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Dual Esprit 150 imaging rig


tomato

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Thanks for all the replies and encouragement. You have probably gathered @Tomatobro enjoys the engineering element of this hobby as much if not more than the imaging side, so relishes the considerable challenge a dual rig of this size presents.

I couldn’t resist putting the scopes back on today (what else is there to do on New Year’s Day?) and trying to balance them up with the additional paraphernalia on board. I seem to have got the Dec balance reasonable ( the dew shields make a nice fine sliding weight adjuster) but my even though I hung the 3 Geoptiks I have out in the breeze, this was not enough to get close to RA balance.

The aperture width looks insufficient in the photo, but there is enough there, just.

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Found the Australian who went down this road - Peter Rejto. A couple of links that might be of interest, and I was mistaken, it wasn’t a twin TEC140 system, but a TEC140 and a TEC180  

https://astronomytechnologytoday.com/2017/05/29/a-practical-automated-multi-camera-astro-imaging-system-design-one-mount-one-computer-two-imaging-cameras/

https://pbase.com/prejto/equipment

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4 hours ago, Davey-T said:

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

The plate is actually a really solid  and heavy Losmandy plate, unfortunately my old EQ6 only has a vixen saddle so for now ( until I find a replacement Losmandy puck going cheap :-p) so ive had to bolt the blue vixen bar to the underside, but surprisingly that connection is really rock solid, the only flex I can find is between the 102 scope and the plate, and a little on both focusers. so tomorrow im going to replace the clamp that holds the 102 for a bigger one with dual locking bolts, I dont think the holes match up so will have to modify it, thats probably why I didn't fit it before. 

I will try what you said about winding the focuser in and use extensions instead.

 

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Of course there is another, more radical solution to the perfecting of the dual rig. A manufacturer could steal a march on the competition by making a 'binocular' instrument - two parallel optical tubes in one body with one piece drawtube to boot. Is Yuri Petrunin reading this??? 😁

Olly

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53 minutes ago, ollypenrice said:

Of course there is another, more radical solution to the perfecting of the dual rig. A manufacturer could steal a march on the competition by making a 'binocular' instrument - two parallel optical tubes in one body with one piece drawtube to boot. Is Yuri Petrunin reading this??? 😁

Olly

And the size of the market would be ? 😜

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1 hour ago, ollypenrice said:

Of course there is another, more radical solution to the perfecting of the dual rig. A manufacturer could steal a march on the competition by making a 'binocular' instrument - two parallel optical tubes in one body with one piece drawtube to boot. Is Yuri Petrunin reading this??? 😁

Hmmm.  Sufficiently well-corrected that all wavelengths came to focus at exactly the same point, too?

James

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Thanks @ampleamp for the link to the article, lots of food for thought, this project will clearly not be as straightforward as I first thought.

I have not come across the ONAG concept before,  I don’t see them widely advertised by the Astro retailers but  I assume IF still have patent protection?

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An off the wall idea. If you have a SX AO unit and an off or on axis guider you could use one on eack scope. As long as the flexure was within the range of the AO unit it would not need to bump the mount and the two would work independently. 

Ok in theory but I doubt it is practical.

Regards Andrew 

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19 hours ago, ampleamp said:

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.

Yes ive been trying the demo version of that, but its limited to 60 sec exposures, and being short on cash at the moment I dint fancy spending out £50 until ive got the flexure issue solved, but then a couple of weeks ago I found the method I mentioned above of just finding out what delay I need on the 2nd scope to keep in sync with the main scope, Ive used it about 6 nights now and as long as I press start on both maxims at same second they stay in sync perfectly all night long. I found the 383 needs to wait an extra 9 seconds longer than the 460 due to the dither and download time etc. I always use a 30 sec dither delay between exposure so the 2nd cam needs 39 secs. im so happy with how this has worked.

Going out to the Obs now to work on the flexure issue 😞 

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20 hours 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. 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

 

 

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Is that a garage ivy propagater  in the background?

Roger

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10 minutes ago, apophisOAS said:

Is that a garage ivy propagater  in the background?

Roger

Yes its quite awful looking isn't it, Ivy is trying to reclaim my whole garden, everytime I try to tackle it its like loosing battle.

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So, I cobbled up an extra counter weight using Mrs Tomato’s gym weights - I don’t need ‘em as I used to lift the Mesu on and off the pier until quite recently, and now I’m regularly lifting 150 mm refractors😊

It is now quite reasonably balanced, as far as you can tell with the drag of the friction drive. One observation, the scope on the adjustable saddle is a lot less rigid than the solidly mounted one, this is to be expected. 

Am I right in saying the primary reason for aligning the two scopes on a dual rig is to not waste any real estate on the camera sensors? As I will primarily be imaging small objects, I’m beginning to wonder how much benefit there will be from keeping the ADM saddle, it throws the two scopes out of balance on the dual plate, and adds a bit to the all up weight on the mount...

 

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Edited by tomato
Typo correction
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Indeed it is..  What cameras are you using ?  It'll make life somewhat easier if one camera has a larger sensor than the other as alignment will not need to be so precise.  I was also wondering whether you could get a bespoke thicker Losmandy bar made up that would extend the full length of both saddles and also move the scopes closer together.  The intention being that this would benefit both stiffness and scope alignment with the shutter aperture.

Dave

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Update, I determined that the Altair astro vixen bar was the weakest point as it is a lightweight design which has quite a lot of material removed for the recessed slots. so spent the afternoon repurposing one of my old homemade Dovetail bars, its 3/4" solid Aluminium vs the 1/2" Altair bar. Cut it in half so now have 2 🙂 but half way through I really wish I had bought a new hacksaw blade 😛 

All back together and rebalanced, Quick wiggle test and seems to have made a difference.

Lee

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Edited by Magnum
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To answer Daves question they are both Kaf8200 sensors (Moravian 8300 and an Atik 383)

The height difference between the two scopes with the adjustable ADM makes joining the two scope ring sets together with top bars difficult but not impossible so I could see that mounting without has some advantages. I have not spoken to Tomato today but it might be worth mounting the two cameras and seeing just how far out the two images are with and without the ADM adjuster

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The initial camera configurations are two KAF 8300 CCD sensors (an Atik 383 and Moravian G2-8300), hence that is why the adjustable saddle was acquired, or two ASI 178 cameras for small targets. One of each would have plenty of overlap but wouldn’t be very sensible.

Way forward is as @Tomatobro has suggested, try aligning the scopes without the saddle, and see how close they are.  

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