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Opportunistic dual rig with small refractor and Samyang 135mm ?

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#1 Gurney

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Posted 20 April 2024 - 04:23 AM

Hi,

I’m currently imaging with a 65mm f6.4 frac / ASI533MC Pro / ASIAIR. Since I live in a very cloudy region and my main imaging site has a pretty blocked horizon, my imaging time gets very limited and I’m having fun trying to find clever ways around this 😝.

One way is to shoot with faster optics. Given my limited budget, I decided to go with faster = wider and ordered a Samyang 135mm f2 to capture more light of (very) wide field DSO … at the expense of image scale (gigantic 5.4´´ per pic with the 533).

I had one thought though: since my mount (AM5) could handle the weight of both scope/lens, maybe I could double my imaging time by having the two scopes image at the same time.

But I need ideas / advices on what would be a adequate « opportunistic » setup. Obviously I need:
- A new Astro cam
- An adapter to be able to connect the two dove plates on my mount
- Either another ASIAIR or a Mini PC to be able control the two cameras.

In your opinion:
- should I shoot with OSC broadband on both (maybe one unfiltered and one with a dual-band) ? Or should I use one with BB and one Mono, with Luminance or Ha ? (Not sure I want/can afford the full mono monty)
- any camera you would recommend for this setup ?
- in terms of target, I don’t think my level will allow me to shoot different targets so I will try to capture the same target but with just different FLs —> should I aim to generate just 2 different final images or is there a way with Pixinsight to get benefit of the dual rig to generate a better blended picture (for example: shooting RGB with the Samyang to capture colors and Luminance with the 65mm to capture details etc).
 

I’ve seen posts about people using two different scopes on a mount to use or or the other depending on the target type/size. I’ve also seen post about people using the same scope/camera twice to double the imaging time with similar sampling/FoV/filters but I could not find a lot of posts with a mix of both (happy to be redirected if you know ones).

I don’t want to make things too complex as this would be really an opportunistic play but thought I could ask experienced imagers about their ideas.

Thanks


Edited by Gurney, 20 April 2024 - 04:31 AM.


#2 OrionSword

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Posted 20 April 2024 - 07:01 AM

You can use OSC on both sides or OSC on one side and mono on the other.  If you don't want to invest in a filter wheel with a full assortment of filters for it, then you can still use Ha for instance on one of the OSC cameras and extract just the Red channel for mixing in Ha with the RGB image.  You can mix image scales from two different optical/camera combos but try to stay within 20% or less in the difference of image scales to keep things better matched.  Pixinsight processing will either up/downscale the registration depending on which image is chosen for the reference.

 

Other costs associated with dual-rig would be the tandem bar with the pointing mount on one side to match up the same alignment star to the stationary scope.  This is a ADM version of such:

 

https://www.admacces...ith-max-guider/

 

Of course your mount would have to accommodate the total weight of all components with some reserve capacity.

 

I use all dovetail bars and clamshell mounts, including attachment to the guidescope and have no differential problems with this arrangement.  My current mount will accommodate a max payload of 110#s but I do not push it to the limit.

 

 

Attached Thumbnails

  • StellarvueDualRig-1.jpg


#3 Gurney

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Posted 20 April 2024 - 07:24 AM

Thank you, that’s super helpful. I currently have a light pollution filter and a 3nm dual narrowband filter. I may try a combo with those 2 first (even though I will likely have a problem of band shifting given the Samyang is f2 and the Optolong l-ultimate I am using is not shifted accordingly).

My main concern from you guidance is the image scale: with typical 3.76 micron sensors, my 416mm FL refractor has a 1.86’´ image scale while the Samyang 135mm will have 5.45’´. Even if I manage to find a camera with smaller pixels , that won’t make the two image scale get to the 20% range you mention …

#4 calypsob

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Posted 20 April 2024 - 11:01 AM

You wont be able to dither if you use 2 ASI Air units. They cannot speak to each other.

You will need to use a PC to control 2 cameras simultaneously. 

As someone who has imaged with a dual and triple samyang 135mm camera rig, you can manually dither every 5 subs. You need to be sure that 3/4 of the data is dithered. Otherwise outlier rejection cannot work very well and FPN will really begin to build up.  

 

Getting the 2 sensors orthogonal requires shimming and patience, but it is 100% doable. 


Edited by calypsob, 20 April 2024 - 11:03 AM.


#5 Gurney

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Posted 20 April 2024 - 11:40 AM

Thanks. I may indeed go the PC route and use NINA to control the two cameras + the mount.

 

I'm not sure I understand your comment about "getting the 2 sensors orthogonal", though. Can you tell me more about this one ?

 

You wont be able to dither if you use 2 ASI Air units. They cannot speak to each other.

You will need to use a PC to control 2 cameras simultaneously. 

As someone who has imaged with a dual and triple samyang 135mm camera rig, you can manually dither every 5 subs. You need to be sure that 3/4 of the data is dithered. Otherwise outlier rejection cannot work very well and FPN will really begin to build up.  

 

Getting the 2 sensors orthogonal requires shimming and patience, but it is 100% doable. 



#6 calypsob

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Posted 20 April 2024 - 09:20 PM

Thanks. I may indeed go the PC route and use NINA to control the two cameras + the mount.

I'm not sure I understand your comment about "getting the 2 sensors orthogonal", though. Can you tell me more about this one ?


The two images will not perfectly overlap and you are going to have to shim one Camera and lens to get it to overlap perfectly with the other combo next to it

#7 Gurney

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Posted 21 April 2024 - 01:12 AM

The two images will not perfectly overlap and you are going to have to shim one Camera and lens to get it to overlap perfectly with the other combo next to it



Ah ok, do you think that will really be a problem given the FoV of the Samyang (135mm FL) will be way larger than the 65mm refractor (416mm FL) ? I was thinking about framing with the 65mm and hoping the Samyang will be wide enough to capture the frame of the 65mm

#8 Gurney

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Posted 23 April 2024 - 08:58 AM

@calypsob: any system you recommend to mount the dual-rig (and adjust the second scope) on my mount besides the one mentioned by OrionSword here? It looks very nice but is a bit over budget for this "opportunistic" rig when I factor in shipping and duties to Europe (900$) lol.gif



#9 nateman_doo

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Posted 23 April 2024 - 02:14 PM

I have attempted this before with success.  I didnt like having 2 scopes pointing at the same thing so I went a different route.  I had my RC8 on top of an EQ6, imaging whatever with an OAG guiding.  On the top rail of the RC I machined an inverted dovetail that I mounted a regular camera ball mount on top of.  I had a 135mm Rokinon with a QHY163C in the ball mount so I could select another target at will. 

 

I installed a second copy of Astrophotography tool, and the 2 instances would sync up as a master/slave relationship.  I was able to just swing the ball mounted camera/lens combo wherever in the sky, and was able to get great images based on guiding @ over 1Kmm focal lengths.  It got old trying to flip things around after a meridian flip and guiding suffered slightly due to the extra bulk up top, but PHD2 did its job.  It really was a poor-mans dual rig, but I liked the ability to control a rig remotely, and while I was able to control the RC, I had to manually take images with the piggy back rig and keep moving it around until I got what I liked.


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