The Cygnus constellation is rich in potential astrophotography targets and since the return of astronomical darkness I’ve bagged three objects from this area with my new widefield Samyang 135 rig: Cygnus Loop, Sadr Region & Crescent Nebula, and the Western Veil & Pickering’s Triangle. As the Cygnus season now draws to a close – in my case disappearing northwards behind my house – I was ready to snap one final Cygnus object using my main William Optics GT81 rig but then looked closer and realised using the Samyang 135 rig with careful framing there was another a more ambitious possibility.
The original object in question was SH2-119 AKA the Clamshell nebula, an emission nebula somewhat overlooked by photographers. Nevertheless, imaged in narrowband there’s plenty of structure to see throughout the nebulosity that makes up the two ‘shells’, whilst the bright magnitude +5 star 68 Cygni might be likened to the pearl at the centre, which would work well with the 81mm William Optics field-of-view. But deploying with care the much wider field-of-view of the Samyang 135 and it’s possible to include the North America and Pelican nebulae as well, just!
With some difficulty (weather) I finally managed to obtain 13-hours integration time over 6-nights, which has resulted in a pleasing SHO image (see main image at the top of the page – below is a dynamic version processed using PI PixelMath), once again demonstrating the capacity of this small but powerful lens. Personally, I find bringing all three objects together within a much larger field-of-view creates greater context, resulting in a more interesting image overall – in football parlance you might call it a hat-trick of nebulae!
IMAGING DETAILS
Objects
North America Nebula (NGC7000) + Pelican Nebula (IC5070 & IC5067) + Clamshell Nebula (SH2-119)
Constellation
Cygnus
Distance
approx. 2,600 light-years
Size
3.0o
Apparent Magnitude
approx. +4 to 8
Scope / Lens
Samyang 135 @f2.8
Mount
SW AZ-EQ6 GT + EQASCOM computer control & Cartes du Ciel
Guiding
Sky-Watcher EvoGuide 50ED
+ Starlight Xpress Lodestar X2 camera & PHD2 guiding
Camera
ZWO1600MM-Cool mono CMOS sensor
FOV 7.5o x 5.67o Resolution 5.81”/pix Max. Image Size 4,656 x 3,520 pix
It’s been nearly two years since acquiring my Samyang 135 lens but since then it’s unfortunately only had limited use in combination with my modded 550D DSLR. Whilst impressed with the results from this set-up, my main objective has always been to combine it with my ASI1600 mono camera for some serious widefield astrophotography but as that was being used with my William Optics refractor it just didn’t happen, until now. After upgrading to a ASI294MM Pro camera in May, at last I was finally able spend the early part of this summer working on a new Samyang 135 + ASI1600 rig and now that astronomical darkness is (just) back I recently managed to catch a few photons with this new set-up of the large SNR Cygnus Loop.
I originally purchased a x2-ring Astrokraken 3D-printed clamping system for the lens + DSLR combination from Philippe in France but since then he’s tweaked the design. In particular x3 built-in M4 nuts have been incorporated on either side of each of the two main lens clamping rings, for the purpose of attaching ancillary equipment, which for me has been a game changer. I therefore bought a new x3-ring Astrokraken bracket, with the said bolt holes, around which to build my new rig:
The two main clamping rings that hold the lens have a shoe immediately above the lens, to which I’ve fitted a Sky-Watcher EvoGuide 50ED guidescope (not yet working), with the rear third ring holding the ASI1600 mono camera & EFW.
I swapped the Canon lens bayonet adapter for a bespoke M42 screw adapter, in order to ensure a more secure attachment, thus reducing any potential lens-camera movement at this critical point of the image train.
I’m continuing to use the excellent Astrokraken micro-focuser, which consists of a ring that clamps onto to the lens’ focus ring, with two small bolts above that make contact with either side of the guidescope shoe, so that when turned the focus ring can be adjusted either way to obtain focus, which is then locked when completed. So far I’ve found the micro-focuser to work very well with this lens, assisted by the addition of an Astrokraken Bahtinov mask which is inserted into the front of the lens casing.
Using this lens with the ZWO ASI1600MM-Cool camera and EFW, the backfocus guideline is 44mm, which I was able to achieve by adding an Altair T2 variable locking extension ring set to 17.5mm = 44mm minus 26.5 (camera + EFW).
