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Dual-telescope rig: seeking advice and strategies

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Rick KrejciIan McIntyreTony Gondola
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Ian McIntyre avatar
Ian McIntyre avatar
I live in an area of the world with seeing that is average on the best nights, non-existent on most. And those nights that are best tend to be extremely short summer nights at 48º north latitude. I am trying to create a rig to best utilize the few quality hours available to accumulate the most data feasible in that short time. My plan is to clone my widefield kit (Askar FRA400 with QHY268m/CFW) and run it side-by-side on my iOptron GEM45. 

I have viewed a number of websites and discussions on the matter, but they tend to not hit the specific questions or address certain nuances of this approach. I have seen a number users over the years post photos of various approaches to dual-telescope kits. I would love to have some feedback on how different approaches have worked and what accessories are necessary.

Specific questions I have:
  1. Am I wasting my time trying to run more than one simultaneous capture session with the same mount?
    1. How difficult/frustrating is it to obtain consistent framing?

  2. Is anybody running a dual rig with Astroberry?
  3. Is it possible to control both camera's with the same computer and if so, what software is capable of doing that (I have not seen that option in NINA)?
    1. If two computer/software instances are being used, what strategy is used to prevent mount operations (dithering, etc) from interrupting the capture occurring on the camera not linked to mount operation? (I would be running at different sub durations initially to capture narrowband with one and LRGB with the other to minimize the initial financial burden of 2 separate complete filter sets)

  4. Any issues with flex to the side-by-side dovetail bar?
    1. Does it make more sense to setup the scopes as piggybacks?


Feedback on any/all of these questions would be greatly appreciated.
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andrea tasselli avatar
andrea tasselli avatar
Save yourself all this trouble; get a faster, larger scope and you'll be sorted and quite possibly save yourself a lot of cash. And 48 deg N seems like deep south from were I stand... 

Tring to answer your questions;

1. If you are capturing the same object I can't see any issue with that

1.1. You need to be able to match the reference scope with the other one, assuming they are identical, which can be tricky

2. don't know

3. Yes, if you have enough ports, no hubs. The reference scope is controlled by one instance of, say NINA, and does all the pointing and synching as well as the other bits like running scripts or sequencer, while another instance of, say, NINA, just control the secondary telescope running the focusing, capturing and other ancillary tasks on the secondary scope only. See below:

4. It the best way to frame and run a side by side config and it is the most stable and less demanding on the mount too. The reference scope just needs to be mounted with dovetail on the saddle but the secondary scope needs to  be mounted on rings.

Still the best option, whichever way you look at it, is NOT to run a side by side setup.
alexbb avatar
alexbb avatar

Sound advice from @andrea tasselli with getting a larger scope with the same focal length. Or even a larger scope and camera with a larger sensor.

I also moved to Celestron Cs, 6, 8 or 9.25, but I ran dual setups on my GEM45 in the past, side by side or piggybacked. I advice side by side. One with fixed rings, the other with a fixed ring at the rear end and an adjustable 3 point ring in front.

I used APT for controlling multiple instances, but NINA also supports that. Best is to use the same sub length so you don’t waste time when one instance waits for the other to finish shooting and start dithering. The other option is to dither less often and throw away some of the short frames and don’t sync the dithering between instances. I used USB hubs with external power supply without too many issues.

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churmey avatar
churmey avatar

+1 on save yourself the trouble and get a larger scope. I have taken on this endeavor many times and have been successful but, more times than not, I would have rather focused on a single scope. Agree with above comments but will add. The difficulty increases exponentially when running dual scopes and increases the chances of failure tremendously. Experienced issues : guiding accuracy for slave scope, premature battery drain, port corruption/failure, alignment slippage, constant focus and/or troubleshooting during acquisition, and processing challenges. Having said that, If you do choose to plow forward like I did, I would say that my most successful duel sessions were Mono master / OSC slave simply because you do not have to be as accurate technically when acquiring color data. I would focus on the Mono technically and let the OSC just run without much oversight. This will produce efficient data and would be my suggestion.

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Roberto Botero avatar
Roberto Botero avatar

NINA with its Target Scheduler can control several telescopes extremely well and automate imaging almost completely. Imaging with two/three scopes is not particularly more difficult than with a single one nowadays. But as others have said, it depends a lot on your hardware. If a cable fails, a driver is buggy, a filter wheel doesn’t turn, you have double the issues. If your hardware is fairly dependable, the software part works really well now.

