Dob Wobble

[mikeyggg]

Hi,Last night I had severe problems with my dob mount not staying where I was pointing it.It would always move half an inch or so especially at or near zenith, so i was trying to compensate for this by moving it a bit to far. Needless to say, this stopped me finding anything.Its a Celestron Starhopper 6".Now there's 2 clutch handles, one with what they call a "variable tension" washer, and another one with no washer.Not sure whether to just tighten one them or mess with both.Doesn't seem to be a method whatever I do.My question is, is this common on dob mounts and just something to live with?I got mine for £100 from David Hinds as an end of line ex display sale item, so I'm wondering if the mount is in some way damaged. (I'm not casting aspersions on David Hinds, had very good service from them.)I was using a new Baader variable eyepiece last night....but surely this shouldn't be to heavy for a 6" dob.Anyhow, any thoughts will be welcome.Thanks,Mike..

[kniclander]

in reality, Mikeyggg the celestron and skywatcher dobs are not premium products and it doesn't sound like there's too much wrong with yours. You can use the tension handle with the washers to adjust tension it sound slike yours might be a bit loose - what I tend to do (especially if I am using a really big e/p that unblances the scope) is keep one hand on the tension handle and when I have found what I want, just give it a quick turn to tighten it a little bit. I'd be surprised if there's anyting wrong with your kit as I'm not sure what could be wrong...

ps - £100 sound like a steal

[G1ZmO]

You should also make sure that the mount is sitting on nice flat ground. If I don't then mine tends to veer towards the point that's lowest on the plane of the mount. A spirit level helps when choosing where to put the mount.

btw if you like to leave the tension loose then another option is to stick a heavyish magnet to the tube and use it's location to counter-balance the eyepiece.

Cheers

Paul

[John]

My 8" Skywatcher dob had the same arrangement. The altitude bearings (the black plastic bits on each side of the tube) actually ride on 2 white plastic / teflon "pegs" (2 on each side - you could try some candle wax on those to smooth the motion. The tension handle without the special washer goes on the side of the scope away from the viewer, should be finger tight (no more than that) and should not have an additional washer on it (I tried that and found I lost some control of the altititude tension). With things set up that way I found that the other tension handle provided quite fine control - especially when I had my heaviest eyepiece (over 1 kg !) on the scope.

Dob scopes have usually needed some tweaking / trial and error to get the motions as good as they can be although I found my Skywatcher pretty good out of the box.

In saying the above I've assumed that your Celestron is basically the same mount design as a Skywatcher.

John

[mikeyggg]

Thanks for all those suggestions.Actually I think I may have a tendency to overtighen in order to make is stay still. Sometimes, the more I seem to tighten, the more it seems to have a tendency to move to where it wants to rest.Will try the candlewax, and also like the idea of the magnet.Very clever!Thanks,Mike..

[ZOG]

Not wanting to hijack the topic, but has anyone fitted adjustable legs (the kind you get on kitchen cabinets for example) to a skywatcher dob base. I was thinking of doing this to make the base easier to level when I have the scope away from home.

[ringz]

Hi Mike,

You should also know that the zenith is called the "Dobson Hole". This is because the nearer the zenith you get, the more difficult it is to point an AltAz telescope.

If it's any consolation an Eq mount has much the same problem when pointing at the pole.

Regards,

Martyn.