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What Size Tandem Bar?

If you are wondering what size bar you need, here is how to calculate it.

Desired bar length = R1 + R2 + C + 4"

First measure the outside dia. of your OTAs.

Divide the numbers in two to get the effective radius of each scope.

Add to each radius any extra for rings or other attachments that would come between the two scopes.

Add the radii together.

Add the clearance space you want between scopes.

Add 4". This is the distance from the center of the OTAs to the ends of the Tandem Bar when using my saddles. On each end of the bar, the center of the scope will be 2" from the end of the bar. The distance is similar with most setups. The Astro-Physics DOVE8 is about 1.75" instead of 2".

When you have a total, select a bar that is equal to or longer than your total.

12" Tandem12
14" Tandem14
16" Tandem16
18" Tandem18

Setup Ideas

These are just some estimations because I do not have actual measurements of all OTA and ring outside diameters. These are just a few ideas. There are many other possibilities. Smaller scopes can be used in any of these setups.
Tandem12 6" & 5" refractors 5" refractor & 6" Russian Mak-Cas, Mak-Newt, or standard Newtonian 6" refractor & 4" refractor
Tandem14 Two 6" refractors 6" refractor & 6" Russian Mak-Cas, Mak-Newt, or standard Newtonian Mewlon 250 & 4" refractor
Tandem16 C11 & 6" refractor, Mak, or Newt Mewlon 250 & C8 C14 & 4" refractor
Tandem18 C14 & 6" refractor C14 & C8 C11 & C9.25

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