Hoping to buy a large Dobsonian - any ideas?

[mikeknowle]

Hi.

I've never owned a Dob. and wondered if anyone can recommend a good place/book to read up on them?

I'd like to buy a large-ish Dobsonian (14"+) and have read good things about the Skywatcher 350P & forthcoming 400P - which look amazing and just what I'm after.

It would purely be for visual use, so no worries about camera/imaging/mount issues. Since the skywatcher has a collapsable OTA, I would also hopefully put it in my car when I am fortunate enough to work in places when the sky is quite dark such as Cumbria, Wales & Scotland that I drive to occassionally (from Birmingham)....I'll measure the boot opening this weekend to see what will fit!

Also I see it has a GOTO - no annoying nudging the tube every minute then! Fantastic!

Any tips/ideas most gratefully received....

Cheers

Mike

[Talitha]

Hi Mike, welcome to SGL.

When i was trying to decide which big Dob to get (got a 16" LightBridge), i 'Googled' the ones which interested me and then did a lot of careful research. Retailers list basic information, but online groups like this one and Cloudy Nights (USA) have members who used the scopes and were more than happy to share their opinions with me.

Btw i was hesitant about nudging too, but it took all of 60 seconds to get used to it.

[Capricorn]

Be sure that you will actually make the effort to use a 14+ inch dobsonian. They are not light and other aspects come into it, cool down and collimation. If 14+ and you can look into the eyepiece the scope has to be fast so needs better eyepieces.

There are more large dobs for sale in used sections then small aperture scopes.

[brantuk]

I agree with both the above. Do the research amongst those who own large dobs. And make sure you're prepared to put the effort into moving it to dark sites cos it's heavy. The 12" is about as much as I'd want to lift without it breaking down into smaller more manageable bits (like a LightBridge).

The auto and/or goto are very handy, but as with most "out of the box" dobs you'll want to mod the balance and friction to eliminate backlash and improve goto accuracy. I've used a manual 16" LB and the object takes a while to travel accross the view - as such nudge'ing is no problem.

I would suggest three essential accessories/mods for a "push to" version. Get an az setting circle for the base, use a Wixey for elevation, and either a good raci finder or telrad. These will transform finding of objects.

Or you can go nuts like me and get the lot lol. Oh and levelling feet will come in handy for both types. Hope that helps.

[Questions]

Best advise is see if you can see one in person, the size, weight etc will more than likely be the defining factor.

[brantuk]

Feel free to join the "Dob Users" group for more info/advice - click the link in my signature

[Talitha]

Best advise is see if you can see one in person, the size, weight etc will more than likely be the defining factor.

If i'd have seen the size of my Dob before buying it, it's likely that i wouldn't have bought it.

That being said though, you're absolutely right.

In my case, i don't need to transport it anywhere, and it's on wheels, fully assembled in the shed. If i needed to transport the scope anywhere, i'd have bought something smaller.

[JAO]

Hi Mike

There is a lot of very good advice in this thread. As a large dob owner my key recommendation is to try and see one operating in the flesh. These scopes are much bigger in reality and though you can glean much from internet research there is no substitute for having a go at using one. The spring star party at Kelling Heath (3hours max from Brum) organised by the Norwich Astronomical Society often attracts a lot of dobs. It might be worth trying to get up there on the main Saturday and having a look at whats there. Many scope owners will let you have a look at and through their kit. Such a visit can save you a lot of time (and money) and test out whether this is the sort of scope for you. Here is a link to the details of the event:

Spring Star Party

Also I completely agree with Talitha, moving a big dob about and tracking with it is very easy indeed once mastered. Also when you have learned the sky an experienced dob owner will often find an object pretty quickly often much faster than 'slow to-go to!'

Adrian (exhile from Birmingham under dark Norfolk skies)

PS If you do want to come the the star party seek out the Norwich Astro Soc big dob group on Red field, mostly home made instruments in the 14" to 20" class, some Light bridges and Flex tubes too, we'd be happy for you to have a close up look!

[brantuk]

I'll second that Adrian - a good manual dob user can beat me hands down finding stuff whilst I'm busy fiddling with a goto handset lol

[perrin6]

A 12" or 14" would give fabulous views of galaxies and nebulae under dark skies. I'd get the biggest I could handle, and at least one good quality wide field eyepiece for lowpower views - ooh fab - I look forward to hearing what M51's spiral arms look like without light-pollution.

[JAO]

Mike/Brantuk

I should also say that I think goto is great (I use it in my observatory) and I am not one of those 'anti goto' types at all. I think it is horses for courses and I know many folk who would not have stuck with astronomy without goto. I do on occasion use an NGC Max Digital settings circles (Mike- google JMI NGC Max or Wildcard Argo Navis -for more info) -'push to' as opposed to goto when I am struggling to find that faint target at the limit of my dobs capability.

All great fun!

Adrian

[Astro_Baby]

Bear in mind weight, even when broken down. The mirror box of a big dob can easily become too heavy for you to lift.

I tried shifting a 16" light bridge and it felt as if it were bolted to the floor. The weight goes up very dramitically even between 8 and 10 inches so you really need to get weights before you buy otherwise it may pack up small but be too heavy to lift and carry.

