Which Dob do I need - help.

[Ainsley]

Im now close to buying a Dobsonian but just need some advice. Im going to get the largest I can afford - 12, 14 or even a 16 (if it will fit though the door).

So that should get me a big apeture.

I also plan to use it to take pictures at a later stage as well as just looking, so am I correct in assuming I need the ability to track objects with it. If so that would mean I need to buy the Go-To type ?

I imagine long exposures would be needed and you cant track by hand.

But there is a big jump in price for Go-To capability. I dont mind hunting round the sky to learn the craft manually, but if I want to take picutures as well later on I might need Go-To in order to track them so they dont blur.

Any advice will be appreciated.

Thanks.

[Moonshane]

I am not an imager and purely observe visually with manual tracking using more often than not a 16" dob. Despite the above, I can advise that the general consensus seems to be that for imaging anything other than moon and bright planets a dob is of little use even if it tracks, assuming you want images of good quality.

For that you'd need a good quality equatorial mount along with a small refractor or newtonian, guide scope and camera of some kind.

Others will advise on this that have forgotten more than I know.

As for a large aperture dob, if you can handle the weight etc then there is nothing better for visual observing in my book.

[Ainsley]

Cheers, I was only thinking of taking pictures of the Moon / Planets initially. The picture taking would be an extra to the experience, which for me would be just viewing.

But why would the Dob not work for pictures of things other than the Moon / Planet ?

[Moonshane]

Generally for longer exposures, an alt-az mount like a dob is not suitable as you get problems with field rotation. You need an equatorial mount of some kind (which could be an equatorial platform if very accurately made). Most imagers seem to use small ED/APO refractors for deep space imaging but I am edging toward the cliff of ignorance now so I'd await other responders more experienced with imaging.

[Ainsley]

OK, but for Moon / Planets can I assume it would be fine ?

[Moonshane]

Yes indeed. Most use a small adapted webcam (again I know very little about what they do). Personally I really cannot be bothered with electronics at the scope - I just want to observe. I took some moon shots once but felt the camera was 'scope-hogging'!

[swamp thing]

Is this to be your only scope?

Will you be using it from home?

Can you simply wheel it out to use?

These are questions you need to give some careful thought to before ordering a large scope.

Regards Steve

[umadog]

Forget about imaging with a Dob. You'll get crappy images and will have to work hard for them. It can be quite tough to debug a Dob's goto mount in order to get tracking good enough for AP, so I really wouldn't recommend such a set up for photography. Even for the planets is may well be more hassle than it's worth.

I also don't recommend buying the largest you can afford. I have a large scope and I know very well what owning one involves.

Beginners have an exaggerated impression of what aperture can achieve. You read this thread as cautionary example: http://stargazerslounge.com/beginners-help-advice/181183-cant-see-much-through-my-new-c11.html You think you're going to see vastly more through a gigantic scope but the truth is that an 8" or 10" will show you most of what you can see through a 14" or 18". The smaller scope will have a nice wide field of view, which the bigger one won't have. I prefer how the veil nebula looks through a 10" than an 18", for example.

It's very, very, important that your first telescope is something that's quick to set up and isn't a hassle to deal with. If it's a hassle, you won't use it. Most people with a >12" scope also have a smaller scope to back it up because the big scope can't do it at all and it takes a while to set up. Consequently, it makes no sense to buy the big scope first. Test the waters with something smaller.

Finally, you should be clear that setting up somewhere dark will make much more difference than aperture. Our club has a 25" in skies that are on the borderline between rural and suburban. When I take my 10" to a dark site I get far better views than what can be provided by the light-pollution hobbled 25".

[dtr42]

can only agree with umadog got the 8" dob and it seems to be excellent [apart from mars ,can never seem to get it clear enough] but it's easily transportable ,quick to set up and pretty good at what it does .in saying that would love a 16" dob myself:)

[Ainsley]

Hi Swamp thing / Umadog,

It will be my only scope.

Most of the time I will use it from home, but have a place in Corsica where I drive to most years.

I will wheel it in/out of the garage / spare downstairs room into my large garden (which is quite dark)

I do have a large van and can transport it easily.

There are two of us, so moving it in / out will be done by both of us.

Id not thought of the field of view in the way you describe it. So would the planets look better through an 8" than a 12" I will read the thread you linked to.

So hopefully the practicalities are sorted, or do you think Im missing something crutial. What I want to avoid is buying something smaller and soon deciding I want to upgrade. Id rather start off over scoped than underscoped.

[swamp thing]

Hi Swamp thing / Umadog,

It will be my only scope.

Most of the time I will use it from home, but have a place in Corsica where I drive to most years.

I will wheel it in/out of the garage / spare downstairs room into my large garden (which is quite dark)

I do have a large van and can transport it easily.

There are two of us, so moving it in / out will be done by both of us.

Sounds to me like you've got the basses loaded.

Go for it.

Your first upgrades gonna be something I wanna see though.

