President’s Corner

The One-Minute Deep-Sky Astrophotographer 

by Michael Watson, President 

(Michael.Watson@gowlingwlg.com) 

Our astronomy club boasts among its members an impressive number of skilled, experienced, and dedicated astrophotographers,
whose staggeringly beautiful and technically accomplished images can be seen in every issue of this Journal. I’m thinking of such craftspeople as Andrea Girones of the Ottawa Centre, Blair MacDonald of the Halifax Centre, and National Treasurer Stuart Heggie. There are many others. Every time I gaze at the images that they produce I am awed, as well as envious of both their knowledge and the technical skills they have developed and honed to produce their detailed, high resolution works of art.
I am also envious of something else: Certainly not all of them, but many of the RASC’s best astrophotographers have their own observatories, with permanently mounted astrophoto- graphic telescopes that they are able to point at a single object during an entire observing session—or even over many nights spanning weeks or even months—in order to capture hours
of photons from which they can work their digital darkroom magic and produce their superb finished images.
Some of us RASC astrophotographers don’t have such observatories. Many of us live in cities that are not the most conducive environments for producing decent deep-sky images. We have to drive, often long distances, to place ourselves in dark-sky sites for the few precious hours that we have between the end of evening twilight and the lightening of the sky as morning comes up in the east. Then it’s time to disassemble our gear, pack the car, and, after a night under the stars, drive back home.
That describes your national President. I live in the centre of light-polluted Toronto, and have to drive some hours to get to an observing site that is dark enough for at least
half-serious deep-sky astrophotography. As some readers will know, my favourite, most readily accessible observing site in the Northern Hemisphere is in Algonquin Provincial Park, about 285 km north of my city home. When I am there, and especially since I am still working full-time and weekends are usually the only available time for astronomy, I want to make the most of the few nights during the year, and the few hours on those nights, to capture on the camera sensor what I can of the sky. Rather than concentrating for hours on a single object, over the past years I have chosen to produce images of as many of the familiar and striking deep-sky objects as I can using integration times of a few minutes to half an hour. Of course, with such short integration times I can’t get nearly the depth and detail as do the astrophotographers whom I admire so much. But I’ve found that even images produced with such short integration times can be of decent quality and are much appreci- ated by deep-sky enthusiasts, particularly when several images are assembled into presentations for RASC meetings, either at the RASC General Assembly or at Centre get-togethers.
The majority of my images, a few of which accompany this article for illustration, are made by stacking from 5 to
30 identical exposures of 1 minute each; that’s right, just 1 minute. For years I have used a 35-mm Nikon D810a
dedicated astro camera for all of my deep-sky photography, and I have found that the full-frame sensor on this camera is of sufficiently high quality that I can shoot at an ISO of up to about 6400 and (stacking numerous frames to reduce the noise in individual subframes) to produce pleasing images.
There is a great deal of image stacking software available, from a simple-to-use beginner’s program such as DeepSkyStacker, to the very advanced, such as PixInsight. Most of these programs also come complete with image processing functions, in addition to subframe stacking capabilities.
I have been a fan of wide-angle astroimages for many years. Many of my images are of entire constella- tions and well-known star patterns, and are made with camera lenses with focal lengths from 28 to 400 mm. The sharpest lenses that I us
for this type of work are the 35-mm and 50-mm ƒ/1.4 DG HSM ART lenses, which I stop down to at least ƒ/2.8 and often to ƒ/4.5. I do this for two reasons: (i) in order to reduce almost to the point of elimination the noticeable vignetting (dark shading) that one sees in the corners of a frame when the lens is used wide open at ƒ/1.4, and (ii) to get the sharpest pinpoint star images out to the very edges of the frame, rather than just in the centre. When I am shooting with my favourite Nikkor AF-S 70-200-mm ƒ/2.8 G ED VRII lens, I’ll stop down to ƒ/4 or ƒ/5.6. Naturally, stopping lenses down in
this fashion requires an increased ISO setting, but very good wide-field images can be made at ISO 1600 to 4000. The sensors on modern 35-mm DSLR and mirrorless cameras are so good that, with stacking of half a dozen to two dozen subframes, noise (or pixellation) is almost undetectable in the finished images.
For higher magnification photography I use either (i) a Tele Vue NP127is apochromat with a focal length of 660 mm and a focal ratio of ƒ/5.2, or (ii) an Explore Scientific 152-mm apochromat, with a focal length of 1253 mm and a focal ratio of ƒ/8, as is typical for refractors of the size. The Tele Vue 127 is a magnificent scope in my experience, giving a 3.1 by 2.1 degree field on a 35-mm frame, and producing images that to my eye are quite pleasing even with short, 1-minute exposures for the subframes.

Of course, the best camera lenses and astrophotographic telescope are of little use without a good mount. I use either a heavy-duty Astro-Physics 1100GTO mount (www.astro-physics.com/1100gto) or a smaller, lighter and more portable
Sky-Watcher EQ6-R PRO mount (https://www.skywatcherusa.com/products/eq6-r-pro?_pos=1&_sid=d38517cfd&_...), both of which keep even my longest focal-length scope pointed precisely at my target without guiding for the short exposures I use.
I’ll conclude by saying this: Certainly hours-long integra- tion times are necessary for the ultra-high resolution, highly detailed observatory quality images that we marvel at in magazines and at RASC meetings. But with the right equipment, pleasing deep-sky astrophotographic images can definitely be made with short exposures. Would-be
or neophyte astroimagers should try being a one-minute deep-sky astrophotographer; you might be very surprised at your results!

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