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on a dob, would 2 inches make much diff?


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A 12" scope captures over 40% more light than an 10" but is quite a lot larger and heavier to move around. I guess it depends on how mobile you need the scope to be and how much you value that additional light gathering.

I've moved down from a 12" dob to a 10" newtonian and on some nights I notice the slightly smaller aperture on deep sky objects but on others (more often to be honest) there seems to be no noticeable difference. Every night I use the 10" I appreciate how much easier it is to move around though :)

Edited by John
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This would on most nights go from my basement to the back yard. I just want to be able to see DSO's and at the very least know what I'm looking at. Maybe I'll just go with a 10"

Well any scope will show DSO's but, IMHO, they get a bit more interesting with 8" and above aperture. A 10" will show some fine DSO sights :)

If you have to move the scope around a lot then the 10" will probably get more use - or at least that's what I found.

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I found that a too large or heavy scope meant that on some clear nights it

didn't get used. I'm happy with my 10" Dob and it gets used a lot.

It's a case of finding what suits you best, not what suits someone else, and that's

not always easy.

Best regards, Ed.

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Magnitude difference between a 10" and 12" is 0.4. The 10" will show stars down to about 7.8 magnitudes fainter than you can see naked eye, the 12" to about 0.4 mag fainter than that. If your sky has a limiting magnitude of 5 you'd hope to see down to 12.8 with a 10" and 13.2 with a 12". This would apply only to point-sources (stars); with extended sources (galaxies, nebulae) the really crucial thing is the darkness of the sky, more than the aperture you use. No amount of aperture will show you M31 in the daytime. So you won't see much difference at the eyepiece between a 10" and 12", unless you're an experienced observer. The most noticeable difference between a 10" and 12" (other than cost) is weight:

Skywatcher 10" flextube (non GOTO): tube 15kg, base 12.5kg, total 27.5kg (61lbs) TELESCOPE SUPPLIERS - SKY-WATCHER TELESCOPE

Skywatcher 12" flextube (non GOTO): tube 21kg, base 18.5kg, total 39.5kg (87lbs) TELESCOPE SUPPLIERS - SKY-WATCHER TELESCOPE

I have an 8" f6 Orion solid-tube dob and a 12" f4.9 Flextube dob. If I want a quick peek in the back garden then I'd use the 8": I can pick up the whole thing (tube plus base) with one hand. It doesn't need much cool-down time, and if Jupiter goes behind a neighbour's tree I can move the 8" in no time. It rarely needs collimating (thanks to the small aperture and rigid construction) and if it does then a punctured film cannister does the job with sufficient accuracy (thanks to the relatively long focal length).

For serious deep-sky work I use the 12" which I transport to a dark site. I only take it out if I'm reckoning on a good few hours of observing. Once it's on the ground it stays there until I pack up: it's too heavy to move in one piece. I collimate it with a laser and cheshire (and align the finder) every time I use it. I generally use a shroud on it. It's a great scope and I love it, but I wouldn't recommend it to a first-time scope buyer. You see lots on the second-hand market from first-timers disappointed that they've hardly used it or find it too bulky. And there are lots of first-time buyers who are delighted with it: you've just got to figure out what's right for you.

A 10" is a sensible half-way house between 8-inch and 12-inch, but if you think you'll ever want a 12" then you might want to start with an 8" with a view to upgrading later. To gain enough extra magnitude to get the "wow!" factor you need to increase aperture by at least 50%, e.g from 8-inch to 12-inch (which gives a 0.9 magnitude gain). Whenever I upgrade from 12" it will be to 18": enough to make all the extra weight and expense worthwhile.

Whatever you get, you want a scope that doesn't feel too small or too big: then it'll be fun to use.

Edited by acey
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forgot to say earlier

the best scope is the one that you will use the most

so if you are in any doubts about shifting a 12" round then i'd say go for a small size, it's no good having that extra aperture if you find yourself thinking that it's not worth the effort of dragging it out and letting it cool down because the nights not going to be perfect -, far better to have 2" less but be willing to set it up just for an hours use.

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I got a 4.5 that I use lots of nights, and find that I spend most of my observing time trying to find a specific target, usually giving into just random star hopping. I want to spend the most of my time observing and not just finding. Do the electronic telescopes come with a way to be plugged into a wall socket?

