Dobs for beginners


Even though its Spring heading for Summer here in NZ and down in the south where we are, it doesnt get dark until well after 9pm, Telescopes are an often looked at Christmas gift.

Dunedin is lucky that we are a smallish city, and you do not have to go too far away from the city to get some amazing night skies.

Most people looking for a night sky telescope want to see the cool things, Saturn and its rings, the great red spot and cloud bands on Jupiter, Jupiters moons and a whole lot more.

Personally, if you are just getting into astronomy and want to find these things, a Dobsonian telescope delivers the best bang for the buck.

Ok i hear ya, the first question you are asking is what is a Dobsonian????

Well, a Dobsonian Telescope aka a ‘Dob’ is a reflecting telescope that sits on a box mount with a turntable to move it around, like this one. As you can see, it is a big barrel like telescope with the box supporting it. the scope is a reflecting teleDobscope, that means that light goes in the front, hits a mirror at the base of the scope, and then is directed out the eyepiece on the side near the front by a much smaller second mirror.

Because the mount is basic, a dob is a  very easy to operate, Place the scope outside, take the aperture cover off, insert eyepiece and move the scope by hand and your ready to observe.

The other advantage of the Dobsonians is that they are generally reasonably large aperture instruments.  Aperture is the size of the light gathering area, so the bigger the number, the more light it lets in, this in turn means you will see objects that are not so bright and harder to see.

I mentioned bang for the buck, a Dob is normally a pretty good telescope for not a lot of money. For example, here at Southern Cameras, we have 6″ Dob for $499 NZ, where as the 6″ Reflector which has the same type of optic setup as the as the dob but is on an EQ3 mount, is more than double the price @ $1099.

This price disparity is the same when you go bigger too,  an 8″ Dob retails for around $800 NZ, where as 8″ reflectors on EQ mounts are at least double.

Talking of styles, there are now a couple of different types of dob that are commercially available. There is the classic solid tube dob like the pic above, and Truss dob’s and Collapsible Truss Dobs.

Truss Dobs generally are in sizes larger than 10″ with some being being as large as 30″ apertures. Truss Dobs are popular in these larger sizes as the design makes them easier to transport and store, but also makes them comparitvely lightweight.

colldobSkywatcher is among the companies that produce collapsable type truss dobs, these collapsible truss dobs have the secondary mirror, focusser etc in one cell, and the primary mirror in a second cell with and they are held apart by tubes that for storage and transport, the secondary cell slides down to rest on top of the Primary cell structure. Then you simply tighten the locks down and lift the tube off the base and your ready to transport.

SkytrussdobThe full Truss dobs, (like the one of the left) are a big units, this one pictured has an 18″ primary mirror and stands  nearly 2m (6ft 5″) tall and weighs in at nearly 70kg when assembled.  These are for serious astronomers, who are hunting for super distant objects. These Truss dobs are generally 16″ and larger, there are many custom builders out in the market who will build to order, with some truly amazing specs. but some of these with primary mirrors over 24″ in diameter also come with a cost to match.

Recent advances in technology have also made some of these DCOLGOTOdobobs even easier to use with the inclusion of GOTO motor drive technology. GOTO is cool, on the side of the telescope mount is a hand controller, this allows you to enter an sky object lets say Venus, and it will automatically find Venus, and guide the scope there, then track Venus until you get bored or want to look for something else, so back into the controller and repeat. Sure this takes the fun out of randomly pointing the scope at the sky and having a look, but you can still do that with a GOTO scope. The pic above shows a Skywatcher Collapsible GOTO dob in both the  active and travel positions.

If you want a pretty neat DIY project, you can actually purchase primary and secondary mirrors, and most of the components to build your own telescope, there are a number of pretty good resources around giving instruction on how to construct a telescope, but probably one of the better ones is Jean Texereau’s how to make a telescope.

We have a couple of Dobs in stock right now, so come if you are in Dunedin NZ, come and visit us, Southern Cameras @ Musselburgh Pharmacy, 59 Musselburgh Rise, Dunedin and ask for Hayden



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