With my Chroma filters now being used with the new ASI294MM Pro camera, I purchased another ZWO 31mm x8 EFW and brought my ZWO 31mm filters out of retirement.
Finally, using the new M4 nut holes I’ve added a Baader SkysurferIII RDF on the left-hand side of the Astrokraken bracket system to help with sky navigation and framing.
After bolting the Astrokraken with the lens, camera and said components to a Losmandy plate it makes a very nice compact rig, that is easy to handle and store. Notwithstanding, as they say – the proof of the pudding is in the eating: SEE top-of-the page for original image & below for 50% crop.
Whilst the recent heatwave produced clear skies, it was far from ideal here for astronomy and was further hampered by a full moon. However, with only just over two hours integration time and a few Dark calibration files, I’m still impressed with the outcome of this quite amazing lens. It is very pleasing to capture the entire Cygnus Loop comfortably sitting within the lens’ FOV – for information on this FOV and comparisons go to this previous WTSM blog HERE. For me context is important with astrophotography and in this regard the astronomical perspective this lens produces is outstanding, no wonder it is so popular. I just love working with this FOV and can’t wait for better conditions for greater integration time and more widefield targets to point this wicked little lens at.
IMAGING DETAILS
Object
Cygnus Loop
Constellation
Cygnus
Distance
2,400 light-years
Size
3.0o
Apparent Magnitude
+7.0
Scope / Lens
Samyang 135 @f2.8
Mount
SW AZ-EQ6 GT + EQASCOM computer control & Cartes du Ciel
Guiding – Not Used
Sky-Watcher EvoGuide 50ED
+ Starlight Xpress Lodestar X2 camera & PHD2 guiding
Camera
ZWO1600MM-Cool mono CMOS sensor
FOV 7.5o x 5.67o Resolution 5.81”/pix Max. Image Size 4,656 x 3,520 pix
It’s been over 5-years since I acquired the revolutionary ZWO ASI1600MM-Cool camera, which went on to completely transform my astrophotography. In the real world such iconic products come along only very occasionally, such as the Mini, Nokia mobile phone, computer mouse & GUI, iPod & Dyson Vacuum cleaner, all have characteristics which redefine a product and went on to literally change the world. Although by comparison astrophotography is something of a niche hobby the development of the ZWO1600 camera has had a similar impact, so much so that it too has redefined the way forwards for astrophotography cameras.
With the move from film to digital, CCD-sensors became the definitive mono camera of choice for “serious” astrophotography but the arrival of the ZWO ASI600MM-Cool camera in 2016 was set to change all that, so what made it so important? At the heart of this transformation is the CMOS sensor. Common to most conventional digital cameras CMOS technology is well proven but for the purist the CCD maintained the edge in astrophotography, until the ZWO1600 and eventually other similar cameras like it came along (see box below for CCD v CMOS background information). Perhaps three features underpin the success of CMOS-based astrophotography cameras, of which the ZWO1600 is considered the first and most successful to-date.
Very low read noise and good well depth both contribute to much shorter exposure times than CCD cameras require, which for the amateur with limited time and light pollution to tackle was a game changer. Moreover, because CMOS-based sensors were already being made for the mass market they cost much less than CCD sensors and therefore so were the cameras, making them a viable choice based on their technology and cost.
It was fortunate that when I was looking to move from DSLR to a mono astrophotography camera at the end of 2016 I was able to purchase a ZWO ASI1600-Cool, just 7-months after its initial release (See First Light for more information). Although an experienced photographer, including +30-years of underwater photography, the difference between what might be called conventional photography and mono astrophotography cameras was like night and day, which took some time to understand and eventually pick-up. Notwithstanding the learning curve, it’s been worth the effort as the impact on my images has been profound. During the intervening period since I brought my camera only a few minor developments have been made (now sold as the Pro version), until in September 2020 a much-anticipated successor to the ZWO ASI1600MM-Cool camera was finally released, the ZWO ASI294MM Pro (see images below).
I waited until now to purchase this camera because at the time I just didn’t need it (the ZWO1600 served my needs very well and still does) and I also wanted to see how the new camera worked out with early users. Apart from a few niggles, the overwhelming response has been very positive and as I now have another use for my ZWO1600, I finally purchased a ZWO ASI294MM Pro and obtained First Light in early April.
