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Dual Scope Mounting

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astroshot's picture
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Dual Scope Mounting

Hi Folks,

I’d appreciate your thoughts on mounting two scopes on one mount please.

In my case, I have a C14 and a TEC140 refractor for a Paramount ME.

I tend to only mount one at a time: C14 most of the year with the TEC mainly reserved for solar observing during summer months.

I’d appreciate the views of those who have two large scopes and how you dual mounted your setups please.

Thanks

Michael

Grant Privett's picture
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11" RASA and 114mm Newt

I use a 114mm Newtonian riding piggyback on the back of an 11" RASA V1 mounted on a Paramount MEII. So, way within the mount weight limit. Seems to work very well (the 114mm is used as a autoguiding scope), but I could envisage trouble if it wasn't being used in a roll off roof shed - as the slit of most domes would be too narrow.  

Xilman's picture
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Slit width.

My 120mm refractor / autoguider is mounted on top of the 400mm Dilworth, all inside a dome. As long as I am observing reasonably close to the meridian the scopes are aligned along the slit, not across it. Observing extremely close to the zenith results in the 120mm being hidden behind the slit shutter.

astroshot's picture
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Hardware

Thanks folks,

What hardware do you use for the piggyback mounting?

Regards,

Michael.

Xilman's picture
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Mounting

See http://www.astropalma.com/equipment.html

Shows it much better than I can describe it.

astroshot's picture
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Thanks for the link Paul.

Thanks for the link Paul.

Impressive setup!

Are they Parallax Rings on the 400mm?

Michael.

Xilman's picture
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Rings

I don't know, to be honest. They were there when I bought it and I have never tried to find out.

Lars Lindhard's picture
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la palma (off topic)

It seems that your observatory is (very?) close to the active volcano-area?

Do you expect problems with that?

Xilman's picture
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La Palma

No significant problems reported so far by the evacuees living there (SWMBO and I returned to the UK on 2021-09-22) other than perhaps 5cm of ashfall, the vast majority of which will not have settled on the dome. Everything inside is wrapped up well each time we leave because even 3 months of regular calima dust is tiresome to clean off the optics. The quakes have been far too small to damage anything.

The original vent is 3.1km due south. A subsequent one is about 500m closer to us. Both are the far side of a substantial ridge which protects us. Of course, if another vent opens up on the north side ...

Our plan is to return in February. Kevin and I will doubtless have a much better idea then.

(added in edit) See https://britastro.org/observations/observation.php?id=20211017_203048_82... for a recent image of the volcano and observatory. Inside the latest The Astronomer magazine is one taken a very few minutes after the start of the eruption.

Grant Privett's picture
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RASA

The RASA comes with a mounting bar along the top...

A R Pratt's picture
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Dual Scope Mounting

Hi Michael,

My C11 is mounted on my Losmandy G11. A local amateur has offered me his side-by-side bar similar to this model

ADM D Series Side By Side Bar With Dual Load Saddles - Rother Valley Optics Ltd

to add my 4-inch apo refractor. I haven't taken the plunge.

The separation between the OTAs provided by this specific bar is probably too small for your 'scopes.

Cheers,

Alex.

Nick Atkinson's picture
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Dual rig

You can use losmondy plates for sise by side. Probably a god idea to guide scope on top to reduce flexure.

Balancing Side-by-Side
In a nutshell, this is what you should do. If you are careful about following
this procedure without shortcuts or “guesstimates”, you will save a lot of
time and effort in the long run. People look at the procedure and say “Heck
with it, I’ll just wing it.” They usually end up sorry!

The key is preparation! You are balancing 3 systems. Balance
accordingly, and balance individually, first. Do ALL of this on a work table,

preferably with a helper.

