someone like me who is relatively unfamiliar with the southern skies but not very tech minded. In other words is GOTO straightforward in terms of set up and use?
- Does at 12" fit in a Corolla sedan?
- I am set on Sky-Watcher but should I consider other brands?

I think the 12" allows for approx 30% improvement in light gathering abiltiy over the 10". The views at the eyepiece are very good once the optics have been collimated.

I find the GoTo very useful. It does help to locate the faint DSO's in light polluted skies. It is also easier to keep my 5 year old interested as it tracks the objects being viewed.

The 12" Flex Tube GoTo Dob fits into my 2002 Astra Sedan. I kept the moulded packing material and the OTA fits into the boot without contacting any surfaces, but it is a snug fit. The base fits on the back seat with some care not to make contact with the door frame. If you need dimensions of the 12" I can measure it up for you. This may assist you in making determining if it will fit into your Corolla Sedan.

There seems to be plenty of happy GSO Dob owners on this forum. I went for the Sky Watcher and am very happy with it. Would have liked an SDM but that will have to wait.

Brian W (Brian) · #3 22-01-2012, 06:07 PM

I personally enjoyed the skills of star hopping. I find that if i am trying to find an object that i enjoy the hunt so goto is not important for me. That being said on those rare nights when high mag is possible tracking would come in handy to keep the object centered.
Brian

EricB (Eric) · #4 22-01-2012, 06:35 PM

Thanks very much Stu and Brian.

The Astra is comparable in size to the Corolla. Stu if it's not too much trouble, it would be great if you could give me the measuments.

So far I have very good deals at Andrews Comm. From what I can gather they seem the cheapest in Australia. Are there other dealers I should be aware of?

Eric

Screwdriverone (Chris) · #5 22-01-2012, 06:36 PM

Hi Eric,

I had the manual 12" truss Skywatcher dob, and while I enjoyed star hopping for a while, I really only looked for the "bright" and easy objects that I knew were there.....if you have GOTO, you simply dial up the object you want or connect the scope to a laptop and use Stellarium to drive the scope, its awesome.

One thing which you will not need any tech skills for is the alignment, enter the time, date, location (coordinates, which you can find using google maps or even your GPS enabled phone) into the hand controller and simply select ONE star alignment.....the manual tells you how.

The scope will slew to where it thinks the star should be (say Sirius - which is south of Orion) and then all you do is use the arrows on the controller to centre the view of Sirius in the eyepiece, press enter and then it should say "Alignment Successful".

Then you can use the TOUR function which will step you through the objects visible that night for the place you are and the time of night....VERY cool as it just gives you a list, you scroll through (or simply start at the beginning) and then the scope slews to the object you want, all you have to do is wait for it to beep, maybe adjust it slightly and then enjoy the views....

All quite easy and my point is, GOTO will give you HOURS of things to LOOK at rather than spend HOURS trying to find things you may not recognise in the eyepiece.....once you have tried and used GOTO, its VERY difficult to go back to manual nudge nudge nudge to keep the object you have spent time finding, in the eyepiece....

If you also want to "share" the scope so others can look at the target too, the scope will TRACK it so it will stay there for as long as you want it to.

If you want to take some (less than 30 sec shots, or video) using a webcam or other camera, then GOTO with tracking will let you do that.

So, my opinion (if you havent already guessed) is GOTO, well worth it.

Cheers

Chris

Screwdriverone (Chris) · #6 22-01-2012, 06:39 PM

Quote:

Originally Posted by EricB

Thanks very much Stu and Brian.

The Astra is comparable in size to the Corolla. Stu if it's not too much trouble, it would be great if you could give me the measuments.

So far I have very good deals at Andrews Comm. From what I can gather they seem the cheapest in Australia. Are there other dealers I should be aware of?

Eric

Andrews is fine to deal with Eric and at the moment, I think they ship Skywatchers free to Australian locations, so thats a bonus....

