Closeup of the Tadpoles from a RASA 8 wide field

[gorann]

@Rodd  just posted a very impressive closeup of the Tadpoles in IC405. This got me inspired to do the same with my last image taken in November before clouds settled here, apparently forever. At this closeup the stars looks a bit odd, dimond shaped. I have not had that with the RASA8 before and think (or rather hope) it is due to a slightly off-centered camera (will plan to fix the wobbly attachment until next time) but it could also be some pinching of the mirror since it was - 4°C that night. Will find out next time it clears, whenever that will be.

Still, I think it shows that the RASA 8 - ASI2600MC combo is quite good at picking up rather small details. 83 x 2 min subs (IDAS NBX dual-band filter), so totally only 2.7 hours.

Here is the full frame (no it is not a mosaic):

And here is the crop:

Edited December 16, 2020 by gorann

[michael.h.f.wilkinson]

Amazing image. I must say, the RASA 8" looks very tempting indeed

[gorann]

1 hour ago, michael.h.f.wilkinson said:

Amazing image. I must say, the RASA 8" looks very tempting indeed

Thanks Michael! Yes, I even contemplate over the possibility of having a double RASA 8 rig one day......

[michael.h.f.wilkinson]

33 minutes ago, gorann said:

Thanks Michael! Yes, I even contemplate over the possibility of having a double RASA 8 rig one day......

I just looked up what a HyperStar conversion plus HyperStar assembly would cost for my old C8 (black tube, bought in 1995), and I think I will simply start saving for the RASA itself

[gorann]

23 minutes ago, michael.h.f.wilkinson said:

I just looked up what a HyperStar conversion plus HyperStar assembly would cost for my old C8 (black tube, bought in 1995), and I think I will simply start saving for the RASA itself

I never used a Hyperstar but from what I have read the RASA is something quite different especially when it comes to collimation issues. My RASA was perfectly collimated and have stayed like that. It is my impression that this is the norm for RASA. It also holds focus very well over the night. I think the Hyperstar concept is a bit of a compromise while the RASA optics are designed for fast imaging from the start. The RASAs (except the first generation of RASA 11) have a much better focusing mechanisms than the ordinary Celestron SCTs and there is no tendency for movements in the mirror. Apparently it is so good that a mirror lock system like I have on my SCTs is not needed and is not there.

Edited December 16, 2020 by gorann

[Rodd]

2 hours ago, gorann said:

At this closeup the stars looks a bit odd

Tough to compare RGB with narrowband--they pick up different details, and for a given system, NB will always out resolve BB in less than pristine skies (if there is Ha structure to be found).  To really get a look at the stars I think you should not use masked stretch--it always creates stars with a fuzzy outer part and pinned core.  The other thing to consider is zooming in on widefield shots is VERY TOUGH on stars--especially if seeing was good and the FWHM is near 1.6x (or less) the pixel scale in pixels  For my FSQ 106 with .6x reducer, the pixel scale is 2.46 arcsec/pix.  On a good night I can achieve a FWHM of, lets say 3.8 arcsec.  That is a bit over 1.5 pixels per star core.  That is not very conducive to zooming.  When I use the TOA the pixel scale is .77 arcsec/pix.   My sky is never much better than 3 arcsec seeing--sometimes 2.  A really good night for me is a FWHM of 2 arcsec (more often 2.5 (rarely 1.8).  For a FWHM of 2.5 that means I am over 3 pixels per star core--that makes for better stars.  A good sense of the resolution in the tadpoles is the degree of separation of the two head stars in the face on tadpole--and if the third star in the head is visible with separation--the masked stretch fuzziness makes this hard to determine.

All in all I love the palette and am starting to shoot more BB nebula.  I have gotten waylaid by the Sh2-240 mosaic, which is taking all the limited time I have.  

[ollypenrice]

Very fine image with spectacular contrast letting the Tadpoles show so much detail. Most impressive.

Have you considered trying a blend of the dual band filtered data with unfiltered to get the star colour?

Olly

[gorann]

2 hours ago, ollypenrice said:

Very fine image with spectacular contrast letting the Tadpoles show so much detail. Most impressive.

Have you considered trying a blend of the dual band filtered data with unfiltered to get the star colour?

Olly

Thanks a lot Olly! Yes, if I had an RGB of it. This was taken while the moon was out and I had resided to do dual band imaging. Right now the sky prohibits any imaging.....

