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Choosing 1st Dobsonion help...


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Hi guys,

Not sure if this should be in the beginners section – but since I'm definitely going to be a beginner with a dobsonian (and any kind of reflector), I'll post my questions here. :rolleyes:

About 3 years ago, I purchased my first telescope, a Celestron OMNI XLT 120 refractor – a good scope, but purchased without research (always bad), and before I found SGL. I soon found out that DSLR astrophotography wasn't really possible with the mount I had, and due to a small sloping garden, and some 3 storey houses around, decent polar alignment was tricky – and when done, still not enough considering it was a manual eq mount. :sad: (Buy Making Every Photon Count before buying scope - oops).

I have only gotten round to more serious viewing over the last year, but have struggled under my heavily light polluted skies – mainly I have viewed the moon, planets, clusters, and double stars – DSOs have been too hard to find mostly. I have enjoyed using a webcam and registax to capture the Moon, Mars, Jupiter, and Saturn, even though the images have been “lacking” :laugh:

So, as we head towards the longer nights, I have decided to sell my current scope & mount, plus some other gadgets, and go for a more simple setup, and infinitely bigger aperture – a Dob! I have spent the last week trawling through dozens of threads on here, and am mostly decided – but still have a few possible options

I would still like to do some basic webcam images of the moon/planets, but it isn't imperative – visual is my main goal. The telescope won't need to be transported – the furthest it will be travelling, is 10-20ft from my garage to garden – and weight/size won't be an issue personally. After my scope has sold, I will be left with a reasonable 5mm EP, moon filter, light pollution filter, UHC filter – all new scopes appear to come with 25mm and 10mm EPs. My budget is approx £650, although for something truly amazing I could run to £750.

My options appear to be:

1) Skywatcher Skyliner 250PX. £450 for scope, then £200 to spend on collimator, Telrad, Eps, filters, Wixey, etc. This was my original plan, and allows for plenty of goodies.

2) Skywatcher Skyliner 200P Flextube Auto. £599 for scope, leaving a little bit for collimator, and maybe 1 EP. I don't really like the idea of “going down” in aperture, but having tracking would allow me to carry on doing webcam images.

3) As above, but with GOTO. I have seen a couple of showroom/reconditioned ones for about £650. GOTO has always looked good, especially since I naff at starjumping on my eq (but never tried dob mount)

4)Skywatcher Skyliner 300P. I have found one online at £700 (although it could sell at any moment I guess). 12 inches!!! I know it is a monster, but the reviews suggest that the views from it make it totally worth it – and 12” is probably the biggest I could ever get (until I come into money). The downside, is that I would only be able to afford the scope and a cheshire – EPs, and gadgets would then have to wait.

5) ??? Something else I'm overlooking that would be large aperture, and no eq mount

Ease of setup is high priority, as I typically observe for 1-2 hours, once or twice per week – and just “plonking” the scope in the garden sounds really nice. With regard to the cooldown of the dob, my plan will be to put the scope outdoors before dinner, then start using it after dinner – is that a good/bad idea??

Sorry for the length of the post – look forward to hearing all of your thoughts :grin:

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I'd put aside the imaging thoughts for now since you say it's not very important to you. It'll just complicate things. If you plan on doing extensive planetary observing with it, then tracking (so the GoTo) is worthwhile. If not, then I'd suggest you skip it. If you're worried about finding things then you could go for one of the Orion Inteliscopes, which is push-to. Meaning that it has encoders and a computer but no drives. They work well enough but, like all elecronic gizmos, may need troubleshooting. I would go for aperture now if possible. You can always add the other stuff later over time. Either a 10" or 12" is great. Make sure you have good collimation gear for those as they're relatively fast scopes.

Your observing plan (scope out before dinner) is what I do too when I observe at home.

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Hi,

I had a 250mm flextube dob, originally auto, but upgraded to Synscan with a second hand handset. The flextubes are a fair bit smaller than Skyliner when folded up, otherwise there isn't much to choose between the two, both weigh and perform about the same.

When buying it, I looked at a 300mm Flextube as I was in two minds. The size of the 300mm wasn't just a bit more, it was a lot more and didn't think my missus would like it very much. Plus the logistics of moving it in and out (only 3 metres) was enough to put me off.

I keep my scopes outside in a very dry shed (summerhouse if I am been posh), and just keep the eyepieces and cameras inside, that way they are always roughly at temperature. I buy wooden blanket boxes to keep the scopes in, not only do they look good, but keep the scope protected.

The Skywatcher range of Dobs are good value for money and if you can afford one go for Synscan or at least auto-tracking and upgrade later. I got some excellent pics of Jupiter and Saturn and still haven't bettered them with my C11.

I sold my dob earlier this year as I went the opposite way to you in to DSO with an EQ mount.

I check the collimation once in a while on my scopes, it seldom changes and a scope I had delivered throug hthe post didn't even loose it's collimation. If money is tight, get the seller to collimate it and then try to borrow a laser collimator from a local once in a while.

Best of luck.

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Thanks for the replies so far...

The 250PX is still looking like the best option overall - the FlexTube option seems to be a lot more money, further increased by the need for a lightshield. I've looked at a few DIY projects to provide very rough & ready "tracking" - enough perhaps to allow for webcam imaging, without going to an 8" - just not sure if I'd actually get around to playing with various motors, wedges, etc though :laugh:

@todd8137 - My light pollution is fairly bad - not as bad as being right in a city-centre, but... Nothing below 20° is visible to the naked eye - on a normal night, there are 2/3 stars visible in the Great Square of Pegasus (6 on an excellent night in winter) - and if it's high up, M31 is visible with averted vision after 20 mins of dark. Through my 120mm, things like M42 look much better through my UHC filter, and some things are improved with a regular LP filter - and since I will soon be looking for more nebulae, I will probably get an OIII filter as well.

