Anywhere Is, project SWANS, day 2: North America, Crescent, Veil and others

WARNING!! Original size image contains 39 tiny megapixels*!

 

Constellation Cygnus, the Swan, is in the trend now, so I want to participate. The black gap in Milky Way (sometimes reffered as the Nothern Coal Sack :) where the Swan resides, is full of emission nebulae, so it is there I pointed the camera this time.

 

SWANS stands for Semi-Wide Angle Nebulae Survey. I'm a big fan of the way how NASA and CERN name their experiments and missions.

 

Lots of upgrades in all aspects of imaging. Prime lens, UHC filter, firmware hack in camera, three overlapping datasets collected in two nights, artificial flat-field image, automatic stitching, formalized processing in Photoshop. This is the positive side. On the other hand, the second night of imaging brought with it the hazard of dewing. That was the negative experience. Cost me a lot of precious time.

Some trailing is apparent at 1:1 view and bugs me, but with the arrival of polar finder it wouldn't be an issue anymore, I hope.

Another issue is the inconsistency of data, since the "Albireo" panel is this image and it differs from two other in ISO value (3200 vs 2000) and in amount of data (10 subframes vs 29 and 20, respectively).

 

And yet another bit of information: the Crescent nebula (see note on the image) is an unusual object. It's an emission nebula produced from the outer layers of so called Wolf-Rayet star. These rare objects are massive - about 10-15 Solar masses - highly evolved stars that had lost the outer hydgrogen shells and are in fact the exposed helium cores that produce tremendous amount of energy and dense streams of "stellar wind". Amazing objects :)

 

Aquisition time: 03 and 04.08.2013 between 00:00 and 01:40 MSK (UTC+4)

The Sun's deepest dive was -17° @01:30, so stricktly speaking I was imaging in the dusk.

Equipment:

Canon EF-S 60mm f/2.8 macro USM lens and Baader Planetarium 2" UHC filter mounted in front of the lens via step-down ring attached to Canon EOS 60D running Magic Lantern 2.3 firmware override riding on Vixen Polarie tracking platform over photo-tripod (alltogether codenamed "Anywhere Is, SWANS configuration").

Aperture 21,4 mm

Focal length 60 mm

Tv = 60 seconds (Magic Lantern's bulb timer and intervalometer rock the suburban skies :)

Av = f/2.8

ISO 2000 for "Deneb" and "Sadr" areas and 3200 for "Albireo" area

Exposures: 29 for "Deneb" area, 20 for "Sadr" area, 10 for "Albireo" area (plus 10 dark frames and 10 offset frames plus 2 fake flat-field frames).

Processing: Contrast was set to "linear" for all images in Canon DPP and 16-bit outputs were fed to DSS.

Flat-field images were made by applying Gaussian Blur of 250 pixel radius to a randomly chosen image from the series. After blurring the histograms were adjusted to end at 70% of saturation. Since I have aquired three series of overlapping fields, I made a Master Flat by combining fakes from both series. Works fine - without it the Veil nebula can't be seen due to vingetting.

16-bit stacking results were then processed in Photoshop with AutoContrast and Levels (namely gamma was set to 3,5), stiched in Microsoft ICE (that's coool!) and back in PS Curves were applied(skewed sigmoid curve was applied at first step, and at step two the segment of red and blue curves corresponding to the brightness of nebulae was elevated).

 

* 1 Megapixel = 1048576 pixels.

Done