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Dual RASA 8 rig - nearly there


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I am so amazed by the RASA 8 performance that I bought a second one this spring:blob9:. Initially I have been using the first one on an iOptron CEM70 mount and I put the second one on my Mesu 200, so in two separate obsies here at my little farm. But I rather use the Mesu for some of my other scopes so I decided to make a double RASA 8 rig and put it on the CEM70. One of the RASAs have an Evostar 72 as guidescope and I put a piggy-back scope on the other: an old Canon FD 200 mm f/2.8 I found cheaply on e-bay with an ASI2600MC. I have ASI2600MCs also on the RASAs. The whole shebang put together turned out to weigh 29 kg so I may really be pressing that mount (iOptron claims that it can take on 32 kg but maybe that is visually). I put it up on the mount today and realized that I need at least one more 10 kg counterwieght, which is now on order from TS. I just hate the price of counterweights😬.

If the iOptron cannot handle it well enough to give me reasonably good guiding, plan B is to put it all on the Mesu 200. I will find out when I finally have enough counterweights to balance it.

Why two RASAs one may wonder? My idea is to either make instant 2-panel mosaics, or collect HaOiii (IDAS NBZ filter) with one and RGB with the other. Or just double the integration time I can get in one night.

Cheers, Göran

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Edited by gorann
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  • gorann changed the title to Dual RASA 8 rig - nearly there

Double RASA canon! Same optics and camera pixels, FOV, give you lots of near-identical options to mix RGB, mono, etc. 

I once saw a quad barrel setup, I think it was teh sharpstar 13028HNT. It had a nice idea to mount all four in a 2x2 single holder, probably only needed a single central mounting plate.

How do you plan a mosiac with parallel optics? And can one scope be offset in DEC after initial platesolving to image two different targets while tracking in RA?

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11 minutes ago, GalaxyGael said:

Double RASA canon! Same optics and camera pixels, FOV, give you lots of near-identical options to mix RGB, mono, etc. 

I once saw a quad barrel setup, I think it was teh sharpstar 13028HNT. It had a nice idea to mount all four in a 2x2 single holder, probably only needed a single central mounting plate.

How do you plan a mosiac with parallel optics? And can one scope be offset in DEC after initial platesolving to image two different targets while tracking in RA?

Thanks! With one of them sitting on an adjustable saddle it should be possible to take two images next to each other, either above or below the other so the aspect will be close to the "standard" 4:3, or side by side for a panorama. To some extent I should be able to maybe point at two separate object but they cannot be too far apart (not sure how much flexibility there is in that adjustable saddle).

Yes, I think I have also seen that Sharpstar 130 quadruplet somewhere. I wonder how they solved the alignment - must be adjustable somehow. Doing a quadruplet RASA is apparently possible:

 

And even more but them we get into professional territory:

https://www.dpreview.com/forums/post/62471743

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Ah, interesting. An array or rasa or other fast newtonians with adaptive optics could acquire a lot of data, deep, over big sky. 

Clever idea, especially when playing the filters. We used to do this with slow RCs to make up time, and they were good for IR imaging with slightly different camera sensors. 

Good luck with your setup. 

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If you have the same camera and filters on both scopes, finish your first panel in half the time then move on to the next one. That’s what I try and do with my dual Esprit 150 rig. 
However, I guess the saddle has enough adjustment to create a 10 or 20% overlapping FOV?

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1 hour ago, tomato said:

If you have the same camera and filters on both scopes, finish your first panel in half the time then move on to the next one. That’s what I try and do with my dual Esprit 150 rig. 
However, I guess the saddle has enough adjustment to create a 10 or 20% overlapping FOV?

Yes Steve, I expect I can use the saddle to get mosaics with 10-20% overlap.

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Looks like another impressive season coming up for the Hole Observatory, and there will be some RASA output from Les Granges to look forward to also. I must dust off my RASA8 at some point. Too much kit, not enough clear nights.😄

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4 minutes ago, tomato said:

Looks like another impressive season coming up for the Hole Observatory, and there will be some RASA output from Les Granges to look forward to also. I must dust off my RASA8 at some point. Too much kit, not enough clear nights.😄

I am excited about what will come out of Les Granges, and slightly worried about what Hole Obsy has got itself into🤔

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Nice. If differential flexure turns out to be a pro lem  you may have to add a bar at the top also, connecting the two scopes there.

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13 hours ago, tomato said:

If you have the same camera and filters on both scopes, finish your first panel in half the time then move on to the next one. That’s what I try and do with my dual Esprit 150 rig. 
However, I guess the saddle has enough adjustment to create a 10 or 20% overlapping FOV?

Yes, maybe that is easier. Thanks!

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Posted (edited)
1 hour ago, wimvb said:

Nice. If differential flexure turns out to be a pro lem  you may have to add a bar at the top also, connecting the two scopes there.

Thanks Wim for pressing me to finally put it together! I am not too worried about flexure since I use an identical rig for my Esprits with longer FL and never had a problem (or at least never realized I had a problem). I did think about it and I think it would make it difficult to do separate framing with the two scopes. Maybe it could also induce some tension and distort the shape of the tubes. In any case, to find out I need a counterweight and a clear sky🙂

Edited by gorann
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7 minutes ago, tomato said:

I definitely needed a bracing plate across the top of my scopes, but RASA8s are much lighter and shorter than Esprit 150s. 

