working with 2 scopes setup, with a 1000mm focal lengh - Forums

Topic starter

May 23, 2021 · Edited: May 23, 2021

hi guys
i hope you are doing well!

I've done this question to Michal Taube, but I would like to share with the experts of this group too.

I am thinking of doing a setup with two telescopes. A 10'' newtonean skywatcher quattro to work in full frame. And another is an apo William optics 81mm, with the asi294mm (smaller sensor).

I have already done the pixel scale calculations and the field will be near the same, both with a focal length around 1000mm. But I can already see the immense challenge of this (the focal lengh and guiding). I have already both scopes (total payload with acessories around 20kg/45lb) , but my observatory is still under construction.

My mount is a ioptro Cem70 (payload 31.8kg (70 lbs) ) and I'm start to think about an upgrade to a cem120. Because I have the experience that Ioptron likes to lie a few pounds in the payload.

Could you give me a sincere opinion on that.

Thank you very much in advance.
Regards
Ricardo

Michael Taube

May 23, 2021

Hi Ricardo, I would gladly share some thoughts with you. When I was planning to build my dual scope setup, first I wanted to go with two 10" Newtonian, but after some initial drawing and calculations, I figured that the total weight of the setup was getting way above and beyond of the initially expected. In my case I was planning to get two big telescopes to work, it was extreme, and I ended up with two 120mm refractors. In your case, as I understand, you want to get one big scope and one small scope to work together, which could be a good working setup. I guess, you can place a smaller scope on top of the big one. It seems to me that you will probably encounter two issues, one is aiming both scopes to the same target with minimum losses of the imaging fields, and second is neutralizing flexibility problem. In my case to solve the aiming problem I ordered a custom side-by-side plate, which holds one scope in a fixed position and second scope in adjusted position. I can adjust the second scope in left-right and up-down directions, and I can rotate the cameras to match both scopes to the same angle. A second problem with scopes flexibility could be a bit more complicated, because in your case the scopes are very different. In my case I put a plastic strap around both scopes to hold the tubes tight and it worked. Without the strap I had an elongated stars from the second (unguided) scope images, I guide my setup with a 60mm guider scope mounted on one of the 120s using PHD2. I think you may try to guide your setup with the same external guider approach. I guess it should work if you will solve the flexibility issues, it is hard to tell if it will work or not unless you try it. As you can see I could give you more guesses than actual experience because my setup is so different from what you want to create.
One more advice, two scope setups could be bulky, heavy, and require an extra space in an observatory, so it might be a good idea to take this too into an account.

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ricardo leite

Topic starter

May 23, 2021 · Edited: May 23, 2021

Gosh, Michael, you helped me a lot and were very kind in the clarifications.
Thank you very much!

In fact, the flexion problem is the main one in these cases. I ordered a 3/8" thick losmandy dovetail, so as not to have problems with the weight of the two telescopes.

I thought about putting the apo on top of the tube. But then I disregarded the idea, for now. The tube will go to flex a lot, I think (it's a long 1000mm newtonean, although rigid carbon tube). It would take a pair of rings that would be very robust (and too heavy) to not cause any bending. And the guidescope, i think, would be a problem (bellow I explain). My dream, maybe one day, is to have a 10micron mount (guiding nevermore). Ideal mount to dual scope set.

I found your solution to have adjustments in one of the dovetals, in order to center the images in the same field very interesting!! Thanks a lot for this useful suggestion!

I read a very interesting article by Sara Wager, which can be of useful to everyone in this group as well (bellow). She encountered the same problems as you, with adjustments and centralization (you may have already read). An interesting thing that she says (maybe that interests you), is that she used a independent guidescope - a "third dovetail"

Her justification is very interesting. If one of the telescopes fails, the guidescope on top of it will also fails, and this will affect the guidance of the two scopes. Having a separate guidescope, at least one of the telescopes will continue to function well.

I thank you again for all your attention. Greetings and clear skies! Sorry for my poor english.

Ricardo

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ricardo leite

Topic starter

May 23, 2021

What is dual imaging? By Sara Wager
https://www.swagastro.com/dual-imaging-set-up.html