Dual Esprit 150 imaging rig

[tomato]

After putting together a permanent dome observatory over the autumn, the next project is a dual Esprit 150 imaging rig. Myself and @Tomatobro have slowly been gathering the components, buying second hand when possible (adjustable saddle, plates, 2nd scope).

With the dome drive nearing completion, I bolted the dual saddle arrangement together and put the two scopes on the Mesu for the first time today. 

I think the arrangement will be stiff enough, but this is unfamiliar territory for me. The good news is the working dual scope aperture is 20” the dome aperture is 23”, precise dome control will therefore be mandatory. Needless to say they were mega out of balance, but I made no progress with this as I wanted to get the single scope back up and running.

More posts to follow as we travel further on down the dual rig road...

[JamesF]

Very nice.  I look forward to seeing the results.

James

[teoria_del_big_bang]

This looks a very interesting project, good luck with it.

Steve

[Dinglem]

@tomato & @Tomatobro Nice dual rig you will have there when up and running.

Mark

[Starflyer]

Looks lovely but that pier adapter is going to ring / resonate like a bell with those long bolts.  An easy fix is to sandwich some blocks of steel or aluminium in between the pier and the adapter plate.

[tomato]

3 minutes ago, Starflyer said:

Looks lovely but that pier adapter is going to ring / resonate like a bell with those long bolts.  An easy fix is to sandwich some blocks of steel or aluminium in between the pier and the adapter plate.

You are not the first to comment on the spindly looking bolts, they have been OK on a single scope, but two up could well be a different story. It should be fairly straight forward to double up on the bolts, and shorten them, as it won’t make much difference to the horizon limit.

[Sunshine]

That is unreal, lucky you! must be an amazing sight in person.

 

[tomato]

14 minutes ago, Sunshine said:

That is unreal, lucky you! must be an amazing sight in person.

 

Thanks, I was determined to make the Mesu work hard before I finish with this hobby. Most of the second hand kit has been shrewdly purchased and would make about 5-10% more if sold again, so I see it as a bit of an investment ( well, that’s what I say to Mrs Tomato😜).

[steppenwolf]

The two 150EDs look great together  - looking forward to seeing the results from this combo!!

[ollypenrice]

A dual rig is so productive! I speak as an addict... 😁

Olly

[Alan White]

Oh my, that looks rather nice.

Spoken as a visual only person, why two scopes?

150mm refractor, that’s a chunk, two of them must be quite a heavy lump.

[Miguel1983]

14 minutes ago, Alan White said:

Oh my, that looks rather nice.

Spoken as a visual only person, why two scopes?

150mm refractor, that’s a chunk, two of them must be quite a heavy lump.

Data aquisition time is cut in half, to quote mr Hadden in Contact "why build one if you can have two for twice the price" 😁

[ampleamp]

Both @Petergoodhew and I set up similar dual scopes using TMB1200/152 scopes. His is in Spain and mine is in bits as I am building a new obs however we both had very steep learning curves along the lines of one scope gives you problems and two scopes gives you five time a the problems but when it works 😁😁😁. And halving acquisition time becomes my “weather beater”. 
A couple of initial thoughts on setup such as I saw them. As has been said already, you definitely need to drop the height of your pier head, ideally to zero, and allow the alt/az adjustments of the mount balance out any alignment. On my home-made pier I welded the mount base (removable) to the pier but on the basis that this is a one time deal for me and it is replaceable  I didn’t see any issues with that. To maintain a height I welded another pipe onto the top of the old one and filled it with concrete. Tapping this gives a lovely dull thud. 
Balance is more tricky than you think with these big long scopes but eminently doable. Gaining alignment and removing rotation is also tricky, but again doable. I think @ollypenrice has a Cassady adjustable plate which is heavy enough to carry the weight and align perfectly (as there is nothing else out there, max weight carrying plate I found was 12kg). THE biggest issue that both PG and I had was differential flexure whilst tracking. Everything would be balanced and aligned, and scope 1 would produce the expected good subs whereas scope 2 wouldn’t and show trailing stars. We both worked out our own methods for reducing this and amongst other methods we both used an additional set of scope rings front and back on each scope and bolted them together, top and bottom. Trial and error got us both there eventually, Peter far sooner than I did as he has the skies to keep trialling (!) and it is quite amazing how much the slightest turn of a bolt moves and aligning star. I forget his name but someone in Australia did all this in a similar project with twin TEC140s and he also ended up using AO active optics to finally solve his issues. I have attached a wip shot of my system showing the additional rings. 
We aren’t too far from each other by the look of things. I would be more than happy to let you see how I have done things - just as soon as I get a roof. Good luck 😉 
 