My Esprit rig is a 150 with OAG and a 100 next to it. The relatively short tube and short FL of the 100 probably help to reduce any problem with flexure. I can see the necessity for a bracing plate with two 150s.

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I sometimes put my WO132 and FS102 up together .

The 102 is in collimatable rings and yes I need a bracing plate which ups the keepers to 90% rather than 50%.

 

Brace not in place but seems to have gained another passenger.

 

1557233981_20201214_1509471.thumb.jpg.8ec06f00237918244e0777e22f04b491.jpg

 

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Wow that's a pretty impressive "sky hoover" Goran! Looking forward to seeing the results of this in action.. when will you have time to process all that data!! 🤣

I've just got a CEM70 myself to set up another rig with my 2 Esprit 80's on a side by side & have the same JTD saddle. I got it a few years ago when the Robin Casady ones were like gold dust.. knowing it would come in handy one day ;) 

I see ADM now do the same design here.. https://www.admaccessories.com/product/tgad-tandem-guiding-aiming-device-altaz-aiming-device-for-side-by-side-systems/ 

I'm still putting the bits together for mine but I saw that the recommended imaging weight of the CEM70 is 2/3rds of the 31.8kg payload so ~21kg?  So it'll be interesting to see how you get on!

How did you go about moving the saddle around to 90 degree? I see there's no option in the handset to re home and when I unbolted and had a look under the saddle I can see there's a cut out for the PCB of the onboard USB/power ports that protrudes down. So it won't rotate and reseat at 90 degrees as the deeper cutout is on the lower side of the DEC housing only. I also read that the hard stops are there to stop damage to the wiring loom and not to remove them?

I'm expecting one of these to arrive today to try https://www.firstlightoptics.com/dovetails-saddles-clamps/cgx-sbs-celestron-cgx-side-by-side-adapter.html but all the bars/saddles and this really knocks the weight up! Plus I'm now wondering if that payload is reduced by any extra counterweights added.. it probably does!

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Weight by itself isn't always the problem. It's more where you put that weight. If too much weight is too far from the mounts rotation axes the moment of inertia becomes too large, and this will cause problems when any movement starts/stops. So you may need to keep the slew speed low. You also have to be careful with guiding. And finally, there will be flexure between the scope and the counterweight bar. It's similar to what you see with weightlifting. (Remember, we're talking about arc seconds here.)

4.thumb.jpg.851a981e9c9352647765c94bc4d82667.jpg

People have overloaded their mounts, and still got good tracking. As long as you know what you're doing.

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1 hour ago, Sp@ce_d said:

Wow that's a pretty impressive "sky hoover" Goran! Looking forward to seeing the results of this in action.. when will you have time to process all that data!! 🤣

I've just got a CEM70 myself to set up another rig with my 2 Esprit 80's on a side by side & have the same JTD saddle. I got it a few years ago when the Robin Casady ones were like gold dust.. knowing it would come in handy one day ;) 

I see ADM now do the same design here.. https://www.admaccessories.com/product/tgad-tandem-guiding-aiming-device-altaz-aiming-device-for-side-by-side-systems/ 

I'm still putting the bits together for mine but I saw that the recommended imaging weight of the CEM70 is 2/3rds of the 31.8kg payload so ~21kg?  So it'll be interesting to see how you get on!

How did you go about moving the saddle around to 90 degree? I see there's no option in the handset to re home and when I unbolted and had a look under the saddle I can see there's a cut out for the PCB of the onboard USB/power ports that protrudes down. So it won't rotate and reseat at 90 degrees as the deeper cutout is on the lower side of the DEC housing only. I also read that the hard stops are there to stop damage to the wiring loom and not to remove them?

I'm expecting one of these to arrive today to try https://www.firstlightoptics.com/dovetails-saddles-clamps/cgx-sbs-celestron-cgx-side-by-side-adapter.html but all the bars/saddles and this really knocks the weight up! Plus I'm now wondering if that payload is reduced by any extra counterweights added.. it probably does!

 

33 minutes ago, wimvb said:

Weight by itself isn't always the problem. It's more where you put that weight. If too much weight is too far from the mounts rotation axes the moment of inertia becomes too large, and this will cause problems when any movement starts/stops. So you may need to keep the slew speed low. You also have to be careful with guiding. And finally, there will be flexure between the scope and the counterweight bar. It's similar to what you see with weightlifting. (Remember, we're talking about arc seconds here.)

4.thumb.jpg.851a981e9c9352647765c94bc4d82667.jpg

People have overloaded their mounts, and still got good tracking. As long as you know what you're doing.

Both of you have good points. Thanks! Now there is only one way to find out🥴

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Posted (edited)
19 minutes ago, tomato said:

Like most good Astro kit they are currently out of stock.😉

you mean like this one. It says 4-6 working days, the same as for the Zarkov Cloud Gun. Could be a code.....

https://www.firstlightoptics.com/optical-tube-assemblies/celestron-rowe-ackermann-astrograph-rasa-8.html

Edited by gorann
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