CAMERA
ZWO ASI1600MM-Cool*
ZWO ASI294MM Pro
Sensor – CMOS 4/3”
Sony IMX492
Panasonic MN34230ALJ
Sensor Size + Diagonal
19 x 13mm 23.1mm
18 x 13mm 21.9mm
Pixel Size
4.63nm (Bin2) or 2.135nm (Bin1)
3.80nm
Resolution
4144 x 2822 px Bin1 8288 x 5644 px Bin2
4656 x 3520 px
ADC
14bit
12bit
Full Well Capacity
66,000
20,000
QE Peak
90%
60%
Readout Noise
1.2 -7.3e
1.2 – 3.6e
Sensor Illumination
Back Lit
Front Lit
Cooling
-35C
-40C
Data Buffer
No
Yes
File Size
22MB (bin1) 85MB (bin2)
32MB
Back Focus
6.5 / 17.5mm
6.5 / 17.5mm
Before commenting on my albeit limited experience of this new camera so far, it’s worth comparing the main features of each camera that are summarised in the accompanying table. Not surprisingly there are many similarities, which make for an easy swap of the two cameras when using the same optical train but there are also some important new developments which make this camera a real step-up from the ZWO1600.:
Greater quantum efficiency (QE) means that 90% of the total light that reaches the sensor is converted into data, compared with 60% with the ASI1600. Thereby for the same integration time the ASI294MM Pro will gather 50% more light than the ASI1600 or put another way in half the time!
Increased full well capacity from 20ke to 66ke means longer exposures without saturation.
Higher 14bit ADC provides more dynamic range of two more stops compared with the ZWO1600.
A choice of Bin1 or Bin2 changes the equivalent pixel size from the basic 4.63nm (Bin2) to 2.315nm.
Sony’s back-illuminated CMOS image sensor (see below) improves sensitivity and noise reduction but perhaps more importantly stops microlens diffraction artifacts of bright stars which has been one of the biggest bugbears of the ZWO1600, particularly when using ZWO’s own filters.
Physically the new camera is identical to the ZWO1600 and changing the cameras over is essentially just a swap, in my case using the same setup of a William Optics GT81 & 0.80 focal reducer + ZWO x8 EFW & 31mm Chroma Filters + just a minor focus adjustment. Using the excellent Astro Photography Tool (APT) for image capture I did encounter some issues setting up the new camera but after some liaison with other users and the APT developer Ivo it was sorted quickly and ready to run!
Unfortunately, by late March / early April most of winter’s exciting objects have moved on but I did manage to quickly grab 60 minutes of the Rosette nebula (HOO + dark calibration only, below) and later the M44 Beehive open cluster (top of the page: 40mins 10x 60secs LRGB + fully calibrated ), the results of which were good clean images that did not disappoint and hold great promise when better objects become available again.
Because of the subsequent seasonal change of clocks and diminishing presence of astronomical darkness as we approach the summer solstice, I’ve been unable to continue using the ZWO ASI294MM for now but at least I know it all works well. As has become normal in recent years, I’m therefore taking a short break from imaging, though have a plan to repurpose the ZWO1600 which I’m working on but that’s for another day – Watch this Space!
First light with the ZWO ASI294MM Pro – 6 x 5mins Ha & OIII + dark calibration
The dark silhouette of the Horsehead Nebula against the surrounding rich HII-region, is one of astronomy’s most iconic images. Surprising then that I’ve never imaged this object in broadband wavelengths before with my mono camera: the first image was in February 2015 using a modded Canon 55OD camera, then in January 2019 with the ASI1600MM + narrowband filters and most recently in January 2021 using a widefield Samyang 135/f2 rig and modded Canon DSLR. Therefore, somewhat belatedly and with the benefit of unusually long spells of clear skies, this February I set out to rectify this omission from my astrophotography repertoire.
Whilst B33 the Horsehead Nebula gets most of the attention, this large HII-region contains many other exciting objects which a broadband image shows off well, aided here by additional Ha-data (see below) to enhance the breath-taking detail that abounds across the area. Situated in close proximity to Orion’s Belt, controlling bright stars such as Alnitak is key to achieving a good image and in this regard my new Chroma filters proved helpful. The final image shows a good rendition of the Horsehead at the centre, framed against the striking red curtain of Ha-rich nebulosity and two other interesting objects nearby.
