The Wall

December 1, 2017 by grahamrob in Deep Sky Objects, Imaging, Narrowband and tagged Cygnus, North America Nebula | 1 Comment

SHO2 FINAL

I first had a peek of the North America Nebula shortly after I started my then nascent astronomy hobby in August 2014. With a Skywatcher 150PL Newtonian reflector and DSLR camera, I just managed to capture the edge of this very large nebula. It was a very poor image and obviously navigation and framing were not my strong point but the mere glimpse of such Ha nebulosity was at the time something of an epiphany. Hitherto I didn’t know such things existed, let alone their size and grandeur and the potential to catch even a part of it on camera was very exciting – that excitement has still not left me.

NGC 7000 unmodded Canon 700D DSLR | September 2015

Armed the following year with a AZ-EQ6 GT mount and William Optics GT81 refractor, I managed to image most of the ‘continent’ and ‘Gulf’ (see above), although ‘Mexico’ was still missing; the title of my related blog at the time encapsulated my emotion at the time – WOW! Since then I have often returned to NGC 7000 and with the combination of a modded DSLR, computer control and guiding gradually improved my technique so as to obtain better images. However, the outcome of imaging the North America Nebula this year with the ZWO1600MM-Cool mono camera has been a revelation, resulting in perhaps some of my best images so far.

I’ve recently been spending time improving post processing methods, which together with increased knowledge gained from using the new camera for more than 6-months is now starting to pay off. Being a very large HII-region the North America Nebula responds well to narrowband wavelength filters and I therefore took Ha-OIII-SII subs, which have subsequently combined well into Bi-colour (below) and SHO images that far surpass what I’ve previously achieved.

BiCol FINAL2

I was particularly keen to capture the Cygnus Wall for the first time, located along the ‘southern California’ and ‘Mexican’ coasts – so to speak. In both cases the Wall shows up very well in detail (below in bi-colour), with its W-shaped edge dramatically illuminated by star forming regions from within. I am particularly pleased with the SHO image (top of the page), which apart from the Wall illustrates delicate details across the entire nebula.

Cygnus Wall BiCol FINAL

Greater care during processing is improving such images but now that I’ve experienced this new camera across a number of different objects, it is clear that further enhancements are likely to be incremental and more difficult to achieve. The one important factor that I suspect will still provide a noticeable improvement to my images will be longer integration time, which requires plate solving. I’m already starting to learn this process and hope to adopt its use in the New Year. In the meantime I feel recent imaging results and especially these narrowband images of the North America Nebula mark a very satisfying climax to my astrophotography year, progress over the past few years is very evident and I’m eagerly looking forwards to 2018.

	IMAGING DETAILS
Object	North America Nebula – NGC 7000
Constellation	Cygnus – near Deneb
Distance	1,600 light-years
Size	Approx. 50 light-years or 2^o
Apparent Magnitude	+4.0

Scope	William Optics GT81 + Focal Reducer FL 382mm f4.72
Mount	SW AZ-EQ6 GT + EQASCOM computer control
Guiding	William Optics 50mm guide scope
	+ Starlight Xpress Lodestar X2 guide camera & PHD2 control
Camera	ZWO1600MM-Cool (mono) CMOS sensor
	FOV 2.65^o x 2.0^o Resolution 2.05”/pix Max. image size 4,656 x 3,520 pix
EFW	ZWOx8 + ZWO LRGB & Ha OIII SII 7nm filters
Capture & Processing	Astro Photography Tool, Deep Sky Stacker & Photoshop CS2
Exposures	18 x Ha, 8 x OIII & 8 x SII @ 180 secs (Total time: 102 minutes)
	@ 300 Gain 10 Offset @ -20^oC
Calibration	5 x 180 sec Darks 10 x 1/4000 sec Bias 10 x Flats Ha, OIII & SII
Location & Darkness	Fairvale Observatory – Redhill – Surrey – UK Typically Bortle 5
Date & Time	27^th August 2017 @ 21.50h

Pelican Brief

September 26, 2017 by grahamrob in Deep Sky Objects, Narrowband, Processing and tagged Cygnus, North America Nebula | Leave a comment

CNV00015

Located 3^o west of the star Deneb in the Cygnus constellation, the North America Nebula is an emission nebula spanning some 50 light-years across, which contains numerous areas of astronomical interest that form some excellent imaging targets. In the past I’ve usually concentrated on the ‘continent’ of North America itself but on this occasion moved my attention off the ‘east coast’ in search of the distinctive Pelican Nebula – it really does look like a pelican!

North American Nebula (left) & Pelican Nebula | WO GT 81 & modded-Canon 550D | 2015

Separated from its neighbour by a molecular cloud of dark dust, the dominant HII region of the Pelican Nebula responds well to Ha imaging and I therefore sought to capture the ‘bird’ in this and other narrowband wavelengths. Detail within the main cloud is further highlighted as a result of ionization from within created by young star formation, making for some pleasing and often spectacular effects.

Whilst image capture went well I was concerned by the outcome of stretching the Ha-image after stacking; the stacked image in DSS looked bright and detailed but after using Levels in Photoshop to establish the dark and light points the resulting image was somewhat dull in appearance and without the finer detail I had previously seen in DSS. Responses to a question on the SGL Forum post made it clear that I needed to be bolder when stretching in order to achieve the desired result; I am further persuaded that I’ve been too timid with such processing techniques in the past and may need to revisit and reprocess some older data when time permits.

