R Coronae Australis – Question

[jase]

Is it possible to go both wide and deep with an amateur telescope only 106mm/4” in aperture?

To answer this question, I would like to present the nebulae surrounding R Coronae Australis (R CrA). (http://www.cosmicphotos.com/gallery/image.php?fld_image_id=106&fld_album_id=11)

Located within the small and faint constellation Corona Australis (CrA, Southern Crown), a magical dust cloud graciously sweeps through this scene, harbouring numerous star forming regions. Visible are the magnificent blue reflection nebulae (NGC6726, NGC6727 and IC4812) produced from young, hot stars reflected by the clouds of surrounding cosmic dust. It’s estimated that the nebulae is around 420 light-years distant. Near the two blue reflection nebulae is a small yellowish arc (NGC6729) which marks the location of the erratic variable star R Coronae Australis. This star is accreting interstellar matter and would appear to be the source of two tiny red patches indicating active stellar creation. The grand globular star cluster (NGC6723) is seen below and left of the nebulae. It resides nearly 30,000 light-years away, well beyond the Corona Australis dust cloud.

Info and processing on the image;
Total exposure time: 3 hours (Luminance:75min, R:35min, G:35min, B:35min). The image is a LLRGB composite and processed similar to my other recent post of NGC6188 Wide Field (see post for info) – so I won’t repeat myself. The only exception, I did no deconvolution/sharpening on this image as I wanted to maximise nebulosity. This signifies the quality of the data captured. I did however use a couple of PS layers to manage highlights ensuring critical/detailed information didn’t get white clipped. Certain not an easy object to process as it has a vast dynamic range – really stretched the data hard to bring out the sweeping cosmic dust cloud.

So how wide and deep?

I feel this image comes close to showing the theoretical limit in resolution for the FSQ and STL11k combination. In its native configuration (530mm F/5), the FSQ-106ED has a documented resolution limit of 1.09”and a limiting magnitude limit of 11.9. I certainly wasn’t expecting such resolution and depth from a 3.52 arcsec/pixel scale. To demonstrate the resolution/depth achieved, I present an annotated version of the image highlighting a few background objects (with a 1:1 scaling ratio - 100%) from this scene. Annotated Image (http://www.cosmicphotos.com/reprocessed/CrA-Galaxies.jpg)

Thanks for looking. I hope you enjoy. All comments welcome.:)

[little col]

:eyepop::eyepop::eyepop: gobsmacked , amazing detail and wow cant believe how much info you have got

[iceman]

Wow Jase, that's a stunning image. I'm not sure if it's the same image I remember fondly from the late Erwin van der Velden - the brown dusty nebula looks very familiar.

A remarkable image, sharp from corner to corner. Absolutely fabulous, Jase. You should be very pleased.

[RB]

You certainly proved your point Jase, wide and deep indeed with a 4" scope !!!

Fantastic image once again Sir.

I know I sound like a broken record but all your images are consistent stunners !!!

:thumbsup:

[Garyh]

Jase, Jase, Jase, thats a lovely image!!!...:thumbsup::thumbsup:
Everything looks just right. The dark neb looks fantastic against the starry background!!!
very well done!!!

[Ric]

Hi Jase, your attention to the subtle details of imaging and processing has indeed produced an amazing image, it's beautifully sharp from end to endand the colours look spot on to me.

The globular sets it of wonderfully.

A fine effort.

[richardo]

Simply superb Jase;)
Love the huge fOV and the colours are spot on showing the dusky redish colour to the large extended cloud.
God I love the blue reflections.... this is one of my favourite objects in our
southern skies and what a ripper:thumbsup:

Top shelf Jase... keep up the great work!

All the best
Rich

[jase]

Thank you Col.:D



Cheers Mike. :thumbsup: Indeed, Erwin van der Velden took a marvellous wide field photo of this scene. Very inspirational. Thanks again.



Thanks Andrew. I’m not going to deny that aperture helps, but with the evolution of sensitive CCD cameras you can still go deep with modest aperture. Paying meticulous attention to things you can control such as guiding and focusing certainly helps. You’re obviously still at the mercy of Mother Nature for seeing. Imaging close to the zenith can mitigate some factors.



