Dual rig DSO imagers, the Moon can be your friend

[tomato]

When setting up a dual rig one challenge is aligning both cameras accurately on the the same point on the sky. The initial alignment is not too bad on a wide field rig as the reference star should at least be in the FOV in both scopes. However on my small galaxy/PN set up with one scope centred the star was nowhere to be seen in the other and after about 90 mins of adjusting the saddle on the other scope there wasn’t even a sign of a flare to help me locate it.

Then I had a bit of a Jim Lovell/Apollo 13 moment and thought all I need is a large bright fixed point in space and the moon was still visible above the house. After slewing and centering the master scope on a couple of small craters in the middle of the terminator, sure enough the moon wasn’t even in the FOV on the other, but there was sufficient glare visible to allow me to move it in the right direction. Once the slave scope was pointing at the same two craters, I slewed to a bright star and finished the job.

I usually grumble when the moon is up, but it got me out of a hole last night.

[ollypenrice]

44 minutes ago, tomato said:

When setting up a dual rig one challenge is aligning both cameras accurately on the the same point on the sky. The initial alignment is not too bad on a wide field rig as the reference star should at least be in the FOV in both scopes. However on my small galaxy/PN set up with one scope centred the star was nowhere to be seen in the other and after about 90 mins of adjusting the saddle on the other scope there wasn’t even a sign of a flare to help me locate it.

Then I had a bit of a Jim Lovell/Apollo 13 moment and thought all I need is a large bright fixed point in space and the moon was still visible above the house. After slewing and centering the master scope on a couple of small craters in the middle of the terminator, sure enough the moon wasn’t even in the FOV on the other, but there was sufficient glare visible to allow me to move it in the right direction. Once the slave scope was pointing at the same two craters, I slewed to a bright star and finished the job.

I usually grumble when the moon is up, but it got me out of a hole last night.

Good idea.

What kind of alignment device are you using and how well do you find it works on your high res setup? There's been considerable discussion of this.  I find that the Cassady T-Gad, which worked perfectly with the dual FSQ106, does not kill flexure entirely reliably with the dual TEC140.

Olly

[tomato]

6 hours ago, ollypenrice said:

Good idea.

What kind of alignment device are you using and how well do you find it works on your high res setup? There's been considerable discussion of this.  I find that the Cassady T-Gad, which worked perfectly with the dual FSQ106, does not kill flexure entirely reliably with the dual TEC140.

Olly

It is an ADM adjustable saddle which I will say right away is NOT capable of holding the scope steady, with an Esprit 150 on there, it is right on the limit of what the adjusters can cope with, let alone holding it stable. @Tomatobro beefed up the standard lateral adjusters which helps, especially having both screws on the outside of the saddle. 
What gives me a fighting chance of keeping them steady is the top bracing plate, again fabricated in the shop. The method is the plate is tightened down onto the tube rings on the RH scope, the holes are drilled oversize on the LH scope and this allows the plate to move as adjustments are made on the saddle. When aligned the nuts are tightened together evenly and very carefully on the LH scope until the assembly is secure. Needless to say, this inevitably causes the scopes to move so it’s an iterative process where you learn how the scopes move as you tighten the plate down, anticipating where the scopes will move. It’s best to set an evening aside for this operation but once tight I can go quite a while before adjustment is required. What usually happens is I will knock a scope in the confines of the dome and then another adjustment session is required.

 

[gorann]

10 hours ago, ollypenrice said:

Good idea.

What kind of alignment device are you using and how well do you find it works on your high res setup? There's been considerable discussion of this.  I find that the Cassady T-Gad, which worked perfectly with the dual FSQ106, does not kill flexure entirely reliably with the dual TEC140.

Olly

In any case the Casady T-Gad is not made anymore, so we all seem to be stuck with the only option: ADM. It has worked fine for me keeping an Esprit 100 next to and Esprit 150, but I can appreciate that it would need the extra screws that Steve @tomato (or his brother) has put in for an Esprit 150. From what you say Olly, the Casady T-Gad may be in the same class, easily holding an 106 but struggling with a 140.