[gorann]

4 hours ago, Rodd said:

Tough to compare RGB with narrowband--they pick up different details, and for a given system, NB will always out resolve BB in less than pristine skies (if there is Ha structure to be found).  To really get a look at the stars I think you should not use masked stretch--it always creates stars with a fuzzy outer part and pinned core.  The other thing to consider is zooming in on widefield shots is VERY TOUGH on stars--especially if seeing was good and the FWHM is near 1.6x (or less) the pixel scale in pixels  For my FSQ 106 with .6x reducer, the pixel scale is 2.46 arcsec/pix.  On a good night I can achieve a FWHM of, lets say 3.8 arcsec.  That is a bit over 1.5 pixels per star core.  That is not very conducive to zooming.  When I use the TOA the pixel scale is .77 arcsec/pix.   My sky is never much better than 3 arcsec seeing--sometimes 2.  A really good night for me is a FWHM of 2 arcsec (more often 2.5 (rarely 1.8).  For a FWHM of 2.5 that means I am over 3 pixels per star core--that makes for better stars.  A good sense of the resolution in the tadpoles is the degree of separation of the two head stars in the face on tadpole--and if the third star in the head is visible with separation--the masked stretch fuzziness makes this hard to determine.

All in all I love the palette and am starting to shoot more BB nebula.  I have gotten waylaid by the Sh2-240 mosaic, which is taking all the limited time I have.  

Not sure what you mean about comparing RGB with NB. They are both NB and my image is a Ha Oiii image (IDAS NBX filter). Actually Rodd I like the soft fuzzy edges of the stars more than the round blown out ones, so it is on purpose and it is probably a matter of taste. However, maybe the stars were a bit too fuzzy at this scale so I now used curves on the stars to reduce them and the fuzziness a bit to make them a bit more descrete. But at a FL of 400 mm and a very aggresive crop I am here really working close to the pixel resolution. But this version shows a bit more separation of stars:

[tomato]

Another fine image from the RASA/2600 combination, with regard to your diamond stars I experienced something very similar but more severe on my initial set up which I put down to tilt, and/or  incorrect spacing.:

These have disappeared since the installation of the custom spacer/filter holder, although the stars are still not 100% in the corners, but the adjustments on the QHY tilt device are super sensitive to the extent that I don’t like rotating the camera with this device for fear of reintroducing the error.

I also saw the RASA as a totem for clear skies following your experience but looks like that hope has been dashed.😉

[gorann]

6 minutes ago, tomato said:

Another fine image from the RASA/2600 combination, with regard to your diamond stars I experienced something very similar but more severe on my initial set up which I put down to tilt, and/or  incorrect spacing.:

These have disappeared since the installation of the custom spacer/filter holder, although the stars are still not 100% in the corners, but the adjustments on the QHY tilt device are super sensitive to the extent that I don’t like rotating the camera with this device for fear of reintroducing the error.

I also saw the RASA as a totem for clear skies following your experience but looks like that hope has been dashed.😉

Thanks Steve. Interesting! For me it happened after midnight when I was done with another object (where the stars later turned out to be fine) and I had to rotate the camera to frame IC405&410. As you now the camera attatchment allows it to move sideways and I may have ended up with it quite uncentered. I hope that is the cause of the problem, but I need a clear sky to find out.......

Edited December 16, 2020 by gorann

[tomato]

Yes, it is very easy to move the sensor off centre with the QHY adjuster. On three targets the other night the stars were Ok after a some adjustments on the first target but went downhill on the second and third targets without me touching the camera. The 268c is quite a heavy camera, I wonder if there is some flexture occurring (eeeek!) when the scope is in different orientations?

[gorann]

4 minutes ago, tomato said:

Yes, it is very easy to move the sensor off centre with the QHY adjuster. On three targets the other night the stars were Ok after a some adjustments on the first target but went downhill on the second and third targets without me touching the camera. The 268c is quite a heavy camera, I wonder if there is some flexture occurring (eeeek!) when the scope is in different orientations?

Yes, the problem as you know is that the outer edge of the camera adapter has to pass through the threads and then behind the threads there is space for it to move sideways. So this what I will try to use: a cirular piece of plastic covered steel wire to put in behind the threads in the Celestron attachment ring to force the camera to be centered. Have not tested it yet.

[tomato]

That’s a smart fix, this was effectively eliminated on my custom spacer as Tomatobro reduced the clearances between the threaded ring and the adapter.

The QHY adjuster is basically three screws 120 degrees apart acting on a tapered face, so it’s quite easy to move the camera off centre when adjusting.