Thank you Gary. Not an easy one to process, but good fun doing so.:)



Cheers Ric. :thumbsup: I actually spent 30mins framing the object the night before I acquired the data. I wanted to capture the globular star cluster to the left and see the dark sweeping cosmic cloud move diagonally from top left to bottom right. Sounds crazy, but composition is something I value to bring out the aesthetics.



Thanks Rich. :thumbsup: Indeed, blue reflection nebs are a real treat to image. This one took quite some work – NGC6726-27 the bottom two blue nebs really burnt out when I started stretching the data. I ended up create three layers of varying brightness to control this dynamic range. I also layered the globular star cluster to maintain core resolution.

Once again, thank you all for your comments. :)

[avandonk]

There are no afffordable optics as good as FSQ106ED or Canon super telephoto. I personally think they have reached the theoretical limit of optical quality due to construction. Unless we develop glass that is more homogeneous we have hit the wall. This is what limits very large refractors. Enjoy all the images. Jase is not too bad at it.

This is almost as good as it gets! I hope I am wrong.

Bert

[Dr Nick]

Amazing. Who would have thoght that that much detail e.g. galaxies could be captured in such a wide field! Congratz! ;)

[strongmanmike]

Ooooh niiiiice!

This area has such a ghostly feel to it when imaged well as you have done here and makes for an impressive vista.

Seeing distant galaxies through all that galacitic crud is quite amazing really.

I must do that region with the AP and ProLine asap, My FOV is about half that so it'd be hard to decide how to frame it and what part to go for actually..?

Enjoyed it I did :thumbsup:

Mike

[glenc]

Amazing image Jase.
James Dunlop discovered NGC 6723 from Sydney on 2/6/1826.
He wrote the first descriptions of this area. Dunlop 573 = NGC 6723
"A beautiful bright round nebula, about 3.5' diameter, moderately and gradually condensed to the centre. This is resolvable. The moderate condensation, and the bluish colour of the stars which compose it, give it a very soft and pleasant appearance. This is rather difficult to resolve, although the condensation is not very great ."

He also discovered the dark nebula nearby, here is one of the first descriptions of a dark nebula. Dunlop 559 = Bernes 157
"A singular dark space in the heavens, of an irregular figure, about 1.5 long, and 1.5° broad; no stars except exceedingly minute stars in the greatest portion of this space. There is a bright star in each side. "
Bernes catalogued the dark nebula in 1977, 151 years after Dunlop.

James Dunlop and John Herschel both missed the reflection nebulae, they were first seen by Schmidt in 1861.

[KG8]

This is a beautiful photograph surely. I especially like the positioning of the globular cluster, the way it forms an asterizm of sorts with the arc of the 4 blue giants to it's right. It looks to me like a sextant.

[2020BC]

Wonderful:thumbsup:

[jase]

Thanks Bert. Indeed, the FSQED optics are pretty good but I’m finding little things about the scope which do frustrate me – such has how rigid you need to couple the camera to the 4” focuser. At F/5, it’s really sensitive to any form of flexure or slight misalignment/squareness with the optical axis. You end up with a degraded image resulting in elongated stars in one corner of the frame. This is a real pain to deal with especially when you’ve got a 2.5kg CCD camera hanging off the back. The FLI and Apogee CCD’s are even heavier! Imaging at zenith places no stress on the coupling hence squareness to the optical axis is achieved easier.



Thanks Dr. Nick



Cheers Mike. Just mosaic it – no brainer. You should be able to keep most of the intricate details within two KAI-11000 frames with approx 10% overlap. What are you waiting for?



Thanks Glen. Appreciate the additional information providing a greater insight into this sky scene. Interesting both James and John missed the reflection neb considering it’s rather predominate.



Cheers KG8. Image composition is often over looked.



Thanks Bill


Once again, thank you all. I've updated the link above to the new gallery where you will find a higher resolution version, if you can put up with jpeg artifacts;)

[montewilson]

Jase - that's hot stuff. I think I need to up my output. My problem is I need to get out more at night. I don't have a permanent set-up so I only take pix a couple of nights per month. Inspiring results.