I have been imaging with two scopes for over 5 years and with three since the beginning of this one. The telescopes are all refractors which makes differential flexure minimal and the smaller ones are all attached directly to the rings of the larger one. They use different combinations of focal reducers/flatteners/cameras to achieve broadly the same field of view and image in L/NB, OSC and dual narrowband the same target at the same time.

I image from suburban London and having three scopes collecting data when the weather collaborates is very good.

Good luck with whatever you choose to do!

📷 Astro-Physics triplet triplet - Third scope added to tandem setupAstro-Physics triplet triplet - Third scope added to tandem setup

https://app.astrobin.com/i/hlbbsq/

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Rick Krejci avatar
Rick Krejci avatar

I’ll put my $0.02 in here with support for the dual scope idea.

I currently run 2 scopes/cameras side by side and really have no issues with it. My seeing is also quite bad, and I found larger aperture fast scopes seemed to be more prone to bad seeing and wind and were more fiddly with tilt and since I didn’t have narrowband filters that were designed for fast scopes, I wasn’t getting the most out of it. I didn’t switch to fast filters since I used the camera on multiple scopes. And one scope /camera locks you into one focal length (or mess with various reducers and such.

My strategy was to use a longer refractor (I started with the Askar 140, now use the Tak TOA-130 which is incredible) and a wider refractor (WO Cat 91 which is great as well). I have a FF mono camera and a OSC APSC camera. If the target fits in the FF FOV of the longer scope, then it would fit in the FOV of APSC of the wider one.

I run them side-by-side on my Mach 2. I don’t guide and use Dec Arc modeling, which simplifies things a great deal. THe side by side setup with solid rings seems to work quite well, and my small scope APSC FOV is a bit wider than my Large scope FF, so allows for some small misalignment.

The best use case is broadband targets, where I capture luminance with the larger Mono FF scope and RGB with the smaller APSC OSC one. The mismatch in resolution is no big deal since color resolution isn’t nearly as important.

I run a mini PC with 2 instances of Nina, one master for the larger scope which controls mount and guiding/dithering and the other that just runs the camera/AF/rotation for the smaller APSC OSC. I use synchronized dithering which, for the most part, works great as long as everything runs smoothly. You just have to make sure your dithering # of frames * exposure/frame match on each instance (so one could be 180seconds dithering every frame and the other could be 60 seconds dithering every 3 frames) so no instance waits on the other more than a second or 2. Dithering using direct guide (since I’m not actually guiding) in Nina is super quick. I try to align when I need to AF as well to avoid waiting on each other.

I use PI WBPP to calibrate, align and stack and it actually works quite seamlessly. It automatically scales up and aligns the APSC frames to match the FF frames (you have to tell it to use a FF frame as the reference image). Once it chugs through all the frames, you have a full set of LRGB just as if you took them all with the same setup. Really not much more difficult than having one rig.

I experimented with narrowband and right now it’s use case isn’t as clear since you really can’t effectively get a balanced mono “lum” for narrowband. My next experiment is to use the FF scope for Ha and Sii and the wide one with a dual narrowband filter and extract the B&G channels for Oiii. This would only be beneficial for targets where Oiii doesn’t hold the majority of detail as Ha and Sii. Veil wouldn’t work as well, but many targets would. Going to try that tonight.

One advantage is I can move the FF camera over to the wider scope for wide vistas without unmounting and mounting scopes. I can also put my small SQA55 on top of my TOA130 and run the Cat91 FF L and SQA55 APSC RGB if I want to capture a wider field.

To the disadvantages:

  • Expensive! Need a very beefy mount, 2 cameras and 2 scopes (at least) plus probably a power/USB box (I use Wandererastro power pro v3). For PC, I use a Quieter 4c and it handles everything fine. A motor rotator on both is super helpful in keeping the FOVs the same.

  • Not very portable. I image from my driveway and roll the whole rig out so not a big deal for me.

  • If something goes wrong and Nina gets out of sync with the synced dithering, one side may be waiting on the other more than expected. Happened more often as I was learning.

  • If your scope geometries don’t match (barrel or pincushion), you’ll need to use slower alignment methods in WBPP to get stars to match throughout the frame. My current scopes (TOA130 & CAT 91) match very well

  • I won’t say having more exposures, since faster scopes generally require shorter exposure times.

