Wide fields: Coalsack, Tail of Scorpius, Rho Ophiuchi

[naskies]

Hi everyone,

Hooray - clear skies and cool weather in Leyburn last weekend meant that I could finally capture some of the images I've been after for months.

(Click on the links for higher quality versions.)

1. Coalsack and Dark Doodad Nebulae (http://dl.dropbox.com/u/13644418/iis/CoalsackDoodad.jpg): 20x 90 sec (total 30 mins), 135 mm, f/4, ISO 3200.

2. Tail of Scorpius (http://dl.dropbox.com/u/13644418/iis/TailOfScorpius.jpg): 18x 180 sec (total 54 mins), 135 mm, f/4, ISO 1600.

3. Rho Ophiuchi (http://dl.dropbox.com/u/13644418/iis/RhoOphiuchi.jpg): 35x (31 stacked) 180 sec (total 105 mins), 135 mm, f/4, ISO 1600.

4. Self portrait under the "emu" (http://dl.dropbox.com/u/13644418/iis/LeyburnMilkyWaySelfPortrait.jpg): 1x 30 sec 14 mm f/2.8 ISO 6400 (fixed tripod).

Images 1-3 were shot with a Canon 5DmkII and 135 mm f/2L lens on an Astrotrac. Thanks for looking!


Cheers,

Dave

[multiweb]

:bowdown: Absolutely gorgeous. Loved them all! :thumbsup:

[iceman]

Amazing images - the first 3 are stunning.

[troypiggo]

Very nice set. The astrotrac seems to do well at that focal length.

[RickS]

Beautiful shots, Dave! You had a very productive night.

Cheers,
Rick.

[DavidTrap]

These are incredible Dave!

I hope I can get my widefield setup humming like yours.

DT

[Martin Pugh]

Great work. I particularly like the Rho Ophiuchi image.

well done
Martin

[DavidU]

Wonderful stuff ! The site looks nice & dark. Well done,

[tilbrook@rbe.ne]

Hi Dave,

Absolutely stunning!!!

These images are so sharp and full of detail

Cheers,

Justin.

[rogerg]

Stunning colour and clarity :thumbsup: I take it the 5D is not modified? I'm surprised at the colour you have. I really must sort out getting the most colour from my DSLR shots, I'm sure there must be more in there than I squeeze out :rolleyes:

[jjjnettie]

Oh wow wow wow

[naskies]

Thanks everyone! :D :thumbsup: I think I'm slowly-but-surely starting to figure out how to make the wide field DSO images pop...

Troy - the Canon 135 mm f/2L lens happens to be one of my favourites.

Rick - thanks! I hope you had some success yourself?

David - I'm looking forward to seeing what magic the D800 can do!

Roger - Yep, it's a stock unmodified camera. Here's one of the Rho Ophiuchi subs completely unedited except for resizing - the dark nebulosity and colours were easily visible on the back of the camera.

[RickS]

I did thanks, Dave, but I used a 2000mm f/8 lens :D I'll processing for a few more evenings to do justice to the data, I think.

[Visionoz]

Wow David - sweet collection there! :thumbsup:

Cheers
Bill

[Lester]

Fantastic views Dave. I really need to brush up on my processing. Wow, thanks for the views. All the best.

[dvj]

Outstanding images, all of them. Great contrast and color.

j

[MrB]

WOW Dave, the Rho Ophiuchi shot is stunning, would love to get a shot like that!

I am confused tho, didn't you sell the Astrotrac a few months back?

[gregbradley]

They are superb images.

Greg.

[CapturingTheNight]

:eyepop:WOW. My jaw just hit the floor. Stunning images Dave. Congratulations.

[rogerg]

It's the colour I'm surprised at .. I think you have very good processing skills, to be able to bring out the colour without making it look too higher contrast or too over processed :thumbsup:

[strongmanmike]

These are excellent David!

My fav is the coal sack and dark doodad :thumbsup:

Mike

[MrB]

Agreed.
I'm still learning, can just do the basics, but I had a quick go with the single sub Dave posted and couldn't coax much out of it.
Would be great if Dave could run thru his processing procedure :thumbsup:

[naskies]

Wow, thanks for all the positive comments! :D Seems like most people on here image either at >= 500 mm focal length, or <= 24 mm... hopefully this can be my little niche :lol:

Simon - err yep, I did indeed sell the Astrotrac :rolleyes:, but then I bought it back in exchange for something else... long story! I then sold my EQ6 but now that I'm hitting my head against the AT's limitations I'm regretting that too :rofl:

Mike - thanks! The Coalsack + Dark Doodad is my favourite too... I'm a huge fan of dark nebulae.

I think you guys give me too much credit for the processing (it's rather rudimentary at the moment), but here's what I did (from memory):

Step 1. Lightroom RAW conversion:
* turn off all automatic processing (brightness/contrast/black point/etc)
* set manual white balance
* enable lens profile correction and adjust settings
* reset contrast curve to linear
* export as 16-bit TIFFs for import into Deep Sky Stacker
* repeat for darks/flats/bias/etc frames.

