Dual Rig

[Carole]

Further to discussion on other threads, thought I'd show you my dual rig set up.

Generally I have two different sized cameras but 3 different sized scopes, so I have had to work out which combination is the closest FOV and none are perfect.

This is the first rig I did using a side by side bar.  I got several images with it:  Rosette, Pickerings Triangle, Witches Broom, M57.  Note I was using the DSLR as one of my cameras when the photo was taken as I hadn't at that time acquired a 2nd Ha filter and filterwheel. 

However there were disadvantages:

1. I used guide rings so I could manipulate the 2nd imaging scope so that both scopes were looking at the same thing.
But my WO scope is a darn sight heavier than the ST80 I used to put in the rings, and it almost slid out one night when I was adjusting the bolts.  Also it's quite tricky trying to manipulate to get both scopes looking at the same thing.

2. I was sometimes getting a bit of flexure on the scope in the guide rings.  Guiding was spot on in the fixed scope.

3. Going to DSC meant only having the choice of one scope to take (SW ED120) or having to de-rig the dual rig.

4. Always a risk of pier clash using the side by side bar which did indeed happen to me the other night. 



So I decided to buy a Skywatcher Guidescope mount to mount the 2nd scope, and this time decided to use the ED120 as the main imaging scope, with the ED80 piggy backed on top of the SW Guidescope mount with the finderguider sitting on top of that. 

Impressions so far:
It was so much easier manipulating the piggy backed imaging scope into the same FOV.
I can probably remove the piggy backed scope and guider intact to go to DSC and with the guide Mount having a puck, hopefully the ED80 will go straight back into the same position when I return.
The guidescope is now set quite a way back from the primary imaging scope and the pier so more likley to get hidden behind the POD dome, so will have to use the Pod Zenith table more frequently.
Guiding has yet to be proven.  If all else fails I'll put the finderguider back into the SW foot. 
Had to use a 3rd counterweight, first time I have had to do that.  N.B. wasn't balanced when I took the photo.

[RobertM]

All that weight in the narrow vixen plate at the bottom, looks like a recipe for problems to me.  It could be that the location of the finder may end up being self correcting to a degree though.

Rigidity is the name of the game so guide scope rings are not a good idea for a heavy scope (been there) like the WO.  It would be best to fix the scope in position with tube rings if you ask me.

Robert

[Carole]

If I put the 2nd scope in fixed tube rings and BTW they don't do them for my WO scope anyway, the two scopes would be looking at different things, I have already tried that.  As far as I can see what I have done now is better than the guide rings as it is fixed but allows movement of the scope left/right and up/down so I can get them looking at the same thing.  I suppose one could try clamping the ED80 directly to the tube rings of the ED120 but I also wanted to have a system I could take apart for DSC without having to move things too much, with the puck of the guidescope mount I can just lift the ED80 out intact without having to undo the tube rings of the ED120 and it will go back in exactly the same position. 

I am unsure until I try an image if the guider is too far away from the axis of rotation, so I am prepared to move it if necessary.

Carole