Edited January 1, 2020 by ampleamp

[The Admiral]

22 minutes ago, ampleamp said:

we both used an additional set of scope rings front and back on each scope and bolted them together

No experience whatsoever here, but I guess from an engineering standpoint it makes sense to first bond the two scopes together to make a single unit, and then mount that as a single item, much like you would for binoculars. Just my 2d worth.

Some rig though!

Ian

Edited January 1, 2020 by The Admiral

[ollypenrice]

1 hour ago, ampleamp said:

Both @Petergoodhew and I set up similar dual scopes using TMB1200/152 scopes. His is in Spain and mine is in bits as I am building a new obs however we both had very steep learning curves along the lines of one scope gives you problems and two scopes gives you five time a the problems but when it works 😁😁😁. And halving acquisition time becomes my “weather beater”. 
A couple of initial thoughts on setup such as I saw them. As has been said already, you definitely need to drop the height of your pier head, ideally to zero, and allow the alt/az adjustments of the mount balance out any alignment. On my home-made pier I welded the mount base (removable) to the pier but on the basis that this is a one time deal for me and it is replaceable  I didn’t see any issues with that. To maintain a height I welded another pipe onto the top of the old one and filled it with concrete. Tapping this gives a lovely dull thud. 
Balance is more tricky than you think with these big long scopes but eminently doable. Gaining alignment and removing rotation is also tricky, but again doable. I think @ollypenrice has a Cassidy adjustable plate which is heavy enough to carry the weight and align perfectly (as there is nothing else out there, max weight carrying plate I found was 12kg). THE biggest issue that both PG and I had was differential flexure whilst tracking. Everything would be balanced and aligned, and scope 1 would produce the expected good subs whereas scope 2 wouldn’t and show trailing stars. We both worked out our own methods for reducing this and amongst other methods we both used an additional set of scope rings front and back on each scope and bolted them together, top and bottom. Trial and error got us both there eventually, Peter far sooner than I did as he has the skies to keep trialling (!) and it is quite amazing how much the slightest turn of a bolt moves and aligning star. I forget his name but someone in Australia did all this in a similar project with twin TEC140s and he also ended up using AO active optics to finally solve his issues. I have attached a wip shot of my system showing the additional rings. 
We aren’t too far from each other by the look of things. I would be more than happy to let you see how I have done things - just as soon as I get a roof. Good luck 😉 
 

I can see the point of the extra rings, certainly, but are they not fighting with the alignment device to some extent? Perhaos this doesn't matter. In our case the system generally works but we do occasionaly get 'slave scope trailing' issues, though not bad enough to scrap many subs. I think the alignment device (a Cassady, as you say, but note the spelling for Google purposes) needs to be kept very tight. 

Perhaps somebody will come up with a purpose built solution. I'll put the problem to my friendly astro-engineer Pieter Vandevelde!

How about a dual tube ring in which the bottom halves of a pair of rings is machined from a single piece of metal? If accurately machined in this way would the scope alignment be good enough? It's probably not going to be pixel perfect because of the focusers, but would it be 'good enough?'  