[ollypenrice]

12 hours ago, gorann said:

Not sure what you mean about comparing RGB with NB. They are both NB and my image is a Ha Oiii image (IDAS NBX filter). Actually Rodd I like the soft fuzzy edges of the stars more than the round blown out ones, so it is on purpose and it is probably a matter of taste. However, maybe the stars were a bit too fuzzy at this scale so I now used curves on the stars to reduce them and the fuzziness a bit to make them a bit more descrete. But at a FL of 400 mm and a very aggresive crop I am here really working close to the pixel resolution. But this version shows a bit more separation of stars:

If you'd asked me whether this picture could have been taken at a FL of 400mm I'd have said, 'Not a chance,' and been totally wrong. I'm a great believer in the power of small telescopes with small pixel cameras (and wrote an Astronomy Now article on the matter) but, even so, this amazes me.

The problem of how one might combine a NB-filtered OSC image with an unfiltered one has been ticking over in my head (because I'm thinking about a CMOS OSC for here depending on how the pandemic evolves.) If the idea were simply to add star colour then I'd be inclined to try the unfiltered image as a bottom layer and erase the top layer's stars. This would let the colour through while preserving the small size of the NB stars. Alternatively the unfiltered layer on top in Blend Mode Colour might work.

While the full image is mighty impressive, I do feel it has that slightly two-dimensional colour seen in HOO images. What looks like a strong OIII presence in the crop makes that that region look richer from a colour point of view. But maybe the impression just arises from a lack of star colour.

One thing's for sure: the game has changed.

Olly

[gorann]

4 hours ago, ollypenrice said:

If you'd asked me whether this picture could have been taken at a FL of 400mm I'd have said, 'Not a chance,' and been totally wrong. I'm a great believer in the power of small telescopes with small pixel cameras (and wrote an Astronomy Now article on the matter) but, even so, this amazes me.

The problem of how one might combine a NB-filtered OSC image with an unfiltered one has been ticking over in my head (because I'm thinking about a CMOS OSC for here depending on how the pandemic evolves.) If the idea were simply to add star colour then I'd be inclined to try the unfiltered image as a bottom layer and erase the top layer's stars. This would let the colour through while preserving the small size of the NB stars. Alternatively the unfiltered layer on top in Blend Mode Colour might work.

While the full image is mighty impressive, I do feel it has that slightly two-dimensional colour seen in HOO images. What looks like a strong OIII presence in the crop makes that that region look richer from a colour point of view. But maybe the impression just arises from a lack of star colour.

One thing's for sure: the game has changed.

Olly

Thanks Olly, I am equally surprised about the capacity of this scope and camera. It now struck me that the star colour situation can be improved with the usual PS methods: S-shaped curves in Lab Color and Increase Star Color in Noel's actions:

 

Edited December 17, 2020 by gorann

[AbsolutelyN]

23 hours ago, gorann said:

I never used a Hyperstar but from what I have read the RASA is something quite different especially when it comes to collimation issues. My RASA was perfectly collimated and have stayed like that. It is my impression that this is the norm for RASA. It also holds focus very well over the night. I think the Hyperstar concept is a bit of a compromise while the RASA optics are designed for fast imaging from the start. The RASAs (except the first generation of RASA 11) have a much better focusing mechanisms than the ordinary Celestron SCTs and there is no tendency for movements in the mirror. Apparently it is so good that a mirror lock system like I have on my SCTs is not needed and is not there.

Can confirm the focus holds very well indeed. Set mine up and focused 2 days ago but clouds rolled in so covered the scope but left it setup. Finally cleared and stopped raining last night and started imaging without refocussing as focus was still as good as I could get it.  Also played with idea of dual rasas but uk weather so hopeless currently having second thoughts about spending more on something that only gets occasional use. 

Fantastic images by the way!

Edited December 17, 2020 by AbsolutelyN

[gorann]

5 minutes ago, AbsolutelyN said:

Can confirm the focus holds very well indeed. Set mine up and focused 2 days ago but clouds rolled in so covered the scope but left it setup. Finally cleared last night and started imaging without refocussing as focus was still as good as I could get it.  Also played with idea of dual rasas but uk weather so hopeless currently having second thoughts about spending more on something that only gets occasional use. 

Fantastic images by the way!

Thanks Tristan! Yes, I have the same experience - focus remains spot on between days, and I have so far not lost a sub due to focus drift. The weak point is the sensitivity for sensor distance and any tilt, but that is probably inevitable for such a fast system.

