Advice on dual rig options

[DaveS]

I now have 3 imaging quality scopes. In order of fl from long to short:

A TS 130 f/7 just arived.

A Megrez 90 with AFR IV. My standard rig.

A TS 80 f/4.4 six element that I' m still sorting out the tilt and spacing.

I've put two dovetails on the 130 so I can mount it on the DDM as a host 'scope then mount one of the others on it as a guest.

I only have one camera as yet so I'll have to swap over. The thing that concerns me is the balance, which is critical with the DDM.

 

I guess I'm thinking out loud, but if anyone has thoughts on the subject that I haven't thought of I'd be happy to hear the.

[Davey-T]

Always good to have a plan to keep you tearing your hair out Dave 

I'm planning on sticking the WO11FLT and WO Star71 on a dual plate on the 10Micron, one of the reasons I wanted a mount that didn't need guiding, it shows this setup in the instruction manual but doesn't go into any detail.

I had them set up like this before on the iEQ45 but it couldn't handle the weight.

There was a post today on the same subject concluding that piggy backed was better the side by side so we'll see.

Dave

[steppenwolf]

There are some potential issues with mounting two dissimilar weight instruments on a side by side mounting because they need to be offset from the centre line to obtain balance which I believe to be very critical on the DDM? This issue can be obviated by weight-loading the lighter instrument so that both instrument's optical centres are equidistant from the mount's centre line.

Other issues to consider pertain to the use of a driven domed observatory but if you don't have one of these then it won't be a concern.

[DaveS]

Yes, I saw Gnomus's very impressive 3nm Eastern Veil with the discussion on dual rigs.

Piggybacking rather than side-by-side does make pier collisions less likely, hence my thoughts. It also makes balance a lot easier to sort out which is *very* critical with the DDM, much more than I would have thought.

I'll be selling a couple of dual bars at SGL12.

Ideally I'd have one camera on the 130 and swap over on the other two, possibly a ZWO 1600 but I cannot justify the expense just yet.

[Davey-T]

I was thinking of getting another QSI683 but goodness knows how much they'll cost now plus a set of NB filters 

Dave

[carastro]

I use a dual rig mounted piggy back and it works very well.  

Options:

ED120 with ED80 mounted piggy back

ED80 with WOZS71 mounted piggy back.

I bought myself a Skywatcher guidescope mount and now leave it permanently attached to my ED80  so when I slap the WOZS71 onto it I know it is always looking at the same thing, then all I have to do is orientate to cameras. 

I found I had clash with the pier or tripod if I tried to mount side by side, and the balance issue was awkward too.  

Although it also worked I have stopped using the ED120/ED80 option as it means keep having to move the Skywatcher guidescope mount and re-orientating the scopes, plus it's slightly overweight for my HEQ5 which I use at camp.

I put my Atik314 on the WOZS71 and my Atik460 on the ED80 and the FOV is almost the same. 

HTH

Carole 

PS: Registrar is a must.  

 

Edited October 23, 2016 by carastro

[Davey-T]

Had this setup on the iEQ45 which worked OK  once balanced in three dimensions it was just a bit too much weight for it to handle, about 30lbs.

Dave

 

[DaveS]

Oh my word Dave that's a rig-and-a-half, and no mistake!

At some point I'll be looking at a Moravian 16200 for the 130, but the cost of 50mm dia Astrodons is a bit frightening.

Thanks for the point about Registar Carole. I hadn't thought about it but yes, more than just useful.

[DaveS]

Little and Large .

Here we have the 80mm f/4.4 mounted piggy-back on the 130 f/7 after balancing in RA and Dec. Don't be misled by the DSLR, it's only there while I adjust the spacing and tilt. I hope to replace it by an ZWO 1600MC in due course. I intend to keep the 130 / Trius as a constant, while swapping the small scope as needed, either the 80 or Meg 90, both with the ZWO.

And here are the coils of USB cables ready for tonight if it clears.

 

Although the mount has a built-in USB hub it's been giving me the run-around. If I can sort it out it will make routing much easier.

The mount also has aux power conections which I hope to use to power the cameras and dew control.

[ollypenrice]

What's the ultimate aim of the venture? Will you one day want to run two cameras simultaneously on the same target? If so, and one has a longer FL than the other, then you'd get away with a rough alignment between scopes if you cropped the short FL image to fit the long. However, that would be a shame because composite imaging can be great fun. Here you'd want the primary scope to be the long one and then have a good tilt pan adjuster to let you frame the widefield independently. This lets you drop in the high res for the bits of the widefield which need it most. We do a fair bit of that here, but using two mounts.

Is the balance critical for tracking performance or for security? Someone told me the DDM becomes totally frictionless if the power is cut, so an imbalance would send you crashing into the pier. Is this really true? If so I'd be thinking about some kind of soft buffering system because you're sure to get a power outage one day.

FWIW our dual rig is side by side with one scope mounted on a Cassady T Gad for alignment with its partner.

Olly

[DaveS]

Hi Olly

The ultimate aim might be to run two 'scopes at the same time, but in the near term it's to simplify the balance when changing between 'scopes. My thoughts (And I might be barking up the wrong tree (Or even just plain barking)) are to get the balance right on the beast, then swapping the small 'scopes only needs a slight re-balancing by moving along the secondary dovetail. It's also why I have one counterweight in the middle of the shaft. When I have all the cameras and spacing sorted out I'll put markers on to show the correct balance points. Balance is also why I've gone piggy-back rather than side-by-side.

Although there's no clutch / brake on the shafts there's enough "stiction" in the bearings that a *slight* imbalance won't send the scope crashing into the mount. However it is *very* sensitive to balance, even to the point of making sure the dew shield is fully open when balancing.  Fortunately there is a tool in Autoslew to help refine the balance by measuring the current needed to move the axis one way then the other. You're in balance when the two markers line up, and the current is as low as possible. Good balance is vital for the best tracking.