A question for Dobsonian owners.

[Gas_mantle]

Hi all,

I know this is going to be a stupid question but I'm going to ask anyway.

I've never owned or even looked through a Dobsonian mounted reflector and wondered how do users manage to move the scope slowly and accurately to maintain an object in the field of view (assuming it's not a goto scope) ?

Obviously with an equatorial or an altaz slow motion controls are used but presumably that's not possible on a Dob ?

Many thanks

Peter

[Peter Drew]

A well made, well adjusted and well balanced Dobsonian works so smoothly that manually moving it becomes second nature with a bit of practice. 

[DeepSkyBagger]

Hi Peter,

If the mount is made well, it will move very smoothly with even a slight push. One of the properties of PTFE is that it will run smoothly against another smooth surface and then stop. It takes just a small push on either axis to move the scope. There's no shuddering and no jarring.

Cheers,

Patrick

[Floater]

Get the target in view. As the target moves across the field of view, move (push, shove, or nudge are all words that are a bit too strong) the scope along. The more you do it the easier it gets.

I expect far more experienced Dob owners will be along soon. Some even have things like 'have I said I like Dobs', or 'Dob the builder' above their avatars ...

[John]

I think Patrick and Gordon have explained it well.

It's one of those things that sounds like it's going to be difficult but it's just not. You don't need to move the scope all the time to keep the object in the field of view. The technique seems to be to nudge the object across the field, let it drift a bit while you observe it, nudge it across again, and so on. Eyepieces with wide fields of view make the process a little easier but I know quite a few dobsonian owners who use orthoscopics with some success as well.

[Luke]

It's the same for me as Peter, I don't even really think about it.

I wait for the object to get close to the edge, then nudge it back to the "start" of the view.

[Digger1895]

As floater said most words like nudge seem a bit strong. I like it when the control is described as "buttery smooth", you really only need a slight touch with your fingertips and after a while you do it without thinking about.

[AndyWB]

Yeah, my dob isn't as "buttery smooth" as I'd like it to be - but nudging isn't a problem, even at fairly high power. It becomes pretty natural, as does judging where something has drifted off to.

[Charic]

The whole system is well designed well balanced and just works.  You select your target using the  finder scope (keeping both eyes open?) then view the target through the eyepiece. I hold the chin handle with my left hand and the Tensioner Handle with my right hand and just move with the target as required. If I select the 32mm EP there is plenty of time to view the target as it gracefully and slowly, slowly,  yes its that slow?  moves across my field of view. If I select the 5mm to view the Moon, I have to move the scope a lot quicker to stay on track, and when I see  satellites pass,  I  follow them  much quicker, no effort required, just practice with orientation.

 I didn't think the Skyliner  had any vices, but  I should point out that  the tensioner handle is designed to  be adjusted when  in use with the  right hand, due to the orientation of the telescopes construction. You cannot rotate the OTA  and set up for left handed operation, otherwise the focuser and finder will be inverted under the OTA, making use impossible, so maybe there is an issue with a standard  Skywatcher Dobsonian, that is, if you're left handed, trying to lock -Unlock the tensioner handle with your right hand, but practice will make you perfect. The Skyliner  is still the UK's most popular telescope?

[Dannae]

Hi Peter,
 
Great input as always from everyone.
 
Whether you 'nudge' or 'pull' the scope depends on which side the focuser is situated; I got used to the 'American' left-sided way of pulling the scope towards me though most European manufacturers put the focuser on the 'right (no pun intended) side' so you can nudge away from you with your upper arm. Having a handle like this helps (First picture on the upper tube ring):

https://sites.google.com/site/thedobsonfactory3/400mm-kompaktdobson
 
You can always buy an equatorial platform and this will allow you up to an hour of tracking before reset. It all depends on how long you wish to observe each object really.

Regards

Dannae

[EnglishNightHawk]

I personally really like the Dob design, sturdy and very easy to use! 

[Moonshane]

I put objects in the centre of field at lower powers but at say 100x or more I place the object to the right side of field and watch it all the way scross. It takes approx 4 minutes for an object to float across a one degree field and this is roughly the same as a 25mm plossl in an 8" skywatcher dob at 48x. Use the barlow for 96x and you have two minutes etc. You dont need to constantly keep objects on axis. Some do but I dont find it necessary.

[Paul73]

It does take a bit of practice at high magnifications though. And it is nvery difficult to steer for targets higher than 70°.

My dob is not buttery smooth. I could make it so with a bit if basic DIY and hanging a few weights off the back. But, even in its current sticky state, it really isn't much of a hassle.

Personally, I feel that the imperfect human element of piloting a dob, adds to the whole experience.

Paul

PS. I have no intention of changing my scope for anything other than a bigger dob (still manual).

[Mr Flibble]

I use a tracking platform. Its simple to set up under the dob base, and without needing to nudge it allows me to concentrate more on what I'm observing.

[Moonshane]

Good point about Dobson's Hole at the zenith but then you rotate rather than nudge. EQ mounts have the same issue near Polaris

[simmo39]

You learn to dance with your Dob very quickly, Use  walts and no teckno! lol. I luv mine!

[Charic]

........I've just inspected/serviced the Dobsonian, and noted some swarf from the three teflon pads that are 'stapled' to the lower section of the base unit. The swarf was statically sticking to the upper section of the base, so a quick wipe with kitchen tissue and the slightest amount of WD40 to help lift the swarf. Could have used water, but WD40 provides additional surface protection, not just lubrication. I also  polished the surfaces with dry tissue before final assembly. I  also needed to tighten one of the black hex-screw bolts that supports the upper cradle to the base unit. Everything else looked ok. Final assembly completed, works well.

[Gas_mantle]

Hi all,

Many thanks for all the replies, it's something I've always wondered about.

I remember about 40yrs ago when as a teenager I bought my first 'proper' scope,  a 4.5inch Newtonian on an altaz.  As a youngster it gave me many hours of pleasure but it didn't have slow motion controls and was a pain to use. Being a simple budget scope years ago it wasn't accurately mounted so trying to position it with any degree of precision was virtually impossible !

[rory]

Also, if you have a budget end dob mount like the Skywatcher flat pack style , it's quite easy to improve its movement with little modifications .

It's not something everyone wants to do , but with so many cloudy nights often doing modifications is often part and parcel of the hobby.

There's a few threads on improving movement and balance of dobsonians on the forums.