  • Doesn’t synchronize meridian flip, so lose an exposure on the non-master instance

Here’s some examples I’ve done using the L/RGB method:

https://app.astrobin.com/u/Ricksastro?i=or2t0h#gallery

https://app.astrobin.com/u/Ricksastro?i=roaf6s#gallery

https://app.astrobin.com/u/Ricksastro?i=h4w8j5#gallery

https://app.astrobin.com/u/Ricksastro?i=4a8kl2#gallery

📷 IMG_5915.jpegIMG_5915.jpeg

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Grigory2020 avatar
Grigory2020 avatar

Hi, I see that nobody in this thread mentioned Voyager. Voyager is specialized software for unattended remote observatory sequence management. It does have a specialized version for dual and more scopes mounted on the same rig. I have been running Voyager for about 6 months now, and I can tell it is much superior to NINA. Currently, I am in the process of setting up my second scope on the PlaneWave L-350 mount. I do not have specific experience of running it yet, but knowing Voyager this far, I know it should be no problem. Voyager does take into account standard synchronization like dithering, focusing runs, etc.

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Tony Gondola avatar
Tony Gondola avatar

Unless you already have the hardware, a dual right doesn’t make an sense. An example will make this clear:

Lets say you build a dual, 150mm rig. What would you have to get in a single OTA setup to equal it? The answer is 212mm or a tad over 8”. Make it an F/4 and you’ve matched the FOV of the dual rig. All at a lower cost and fewer headaches.

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Rick Krejci avatar
Rick Krejci avatar

Tony Gondola · Oct 31, 2025, 05:41 PM

Unless you already have the hardware, a dual right doesn’t make an sense. An example will make this clear:

Lets say you build a dual, 150mm rig. What would you have to get in a single OTA setup to equal it? The answer is 212mm or a tad over 8”. Make it an F/4 and you’ve matched the FOV of the dual rig. All at a lower cost and fewer headaches.

I tend to agree if you have 2 of the same scope/cameras. Which is why I use 2 different focal lengths and 2 different size cameras which can complement each other and offer more flexibility when used not in dual mode.

Roberto Botero avatar
Roberto Botero avatar

Tony Gondola · Oct 31, 2025, 05:41 PM

Unless you already have the hardware, a dual right doesn’t make an sense. An example will make this clear:

Lets say you build a dual, 150mm rig. What would you have to get in a single OTA setup to equal it? The answer is 212mm or a tad over 8”. Make it an F/4 and you’ve matched the FOV of the dual rig. All at a lower cost and fewer headaches.

Tony,

Forgive me but I fail to see the logic in your argument. Typically we are all aiming to optimise the imaging time we have. Either by exposing as many hours as possible to increase the SNR and capture the faintest detail or to capture an object as quickly as possible before it moves off and/or the weather catches us.

Surely having a couple or more scopes capturing data at the same time is better than one? It used to be very difficult to do so because of software not being able to coordinate all the sequencing of events but now that it is, the only thing stopping anyone from trying is availability of funds to acquire the hardware! A difficult problem to solve but if the OP is looking already at a tandem setup I fail to see what the problem is if he wants to try?

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Tony Gondola avatar
Tony Gondola avatar

Roberto Botero · Oct 31, 2025, 06:01 PM

Tony Gondola · Oct 31, 2025, 05:41 PM

Unless you already have the hardware, a dual right doesn’t make an sense. An example will make this clear:

Lets say you build a dual, 150mm rig. What would you have to get in a single OTA setup to equal it? The answer is 212mm or a tad over 8”. Make it an F/4 and you’ve matched the FOV of the dual rig. All at a lower cost and fewer headaches.

Tony,

Forgive me but I fail to see the logic in your argument. Typically we are all aiming to optimise the imaging time we have. Either by exposing as many hours as possible to increase the SNR and capture the faintest detail or to capture an object as quickly as possible before it moves off and/or the weather catches us.

Surely having a couple or more scopes capturing data at the same time is better than one? It used to be very difficult to do so because of software not being able to coordinate all the sequencing of events but now that it is, the only thing stopping anyone from trying is availability of funds to acquire the hardware! A difficult problem to solve but if the OP is looking already at a tandem setup I fail to see what the problem is if he wants to try?

Yes, of course it would be better than one. My point that others have made on this thread is that, a larger aperture will be able to gather the same amount of data at a lower cost and complication. Not to mention at a higher resolution. Of course, there’s nothing wrong with wanting to try. It can be a fun and challenging project. You just need to be realistic about the gains.