Olly

Edited January 1, 2020 by ollypenrice

[ampleamp]

Believe me, I’m all ears for a better solution, this is just what was tried and as said, is wip. 😁. The problem we had was that the df was obvious and the solutions tried were all along the lines of firming everything up in a solid binocular-type approach. There were many attempts and it is very easy just to bolt two scopes together but the fundamental issue of lack of alignment was that without a Cassady (spelling duly changed - I think Apple intervened there) the commercial dual saddle i used (ADM) didn’t even get close to having the same image on each ccd to start with. I tried shims to sort the alignment (and I know Pete did as well) but that wasn’t great. In the end when alignment was solved to be close enough, then the df issue became the next biggest issue. I think ideally having the scope rings as far apart as possible will go a long way to reduce this but having heavy glass at one end and heavy imagining gear at the other meant there was some overhang. The additional rings were an attempt to reduce the influence of this. I know Pete has tried something else on his rig which involved tightening bolts against each other but he is far better placed to talk about that.

@tomato and @Tomatobro you have a fabulous setup there and I hope it works  well for you 👍🏼

[Davey-T]

I think the problem with adjustable mounting solutions such as Cassady and similar is the over engineering to achieve masses of un-needed adjustment, the adjusters that I made for my triple rig, admittedly for small Star 71, have a few millimetres adjustment which is all that is needed if care is taken getting the mounts parallel to start with.

They can also be mounted forwards to help balancing.

Using the orthogonal error readout from the 10Micron and crosshairs on Maxim DL I can get all scopes aligned.

Made a Losmandy one for the WO110FLT which works fine.

Dave

[JamesF]

1 hour ago, ollypenrice said:

How about a dual tube ring in which the bottom halves of a pair of rings is machined from a single piece of metal? If accurately machined in this way would the scope alignment be good enough?

This idea is something that has been nagging at my brain for some time.

James

[Petergoodhew]

1 hour ago, ollypenrice said:

I can see the point of the extra rings, certainly, but are they not fighting with the alignment device to some extent?

Olly, in my case the rings ARE the alignment device - there's nothing else to align them! I decided to exploit Alistair's point that the slightest turn of a bolt moves everything. In my case, with focal length of 1200 and small sensor (my field radius is 0.36 degrees) I needed a very precise way of aligning. Assuming I want, say, 90% overlap between images I need to adjust the alignment to around 0.04 degrees. My simple solution was to stick heavy-duty steel brackets on the extra rings that are as close as possible to the focusers, with hex bolts connecting them. I can now, using an allen key, finely adjust to with 0.01 degrees.

The other issue of differential flexure proved more problematic.  I had naively thought that by having the same OTAs,  both with Feathertouch focusers  and QSI6120 cameras that both scopes with flex in pretty much the same way.  However life is never that simple! One of the scopes was bought second hand a few years back, the other was brand new. So the tubes were slightly different, the Feathertouch focusers were different, one of the QSI cameras was an OAG version, the other had a separate OAG. The net of this was that the two scopes flexed in different ways. It wasn't just the tubes, but the gear hanging off the back of the tubes too. No amount of tightening could stop the second scope from having oval or trailing stars.  The solution was to fit a Starlight Xpress Active Optics device to the second scope. I now have better stars on the second scope that I have on the primary scope!

[Magnum]

3 hours ago, ampleamp said:

THE biggest issue that both PG and I had was differential flexure whilst tracking. Everything would be balanced and aligned, and scope 1 would produce the expected good subs whereas scope 2 wouldn’t and show trailing stars. We both worked out our own methods for reducing this and amongst other methods we both used an additional set of scope rings front and back on each scope and bolted them together, top and bottom.

