Dual imaging rig

Hi Robert,

I have a similar setup with an FSQ and a WO71 on a side by side saddle. I find balance is not a problem, on the contrary it almost seems easier as you can move sideways and for and aft to achieve balance all round. To help I did come up with a fine tuning mechanism in both axis , as especially laterally it's a bit of a pain to shift the whole setup. Laterally I achieved this by using a small clamp at the bottom of the saddle plate which can be moved and for fore and aft fine tuning I just move the guide scope in it's rings. Once you have balance it's worth marking the positions for future use as this cuts down the next setup considerably.

Achieving a similar field of view might be difficult if you don't have an adjustable saddle plate of some description. I tried it and it didn't work for me. In the end I got an Avalon X-Guider (it can take 5kg) which is really light and works for the WO71. It's quite expensive though and there are other beefier options out there for similar money so if mount load is not an issue they might be better.

I also have auto focus running on both scopes. Initially I was using an off-axis guider but this didn't work well as guiding is all over the place when focusing that scope which then affects subs from the other scope (and unfortunately there is no synchronisation in SGP - yet). So I went with a guide scope instead and now each scope does it's own thing and I only really loose subs during the flip.

Hope this helps!

I struggle to get my head around the geometry.  For example, some folks with only one scope on top of a mount get concerned about cone error.  With a side-by-side dual rig it strikes me that you have both scopes hanging out to the side of the mount.  One will be parallel (within the tolerances of the plates and saddles) to the main mount axis.  The other scope will be ‘toed in’ to a lesser or greater extent.  What effect (if any) does all of this have on the final result?  I don’t know, but I am hoping that someone will.

Michael Poelzl:
Hi Steve,I'm no expert and don't really know the theory behind it all but practically I've not had any noticeable problems imaging around 400mm focal length. From what I have gathered of others, cone error only really affect the pointing accuracy and not really tracking and it's flexture and field rotation can can cause bigger problems with a dual scope setup. There is an interesting article from Peter Rejto and his woes of trying to sort out problems with his dual rig including a Tec140 and a Tec180:

https://astronomytechnologytoday.com/2017/05/29/a-practical-automated-multi-camera-astro-imaging-system-design-one-mount-one-computer-two-imaging-cameras/

Thanks Michael.  I'll take a read of that article.