I bought my 12" dob and my HEQ5Pro with 8" reflector from there and I am quite happy with both, as well as the service etc.

Cheers

Chris

Screwdriverone (Chris) · #7 22-01-2012, 06:45 PM

Oh, one more thing in favour of the goto Eric, if you accidentally (or on purpose) move the scope away from what you were looking at, it doesnt forget where it is, so you can simply press ENTER on the hand controller and it will go straight back to the object you were on.

VERY cool as I used to spend AGES getting an object into view and then someone (usually me, or the wind) would move or bump the scope and I would have to spend more time getting it back on target again and then get frustrated that it wouldnt stay put for long....quite annoying after a while.

Also, the 12" is quite a big bugger, so carting it around is hard (I am 6 foot 9 with no back problems but it was a lump even for me).

For that extra portability (and a bit cheaper too) the 10" will be more than adequate to go DEEEEEEP, I dont think you will miss the extra aperture as I have gone from a 12" manual down to a GOTO 8" and am quite happy with the views as I can spend MUCH more time at the eyepiece than I used to.

Hope this all helps, sorry for waffling....

Cheers

Chris

Vegeta (Ibrahim) · #8 22-01-2012, 06:59 PM

hi, I own a 12" dob and am really happy withe the results. my mate owns a 10" skywatcher goto dob. iv'e looked through both. The difference is there, but its not like the difference between night and day. the goto was handy on his dob as it kept the image centered as we shared the scope, but i personally prefer manual as i enjoy the "hunt" for the object i'm viewing and it sort of defeats the purpose. don't get me wrong though as the goto is still a handy feature as the traking is extremely useful.

hope this helps, clear skies

AG Hybrid (Adrian) · #9 22-01-2012, 07:26 PM

Id go for a manual 10" and then with the rest of your money get some decent eyepieces. I have a 12" and I find that quite often I cant be bothered taking the bugger out and setting it up. The portability of a 10" is actually substantial compared to the 12". I often wish I had the 10" instead. You really don't give much away in the view at all.

If you have an iPhone or a Android smart phone. Buy Sky Safari Plus for like $15 and use it as a sky atlas to find stuff. Don't need any of this goto malaki unless your a serious planet, double star and planetary nebula observer.

Besides a 12" in the city is crushed by a 6" at a dark sky site. I know this because I have both. Still the 10" will show you lots. Open star clusters and any to about mag 7 will be cake. At a surface brightness of Mag 7+ the individual stars in the clusters are Mag 12-14. A bit tough in the city. Some bright nebula's can be seen too with a filter. I am able to pick up some of the brighter galaxies with the 12". Ive seen Mag 10 galaxies in the Fornax cluster from where I live when they are at zenith. So the mag 9 stuff should be doable in the 10". I also live right in the middle of Sydney.

So try a 10" take it to a dark sky site as often as you can. The views will keep you occupied for years to come. Also if you get a skywatcher 10" it will fold up like an accordion.

I hope I have made your decision even more confusing.

Shark Bait (Stu) · #10 22-01-2012, 07:53 PM

Hi Eric,

Back with some dimensions for the 12" Collapsible GoTo Dobsonian.

Quote:

Originally Posted by EricB

The Astra is comparable in size to the Corolla. Stu if it's not too much trouble, it would be great if you could give me the measuments.

Eric

Optical Tube Assembly (OTA):

Fully Extended - 1400 mm
Collapsed for Transport - 925 mm (1025 mm with packing at each end)
OTA Diameter - 365 mm
OTA Dimension including frame for extension rods - 400 mm Max
Focuser Assembly - 125 mm protrusion from face of OTA

Base:

Height - 820 mm
Diameter - 640 mm

Packing Foam Blocks:

Length - 495 mm
Height - 245 mm
Depth - 145 mm (a 95mm moulded recess is cut into the depth for the OTA)

This scope is a heavy lump, but I can move the OTA / Base in stages and then reassemble without any assistance. Hope these dimensions help.