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andrea tasselli avatar
andrea tasselli avatar
The OP will need to buy another imaging setup entirely and in terms of efficiency (pounds per photon) it doesn't make sense, at least to me (and Tony).
Bob Lockwood avatar
Bob Lockwood avatar
To the OP,

I think some of them are missing the point. Just say cost is not an issue, I have two scopes imaging the same object at the same time, a larger scope will still only capture say 6 hours in one night, my two scopes will capture 12 hours in one night. I did this so I can get much more time on an object in the short summer nights, and it really doubles in Winter when I can get 18 hours on a single target in one night. In my case, I have two mounts and can image the same target and not half to worry about guiding/filter-change/ dithering, but I did do side-by-side at one point, two setups are just easer.
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Tony Gondola avatar
Tony Gondola avatar

And there’s the rub. If you image with two 6” F/6 instruments for 6 hours and combine the results, you’ll get a certain SNR. To get that same result with an 8” F/4.5 (same focal length) you’ll need to expose for approximately the same amount of time, 6 hours. Ignoring resolution, it’s two different ways to get the same result, just with fewer complications.

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Rick Krejci avatar
Rick Krejci avatar

Bob Lockwood · Oct 31, 2025, 08:36 PM

I think some of them are missing the point. Just say cost is not an issue, I have two scopes imaging the same object at the same time, a larger scope will still only capture say 6 hours in one night, my two scopes will capture 12 hours in one night.

I think their point was that it would be simpler to have one larger, faster scope that would capture the same amount of photons in that 6 hours as a smaller ones could in 12, and probably better resolve fine details.

But I’ve found with my not great seeing, my 5” refractor gives tighter FWHM on average for similar conditions than my larger reflectors and still captures the dim stuff when I can dedicate one scope 100% to luminance for an entire night while the other picks up the color.

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Ian McIntyre avatar
Ian McIntyre avatar
I appreciate everyone's feedback. 

The idea of simply getting a larger scope is not without its own set of complications. There are space and financial considerations. I am already housing a rather larger rig (12" RC on a CEM120 with wheels) that I made a substantial cash drop on. Pushing those limits too much further threatens domestic bliss. Especially when paired with the idea of a camera with a larger sensor. And there is only so much speed you can do without having to upgrade filters independent of the larger format issue. Don't get me wrong, I have certainly looked at some options in that department. Its an idea not without merit. But I am pretty much at the "do it or not" phase with the dual rig rather than the larger scope as an alternative.  

I like the idea, at least in the short-term to limit dropping a ton of money while I'm testing this plan, of running OSC for the slave camera. I have an OSC sitting idol that is the same sensor as my mono cameras. I know there are opponents to the idea of blending in inferior OSC data, but it will provide a valid "try before I buy" opportunity.
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Jeff Marston avatar
Jeff Marston avatar

It took me about a month to get all the parts and the setup sorted with my tandem kit. I took it out a few nights and it worked pretty well but since I am running two Asiair’s I was losing up to 20 percent of secondary scopes data because of dithering. I decided to dismantle the tandem setup and just buy another mount. I got a Losmandy G811 which does auto guiding really well. Now I do two setups with separate mounts. It’s a bit more of a pain to set up when I travel to dark sites, but I get to use all of the data from both scopes.

I have heard that NINA is a good app for running a tandem setup but I didn’t want to learn another new system.

Image.jpg

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Rafa avatar
Rafa avatar

Been there done that.

Look at my cheer profile pic

I went all out with his and managed to get it working. Even bought the GM 3000 so it could manage the twin TOA 150s.

IMO, it’s important to understand that the main issue is flexure rather than pointing accuracy between the two. If you put in a dovetail with alt az settings to help with matching FOV, you will introduce flex.

I almost would not worry unless you have identical set ups, it’s just so much easier and intuitive. WBBP can spit out a single master light from the two..

I got it to work doing unguided images of up to 15 minutes without any elongation on either scope. Truly a feat.

Here’s the rub, after all that work and producing a couple of images, I just did not care for the workflow.

A single bad solve, or a faulty auto focus, and everything goes astray until both scopes are on the “same page”.

I ended up separating them, and I am much happier and living an stress-free life….

However, if you insist, and I had only one thing to say, it would be the rigidity of the set up is the most important thing….

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Rick Krejci avatar
Rick Krejci avatar

Here’s one I did last light with my dual dissimilar scope setup, yielding almost 18 hours of data in one night. As I mentioned earlier, I did Ha and Sii with my TOA-130 and I extracted Oiii from the B&G channels of my OSC camera with Radian Triad Ultra filter on the Cat 91. Turned out just as I hoped!

https://app.astrobin.com/i/cjvmsx

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Kaptas Attila avatar
Kaptas Attila avatar

Hi guys i am actually planing a dual epsilon 160 in Namibia, it seems like lot of people here suggest not to doing something like this, should i forgot and break up before i get into it??

Rick Krejci avatar
Rick Krejci avatar

Others were suggesting using a faster, larger aperture scope that would be able to pull in the same number of photons per unit time at the same focal length/FOV.