Actually the Casady looks very similar to the ADM, maybe ADM just bought the design after Cassady's cousin retired and the workshop closed down:

http://www.robincasady.com/Astro/TGAD.html

Edited May 20, 2021 by gorann

[Davey-T]

JTD Dual Rig Telescope Alignment Saddle | First Light Optics

Or you could just make your own.

Dave

 

[ollypenrice]

14 hours ago, gorann said:

In any case the Casady T-Gad is not made anymore, so we all seem to be stuck with the only option: ADM. It has worked fine for me keeping an Esprit 100 next to and Esprit 150, but I can appreciate that it would need the extra screws that Steve @tomato (or his brother) has put in for an Esprit 150. From what you say Olly, the Casady T-Gad may be in the same class, easily holding an 106 but struggling with a 140.

Actually the Casady looks very similar to the ADM, maybe ADM just bought the design after Cassady's cousin retired and the workshop closed down:

http://www.robincasady.com/Astro/TGAD.html

What happened, if I remember correctly, is that FLO were offering a comparable product but, when I tried it, I found it too flexible, as did another customer. I sent some pictures of the out-of-production Cassady off to them to show how it worked and FLO inspired a new version which may be the present ADM, I don't know. My acquisition of a used Cassady makes a mildly amusing tale of subterfuge which I'm afraid I can't relate on here! Despite being used it cost a fortune and is, I must say, about as good as it gets. Construction is distinctly massive. Maybe I'll try 'The Tomato Variation!'

Olly

[alexbb]

I use a fixed ring at the back of the scope and a large guiding ring at the front of the scope and never had any differential flexing. However, I never exposed longer than 5 minutes.

[gorann]

On 21/05/2021 at 12:06, ollypenrice said:

What happened, if I remember correctly, is that FLO were offering a comparable product but, when I tried it, I found it too flexible, as did another customer. I sent some pictures of the out-of-production Cassady off to them to show how it worked and FLO inspired a new version which may be the present ADM, I don't know. My acquisition of a used Cassady makes a mildly amusing tale of subterfuge which I'm afraid I can't relate on here! Despite being used it cost a fortune and is, I must say, about as good as it gets. Construction is distinctly massive. Maybe I'll try 'The Tomato Variation!'

Olly

I messed up the three letter abbreviations. I wrote I had an ADM but it is a JTD adjustment saddle from FLO (actually I now have two of them since I aim at having two dual rigs, one for RASAs and one for Esprits). But as far as I know it is the only option available out there and it is the JTD. It is odd that not more options are availble to us brave few that realized that a dual rig can offer twice the data in a night. There are even problems connecting two cameras (at least ASIs) to one computer so I usually play it safe and have one computer for each camera.

Is JTD an FLO brand? They appear to be the only one selling it.

Edited May 23, 2021 by gorann

[ollypenrice]

10 hours ago, gorann said:

I messed up the three letter abbreviations. I wrote I had an ADM but it is a JTD adjustment saddle from FLO (actually I now have two of them since I aim at having two dual rigs, one for RASAs and one for Esprits). But as far as I know it is the only option available out there and it is the JTD. It is odd that not more options are availble to us brave few that realized that a dual rig can offer twice the data in a night. There are even problems connecting two cameras (at least ASIs) to one computer so I usually play it safe and have one computer for each camera.

Is JTD an FLO brand? They appear to be the only one selling it.

That makes sense. The JTD may be the one which appeared after my conversation with FLO. I think the one I found too flexible was the ADM/

An idea came to me in bed last night! Why not put a second dual mounting system on the top of the scopes?

Hang the expense. 

Olly

[carastro]

I use the Skywatcher Guidescope mount for my dual rig.  Works well and when I remove the top scope and camera, it is just the same when I re-assemble the kit with just an occasional tweak to alignment. 

 

Edited May 24, 2021 by carastro

[whipdry]

This one is still showing on the ADM website;

https://www.admaccessories.com/product/tgad-tandem-guiding-aiming-device-altaz-aiming-device-for-side-by-side-systems/

Looks like a Robin Casady copy... 

Peter

[tomato]

I must have the JTD version then, the ADM saddle does look more substantial.