Within the large molecular cloud, located just below and to the left of the Horsehead, is the emission and reflection nebula NGC 2023. Discovered by William Herschel in 1785, at 10 x 10 arcminutes it is one of the largest reflection nebulas, illuminated at its centre by the Herbig Ae/Be starHD 37903 (a pre-main-sequence star). Then, just to the left (north) of NGC 2023 is the dramatic NGC 2024 Flame Nebula, an emission nebula energised by the adjacent and very bright Alnitak star and a cluster of young stars within. I was keen to preserve its more natural colour during processing and am very satisfied with the outcome, which captures its relationship with Alnitak to best effect.
Overall, I’m very happy with the resulting HaLRGB broadband image of the Horsehead and its neighbours. Armed with better filters, guiding, integration and processing I feel the long wait was perhaps worth it, so that this image does justice to one of winter’s most spectacular views. As the Horsehead now moves out-of-sight over the western horizon for another year, I trust my next image of these objects will be sooner than it took this time!
IMAGING DETAILS
Object
B33 Horsehead Nebula + NGC 2023 & Flame Nebula
Constellation
Orion
Distance
1,375 light-years
Size
Horsehead only approx..8.0’ X 6.5’
Apparent Magnitude
Varies, Horsehead +6.8
Scope
William Optics GT81 + Focal Reducer FL 382mm f4.72
Mount
SW AZ-EQ6 GT + EQASCOM computer control & Cartes du Ciel
Guiding
William Optics 50mm guide scope
+ Starlight Xpress Lodestar X2 camera & PHD2 guiding
Camera
ZWO1600MM-Cool mono CMOS sensor
FOV 2.65o x 2.0o Resolution 2.05”/pix Max. image size 4,656 x 3,520 pix
Long on my to-do list has been the spectacular Simeis 147, also known as SH2-240 or the Spaghetti Nebula. A large supernova remnant (SNR) spanning the border between the Taurus and Auriga constellations, which despite its size is one of the faintest objects in the night sky and therefore not an easy astrophotography target. Moreover, given my equipment’s field-of-view the large size of the SNR would require a mosaic to fully image, which is generally out of the question here at Fairvale Observatory with the limited clear sky conditions that prevail here. Therefore, for the moment I’ve concentrated on a close-up area of the southern lobe, imaged and processed in HOO narrowband to highlight the beautiful complexity of this cosmic cataclysm that is the product of a massive stellar explosion that took place some 40,000 years ago.
Simeis 147 Location
Furthermore, imaging was not helped by the presence of a waning full moon and even with 10-minute exposures, only very limited detail was evident in the Ha wavelength and none in OIII, thus also making framing tricky. However, with over 12-hours integration time eventually obtained over four nights and very careful processing, my first image of this wonderful SNR does not disappoint. I hope to return to this magnificent object again in the future to add more exposures – you really cannot have too many – and perhaps eventually capture this bowl of cosmic spaghetti in its entirety one day too.
Ha Stack 6-hours 30 mins OIII Stack 5-hours 40 mins
IMAGING DETAILS
Object
Simeis 147 AKA SH2-240 or Spaghetti Nebula
Constellation
Taurus
Distance
3,000 light-years
Size
Total object +3.0o
Apparent Magnitude
Extemely faint
Scope
William Optics GT81 + Focal Reducer FL 382mm f4.72
Mount
SW AZ-EQ6 GT + EQASCOM computer control & Cartes du Ciel
Guiding
William Optics 50mm guide scope
+ Starlight Xpress Lodestar X2 camera & PHD2 guiding
Camera
ZWO1600MM-Cool mono CMOS sensor
FOV 2.65o x 2.0o Resolution 2.05”/pix Max. image size 4,656 x 3,520 pix
Every year since 2014 I’ve published a retrospective blog of my astrophotgraphy year just ending called Reflections. It’s been a useful task that enables me to bring together the best and sometimes the worst of my images, in order to consider the good and bad points + progress made + set some objectives for the coming year. Eight years on, after which I believe I’ve now reached at least a respectable level of imaging and processing, I’ve decided to stop this format for the time being.
Notwithstanding, at this time of the year I also produce an astrophotography calendar for members of my family, which consists of the better images from the year just ending; I think they like them and certainly all use the calendar during the coming year. Moreover, I also recently started to compile a video of the said calendar images set to appropriate music, which we all watch together prior to seeing the actual calendar. It’s a great way to present the images, which look really stunning on today’s large Smart TV’s and is fun to watch with the family too.