EricB (Eric) · #11 22-01-2012, 09:25 PM

Thank you very much every one. It much more advice than I expected (thanks Stu for the dimensions).

The GOTO functions as described by Chris sound very appealling. I am not exactly a model of patience, so the easier it is the better.

At this stage, I think I stick with my initial impression: SW 10' GOTO, but I take Adrian's point about the quality eye pieces.

Thanks again. I sleep on it for a little while and let you know how I go.

Happy sky watching!

Cheers,

Eric

EricB (Eric) · #12 23-01-2012, 08:07 PM

Hi there, I have one more question, if I may:

What important accessories should I get with the SW 10' goto? It comes with two eyepieces. What additional ones should I get? Also, should I get a light shroud? ( that's two questions...)

Thank you in advance for your advice.

Cheers,

Eric

sopticals (Stephen) · #13 24-01-2012, 09:21 AM

Add a 2x Barlow. GSO produce very good, inexpensive, quality barlows. I have all three of theirs available: 2" ED 2x (this has a 1.25" adapter), 1.25" ED 3x, and a standard 1.25" 2x. All of these work well with my 14" f5.1 Dob. A great way to double/treble your range of available magnifications, and at the same time preserve eye relief.

Stephen

AndyK (Andy) · #14 24-01-2012, 10:58 AM

Quote:

Originally Posted by EricB

... What important accessories should I get with the SW 10' goto? ...

You may want to consider a collimator, particularly if you're buying the collapsible. My 8" SW flex-tube holds collimation quite well ... but it still needs to be done.

jjjnettie (Jeanette) · #15 24-01-2012, 11:29 AM

Added extras....a collimator and a good barlow. I agree with Stephen, the GSO ED barlow (make sure it ED) pairs up very well with the eyepieces that come with the scope.
Down the track, if you decide to invest in some high end glass, upgrade to the equivalent barlow.

EricB (Eric) · #16 24-01-2012, 01:08 PM

Thank you very much. So what about a light shroud (I think it's the right term) to cover the gap when the telescope is open? Is it useful?

Cheers,

Eric

erick (Eric) · #17 24-01-2012, 01:28 PM

Hi Eric.

Yes to a shroud - but you would be able to make up one with a bit of design work and a friendly person with a sewing machine.

I think there are three purposes for the shroud on truss or strut dobsonians:-

1. To prevent extraneous light from finding its way to the eyepiece leading to loss of contrast and strange reflections.

2. To reduce dew formation on the primary mirror

3. To protect the mirror from damage when do do finally drop something between the trusses or struts.

Shark Bait (Stu) · #18 24-01-2012, 01:45 PM

Yes, a light shroud is nice to have but you can get away with not using it in the short term. The shroud assists in preventing 'stray' light finding its way into the light path of the object being observed. A shroud will also assist with helping to prevent some dew build up on the mirror surfaces with the added benefit of preventing people from dropping / spilling items onto the primary mirror at public observing events.

I ended up making my own with some matt black elastic material, velcro and some corset boning purchased from a local fabric shop. When I asked for the material and told them it was for a shroud, the staff thought I was preparing for a burial. Some Goth's had picked the same fabric for that exact reason a few weeks earlier (I am not a Goth).

EricB (Eric) · #19 24-01-2012, 07:36 PM

Thanks Eric and Stu for you advice. I think I will get a shroud. As I am not handy with the sewing maching ( nor is my mrs), I will need to buy a ready-made one. Do you know where I could get one?

Also Andrews doesn't sell online, is that right?

Thanks,

Eric

Shark Bait (Stu) · #20 24-01-2012, 07:58 PM

Astrozap make light shrouds for Sky Watcher Collapsible Dobsonians. I know that Sirius Optics sell this brand and would be surprised if the other retailers did not carry them.