Step 2. Deep Sky Stacker stacking:
* load light/flats/dark flats/darks/bias frames
* tweak the star detection threshold to aim for about 1000 detected stars (too few seems to result in incorrect alignment, same with too many - or it crashes DSS)
* use the middle light frame as reference
* stack 100% of the light frames and see what the result looks like
* if the stars aren't pinpoint across the field (i.e. alignment errors), then figure out what went wrong and/or which light frames to omit
* for the Rho Ophiuchi shots, I had to drop 4 frames for it to stack perfectly

Step 3. Deep Sky Stacker stretching and curves:
* click the checkbox to move RGB sliders simultaneously
* increase the black point until any clipping starts to occur (i.e. you see a pixel in any channel appear at 0/black on the histogram)
* unclick the above checkbox, and each the black point for the other channels so that the RGB peaks all line up
* click apply to see what the data looks like (you may have to adjust the midpoint slider of the curve so that it's not too bright/dark) - make sure the dark nebulosity isn't clipped
* leave the white point alone as the bright stars are already overexposed
* set saturation to 20% (there will be a huge colour cast over the image) and then carefully tweak the black points of each RGB channel to cancel out the colour cast
* fiddle around with the curves sliders to get a nice balance and contrast between background, dark nebulosity, bright nebulosity, and stars
* tweak saturation slider
* export as 32-bit TIFF

Step 4. Photoshop tweaking:
* mask any edges or corners that didn't get flat-corrected properly
* clone out the dust spot in the corner that didn't get flat corrected
* perform a fine-grained Levels or Curves (as 16 bit image) tweak
* vibrance/saturation tweak to boost colour of nebulosity
* boost red+magenta channel saturation to compensate for reduced H-alpha (e.g. somewhere between +15 to +30)
* convert to 16-bit using exposure 0 gamma 1
* resize image, e.g. 1200x800 for web
* apply local contrast enhancement of dark dust lanes and nebulosity (e.g. unsharp mask with settings 12%, 12 px, 0)
* export as JPG

That's it! It's all really quite straightforward, perhaps except for the stretching and curves step in DSS. It's a very, very finicky step where even just having a slider a couple of pixels in the wrong position messes up the whole image.

When the curves sliders are set right, you can adjust the dark dust, nebulosity, star intensity, and star field background individually on separate sliders.

If you'd like to give it a go yourself on my data, you're very welcome:

* RAW file from a single sub taken with my SLR (http://dl.dropbox.com/u/13644418/iis/RhoOphiuchiDemo/IMG_3296.CR2) (28 MB)
* converted TIFF file from Lightroom - one sub (result of Step 1) (http://dl.dropbox.com/u/13644418/iis/RhoOphiuchiDemo/RhoOphiuchi-Lights-27.tif) (126 MB)
* stack of 31 subs from DSS - no curves/stretching (result of Step 2) (http://dl.dropbox.com/u/13644418/iis/RhoOphiuchiDemo/Autosave002.tif) (202 MB) - download and load this file into DSS if you want to play with stretching/curves
* output TIFF from DSS after stretching and curves (result of Step 3) (http://dl.dropbox.com/u/13644418/iis/RhoOphiuchiDemo/RhoOphiuchi.tif) (125 MB)

Enjoy!

[CapturingTheNight]

Guess what I'm doing this weekend? Reprocessing some widefield images. :D
Thank you so much for the write up on your image processing Dave. That's incredibly kind of you :thumbsup:
Not sure if my data will be as good as your initial data but can't wait to see if I can dig some more out of my images with this process.
Cheers

[MrB]

You are a legend Dave, definitely giving your processing a go, cheers!

I've been ummming and ahhhhing about the AT for some time now, expensive for what it is, but I'm pretty much about to bite the bullet!
If you're considering selling again, I'm interested! haha


Too right Greg! I'll be doing the same.

[stevous67]

Great job dave, beautiful colours and nicely captured.

Steve

[DavidTrap]

Dave - what is a fine grained levels or curve tweak?

Thanks again for the processing recipe!

DT

[dvj]

I gather then that I would not be disappointed in the 5D MK II if I got one for the Venus transit? I know the MK III is out but pricy.

[dvj]

Thank you for posting this. This is more information than I get at the annual AIC conference in San Jose. They totally blow off digital camera photography as not being "advanced". :eyepop:

[naskies]

Cheers guys - hope this helps. I'm sure there are better ways of processing (please tell me if you know how!) but this works for me.

John - the 5DmkII is an awesome camera, except for the focusing system. Since I don't shoot action (mainly portraits + astro) I probably won't be upgrading anytime soon... bigger mount and scope first! :-)

David - the levels slider in DSS only lets you set whole numbers (0, 1, 2, 3, ...) and not fractions (0.1, 0.2, 0.3, ...) so sometimes I'm unable to subtract the skyglow without leaving a colour cast - eg my example image from DSS is a bit green. Once I open it in Photoshop, I apply levels only to fine tune the skyglow subtraction.

[Lester]

Thanks Dave for your processing recipe, makes my recipe seem like "two minute noodles" in comparison. So will be saving yours to favorites and gives me much to work on. All the best.