The video for this last year 2021 can be viewed on YouTubeHERE and below is a brief very general overview of each image. More detailed background information and imaging details for those interested can be found in relevant blogs posted on this site during the past year.
2022 CALENDAR
A new set of filters, improved processing techniques and access to data from a telescope at a dark sky site in New Mexico, USA (shown by an asterisk *) contributed to an exciting astrophotography year in 2021.
FRONT COVER
The Carnival of Animals: Special processing of the inner region of the Rosette Nebula highlights the ‘animals’ or Bok Globules – clouds of dust undergoing gravitational collapse as part of the process of new star formation.
JANUARY
LDN-1250 Dark Nebula*: Dark or absorption nebulae are a type of interstellar cloud which are so dense they obscure or absorb visible light emitted from objects behind or within and thereby contrast with the general light flux of the Universe as dark areas.
FEBRUARY
CTB-1 Supernova Remnant*: The overall structure of this supernova remnant is that of a circular shell, with a conspicuous rupture towards the north (lower right of image). The main red Ha-shell is composed of multiple interlocking filament limbs, with a blue / green OIII arc along one side.
MARCH
Jellyfish Nebula: Locatedin the Gemini constellation some 5,000 light years from Earth, this is a remnant of a supernova that took place during the past 30,000 years. With a diameter of 70 light-years, the object is visually speaking nearly twice the size of a full moon.
APRIL
Markarian’s Chain: The Virgo cluster consists of more than 2,000 galaxies, within which Markarian’s Chain forms a J-curve string of bright galaxies that share a common motion through space.
MAY
M13 Great Globular Cluster of Hercules*: Consisting of several hundred thousand stars and 145 light-years in diameter, M13 is considered to be the finest cluster in the Northern Hemisphere.
JUNE
Cave Nebula*: Located along the plane of the Milky Way is the diffuse emission nebula referred to as the Cave Nebula. The Cave at the centre is critically located at the boundary of the Cepheus molecular cloud and the hot, young stars which ionize the surrounding gases to great effect.
JULY
Orion Widefield: Framed around the area of Orion’s Belt, the Horsehead Nebula and the Great Orion Nebula, look hard and the refection nebula M78 can also be seen in the lower left corner.
AUGUST
Elephant’s Trunk Nebula*: A very large emission nebula, the so-called Elephant’s Trunk Nebula is rightly viewed as one of astrophotography’s most iconic images. The ‘trunk’ itself dominates the centre of this image and is illuminated from behind by a bright star forming region.
SEPTEMBER
M31 Andromeda Galaxy: The full benefit of new filters, improved guiding, clear skies over 6-nights and extensive use of new processing techniques can be seen in my best image yet of Andromeda.
OCTOBER
Butterfly Nebula: Situatedwithin the Orion Arm of the Milky Way is the Gamma Cygni nebula, a diffuse emission nebula surrounding the star Sadr. Either side of the dark rift which divides the image from top to bottom are two large bright areas that together form the so-called Butterfly.
NOVEMBER
M33 Triangulum Galaxy: Like it’s neighbour Andromeda, better data and processing has produced an exciting new image of M33 this year, the red areas highlight Ha-rich star-forming regions
DECEMBER
Flying Bat & Giant Squid Nebula*: This very faint OIII emission nebula Ou4 required an imaging time of 40-hours. For obvious reasons Ou4 has become known as the Giant Squid Nebula which, moreover, lies within the much larger SH2-129 HII emission region or the Flying Bat Nebula.
A year after taking up astronomy as a hobby, at the behest of my elder daughter I started this blog in 2014. Describing the objective and content of the blog I adopted the strapline “A personal discovery of the Universe through astronomy and astrophotography”, which could also be described as a journey. In reality it’s been an adventure consisting of two threads: the knowledge and related science of astronomy and the challenge of astrophotography. As we on Earth pass through space whilst at the same time rotating 360o each year around the sun our view of the night sky changes month-by-month, inevitably returning to the same perspective each 365-days. Against this background I therefore often return to certain objects every few years hopefully armed with new astrophotography skills in pursuit of an even better image.
