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side by side mounting on a GEM

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#1 john 127

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Posted 12 May 2010 - 01:12 AM

I'm thinking about getting a tandem bar for side by side mounting on an AP 900. I'm interested in mounting a Mewlon 250s and an AP-155. I understand the balancing can be a bit tricky but after exchanging e-mails with Robin Casady he says it's pretty easy once you've used a pair of scopes a few times and have marked the position for them on the saddle. If the seeing not so good I'd end up using mostly the refractor. If the seeings quite good I'd spend more time with the Mewlon. Does the different viewing positions for each scope make tandem mounting less attractive than it sounds? It shouldn't take me much longer to set up both scopes on one mount, but it does to drag out two mounts. What's your experience with side by side mounting on a GEM?

John

#2 mclewis1

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Posted 12 May 2010 - 10:17 AM

I agree with Robin, do it a few times and mark the general locations and you'll have no issues. Particularly if you're a visual observer (I spend a bit more time on the setup if I'm imaging). I've been using a CGE with a tandem SbS bar for my C11 and TMB115 on most clear nights for a couple of years. I also change the setup to accommodate the refractor by itself (imaging) or maybe the C11 and C6 together (different positions than the C11 and TMB).

I find the observing flexibility of having two scopes available at all times far outweighs the couple of extra minutes I spend setting and balancing them. This assumes that I had a different setup in place the night before ... otherwise I just roll the mount/scopes out and observe (with no extra setup).

The only times I consider setting up two mounts are either when I've got a few folks over to observe with me or I might have a small alt az setup for a quick look at a planet or moon while the larger scopes are acclimatizing.

#3 john 127

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Posted 13 May 2010 - 12:19 AM

Thanks Mark, that's encouraging to hear. Did you use a Robin Casady set-up? When you change the set-up to use just the refractor do you take the whole set-up off the GEM and mount a single saddle or is your tandem bar set up with a third middle position?

John

#4 mclewis1

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Posted 13 May 2010 - 11:31 AM

John, No I wish I had the money for Robin's stuff. I use the ADM Losmandy SbS setup.

I have been just leaving the SbS bar in place and putting the imaging scope in one position and the guide scope in the other. Recently in an effort to simplify and reduce the overall weight of things when I'm imaging with the C11 I remove the SbS setup and put a small lightweight autoguider (based on a finder scope) underneath the scope on the Losmandy D plate. I've started to do the same thing with the 115mm refractor as well, but I haven't done much actual imaging with that setup yet.

I don't have any specific problems with the SbS when imaging other than the extra weight when using the C11 and the 80mm scope as an autoguider. When I go with the lighter weight setup I'm saving 12lbs or so (5lbs for the SbS, and the difference between the 80mm scope and rings and the 50mm scope and smaller rings).






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