Dual-Rig - what use / benefit?

[Jannerland]

I'm curious what motivates folks who have dual rig setups and how they use them from imaging perspective?

Background to the question is that I was toying with the idea of piggybacking my Redcat51 or Tak 60 on top of my 650mm FL refractor.

I can see the benefit purely from the perspective that it would mean the secondary scope would get a bit more use with possible downsides on flex etc.

Do folks have dual rigs to image concurrently and merge the data? 

If so how to cope with differing pixel scale? main scope is 1.16 while say the Redcat and an imx585 based camera would be ~2.4 (ie neatly nearly double)

Or is it just a case no merge but here's a nice (hopefully) wide field image and here's one that's a bit tighter of the same target?

 

[Elp]

1. Quicker capturing in shorter amount of time (a bonus if weather isn't particularly good or you're imaging a rarer target off site).

2. Image different FOVs if desired, can also combine the data if needed.

3. Imaging mono, take two different bandpasses at the same time, alternatively image RGB, and pure mono luminance at the same time. Or have both cameras imaging the same thing, double the exposure time.

4. If two different mounts, image two different targets at the same time.

5. If same mount, one mount, two cameras, less input power.

6. Can mosaic quicker if you setup the cameras to image different panels.

[ollypenrice]

I've run two dual rigs in the past, the idea being to halve the exposure time. This was in the days of CCD and not particularly fast optics (or, more precisely, not particularly fast systems - since we don't want to fall into F ratio myth territory.) These were systems on which I was typically looking for 15 to 20 hours per image, this reducing to 7.5 to 10 hours telescope time. The scopes were the same, a pair of TakFSQ106Ns and a pair of TEC140s.  I'm not a millionaire and never owned both halves of either rig. These were collaborative efforts.

Cameras were sometimes identical, sometimes slightly different. Differences in pixel scale are solved by Registar in one click, which pairs up the data perfectly. Other programs can now do the same.

If pixel scales were very different,  you'd have to think abut how to work the rig. The low res side could shoot colour, for instance, while the high res side shot luminance or Ha. On many targets, low res OIII would also be acceptable.

Aligning the scopes is harder than you might think. I ended up buying the staggeringly expensive, and now out of production, Cassady T GAD - currently for sale in the classifieds. If one FOV is larger than the other, alignment is less critical because you can crop the larger to fit the smaller.

Our dual rigs were very productive and much appreciated by our guests in the days when I ran manually-operated all-nighters here. Old age and decrepitude have required a change in technology so I now run screamingly fast F2 CMOS systems robotically. One is a RASA 8, the other a Samyang 135 working wide open - on separate mounts. With CMOS cameras the new rigs are more than twice as fast as the old dual rigs which were twice as fast as they would have been as singles.  Quite honestly, if you want super speed, the Samyang and RASA are fabulous with CMOS cameras.

I loved the dual rigs but love the new rigs even more!

Olly

[900SL]

I'm setting up a 70mm f6 at 1.0x and a 90mm f6 at 0.8x with a Nikon D5600 and a 533MC Pro, to get similar FOV and pixel scale.

The 70mm for colour, the 90mm for OSC dual narrowband. I might get a 533MM Pro mono at some point if it works out OK

I may also use this for running two separate set ups, the 90mm and a 135mm or Redcat 51 widefield, and not merging the data

As Ollie noted, gettinf both scopes accurately aligned is important, as is dual control of imaging/dithering/focus etc (synchronising)

[Elp]

Think I've kind of sorted mine, both lenses and cameras being the same. Update to be confirmed later in the year...

I use one lens as the driver, and let the second one just autorun and keep taking images regardless of lens one activating the dithering or not. Makes things much simpler, also taking short subs 30s-60s so doesn't waste many images.

[tooth_dr]

Pretty much echoing above. I love my dual rig. I have identical scopes and cameras (one mono and the other OSC).   On a good night in the winter I capture 20+ hours of data in a single night.   Alignment is tricky being an identical FOV so I bought a JTD saddle and utilise the manual rotators on my Starlight Instruments focusers. 

Edited July 10, 2023 by tooth_dr

[Elp]

Plate solving and annotation is a boon for checking alignment I find.

[Jannerland]

Thanks all.

Given both my cameras are OSC I also  was thinking of Ha rich targets where I'd perhaps  use the bigger scope with dual narrowband ALP-T  filter and then colour only  for stars from the small one? Nothing to lose by giving it a go I guess..:-)

[tomato]

I’m a massive fan of dual rigs for all of the reasons listed above. I run two Esprit 150s either with dual mono cameras, capturing L on one and RGB on the other, or two identical OSC cameras, or a mono and OSC. All of this kit is a co-owned project between myself and @Tomatobro. I also like the RASA8 and SY135 coupled with sensitive CMOS cameras, these go on the mount when the Esprits come off. Clear sky time in the UK is just too precious IMHO not to point two scopes at it if you are fortunate enough to have the kit required and a permanent set up.

Big dual rigs need a high capacity well engineered mount (Mesu 200 was my choice) and a fair bit of upkeep if you regularly change the configuration like I do, but hey, I need something to do in my retirement.

[tooth_dr]

9 hours ago, tomato said:

a fair bit of upkeep if you regularly change the configuration like I do, but hey, I need something to do in my retirement

I agree on this. This year I didn’t bother swapping my dual rig off for a larger galaxy scope due to the effort required to get all aligned, rotated, tilt corrected etc.  You couldn’t really have a dual rig without a permanent setup, but once set up you can really gather a lot of data quickly. 

[carastro]

I have been using a dual rig for years.  You can capture twice as much data so really speeds up imaging time. 
 

As Olly says l use Registar to re-size and orientate the data and then combine in photoshop or your chosen software.  
 

Mine are not matching FOV’s as try as l might l rarely manage to get them exactly rotated the same so one having a slightly larger FOV allows the edges to be cropped off the larger FOV. 
 

Carole

Edited July 11, 2023 by carastro