In your case, you’d be looking in 9.25” RASA territory to meet that criteria which doesn’t have the pinpoint edge to edge full field coverage and has many limitations especially if you want to shoot mono with filters.

If you can afford it, I think it would be a great dual rig. Just need to make sure there’s no flexure

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Bob Lockwood avatar
Bob Lockwood avatar
Kaptas Attila:
Hi guys i am actually planing a dual epsilon 160 in Namibia, it seems like lot of people here suggest not to doing something like this, should i forgot and break up before i get into it??

I'd say go for it, why not try.
Rick Krejci:
If you can afford it, I think it would be a great dual rig. Just need to make sure there’s no flexure


This is why I said if cost is not an issue. Look at what Bray at Starfront is doing with his triple RASA.
Kaptas Attila avatar
Kaptas Attila avatar

Bob Lockwood · Nov 2, 2025, 05:25 AM

Kaptas Attila:
Hi guys i am actually planing a dual epsilon 160 in Namibia, it seems like lot of people here suggest not to doing something like this, should i forgot and break up before i get into it??


I'd say go for it, why not try.

Rick Krejci:
If you can afford it, I think it would be a great dual rig. Just need to make sure there’s no flexure



This is why I said if cost is not an issue. Look at what Bray at Starfront is doing with his triple RASA.

Yes it is amaizing what he is doing, but dont forget he is always on site so he can directly manage all the issues. I ll thinking about it, i wont have so much issues, more i really want to enjoy doing it.

Wei-Hao Wang avatar
Wei-Hao Wang avatar

Dual WO RedCat + FF sensors (plus another camera lens):

https://app.astrobin.com/i/555cl7

Dual AP Stowaway 92 + medium format sensors:

https://app.astrobin.com/i/bj3lc5

Personally, I agree it’s better to have a single larger scope of the same light collecting power and same focal length. It’s much easier to setup, and less room for mistakes. In reality, this is not always possible. For example, someone mentioned dual Epsilon 160. Can you find a system with an aperture of about 230mm and same focal length as the Epsilon to equal the light collecting power and FoV? I suppose an RASA is probably the closest. But does an RASA have Epsilon’s image quality? (I am not yet convinced about this, after years.). What if someone is thinking about a dual RASA system? What larger alternative we are going to suggest?

In my examples above, I use two refractors with intermediate or long focal length. It’s indeed possible to find a system with twice light collecting power and equal focal length. The problem is, if this is a larger refractor (of equal quality), it would cost more than twice the smaller refractor. If it is a reflector (like Epsilon), either it’s hard to maintain collimation for my mobile imaging usage, or it cannot cover the medium format FoV. That’s why I opted for a dual refractor system.

Ian McIntyre avatar
Ian McIntyre avatar
Wei-Hao Wang:
Dual WO RedCat + FF sensors (plus another camera lens):

https://app.astrobin.com/i/555cl7

Dual AP Stowaway 92 + medium format sensors:

https://app.astrobin.com/i/bj3lc5

Personally, I agree it’s better to have a single larger scope of the same light collecting power and same focal length. It’s much easier to setup, and less room for mistakes. In reality, this is not always possible. For example, someone mentioned dual Epsilon 160. Can you find a system with an aperture of about 230mm and same focal length as the Epsilon to equal the light collecting power and FoV? I suppose an RASA is probably the closest. But does an RASA have Epsilon’s image quality? (I am not yet convinced about this, after years.). What if someone is thinking about a dual RASA system? What larger alternative we are going to suggest?

In my examples above, I use two refractors with intermediate or long focal length. It’s indeed possible to find a system with twice light collecting power and equal focal length. The problem is, if this is a larger refractor (of equal quality), it would cost more than twice the smaller refractor. If it is a reflector (like Epsilon), either it’s hard to maintain collimation for my mobile imaging usage, or it cannot cover the medium format FoV. That’s why I opted for a dual refractor system.

I think what you are getting at here speaks to my logic on going this route. If I want to image at a wider FOV and improve my photon/area/time ratio and limit cost, a larger scope is not going to accomplish that. It is going to do quite the opposite. 

With all this in mind I have managed to find a used twin for my Askar FRA400. I saved a considerable amount. I will test the dual scope on single mount concept starting with a the mono/OSC blend as that will get me off and running without further spending in the short-term. If things work well I will add the mono kit to the secondary OTA. If it becomes problematic, I will hang on to the GEM28 and run the scopes on separate mounts. Some servicing of both the GEM45 and 28 are required, regardless. 

Fantastic images by the way.
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