[jase]

Cheers Monte. :thumbsup: Mate, same focal lengths and cameras (not that it makes a big difference). If you want to do some collaborative work some time, just PM me. I'll provide the RGB, if you want to provide the narrowband (ha) or vice-versa. You use TPoint. I use Maxpoint. We should be able to frame an object with precision to register and combine despite our environmental differences. Start small, but eventually get into multi-frame mosaics with large integrated exposure times collected from two FSQ/STL11k combos. :D

[strongmanmike]

Ah yes..thougt of that but my time and weather is so fickle that doing it in one night properly would be impossible really and setting up over two nights that might be weeks apart is not atractive either ..OH how I need an observatory like this one again, imaging life was so easy :sadeyes: :sadeyes: one day soon...one day soon....

http://www.pbase.com/strongmanmike2002/observatorygeneral

Mike

[montewilson]

Hmmm - I'll think about that. It´s an interesting idea. I enjoy doing Ha stuff. Any suggestions on a suitable object that we could consider?

BTW - are you having troubles focusing? I use RoboFocus and although I can get focus it is rarely quick or easy and the @Focus feature in CCDsoft is not much chop if you don't have an absolute encoder value for the focus position. The backlash in the stepper motor confuses it.

[glenc]

Jase you wrote "Interesting both James and John missed the reflection neb considering it’s rather predominate."
Here is my theory about that.
Modern aluminium mirrors reflect 85% of the blue light, at 400nm, and 89% of the orange light, at 600nm.
I estimate that the speculum mirrors used by Dunlop and Herschel reflected about 47% of the blue light and 76% of the orange light. Maybe that is the reason why they missed the blue reflection nebula.
Silver on glass mirrors were first used in 1856. Schmidt discovered NGC 6726-7-9 in 1861.
Copper only reflects 35% of the light at 400nm and tin 76% at 400nm.
Speculum was 12 parts copper and 5 parts tin according to:
http://www.saao.ac.za/assa/html/his-obj-tel_-_herschel__14ft_.html

[jase]

Monte, I’ll let you pick the first target if you like. There are endless objects in the night sky to target with the FSQ. There is nothing it won’t frame well with exception to small planetary nebs and galaxies as you generally need a longer focal length. Try to pair two interesting objects in the FOV, such as a neb and cluster to provide something unique. In future, we can use TheSky mosaic tool to ensure both our frames are centered as we collectively acquire data. I’m presently working on a small mosaic project at the moment, of which I’ve only collected 3 hours worth of one frame. I’ll come back to that when the moon disappears again.

The hardest part will be the differences in CAA rotation. If my CAA is slightly different to yours, we’ll crop data. In the grand scheme of things, this is only a minor issue. A plate solve may sort it out, but we will need to test this. Just take exposure of the target – full frame and upload it to my website. I will provide you with login details via PM. I can then center the object and commence data acquisition.

Re: Focusing… You don’t have to teach Robofocus so it moves the focuser physically all the way in from out. I’ve only taught it ~400 steps of either side of critical focus. Also adjust the step size so it is reasonably small. You can also tune backlash in the Robofocus control panel. I’d imagine it wouldn’t be much, perhaps 5 to 10 steps. The critical focus zone for the FSQ is only 55 microns so the lower step size will assist. I usually work around 5 or 6 microns per step. Providing you consistently hit this zone, you’ll be fine. Not all my filters are parfocal so I refocus regularly. You get focus shifts as the temp. changes anyway. Mine haven't been large enough to worry about. I've actually acquired RGB data in one night without having to refocus. Imaging in an observatory does provide a stable environment.

I have no focusing problems, but I don’t use @focus which I believe is CCDSoft specific. I use MaximDL for image acquisition which has a similar automated focusing routine, but I don’t use it either. FocusMax all the way my friend. I reach precise focus generally under a minute every time. Works a treat once you’ve built a good v-curve model – around 40-50 steps as it moves through the critical focus zone (you’ll need at least 6 v-curve runs to build a good model). What I like about FocusMax is that as it begins to reach close to focus, it stops and takes five or six exposures. This allows the software to accurately determine the FWHM and other measurement calculations on the star based on seeing conditions. Using this information it calculates where precise focus is located and moves focuser to that position. There is no way I could obtain this level of focus accuracy and consistency manually The only time I’ve experienced issues is when the star automatically targeted to focusing is in a cluster. Hope this helps. FocusMax - Highly recommended.



Thanks for the info Glen.:) Good point. Mirror coatings were very different back then.