Im also in the process of trying to get my (miss matched) dual rig working properly, and my biggest issue is also differential flexure, For the last few weeks I thought it was focuser sag as im guiding on the 127 Meade with an OAG and that rig always has pin point stars, but the 102 has slight trails, found a loose tension pad inside the focuser of the 102 but still getting the same issue. Theoretically the Altair should have amore rigid focuser than the Meade and thats confirmed by some aggressive flexing tests. But then when I think about it it could still be the focuser on the Meade thats casting it ,as that could be flexing yet still give round stars one its camera as its guided by the OAG. However im starting to think its the single bolt dovetail clamp on the smaller scope, if I grab both scopes  and move up and down there seems to be slightly more movement on smaller scope. Does any of that make sense? Also last night the images taken on the east side of the meridian had trails but on the west side they were almost perfect.

Thing I haven't had a problem with funny enough is alignment, all I did was use the pre drilled holes on the plate and clamps, and made sure the edges were square with each other before tightening, Can centre star in one and its always centred in the other one.

Not much point to my post as ive kind of answered my own questions, but thought I would share anyway.

With regards to capture itself and dithering, ive worked out a really simple method of having the exposures of both scopes synced to the dither.  Guiding in Maxim I enable dithering with my normal 30 second delay between exposures using the ATik460. Then on a separate computer I have another Maxim running connected to just the 383, obviously this one knows nothing about the guiding so I found if I set the delay on this cam to 39 seconds and make sure I press start on both machines at the same moment, then it stays in perfect sync all night.

Lee

 

 

Edited January 1, 2020 by Magnum

[carastro]

Quote

Spoken as a visual only person, why two scopes?

Enables twice as much data to be captured as one telescope would.  Imaging requires hours and hours of imaging time so this speeds up the process.  Some people capture colour on one scope and Luminance or Ha on the other (you need that for better detail. 

I have a dual rig also.

Carole 

[ollypenrice]

Resolution has a lot to do with it. When we ran dual Tak 106 scopes at 3.5"PP we saw no problems at all. We just bolted the dual rig together and it worked from the off. At 0.9"PP it isn't quite as simple.  The SX active optics gadget is a good idea but we can manage without it - I think! Of course, the other solution would be two mounts...  Eek.

Olly

[ampleamp]

43 minutes ago, Magnum said:

With regards to capture itself and dithering, ive worked out a really simple method of having the exposures of both scopes synced to the dither.  Guiding in Maxim I enable dithering with my normal 30 second delay between exposures using the ATik460. Then on a separate computer I have another Maxim running connected to just the 383, obviously this one knows nothing about the guiding so I found if I set the delay on this cam to 39 seconds and make sure I press start on both machines at the same moment, then it stays in perfect sync all night.

Lee, you might want to take a look at this software if you are using Maxim - http://astro.neutral.org/software/astronomy-software.html I used it when i was Maxim but I am an SGP convert now and it was very simple and very reliable. I tend not to use dithering now as I usually try and get L or H channels on both scopes and the integration of both datasets works wonders, usually.

[Davey-T]

1 hour ago, Magnum said:

Im also in the process of trying to get my (miss matched) dual rig working properly, and my biggest issue is also differential flexure, For the last few weeks I thought it was focuser sag as im guiding on the 127 Meade with an OAG and that rig always has pin point stars, but the 102 has slight trails, found a loose tension pad inside the focuser of the 102 but still getting the same issue. Theoretically the Altair should have amore rigid focuser than the Meade and thats confirmed by some aggressive flexing tests. But then when I think about it it could still be the focuser on the Meade thats casting it ,as that could be flexing yet still give round stars one its camera as its guided by the OAG. However im starting to think its the single bolt dovetail clamp on the smaller scope, if I grab both scopes  and move up and down there seems to be slightly more movement on smaller scope.

Your dual plate looks a bit skinny and I'd prefer Losmandy dovetails.

On the focuser front I've wound mine nearly right in with just a bit of the rack peeping out then used T thread adapters to take up the space to reach focus, this way the focuser stays pretty much right in when focused as I found they get very floppy as soon as they're wound out a bit.

Dave

[Tomatobro]

We really appreciate the comments and advice on dual rig issues. We have discussed the possibility of DF between the scopes but we still  have a lot to do on the dome automation first. I can see us ending up with a fabricated cradle if its an issue