Maybe:

32_inch_f36_telescope

Regards Steve

[umadog]

Planets will look good through any >8" scope with good optics.

You're right about not wanting to buy too small then hankering after an upgrade. I totally agree with that notion. A 10" is a very nice sized scope: it's not a "small" scope by any stretch.

You can see a vast, vast, amount with such an instrument. A larger scope isn't so much an upgrade but a complement to the smaller scope. Given your set up you could easily manage a 12". Most mass-produced scopes larger than 12" become excessively heavy and bulky. Larger scopes from premium builders are lot lighter and easier to manage. For example, Webster's 18" (the scope manufacturer linked to above) weighs substantially less than Orion's mass-produced 14" scope.

My suggestion is that you go for a 10" or 12" now and then shoot for a 16" to 20" non-mass-produced scope later down the line if interest still holds. You'll end up with a nicer scope that way.

[Ainsley]

OK, I will look for a 12" and ignore my lust for 16" as you suggest. But do I really need the Go-To variety ? Can I get OK pictures without it if I cant track the planets ?

Im happy learning to look for the objects, but again I dont want to be upgrading a few months later.

[umadog]

Hmmm... Good question. I'll tell you my experience and hope that helps. My larger scope has GoTo and tracking but I observed for years without until I got it. I don't take photos but I really like the tracking for planets. It's much easier to see detail. I hardly ever use the GoTo, though. My drives can be engaged and disengaged in a few seconds so I star hop then flip in the drives. Star aligning only needs to happen once, at the start of the night. When the drives aren't engaged the scope feels like a regular Dob. I think I would be less keen on the system if the presence of the drives disrupted the feel of the scope when they're not engaged.

The other option you have is to build or buy an equatorial platform. e.g. Equatorial Platforms: Home Page The advantages of those is that they can be added at a later point, they preserve your scope's motions 100% and they compensate for field rotation. I have seen some very good DSO photos taken on a scope with such a platform but achieving the results seems very challenging technically. You're much better off learning with a more standard AP rig.

Photography of any sort is pretty hard with a Dob because it's not easy to achieve nice results. This page will give you some idea of what's possible with fairly standard gear and a reasonable amount of effort: Astrophotography with a Dob - IceInSpace

[Ainsley]

Umadog, thats a great website that explains it very well.

So if i summarise it correctly:

• Planets / the Moon move through the FOV, but they are bright, and so only need an exposure of say 1/30s to 1/1000s.
  
• Therefore photos of Planets / the Moon should be OK.
  
• Given Im a beginner, the photos will be secondary to my experience, I reckon whats possible is good enough.
  
• Its only DSO that are not really possible with a Dob, I can live with that.
  

So I can, according to that site, take shots of the Moon and Planets, for normall viewing I can just nudge the scope.

Mmmm, seems like Go-To is a luxury then. A £500 luxury for say a 12" scope.

[devlin]

Hi all this is my first post iv got a 12 inch Orion xti dob great for looking but you need to track to get good images. I have been a avid photographer for a long time mostly close-up and macro and you need to look at the f rating of the scope the higher the f stop rating the better the depth of field the lower the f rating the more light but the shallower the depth of field. As one of the previous posters said a 10 inch scope will give you better images but you need longer exposure times so accurate polar alignment and tracking is crucial. That said where there is a will there is a way but a big scope could turn out to be a rod for your back.

[knobby]

I strapped my Nikon D300 to my 150 dob with a 2x Barlow and t ring

the hardest bit I found was focusing, that said I have taken a moon pic I'm happy with, tried Jupiter but achieved very little detail.

for focussing look at getting a Bahitov mask ( I suspect that's probably spelt wrong )

Good luck

[littlebeagle]

I have an 8" dob and it's more than enough for me, unlike most who hanker after more appeture I want a smaller scope (to compliment it not instead of). When you take into account set up and cool down times for an 8" scope sometimes in the UK it just isn't worth it unless it's going to be clear for several hours.

Probably going to get a 5" mak next year for those nights when it's a bit cloudy but some observing can be done.

[umadog]

devlin, remember the f-stop thing is different for astrophotography because you're focusing at infinity so depth of field is irrelevant. Basically, the brightness of the image is proportional to the angle subtended by the objective when viewed from the focal plane. The focal length determines magnification, of course. So a smaller faster mirror can potentially produce an image the same brightness as a larger slower mirror. The difference between the two will be the magnification.

Ainsley, yes what you say is the case. Remember that you take many short exposures of the planet, pick the nice ones when seeing is good, and stack them up. At a pinch you can get away without tracking to do this. Tracking is a nice luxury, but when you're starting out you will find there are many expenses: eyepieces, books, star charts, etc. You'd probably get more value for money building up a nice eyepiece set. It all depends on budget.

[Ainsley]

Thanks Umadog, does anyone know then if its possible to fit the Go-To on a normal classic Dob Skywatcher then. I could buy a standard classic now, then perhaps upgrade it to Go-To in a year or two if I still felt I needed it.

Or are they not retro fittable ?