Edited by Manok101
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You could get a 10" tube Dob and then mount the tube on an EQ6 with GoTo later, or you could get a Skywatcher FlexTube collapsible Dob with drives and encoders (i.e. either the "autotracking" or the "GoTo" version.)

If you get a version without any drives ( the "plain" Dob) then the upgrade kit to GoTo will be quite expensive, as it replaces the entire Dob mount (making it almost as expensive as a brand new scope).

Officially the "Autotracking" version can't be upgraded to a GoTo version, but that's because Skywatcher has made the drive/encoder combination a bit more robust on the more recent models, and they still want to sell some of the older stock as "autotracking" for the moment (there's quite a price drop), because something that tracks so-so is still more useful than something that does GoTo with little accuracy.

But the SynScan handcontroller can actually be bought (with a special cable) and connected to the Autotracking Dob. And if you actually make sure the balance is OK, the firmware is upgraded, some of the nuts are well tightened, the backlash is correctly punched in the controller etc. you can usually make even the older mounts GoTo successfully.

You're a bit on your own, though, if the GoTos don't work well, unless you can debug the problem with Teleskop Service (who actually sell the handcontroller plus cable for use on the Autotracking Dobs.) So there's certainly some peace of mind to be had by buying the GoTo version from day one.

It's easy to predict whether SynScan will like a given autotracking mount: if it tracks extremely well, an autotracking Dob will usually GoTo well with a SynScan handcontroller. If it tracks more or less but not very precisely, well, then GoTos are going to be even more so-so (if they work at all), and then the hand controller won't actually have been worth the money.

Edited by sixela
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One final question just how important is focal length, if I'm not interested in astrophotography?

Not that much, unless the scope becomes too short and coma becomes an issue. In general, you make it as long as possible to reduce aberrations, and as short as possible if you want wide field views.

And practical issues often trump all of that (my 400mm would be more than three meters long at f/8, making it rather "interesting" to observe objects close to the zenith; a 200mm f/5 will go on a HEQ5 mount but a 200mm f/10 would be rather impractical).

Dobs are usually as long as they can get away with while allowing you to observe flatfooted, larger Dobs (over 12") are usually shorter still for the same reason (although eventually even with an f/3.66 scope you will need a ladder, given enough aperture), Newts for EQ mounts are usually shorter to avoid making it more difficult for the mount.

Edited by sixela
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I've got a 6" Newt and the advice I got was not to bother upgrading to an 8", but go for a 10" or more (if I can easily move a 12" scope). One of my mates has a 12" beast and it weighs a ton and is awkward to move round. He's now got in installed in an Obsy (lucky erm, person). Having looked through an 8" with whatever % more light gathering power I didn't really see much difference. So for me, getting that extra 2" of aperture plus all that extra bulk may in the end make you think "won't bother tonight" more often.

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It's deffinetelly a good and wise decision.

Years ago I faced the same dilema and ended bying a 12.5" dob. The hard tube is heavy enough to make me think twice before I take it out of the garage, just a few meters for my patio. However, when I do that and I get a good clear night, I forget all those doubts.

In any case, I always feel that I would use much more often a 10 incher.

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I thought of another question, it's about the push to scopes I was wondering exactly how those worked? I know they dont have the mechanics to move it automatically to your target, so how do you know when you're at what you're looking for?

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Usually you can see it Manok. But mostly what you'll be seeing is faint smudges. You get a little more detail from 16" and upwards. Of course open clusters glitter like jewels in the sky, globulars you can resolve more stars than smaller apertures, you can split more doubles and see colour differences, nebulas have more shape depending on distance, and galaxies are smudges. Planets look great - and the moon shows considerable detail. :D

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I thought of another question, it's about the push to scopes I was wondering exactly how those worked? I know they dont have the mechanics to move it automatically to your target, so how do you know when you're at what you're looking for?

There's a display on the controller pad telling you in what direction to move both axes and how far you are off target on them. When the target is reached you just see 0.0 0.0.

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I fell into this trap as a beginner, I thought bigger aperture would enable you to see more so I bought a 16" dob.

I now know that it is true to some extent but 16" in a light polluted enviroment is not as good a a 12" under dark skies.

Dark skies is really important for DSO's.

When I take my scope to say Kelling for a star party it's another beast completely, I can see so much more and the contrast is increased by so much.

So my advice would be if you have dark skies get the biggest scope you can handle as you have no need to travel. If like me you live under light polluted skies get a scope you can easily travel with and try to escape the light pollution as much as you can.

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