I did look at the GSO dobsonians from teleskop-express.de - their prices are pretty good (with shipping, £570 for standard 12", and £670 for deluxe 12" with 1:10 dual crayford) - but I'm not sure about ordering such an expensive and big item from Germany - and the couple of reviews I have read have involved people changing springs, knobs, etc.

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Hi

If deep sky observing is where you want to be spending your time and diffuse nebulae float your boat. Then I suggest a mobile set up ie one you can get to a dark sky. Nothing and I mean nothing kills diffuse nebulae faster than LP. Objects like the NA nebula just aren't visible from LP skies even through giant Dobs. Nearly all diffuse nebula disappear when LP appears. For diffuse nebula you would be better off with a small RFT from an ink black sky site than a huge Dob in a town.

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Hi,

I didn't realise that the Flextubes were more expensive. I started without a light shroud and then made one from sheets of thin black foam (Fab Foam) sandwiched on to a backing sheet (thin camping mat). Total cost was less than £10.

The only advantage of the Flextube is that it is small to store, in all other respects the PX series are just as good or better. The Flextubes aren't any lighter either as the truss rods are made of steel and are fairly thick.

I would suggest looking on the second hand market, either on here, but you need 50 posts to see classifieds, the dealers (some sell second hand and ex demo), Fleabay or Astrobuysell. Dobs come up all the time and represent good value for money.

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It is very unlikely that the scope will ever leave my garden - I don't personally drive, and most holidays I go on are to cities on the Continent. Compared to binoculars, my 120 has given lovely views - and even though LP is bad, I'm presuming that any aperture increase will result in much better viewing (even if somebody with a much small scope has better viewing in dark skies). Some of the reviews reckon that an OIII or Neodymium filter will overcome a significant amount of LP anyway (fingers crossed)...

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Larger aperture does help from LP skies, that is very true. Also, you can push OIII and UHC filters harder with more aperture. Just keep in mind, as Steve says, that once an object has been swallowed up by LP no aperture is ever bringing it back. As a consequence, big scopes really shine from dark skies not LP skies.

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+2 for the 250px, it would still leave you enough cash for some binoviewers ,collimator and a wixey. Personally I wouldn't bother with a telrad if you are going down the pushto route, as your setting circle and wixey, combined with skEye will find the object for you, but if you want to learn to star hop then get a tetrad.

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Hi guys - thanks for all the responses - the general concensus always seems to be bigger aperture... I've double checked all of the weights and sizes, and since I will be unable to take any scope to a dark site (not having a car) , any size of scope won't be a problem :tongue:

I've now found several reviews of the GSO dobs, and all of them have been very positive - so long as the primary mirror springs are replaced with Bob's Knobs Springs. Also, they come with a 1:10 dual speed Crayford, which I was planning on buying with the 250PX anyway - so the inclusion will "save" me about £130.

I've just sold some more non-astronomical stuff, and now have about £750-800. So, the plan is to go with the GSO 12" deluxe model (£670), which has the 1:10, and 32mm 2" Erfle & 9mm EPs. I will then have enough money to buy a collimator, a Wixey, a Telrad, and possibly 1 more EP. The tube weighs about 21KG, which I don't forsee causing any problems, since I have to carry 30KG and 40KG boxes at work :rolleyes:

Other nice gadgets can wait a bit longer, as I can get them in a couple of months (birthday), but I can't upgrade the actual scope at a later point... I'll get it ordered this coming week, and do a post once it's arrived. :laugh:

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I had the same refractor as you and sold it almost immediately after I bought a 12" dob. the views are just sensational through a 12" newt and virtually all objects are improved against the 120mm refractor. this caveat is removed if you make an aperture mask (I think you'd be able to use a 125mm mask in a 12" giving a 125mm f12 dobfractor (see http://stargazerslou...6-f4-dobsonian/). in other words, if you can handle the weight, the storage and the eye-socking views then a 12" dob will be a scope for all objects and be truly hard to beat (other than with a serious investment of cash or a bigger dob still (I have a 16" dob now)).

others may not agree but even in light pollution where we live (I am <9 miles from Manchester) the views of everything is better with more aperture. darker skies just make this even better.

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Thanks for the link, Moonshane... There's a massive list of things to make/buy at some point - for the time being, I'll be sticking to cheap and DIY stuff - then some more EPs and filters once the bank account recovers :grin:

My scope has now been dispatched, so am getting more excited already to see what it is like (although my 2 week weather outlook says cloudy and rain pretty much every day - just hope it is really wrong!). Whatever the level of LP, 6 times more aperture has got to have a massive effect - and maybe in the future I will get somewhere less polluted. I've lived in 13 homes so far, and this is the least light polluted - rather sad really, considering I've always liked the night sky...

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Congrats on the scope a 12" Dob is a monster scope that'll keep you busy for a lifetime of observing. The views will be great with it. I would seriously consider learning to drive, getting that big lump out to dark skies would be my goal if I was you. The difference with big scopes is truly astronomical :D sorry!

Enjoy

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Agreed with Steve. The 12" is a great instrument. Plenty of people buy a bigger scope then drop back down to 12" because it offers such a nice compromise between aperture and portability. Going to dark skies is a must too. Even if you can't take the 12" there, get some binos and go with those. It's be worth it!

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  • 3 weeks later...

I agree on the v12". Mine gets rolled out on a three wheel dolly, concrete floor in garage to concrete driveway. I set up in the shadow of my house and enjoy. Perhaps some sort of cart/dolly would be easier on your back. Good luck, Bob

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