Dobsonian

[wildlifesnapper]

Hi,

just been looking at some skywatcher telescopes and I've noticed the huge price difference between dobsonian mounted scopes and EQ mounted of the same size.

Are dobsonians easy to track objects with? ( just for viewing,not photography) I have used an EQ mount before and find they are straight-forward once set up, but never tried a dob.

What are the pros & cons?

Thanks

Neil

[Jolanta Zofia Nowak]

Originally Posted by wildlifesnapper

Hi,

just been looking at some skywatcher telescopes and I've noticed the huge price difference between dobsonian mounted scopes and EQ mounted of the same size.

Are dobsonians easy to track objects with? ( just for viewing,not photography) I have used an EQ mount before and find they are straight-forward once set up, but never tried a dob.

What are the pros & cons?

Thanks

Neil

I've been given the use of dobsonian mounted scopes before and have always found them to have the tracking problem which goes with any altazimuth. It's a pain, to put it mildly, but if you're not all that worried about photography, then you might tolerate it. A Poncet platform can go a fair way to resolving this.

In their favour is the fact that they are usually very stable. This comes from the weight/low c of g - but which in turn gives you a problem with mobility and transport!

All in all I prefer an equatorial for the sheer simplicity. You're one step ahead of things already.

[carlos_dfc]

Originally Posted by wildlifesnapper

Hi,
just been looking at some skywatcher telescopes and I've noticed the huge price difference between dobsonian mounted scopes and EQ mounted of the same size.
What are the pros & cons?

Thanks
Neil

the huge price difference comes down to the fact that a decent equatorial mount will cost as much - if not more - than the optical tube. Whereas a Dobsonian mount is far simpler, and cheaper to make.

Personally - I much prefer an equatorial mount, much easier to track.

At high magnifications, objects can really whiz through the field of view, and the constant nudgity-nudge that you have to do with a Dob, very quickly gets on my nerves. With a motorised EQ, you just find the object, and let the motor follow it for you - and even without a motor-drive, it's far easier to just slowly twist the slo-mo knob.

Another problem with Dobs, is that it is easy to 'lose' your target when changing eyepieces, especially at higher powers - so you have to back off the power, and find the target again.
With an EQ, if the target strays out of the FOV, a little twist of the slo-mo knob, and you're straight back onto it.

You also need a patch of flat, dry, land to set up a Dob - you can't just set a Dob up on the grass - even you find a flat place, the moisture in the grass is BAD for the composite chipboard that most Dob bases are made of - an EQ on a tripod can be set up just about anywhere.

Having said that - A Dob is the way to get maximum aperture for your money - so if that's your goal, and you can put up with the constant nudging - a Dob may be preferable FOR YOU over an EQ - it's a matter of personal preference.

Dob tip....
If you want to go somewhere and set up on grass (say - a campsite maybe) - take a paving slab in the boot of your car, and put that on the grass, under the Dob - keep the damp grass away from the Dob base.

[wildlifesnapper]

Thanks guys, very informative.

I did think the tracking with a dob. would be a pain compared to the EQ-mount and from what you say it is.I don't think I could put up with the hastle of the nudgeing bit compared to the ease of turning the knob.

Equatorial mount wins then (for me anyway ) just means a bit more saving!!

Thanks again

neil

[Boddie]

Is Dobsonian a brand or a type?

[Blackdog]

Originally Posted by Boddie

Is Dobsonian a brand or a type?

Have alook at this Bods Dobsonian telescope - Wikipedia, the free encyclopedia

I was going to get all clever and say they made sidecars for motorbikes; then I remembered it was Watsonian that did that

[carlos_dfc]

Originally Posted by Boddie

Is Dobsonian a brand or a type?

It's a newtonian reflector telescope, on a swivelling box-type mount - Technically speaking, 'Dobsonian' is the MOUNT.

Optically - a Dobsonian, and a tripod-mounted Newtonian are identical.
However - to distinguish between a Dob, and a tripod-mounted newtonian - astronomers tend to refer to the whole thing as a Dobsonian - or 'Dob' - and reserve the term 'Newtonian - or 'Newt' for the tripod-mounted style.

[Blackdog]

There are obviously good reasons for the two types of mount, are there significant differences in use?

[carlos_dfc]

The Dobsonian is the simplest (cheapest to make) possible sturdy mount - the scope goes up and down, and the whole base rotates left-right - you simply push the tube, to point at your target - and that's about it.
Because of it's simplicity and cheapness - it is the best way for a beginner to get the maximim aperture for minimum money.
None of the bells-and-whistles of more expensive scopes - just straightforward point-and-view - main disadvantage is the lack of 'tracking' (you have to manually nudge it to follow a star's motion across the sky)

With a Newtonian on an equatorial mount - the mount is designed to rotate and counteract the Earth's rotation - so when you find your target, it's just a matter of twisting the knob on the RA axis of the mount, and it follows the star as it slowly arcs across the sky.
Also - most equatorial mounts can accept a motor-drive, so that they will automatically 'track' your target across the sky.

Also - if you intend to do long-exposure astrophotography, you NEED an equatorial mount - an Alt-Az (left-right/up-down) mount like a Dobsonian - even if it is motorised and electronically controlled, cannot counteract an effect called 'field rotation' (as a star moves across it's 'arc' - it - and everything around it - appears to rotate) which will show up in a long exposure.
Because an EQ mount has one axis (RA - Right Ascension) aligned to the Pole, it can follow celestial motion without giving you field-rotation.

In short..
A Dob is cheaper, and easier to use, but is ultimately limited to simple techniques
An EQ-mounted Newt is more expensive, and has a steeper learning curve - but once you get used to it, it is far more versatile, and useful, to an jntermediate-advanced user.


However..
That's not to say that a Dob is only for a beginner - many advanced astronomers own Dobs - mainly because it's a cheap and simple way to get maximum aperture.
Personally - I'm not keen on the nudgity-nudge method of tracking with a Dob - but in order to get a BIG aperture, at a price I can afford, I'd put up with it...
(I'm seriously thinking of saving for SkyWatcher's new 300mm f/1500mm Dob)

[Blackdog]

Thanks Carlos. I've just had a quick look around the web, what an amazing array of toys you could have to play with

I had no idea about different types of telescope mounts. I'm more of a daydreamer than starwatcher. Best of luck with it though.