1. Balance the first system.
a. Fully assemble one of the telescope systems you will be using.
This includes, but is not limited to:
i. The dovetail for that scope
ii. The rings or other attachment medium
iii. The complete imaging train including all adapters,
correctors, telecompressors OAGs etc.
iv. All guiding hardware if it will be on this system
v. Any finders or other devices
vi. Any special wiring harnesses or electronic devices
vii. Dew Heaters and controllers.
viii. ANYTHING that will be attached to this system!!
b. Adjust focus as close as possible to where it will be for imaging.
c. Place a dowel rod under the mounting plate to create a see-saw.
BE CAREFUL!!
d. Using the dowel rod as a fulcrum, find the exact balance point of
the system.
e. Mark the exact balance point with a piece of blue painter’s tape.
2. Balance the second system.
a. Basically, repeat the above steps.
3. Since the two parallel dovetail saddle plates are probably somewhat
offset, we need to next balance the side-by-side plate trio FRONT TO
BACK first.
a. This should just be the bottom transverse dovetail plate and the
two parallel saddle plates that are bolted on top. Nothing else.
b. Run the dowel rod lengthwise under the bottom dovetail plate. Try
to keep it parallel with the transverse plate.
c. Balance the trio of plates front to back on the dowel rod. d. Mark each saddle plate at the point where it balances over the
dowel.
e. Remove the dowel rod.
4. Attach each scope system. Simply line up the tape balance points on
each saddle with the tape balance points on each of the parallel
saddles.
5. Now place the dowel rod back under the bottom dovetail plate, but this
time it is perpendicular to the dovetail (parallel to the OTAs).
a. Rock the system back and forth until you find its balance point.
b. Mark the bottom dovetail with tape at the exact balance point.
6. Put the entire system into the primary saddle plate. This plate will have
limited adjustment because it is fixed by its mounting holes. The final
part of this is the trickiest.
a. Our saddle plates offer several mounting options. Look at the
setup in front of you and decide which set of mounting holes will
best serve your needs.
b. Mark the center of the mounting hole pattern that you will be using
with tape. This may not necessarily be the perfect balance point.
7. Place the dowel rod under the center of the mounting hole pattern..
8. Now, adjust the bottom dovetail in the saddle until the system is
balanced above the dowel that is in the center of the Dec mounting hole
pattern.
9. Mark the saddle and bottom dovetail so you know exactly where the
dovetail needs to be positioned.
10. Take everything apart, but DON’T LOSE THOSE TAPE PIECES!!
11. When you reassemble, simply line up your tape pieces and 95% or
more of your Declination side-by-side balancing will be done.
12. Final note: When balancing RA, more weight higher up on the shaft
is better than less weight further down the shaft. See the attached PDF.

I hope this is helpful. If the preliminary work is done carefully, you will blow
anyone away who might be watching you. Most experienced observers
shake their heads when they see someone trying to set up a side-by-side
system because they know how hard it can be to get the thing properly
balanced. It is very satisfying to put the pieces together and have near
perfection right from the get-go!

A R Pratt's picture
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Dual rig

Thanks Nick,

It's certainly a balancing act! That would be useful advice for the Equipment and Techniques News, if not submitted already.

Clear skies,

Alex.

astroshot's picture
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Dual rig

Thanks folks.

Nick, that procedure seems quite an effort.

At this stage, I'm thinking of leaning towards piggyback as it is easier to configure and adjust.

Problem is the cost of these rings and saddles...

Michael. 

Nick Atkinson's picture
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Parallax

Hi Michael,

I had a plate made up for me in order to top mount my Tak 85 on top of the rings for my main skope a 150, I used parallax to make them up for me. They are based in New York and the plate can be moved up and down to adjust the balance. I think this is much more stable and eliminates flexure

parallaxinstruments@gmail.com

Nick

David Arditti's picture
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Dual Scope mounting

See also my article in the Journal, 2019 December

https://britastro.org/journal-pages/20050

astroshot's picture
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Thanks

Thanks Nick.

Thanks David. I'll have a read of your article.