Side by side mounting on a GEM

[5ash]

What are the balance problems of mounting two scopes side by side on an equatorial mount. I would like to mount my Ed 80 with my c9.25 side by side as it would be more convenient. What are the balance problems with this configuration? will it balance in all orientations of the mount?
I have two gso mounting pucks and thought I might construct a saddle mount using them and a vixen dovetail bar , it may not be sturdy enough for long exposure but should be OK for visual and unguided exposures.
Philip

[traveller]

Try contacting Nico13 (Ken), he has a very similar setup and will let you know all the in and outs of it.
Bo

[Nico13]

Thanks Bo,
I,ve PM'd Philip with a response but thought I'd post it here as well as it may be useful to others.

Quote

Hi Philip,

Yes I have done this and find that I can achieve balance without much trouble and without having to add extra weights.
The balance is OK in all orientations and I am able to swap my camera and eye piece from one to the other without upsetting things to any great extent so I'm very happy with the setup as it is ver useful like that in particular with the addition of focal reducers or doublers my field of view is quite flexible.

My Original setup was with Meade SCT 8" and the ED80 mounted on a Losmandy saddle plate and you can see this in this thread you will see the old setup and a new setup as described below.
http://www.iceinspace.com.au/forum/showthread.php?t=93566

I have now changed that to include an ST80 guide scope as my original guider was not good enough for very feint stars so I am very close to my weight limit for the mount.
Anyway as for flex on a side by side I think you would have problems if you were to use a vixen dovetail bar as the saddle as I think your C9.25 is gunna be a bit heavier than my Meade 8" because I am seeing flex with the ED80 with the piggy back ST80 so personally I wouldn't go that way I would wait until I had the funds fore the Losmandy saddle or similar.

I must mention that the setup pre the ST80 guider addition worked very well and the picture in the above thread is from the Venus Transit day, I was looking out from under my carport as the clouds were threatening all day, only saw about 15-20 minutes of the transit.

The new setup hasn't fired a shot as yet :rolleyes: due to our lovely weather down here in southern Vic :mad2:
The balance with the new ST80 added is still fine just a little sideways and for and aft adjustment and I can park it anywhere unlocked and just sits there so no probs there at all.

As both scopes are mounted to the Losmandy saddle with vixen dovetails I am considering getting a couple of the wider Losmandy ones (the saddle takes either) as I am using this for guided photography so I want it as solid as I can get it without going over the top.

I hope this helps with you choices. :thumbsup:

[traveller]

Thanks Ken, didn't mean to dob you in, but i was very impressed with your set up, not to mention the multichannel dew heater controller!
Glad you were able to share your experience with Philiip.
Cheers, Bo

[sheeny]

I have a side by side setup on my EQ6: C11 and ED80.

Its not too difficult to achieve good balance especially if you know where the balance point is for each of your scopes individually. If you do, front to back balance will be close when they are mounted in the clamps at that location and you'll only need to do a little bit of fine tuning front to back (RA axis level and scopes level).

Rotate to RA axis level and scopes vertical to check your side to side balance.

Once you've got it right, it shouldn't matter what direction the scopes point when the RA axis is level, it should balance. If it doesn't, but your side to side balance is good, then you must have one scope forward and one back of their balance points (balancing each other front to back). Move it to scope at 45° from horizontal (maximum imbalance if you are close to balanced side to side and front to back) and the direction of imbalance will suggest which way you have to move the scopes.

Al.

[Nico13]

That's OK Bo, I'm no expert but I enjoy sharing what I can.




Thanks for the input Al, this should see Philip in the right direction. :thumbsup:

[Poita]

I tried for months to get a good SBS setup with a 105mm refractor and the C9.25.
I gave up in the end and put a rail on top of the C9.25, I just couldn't get it solid enough for imaging otherwise.
But that is probably down to my own lack of skill more than anything.

[Nico13]

I can understand your frustrations Peter as although I haven't tried the new configuration with the ST80 piggy back on the ED80 I am already considdering a different setup where I may position the ST80 between the other two scopes to bring the C of G a bit lower and at the same time remove the flexing from the ED80 so it will be three in a line.

PS

Just had another look at that and I don't think there's enough room to go three in a row :question: oh well it was a nice thought anyway.

[5ash]

Thanks everybody for their input , I should be able to sort it out. Many thanks
Philip

[g__day]

Suggestion, get a 4" * 2" block of wood about a foot long and drill two holes about 5mm - 10mm deep with the largest drill you have (I used a 1" wide drill). Separate these holes by about 2/3 of the width of your cross bar )for me using Losmandy D rails (4" wide) that meant centre of cavities I drilled was 3" apart).

Now in each hole put the largest glass marble you can find (I used ones that were 1" diameter). This leaves you with a block of wood with two marbles of equal height (check this with a spirit level).

Use these two marbles as a perfect surface to determine the balance point of each component of your side by side set up individually - and mark these positions on your individual OTAs dovetails with a pencil. When you do this make sure you attach all the gear that will be on your OTAs - dew shields, cameras, focusers - even allow for cables if you can. So what we are attempting to do is find the balance point of each individual OTA.

Now place each OTA and all its gear in its desired dovetail of your side by side dovetail holder. Centre each OTA on the point of suspension you marked previously. Now with the fully loaded side-by-side set up - balance this on the marbles and mark the exact balance point. This is the spot you want to be centred over the top of your mount.

The two marble approach gives you a very effective and cheap means of finding the exact balance point of your gear and makes it very easy to balance the whole rig before you place it on your mount.

[Nico13]

Sorry but this seems like an awful lot of work just to check the balance point :question:

Option 2 get a knitting needle or similar and sit it on your kitchen bench.
Next sit your fully rigged scope on top of the needle so you can roll the dovetail forward and backward on the needle until it rocks over the CofG.
Mark the centre balance point as above, no drilling no marbles and nothing for it to fall off except a knitting needle. :P

[g__day]

That would certainly work - its just I don't knit :)

[Nico13]

OK I'll pay that one :thumbsup: