Gemini-Bar for Sky Watcher

[Astroblagger]

Just wandered does anyone use one of these for a two scope guide set up and how do you find it, does it do the job, is it rigid enough?

[E621Keith]

Do you mean one of the AstroEngineering AC694 bar? They feel quite solid and stiff, but after I got it, I found my 2 scopes arrangement too heavy for my EQ5, so I couldn't give more detailed comment on the bar's rigidity. There doesn't seems to be any flex between the two scopes, but the mount flexed a bit due to the weight.

[Carbon Brush]

I agree with Keith's comments. As soon as you put a bit more weight, or momentum (off centre weight) onto a mount, you really show it's limits.

But then again, the job of the guidescope is to correct the errors.

David.

[Astroblagger]

Iv got an heq5 and only plan to use a metres 72 and st-80 on it so should handle that hopefully?

[Carbon Brush]

Probably is the honest answer. The HEQ5 is quite a lump.

Remember though every part of the mount assembly has some flex somewhere. Right from tripod legs, through tripod to mount fix, through scope to mount fixing, through to the scope clamping. These all add up. Whether this matters depends on the amount of flex compared to the magnification you are going to use. Then consider if the guide method can correct the errors.

If you buy (or make) a dual mount bar with removable dovetail clamps, then you can drill & choose your scope spacing to suit your small diameter tubes. As the bar is made, you could put a couple of decent size reflectors side by side. Putting weight away from the mount centre causes more balance issues.

Using small refractors, you could even piggy back the scopes. The standard rings for the ST80 are far too flimsy to use as the bttom deck here. My ST102 has very flimsy rings. But the principle stands.

A test that I have yet to hear anyone do is to actually measure mount flex. That is set up a scope/mount on a solid surface. Then put a dial gauge, or ruler, or whatever on a stand next to it. Then put a bit of off balance weight on the scope and see how far everything moves.

Sorry its a long one, but I hope there is something useful there somewhere.

David.