[ollypenrice]

3 hours ago, whipdry said:

This one is still showing on the ADM website;

https://www.admaccessories.com/product/tgad-tandem-guiding-aiming-device-altaz-aiming-device-for-side-by-side-systems/

Looks like a Robin Casady copy... 

 

Peter

That is not the flexible thing I tried.

Olly

[whipdry]

1 hour ago, tomato said:

I must have the JTD version then, the ADM saddle does look more substantial.

I guess you could have one of the others seen on this page;

https://www.admaccessories.com/product-category/miscellaneous/altaz-aiming-devices/

[gorann]

My conclusion is that the JTD and ADM are in the same league as the Cassidy one. As Olly said his Cassidy works fine on his 106 Taks but wobbly for the bigger scopes. I would think the same about my JTD. There is probably nothing for sale that could handle a 6" refractor.

And they are both still rediculously expensive..... Maybe a buisiness idea for Tomatobro?

Edited May 24, 2021 by gorann

[tomato]

As a machining job it would require some decent sized billets and then there is the set up time and all those hours making all that swarf. It can be done though, see @Davey-T’s post further up this thread.

The top end bracing plate was a whole lot simpler to fabricate,  just more hassle to adjust.

[Davey-T]

5 minutes ago, tomato said:

It can be done though, see @Davey-T’s post further up this thread.

Mine cost about £30.00 in materials and I made the prototype with just a pillar drill, solid as a rock once adjusted and locked and no movement caused by locking, the overly complicated commercial ones have loads of unnecessary adjustment, if care is taken with the setup there is very little adjustment needed.

Dave

[JamesF]

And then there's this piece of, errrm, well, I'm not sure how to describe it really.

https://astronomytechnologytoday.com/2018/06/28/miniwasp-parallel-imaging-array/

James

[tomato]

I tried a triple rig with 2 x Esprit 150s and the RASA8 on the Mesu, but even that mount has it’s limits.

On the subject of telescope arrays, @Tomatobro now has his dome operational with a SW MN190, which happens to have  a very similar imaging FOV to the Esprit 150, so look out for some images from the SNSLA, the Shropshire Not So Large Array.🙂

[gorann]

12 hours ago, tomato said:

I tried a triple rig with 2 x Esprit 150s and the RASA8 on the Mesu, but even that mount has it’s limits.

On the subject of telescope arrays, @Tomatobro now has his dome operational with a SW MN190, which happens to have  a very similar imaging FOV to the Esprit 150, so look out for some images from the SNSLA, the Shropshire Not So Large Array.🙂

Nice to see that someone more than @wimvb is aiming to show what an excellent scope the SW MN190 is! I am embarrased to admit that I have one of them stored in my closet (no space for it on my rigs right now) but I could maybe sell it to Wim (with a good profit or a share in the subs😁) if he decides on a dual MN190 rig.

Edited May 25, 2021 by gorann

[wimvb]

1 minute ago, gorann said:

Nice to see that someone more than @wimvb is aiming to show what an excellent scope the SW MN190 is! I am embarrased to admit that I have one of them stored in my closet (no space for it on my rigs right now) but I could maybe sell it to Wim (with a good profit😁) if he decides on a dual MN190 rig.

If I ever go for a dual rig, it may very well be with 2 * MN190. But not on the same mount.

Btw, does @Tomatobro have the original focuser on his MN190, or an upgrade?

[JamesF]

4 minutes ago, wimvb said:

If I ever go for a dual rig, it may very well be with 2 * MN190. But not on the same mount.

  Two MN190's would squash many mounts.

James

[gorann]

6 minutes ago, wimvb said:

If I ever go for a dual rig, it may very well be with 2 * MN190. But not on the same mount.

Btw, does @Tomatobro have the original focuser on his MN190, or an upgrade?

If it is not on the same mount, it does not count as a dual rig, does it?

Edited May 25, 2021 by gorann

[JamesF]

1 minute ago, gorann said:

If it is not on the same mount, it does not count as a dual rig, does it?

A good point, well made.

James

[gorann]

Quite a few mounts would handle a dual MN190 rig but the question is if the primary mirrors stay steady in place - dual reflectors could be a challenge if the mirror move on the scope that does not have the OAG on it.

Edited May 25, 2021 by gorann