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ASNSW's Astroimaging Section

Section Leader: Trevor Gerdes
Meetings: Committee and Section Meetings

The Astro-Imaging section meets on the Wednesday closest to the full moon. The next meeting date is usually shown top right on the front page of the Club’s web site, and the site has a calendar of meetings for the year. The doors are usually open by about 19:15. The group varies in size between one and two dozen depending on weather. New folk and visitors are most welcome, and we have an abundant supply of tea, coffee and Double-Choc Tim-Tams. The meeting runs from 19:30 to 22:15, whereupon there is a mad scramble to be packed up and out before the alarm goes off at 22:29:59.

The regulars use equipment ranging all the way from nothing at all to a DSLR on a tripod to heavy permanent observatory-class kit weighing a couple hundred kilos, and absolutely everything in between.

Damp photons

During the current ultra-deep La Nina event combined with an especially cold wet summer monsoon trough, some of us have turned to producing quite beautiful time-lapse videos of the milky way glimpsed through scudding cloud, beautiful sunsets and the occasional spectacular comet. Others have dug permanent piers in their suburban back yard and become expert at whole-constellation shots in light pollution resistant hydrogen alpha. It’s been a good time for building an observatory. 

Range of interest

Over the last few years, the emphasis has been on deep sky rather than lunar/planetary work, and with the wet weather there’s been a drift toward ever wider field, but that is just historical and fixable. As well as capturing the detailed morphology and colour of beautiful galaxies, there’s a strong interest in narrowband (H-alpha, O-III, S-II) especially for examining star birth and death, emission nebulae, shock fronts and evaporative gaseous globules and elephant’s trunks emerging from juicy dust, Herbig-Haro objects, planetary nebulae, Wolf-Rayet stars, supernova remnants. One or two of us are into spectra, quantitative light curves, and the like. The group has a very strong background in software and electrical engineering, and consequently some of us have built our own mount control software and electronics, and are happy to share secrets. Others are excellent at creating wide multi-shot panoramas and can help with the fine details of fairly complex image processing. 

Getting started

Astrophotography nicely complements visual astronomy, but requires quite different kit and a very different approach.  If you’d like to get started in astrophotography, the path to the Vale of Tears is to put your camera on a commercial 8 inch SCT on a rattly mount. Much more fun is to put an F/2.4 lens on your existing DSLR, whack the DSLR on a tripod, point at Orion or Sagittarius, take a stack of twenty 15-second subs with the lens one or two stops off wide open at ISO 1200, rattle off a set of matching darks, and capture a dozen Messier objects and the Horsehead or the Pipe nebula in your very first shot. Once you’re addicted (about one night does the trick), you’ll be thinking of hocking the cat, swapping the tripod for a good equatorial mount, and taking whole-constellation shots or shots of the larger galaxies and star-forming regions, still with the DSLR but now using 10 minute subs. We can show you how focus with test shots or a mask, how to do darks and flats, how to register and stack the images, and how to digitally process to extract superb photos from apparent blackness. Round about now you’ll learn about dark current and readout noise, sell the lounge suite, and buy a dedicated astro-camera thermoelectrically cooled to 50 degrees below ambient, with stunning results. Only now is it time to put the cooled camera on the back of a good rich-field scope, say a 3 inch refractor of around 600-900 mm focal length, start learning about polar alignment, periodic error correction, guide-scopes, narrowband filters, dew shields, wind buffet, balance, worm gear adjustment, managing batteries, laptops, and a maze of cables and the like. You may never get bitten so badly that you have to sell the Audi TTS and the cat, put the 12 inch astrograph on the permanent pier, and get stuck into one-hour subs with dual differential guiding, but it does happen. 

A typical meeting

We usually start by showing the “Sacculum Venaticorum” or hunting bag, for the last month. It’s fine to just put up a finished slide and wait for the applause if that’s what you’d prefer. Everything from “My First Red Smudge” to jaw-droppingly superb shots of arcane and obscure targets. However, folk are strongly encouraged to remind us yet again what gear they used and why, give technical details of exposures and techniques (and why they did it that way), and explain why they photographed that particular object. The old hands are expected to read up a little on the astrophysical significance of the object, and compare with some professional shots from ESO or Hubble. 

From time to time we have a mini-tutorial followed by an open workshop on a particular issue. It might be on “What’s out there”, eg on “What is a Wolf-Rayet star and is Eta Carinae one?”, or everyone might be asked to dig into their archives and bring their best shot of Object X, and we compare the view with different classes of kit, wide field vs long focal length, cooled vs DSLR, narrowband vs single-shot colour, and so on. Or the workshop might be on technique (eg how to polar align using the drift method vs formal sky-mapping, or how to really focus by fitting a parabola to FWHM versus focusser position), or how to retain colour saturation, or what is deconvolution and how to do it. Members are strongly encouraged to suggest topics for next month’s workshop, or to volunteer to give one. It could be 5 minutes or 2 hours, depending on your level of expertise and fluency.

On other occasions we have an informal “Image Doctor” session – you show a shot that you’re not happy with or which has puzzling features, and we try to work out what went wrong and how to do it better. The Group will include a dozen or so members who have made every mistake in the book at least twice, and will delight in sharing, both at the meeting and in the field. We tend to be quite competitive, but in the sense of playing against the universe rather than each other. The section leader (combined tea lady and chair) is responsible for sending anyone who makes bitchy unhelpful unscientific comments to re-education camp. As a result of the generous sharing of information within the group, the quality of work that we have produced has increased astonishingly over the last several years.

Bringing your talk

In summer when the sky is soggy, we tend to have a fairly relaxed and informal approach, but in Winter when the sky’s been crystal clear, we have a lot to get through. Bring your work as JPEGs or 8 bit TIFF’s, on a USB memory stick, in a single directory with your name on it. Inside the directory, it’s best if you name the individual slides with names in alphabetical order of how you wish to present them, eg “0001 Orion nebula”, “0002 Omega centauri”, “0003 Hubble shot”, etc. Rummaging in silence through a directory with your life’s work in random order is gently discouraged. Material is loaded onto the Chair’s laptop, either between 07:15 and 07:29:59, or over coffee. 

Communications

We mostly communicate via email to astroimaging @asnsw.com. The Section Leader cannot put you on the mailing list. You must do it yourself via the club’s web site. A particularly important use of the email group is to let us know what material you have bagged over the last month, so that we can set up some sort of smooth and equitable agenda. Although last minute, unscheduled, and impromptu talks are fine and even strongly welcomed, the Chair may have to ask you to hold over till next month so they can be put on the agenda. 

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