Counterbalancing an alt/az mount

[cajen2]

Before I begin, a disclaimer: I know nothing about mounts or go-to - I've always used dobs.

I've just bought a SW AZ GTiX dual go-to mount for my new (to me) Starfield 102. The specs say that the max payload for one side is 6kg. I weighed the Starfield at 5.2 kg with all the fittings (dovetail, rings, diagonal, finder and a medium-sized EP). The mount comes with an L-bracket for mounting another scope, giving a max payload of 10kgs with two scopes.

1. Is it a good idea to counterbalance the Starfield as it's fairly near the one-side weight limit?

2. I've ordered a Baader 1kg weight which is attached to a dovetail clamp. I've calculated that if I fit this to the end of the L-bracket, I'll get an effective weight of 2.5 kg. Will this help to ease the strain on the mount significantly or make no difference? I can also order another weight, giving an effective load of 5kg, which will all but balance the scope perfectly. Is that worth doing, remembering it's an alt/az mount, not an EQ and I don't do AP?

All advice gratefully received.

[Roy Challen]

I have no experience with the telescope or mount you mention, but when I had a Tal 100RS on a Vixen Polaris, I would balance it in EQ mode before putting the mount into AltAz. If I didn't do this, it would be fine, but it was much better if I did do this. More for system stability than anything else.

I also balance with my Altair Mini AZ and Skymax 90. Again, it's not strictly necessary, but it does work better like that.

So, unless extreme portability is the priority, yes it's worth doing.

Edited April 3, 2023 by Roy Challen

[Peter Drew]

Best to improve balance if possible.   🙂

[Franklin]

A side mounted alt-az does not need to be finely balanced like an equatorial mount does, as the azimuth axis is always level. Having said that, when mounting a scope which is beyond 50% of the recommended payload it is a good idea to add some counterweight on the other side. This weight does not need to be equal to the weight of the scope. I have an APZ with a payload capacity of 8kg, when I mount a small scope (about 3kg) I can get away with the supplied counterweight which is about 1.5kg but when I mount my larger scope which weighs about 6kg I will fit the longer counterweight shaft and use a 3.7kg weight. So it's still below the weight of the scope, but without it I think the heavier scope would be putting unnecessary strain on the axis and with it, it all seems to work much better, I can feel a difference in the slo-mos, so I'm sure the motors in your mount will feel a difference as well. I'd put 3 or 4 kg on it with the scope you mention.

[cajen2]

Thanks very much all. I think I'll try the 1kg at the extreme end of the bracket first and see if the mount sounds as if it's straining. I was a little worried about using much more as I'd be approaching the total payload limit.

[markse68]

If the bearings are up to it you don’t really need to balance the alt axis although it  does help reduce the importance of levelling the az axis- if that isn’t perfectly level then an out of balance alt axis will make the head want to swing under gravity. This loads the motors on a driven mount and makes it a pain to use a manual mount. I don’t usually bother with the counterweight on my manual mount anymore but setting it level then becomes quite critical

Mark