Following such a path I’ve already imaged M31 the Andromeda Galaxy on four separate occasions since 2015, each time enthralled by the majesty and beauty of this barred spiral galaxy. Notwithstanding, it was clear to me that there was significant scope for improvement of the previous images with both better data and processing. Since the last attempt in October 2019 a myriad of positive developments have taken place of which perhaps three stand out: multi-star guiding, the purchase of Chroma filters and in particular the use of PixInsight image for processing – all have been game changers, so much so that reprocessing that image now also looks good – see below.
However, whilst the said progress has already been transformative to my astrophotography during the past year, inevitabky it is imaging conditions that play the most critical role, especially in England. Fortunately during this autumn in both October and November for once the new moon coincided with clear skies, providing no less than six nights over which I was able to obtain almost 12-hours of some of perhaps my best ever data. Based on this I’ve been careful to apply my best new processing skills and am thankful that the final HaLRGB image has turned out very well. In particular, the dust lanes stand out against the bright core and surrounding blue intergalactic dust and gases, which are themselves punctuated by the bright red regions rich in Ha light.
In the blogs that accompanied previous Andromeda images I’ve often referred to the galaxy as a neighbour of the Milky Way but really we are part of the same family known as the Local Group. Some 10-million light years in diameter, more than 30 galaxies form two collections around the two largest galaxies of Andromeda and the Milky Way. Gravitational forces play the central role in controlling this group, especially Andromeda which is itself moving towards the Milky Way at about 70 miles per second and is destined to merge in about +/- 4 billion years; recent studies indicate that an outer halo of stars extending up to 2-billion light years from Andromeda may be in the influence of the galaxy, suggesting this event may already have started!
Thereby my personal journey of astrophotography is set to continue somewhat in parallel with that of Andromeda, which will I am sure lead to further hopefully even better images of this exciting deep sky object that is perfect for my equipment – after all we’re getting closer at the rate of 2,207,520,000 miles each year!
IMAGING DETAILS
Object
M31 the Andromeda Galaxy.
Constellation
Andromeda
Distance
2.5 million light-years
Size
3.2o x 1o or 220,000 light-years
Apparent Magnitude
+3.44
Scope
William Optics GT81 + Focal Reducer FL 382mm f4.72
Mount
SW AZ-EQ6 GT + EQASCOM computer control & Cartes du Ciel
Guiding
William Optics 50mm guide scope
+ Starlight Xpress Lodestar X2 guide camera & PHD2 guiding
Camera
ZWO1600M M-Cool mono CMOS sensor
FOV 2.65o x 2.0o Resolution 2.05”/pix Max. image size 4,656 x 3,520 pix
Located within the Orion Arm of the Milky Way galaxy is the Gamma Cygni nebula, a diffuse emission nebula that surrounds the star of the same name, otherwise better known as Sadr. Moreover, this large area forms part of an even bigger HII-region that is mainly (80%) located in the north and east quadrants of the so-called Cygnus Cross, which is defined by the stars Deneb – Sadr – Delta Cygni – Albireo – Aljanah (see below).
This vast area passes directly high overhead at this time the year before disappearing behind the house roofline in the early morning hours and has already provided many exciting imaging opportunities for me in the past. The heart (not the centre) of the region is the supergiant star Sadr and I first imaged this area in autumn 2015 using my modded DSLR camera. A return visit was therefore long overdue and this time I set out to better capture the so-called Butterfly Nebula in narrowband wavelengths.
The resulting data has been processed to good effect as an SHO image (see top-of-the-page) using the Hubble Palette techniques. Other than the dominant supergiant star Sadr and widespread colourful nebulosity, two significant features are worthy of note in the final image. Either side of the almost central dark rift that divides the image laterally, are two large bright areas which together form the ‘wings’ of the so-called Butterfly Nebula IC 1318-C (right = south) and IC 1318-B (left = north). Furthermore, just beyond the Butterfly’s left wing north of Sadr is the young, bright open star cluster NGC 6910.
Finished well with submersible water pump & floodlight (turned off for astronomy!)
I’m very pleased with this image, which is my first since the end of March, in part because nowadays I take an astronomy break during the long late spring / summer days when astronomical darkness is largely absent. However, this year the pause has been protracted as the patio on which Fairvale Observatory is situated was re-laid, during which a hitherto unknown water well was discovered. Thereafter one thing led to another and turned into a summer project to recommission the well, thus delaying completion of the patio. As a result I’ve only recently been able to reinstate the astronomy equipment, a job that is still ongoing. The new patio is firm and flat, providing a much better surface for the mount than before and I’m hopeful that once recalibration is completed will result in improved tracking results – watch this space!
