Dobs info please.

[tasview]

Hi everybody,I would like to know how a Dob tracks objects,i can't see in pics how the movements work.These scopes look impressive and affordable.And also what does focal ratio really mean?What is the difference in viewing the night skies?

[ving (David)]

g'day tas view

dobs are basic alt/az, that is up and down/left and right. if the mount is smooth then tracking at low magnification is pretty easy. just a nudge here and there its all done by hand of course...

[ballaratdragons (Ken)]

Yep, Vingo is correct, but you can make a Dob track with the use of a Tracking 'Platform' or place it in an EQ mount. Neither is cheap to do.

But most people buy Dobs because:

1. They are cheap! More bang for your bucks: and

2. They love the Hunt! Hunting and finding is 70% of the fun.

[davidpretorius]

$1000 and below will get you a dob, another $1000 and above will get it tracking!

Are you coming ot lton anytime soon, maybe over the ,long weekend. Come and have a look at mine. It has been motorized, but it will give you a great fell for what it is all about

[Blue Skies (Jacquie)]

No one has answered the focal ratio question so here goes...

Focal ratio gives you an idea of the 'speed' of the telescope, similar to camera f-stops. It is worked out by dividing the diameter of the mirror into the focal length of the telescope. An F-ratio gives a handy summary of how a particular telescope will form once you get a handle them.

The rule of thumb is that the lower the ratio, the wider the field of view in the eyepiece - great for photography, comet seekers and variable star observers. Also associated with low F-ratios are shorter focal length, which means less potential magnification. And in the past they were also more expensive, as more glass was removed to make the mirror and it is also harder to get the parabolising right. A downside in Newtonians of a short F-ratio is that the coma at the edge of field is often more pronounced. All parabolic mirrors produce some sort of coma at the edge of the mirror. Some people like me don't even see it, but I've met people who notice it straight off and hate it. It is also harder to get the collimation spot-on.

Conversely, a slow F-ratio will give you more magnification but a narrower filed of view, which is great for people who like observing the planets and planetary nebulae. For Newtonians it means they collimate easily and are often cheaper (closer to being a sphere so less work involved in parabolising), but you end up with a long tube that wont fit in your car easily.

[mickoking]

The great thing about Dobs apart from the value:aperture ratio is their simplicity. A coupla minutes and you are there under the stars observing and having a ball.

Nuff said.

[astro_nutt]

Dobs are easier to set up..just point and go!!..and they have a good fun factor rating..also the challenge of find objects is rewarding in itself!

[robagar]

Dobs are for people who can find stuff without relying on a computer to do it for them.

I'll go and hide now

[Starkler (Geoff)]

Originally Posted by robagar

Dobs are for people who can find stuff without relying on a computer to do it for them.

Not necessarily true if you fit your dob with a DSC

[josh (Luke)]

Dobs are cool. I had one {my first scope} was a 10". you move them by grabiing the tube with your hands and pushing/pulling and such. Great views through them but i had too much difficulty finding things and they are pretty big!
If youre thinking about getting into deep sky photography i wouldnt get one. Really think about what you see yourself doing in a year or so as time goes by fast and you may find yourself doing what i did and trading it in for something with a motor and maybe go-to.
They are great value though
Good luck

[tasview]

Thanks for all the info guys,i am finding out a lot of info off this forum.I can see myself buying one of these in the future,but at the moment learning with my 4.5 newt and binos.I really need to study the sky more so i know what i am looking at. Thanks for the offer david,i only ever seem to get to lonnie when i pick up daughters from airport,but you never know we might catch up one day.