Pelican Images 10th August 2017 in order below:

Ha – Bicolour – SHO narrowband

WO GT81 & ZWO1600MM-Cool + x0.80 focal reducer | 180 sec Gain 300 Offset 10 @ -20C

10xHa + 10xOIII + 5x SII + full calibration

Picture saved with settings embedded.

I went on to process the full narrowband data in both SHO and Bicolour, with interesting results. The aforementioned assessment of linear stretching resulted in a much improved Ha-image, which subsequently impacted positively on the final compiled image. However, there’s still much to consider when processing the combined channels, in particular in narrowband.

Some aspects of manipulation used during processing can have a material impact on the final image and I’ve long been concerned whether the resulting astrophotography presents a factual representation – in the case of narrowband the answer must surely be no. Depending on the quality of data capture, detail and structure will usually be accurately recorded but subsequent ‘playing’ with the colour channels is most likely to produce a final image that is pleasing aesthetically to the photographer rather than factual; in the case of narrowband the colours available will be correctly determined by the respective filter wavelengths but there is no definitive measure of what actual colour should be in the final image.

RGB2crop (Large) In this case the Ha-image of The Pelican that was obtained demonstrated the significant improvements that can be achieved with the CMOS based ZWO1600MM-Cool camera compared to a DSLR. I’m still learning about processing and in particular, with the plethora of options available when using LRGB and narrowband subs the issues have now escalated exponentially. Notwithstanding the aforementioned issues I’m very pleased with my ‘new’ bird The Pelican Nebula.

SHO2 Crop (Large)

The Dutch Gadget

July 25, 2017 by grahamrob in Deep Sky Objects, Imaging, Narrowband, Processing, Solar system and tagged Eagle Nebula, Galileo, North America Nebula | 1 Comment

IMG_8370x (Large)

I have just finished reading J.L. Heilbron’s biographical tome on Galileo, which though very interesting I found a difficult book and somewhat academic in style. In 1609 Galileo became aware of a Dutch spectacle maker’s device that made distant objects appear closer. He subsequently became known for developing the so-called ‘Dutch Gadget’ into what we now know as the refracting telescope and moreover, applying its use to understanding the Solar System with the discovery of Jupiter’s four largest moons, confirmation of the phases of Venus and the observation and analysis of sunspots; the word telescope was subsequently coined in 1611 from the Greek tele “far” and skopein “to look or see” i.e. far-seeing. In so doing he also helped to confirm the then controversial truth of the heliocentric astronomical model, whereby the Earth and planets orbit the Sun. Against this background it is no surprise that Galileo is today much revered by mankind and has become known as the father of observational astronomy.

GalBook

Drawn into the complexity of obtaining images of the Solar System and beyond, it is the curse of astrophotography that we inevitably neglect observing the spectacle itself. Notwithstanding, I am sure that Galileo would understand the power and beauty of today’s astrophotography, which in its own way is producing a quantum leap in our understanding of the Universe comparable to the impact of the original application of the telescope.

This summer the Solar System will hopefully provide both good observational and astrophotography opportunities here at Fairvale Observatory: Jupiter, Saturn, Comet C/2015 V2 (Johnson), the Perseids meteor shower and the Sun – sadly though I will not witness next month’s solar eclipse which takes place mainly over North America. During recent summer months the lack of astronomical darkness, short nights and absence of DSOs has frustratingly continued to limit potential imaging targets for my new ZWO 1600MM-Cool camera but utilising a period of good weather there have recently been a few fleeting opportunities just before dawn related to the appearance of the summer arm of the Milky Way on the eastern horizon.

solstice sky

NGC 7000 The North America & Pelican Nebulae WO GT81 + modded Canon EOS 550D + FF | 30 x 120 secs @ ISO 1,600 + calibration | 19th September 2015

I first imaged the North America Nebula (NGC 7000) in 2014 and have since returned each year to image the nebula or its various parts using a DSLR camera. Being a very large Ha-object the nebula is an ideal target for the ZWO1600MM-cool camera and I have been anxiously waiting its arrival again this year. On this occasion, early on the morning of the summer solstice, high in the sky and 90^oeast the nebula was only just visible from my location, being very close to the roof-edge of my house! Consisting of just six Ha-frames plus three OIII and SII taken just before dawn broke, the resulting image was never going to be my best but is nonetheless interesting in SHO format and quite different to previous DSLR images.

North America Nebula in Ha-OIII Bicolour

North America Nebula in SHO

At the other extreme, located low on the southern horizon and only briefly visible as it passed between the trees at the end of my garden is the Eagle Nebula AKA M16, home of the Pillars of Creation. At 7-arcminutes in size and an apparent magnitude of +6.0, the nebula is at the lower end of possible for my set-up and at some 27^oaltitude with just 40-minutes imaging time between the trees it was a challenging target. Notwithstanding, I’m pleased with the Ha and SHO narrowband images obtained, which quite clearly show the Pillars too.

M16 Eagle Nebula in Ha

Pillars of Creation in Ha

M16 Eagel Nebula in SHO: William Optics GT81 & ZWO1600MM- Cool & Field Flattener | 6 x 180sec Ha, x3 OIII, x3 SII Gain 300 Offset 10 + full calibration | 21st June 2017

As astronomical darkness is now slowly returning and with clear skies and weather permitting, I hope to attempt longer imaging sessions of both these and other targets during the rest if the summer and into autumn – I might even get to see M16 again as it eventually emerges from the other side of the trees! Thanks to the development of the Dutch Gadget and modern cameras it is now possible for amateur astronomers to image such spectacular objects – I’m sure Galileo would be impressed and highly approve.