[kharga]

I used a 16" Dob last night with WPAOG and its base is HUGE!!!! But the views were ace!

[Peter Drew]

16" Lightbridge for sale on AB&S at the moment. .

[umadog]

Hang on... I don't think anyone has asked this yet, but what is the scope you're using right now? It would help to know this in order to calibrate advice.

Would a 12" be suitable? The reason I ask is because a 12" can be substantially lighter than a 14" yet the views through the two will be very similar. I remember when I was choosing, the weight difference between the Orion 12" and 14" was too large to justify the increase in aperture. You won't be disappointed with the views through a 12". I'd say either go for a 12" or head all the way up to 16". Which you choose to do will be influenced by what you've used before.

As others have said: do not underestimate the size of these things. A large Dob is wonderful but you need to be sure you can deal with it.

[mikeknowle]

Hi All. Talitha, thks for the welcome and to all for the excellent advice...I knew this was the place to come!

Umadog hit the nail on the head with the killer question on current scope - sorry I didn't make a signature line yet (will figure that out next!).

I've been looking upwards every since I can remember (too much time in the pram as a baby maybe?) and just love naked-eye stargazing. But when looking down, its through the eyepiece of Meade LX200 or LX90 (about 6 years now), and occassionally hook up a Canon 300D or DSI Pro.

Am studying Bsc. Astronomy p/t at the mo. which is excellent. In fact, I should be doing an assignment on KBO orbital period calculations now so this is nice distraction!

I'm building an observatory/office in the garden, so should have a warm room with an attached roll-off section where the meade will be pier-based and reserved for spectroscopy and photography. So there's the logic for the Dobby.....I really like visual wide-field views the most!

So the priority is the back-yard.....putting in the back of the car would be an added bonus but secondary. Based on what everyone has said......I'm still inclined to the larger size, but not so large as I need steps.

Brantuk, many thanks....I sure will click on that link and join the Dob group as you suggest. But the key is definately to see them in the flesh as pointed out. I'm going to astrofest next week for a look, but Adrian's suggestion to go to Kelling Heath starparty and see various large Dobs. in action is now in my diary. I'm in no rush....can't afford to make a mistake!

Anyway, those KBO orbits don't calcuate themselves so it's back to studies!

Thanks all.....

Mike

[brantuk]

Mike - if you make it to the spring star party at Kelling then do look me up and I'll be happy to show you round the SW 12". Adrians group will show you the larger dobs. Also I'll be starting a Kelling chat thread in the star parties section round the end of Feb start of March so feel free to drop in and say hi

[mikeknowle]

Thanks Brantuk, I sure will!

Mike

[iamjulian]

I cannot add anything further to the bit about making sure you realise how big they are. Mine is only small compared to what you are looking at, but it is still bigger than I thought it was going to be, even after having looked at many photographs.

What I would say is make sure you have a go with a dob before deciding whether the goto/tracking is an essential. I can see why people like it, but you soon get used to manual. Only three observing sessions in, I find myself nudging it without realising I am doing it. And as for finding objects to start with, the night before last, in the time it took the kettle to boil, I found 5 galaxies and a supernova remnant.

[JimB]

I second Thalitha. If I'd known the size of my lightbridge 16 I would have settled for the lightbridge 12. That said, one look through it and there's no going back.

[mikeknowle]

I cannot add anything further to the bit about making sure you realise how big they are. Mine is only small compared to what you are looking at, but it is still bigger than I thought it was going to be, even after having looked at many photographs

How very true! I'll be the one wandering around Kelling with a metre rule for scale, a note-book and a camera!

Mike

[John]

I had a look through a 20" David Lukehurst dobsonian at the SGL5 star party last April. The owner said that he had gone for the largest that was usable without the need for a ladder - I think it was an F/4 or something like that ??.

I saw M51 and M13 and the views were gobsmacking to say the least

Having owned a 12" dob I know that is the max for me with my current observing circumstances and even that did not get used as much as it deserved because of it's bulk. I've got a 10" newtonian now which I use on a giro-style alt-az mount and that's pretty portable - I can pick the whole lot up and move it around the garden with not problem. Needless to say the 10" is getting a lot more use .....

If you can put the scope in some sort of roll out / roll off situation where it's stored near to outside temperature then go for the biggest you can manage - the views are superb though a large aperture instrument

Do budget for good eyepieces as well though - large aperture, fast scopes need and deserve them.

[mikeknowle]

Do budget for good eyepieces as well though - large aperture, fast scopes need and deserve them.

V. good point - would you say e/p selection is similar as for SCT's?

Mike

[umadog]

It's true that faster scopes show up defects in poorly designed eyepieces. I've seen this with even my F4.9. For instance, I bought a 13 mm Baader Hyperion and had to return it due to astigmatism in the outer 1/3 of the field. Apparently these eyepieces work quite well on slower scopes. Similar story with the Orion Plossls that that came with the scope. Never use them.

Anything by TV will work well. I have a 14 mm 82 degree Explore Scientific which also works well. Pentax and Vixen are probably good too. There are lots of options so you won't have problems finding eyepieces, but you should make sure that you can return anything you buy just in case it's not suitable.

[tiwar]

16" Meade Light Bridge on buysell atm, i`ve just had my CC wrestled from me by my other half....

T x