Edited December 17, 2020 by gorann

[AbsolutelyN]

7 minutes ago, gorann said:

Thanks Tristan! Yes, I have the same experience - focus remains spot on between days, and I have so far not lost a sub due to focus drift. The weak point is the sensitivity for sensor distance and any tilt, but that is probably inevitable for such a fast system.

Yes I'd love to be-able to rotate camera for framing but dare not touch it as currently have reasonable stars. Will have to try that Artesky adaptor at some point. 

[gorann]

4 hours ago, AbsolutelyN said:

Yes I'd love to be-able to rotate camera for framing but dare not touch it as currently have reasonable stars. Will have to try that Artesky adaptor at some point. 

I made some modifications to the Artesky adapter. In this image you see the side attaching to the scope. I have drilled two holes so I kan use a tool like the one in the image (found on ebay) to unscrew it safely from the camera since I realized that it could easily get stuck on the camera. Especially when I have a filter in there centrally I could not get a grip on it since the threaded ring from Celestron (not in this image) will just rotate freely (if you see what I mean). The second modification is the brown adhesive teflon tape (also ordered from ebay) that provides low friction so that the camera hopefully can be easily rotated. The tape is only 0.13 mm so it should not have much impact on the sensor distance. Further up in this thread you can see the wire ring I will introduce  between the Artesky adaper and the threaded Celestron ring so that it cannot wobble sideways. Now I just have to get a clear night to test it all.....

Edited December 17, 2020 by gorann

[AbsolutelyN]

40 minutes ago, gorann said:

I made some modifications to the Artesky adapter. In this image you see the side attaching to the scope. I have drilled two holes so I kan use a tool like the one in the image (found on ebay) to uscrew it safely from the camera since I realized that it could easily get stuck on the camera. Especially when I have a filter in there centrally I could not get a grip on it since the threaded ring from Celestron (not in this image) will just rotate freely (if you see what I mean). The second modification is the brown adhesive teflon tape (also ordered from ebay) that provides low friction so that the camera hopefully can be easily rotated. The tape is only 0.13 mm so it should not have much impact on the sensor distance. Further up in this thread you can see the wire ring I will introduce  between the Artesky adaper and the threaded Celestron ring so that it cannot wobble sideways. Now I just have to get a clear night to test it all.....

Brilliant, hope it does the job. Certainly looks a lot more precise than the Celestron one with it's soft foam backing! You'd think Celestron themselves might bring out some kind of advanced version of the adaptor making some of this stuff easier.  

[ollypenrice]

1 hour ago, AbsolutelyN said:

Can confirm the focus holds very well indeed. Set mine up and focused 2 days ago but clouds rolled in so covered the scope but left it setup. Finally cleared and stopped raining last night and started imaging without refocussing as focus was still as good as I could get it.  Also played with idea of dual rasas but uk weather so hopeless currently having second thoughts about spending more on something that only gets occasional use. 

Fantastic images by the way!

Beware of dual rigs (ie on one mount) at high resolution. Most who try it find it is difficult/impossible without recourse to Peter Goodhew's solution of an AO unit on the slave scope. We found it worked sweetly at 3.5"PP but is a pain at 0.9.

Olly

[AbsolutelyN]

4 minutes ago, ollypenrice said:

Beware of dual rigs (ie on one mount) at high resolution. Most who try it find it is difficult/impossible without recourse to Peter Goodhew's solution of an AO unit on the slave scope. We found it worked sweetly at 3.5"PP but is a pain at 0.9.

Olly

Thanks Olly - if I was ever to make the RASA dual I think I'd just mount it separately - much simpler and have option of imaging different targets at the same time. 

[gorann]

2 hours ago, ollypenrice said:

Beware of dual rigs (ie on one mount) at high resolution. Most who try it find it is difficult/impossible without recourse to Peter Goodhew's solution of an AO unit on the slave scope. We found it worked sweetly at 3.5"PP but is a pain at 0.9.

Olly

If I ever do it I will virtually bolt them together. Good thing is that there is no tendency for mirror flips in the RASA and the short FL and wide field makes them easy to align to a sufficient degree. And I would not be a pioneer. Just wish I have had a chance to tell him to arrange his cables better - he will get a mess of star spikes:

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

Edited December 17, 2020 by gorann

[ollypenrice]

1 hour ago, gorann said:

If I ever do it I will virtually bolt them together. Good thing is that there is no tendency for mirror flips in the RASA and the short FL and wide field makes them easy to align to a sufficient degree. And I would not be a pioneer. Just wish I have had a chance to tell him to arrange his cables better - he will get a mess of star spikes:

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

There's no tendency for mirror flop in TEC 140s either but it still doesn't work...

Olly