IMAGING DETAILS
Object
IC1318-B & IC1318-C Gamma Cygni Nebula or Butterfly Nebula NGC 6910 Open cluster
Constellation
Cygnus
Distance
3,700 light-years
Size
1Approximately 100 light-years
Apparent Magnitude
Varies
Scope
William Optics GT81 + Focal Reducer FL 382mm f4.72
Mount
SW AZ-EQ6 GT + EQASCOM computer control & Cartes du Ciel
Guiding
William Optics 50mm guide scope
+ Starlight Xpress Lodestar X2 camera & PHD2 guiding
Camera
ZWO1600MM-Cool mono CMOS sensor
FOV 2.65o x 2.0o Resolution 2.05”/pix Max. image size 4,656 x 3,520 pix
Somewhat tongue-in cheek, astrophotography is often referred to as something of a dark art and to be fair it sometimes seems that way, particularly when it comes to processing. My main interests in astrophotography are Deep Sky Objects such as emission nebulae, galaxies and planetary nebula but have long aspired to capture a more elusive category that abounds throughout the Universe – dark nebula.
Popular with astrophotographers, emission nebulae consist of vast clouds of ionised gases and regions of interstellar dust which reflect light from the said gases and or from stars and stellar nurseries that lie within – depending on their make-up the results are colourful in both broadband and narrowband wavelengths. Dark or absorption nebulae are also a type of interstellar cloud but are so dense they completely obscure and / or soak-up visible light emitted from objects behind or within, which as a result contrasts with general light flux of the Universe forming large dark regions. Because of their darkness they are usually faint, hard to see and moreover, difficult to image, especially from locations with light pollution.
The Horsehead Nebula is a dark nebula that has formed a part of my previous images but I’ve only imaged an isolated dark nebula once before – Barnard 142-3, which for obvious reasons is also known as the E-nebula (see above & here). Larger more complex dark nebulae require much darker skies to image than prevail at Fairvale Observatory, such as in New Mexico, USA where the Deep Sky West observatory is located and on this occasion has produced my first ‘serious’ image of a stand-alone dark nebula.
Cepheus & the aproximate location of LDN 1250 image indicated by the red square
Lynds Dark Nebula (LDN) catalogue of dark nebulae was compiled by the eponymous Beverly T. Lynds in 1962 and is based on the study of red and blue photographic prints from the National Geographic-Palomar Observatory Sky Atlas. Situated in the north close to Polaris, the constellation of Cepheus has a number of dark nebulae, of which LDN 1250 is part of a huge complex of dark nebula surrounded by dust and scattered light from the stars of Cepheus.
LDN 1250 luminance – RGB wavelengths are also strong
Imaged here in LRGB the features come out well in all wavelengths, however, such are the subtleties of the dark nebula components I found processing difficult and required plenty of ‘dark art’ techniques. The final image at the top of the page shows to good effect the main dark nebula, togeher with widespread but less opaque nebulosity and star colours, as well as some distant galaxies lurking in the background that together has produced a satisfying and very interesting outcome.
Originally thought to be a planetary nebula, Abell included this object in his catalogue as Abell-85 but later in 1971 it was revised as a supernova remnant (SNR) and renamed CTB-1, thus also denoting it as a radio source. The overall structure is a circular shell with a conspicuous rupture towards the north (bottom right of image). The main red Ha-shell is composed of multiple interlocking filament limbs, with a blue / green OIII arc along one side (see main image above).
I experimented extensively processing the data because of its overall complexity and is an interesting object, which is therfore also presented below as greyscale Ha-wavelength only and starless versions. The main Ha and OIII data is shot at long 1,800 second exposures, which together with RGB adds up to a whopping 29 hours of integration time. However, CTB-1 is an extremely faint object, which probably still requires considerably more time – I’ve seen somebody else’s 61-hour integration which they described as “not enough” and despite the quality of their image I’d probably have to agree.
CTB-1 is a very exciting object, which might have been what Douglas Adams had in mind when creating Milliways or The Restaurant At The End Of The Universe in the Hitchhiker’s Guide, from which such spectacular events could be ordered to view with your meal!
WATCH THIS SPACE(MAN) 