PHSC - Photographing the Night Sky - Terence Dickinson CM

Astronomer Terence Dickinson CM lives near the small community of Yarker, Ontario north of Belleville. Its attraction is a dark night sky with little light pollution - ideal for astronomy. Mr Dickinson has written 14 books on astronomy, issues an annual calendar illustrated with astronomy photographs, edits and publishes SkyNews - the Canadian magazine of astronomy and stargazing, and teaches astronomy and participates in programs on CBC radio and the Discovery channel. In 1981 an asteroid was named after him (5272 Dickinson).

Paul Mortfield of the Royal Astronomical Society of Canada (RASC) was in the audience and Terry asked him to speak about the David Dunlap Observatory (DDO) which is no longer used for research at the University of Toronto due to the massive light pollution in this part of Ontario. Metrus, the developer who purchased the land where the DDO stands, offered RASC the opportunity to keep the DDO open for public education (see the program schedule at www.theddo.ca).

Terry noted that astrophotography is a major sub-division of astronomy. It attracts a reasonable size group of about 30,000 enthusiasts in Canada (8,000 in Ontario, 3,000 in the GTA). While special equipment is needed for serious astrophotography, many sky objects can be photographed with an ordinary digital SLR set-up.

The use of film for astrophotography was killed by reciprocity failure. Today, astrophotography is the domain of the digital SLR with its higher sensitivity (ISO) and much lower noise levels (compared to the less expensive point and shoot digitals and film cameras with their media limitations). A two minute exposure with a DSLR, for example, gives a better image than a one hour exposure on film. As well, the DSLR’s spectral response is more suited to the light emanating from celestial objects. This spectral response and sensitivity can be improved even further by having the filter in the internal light path of the camera replaced. Terry used two photos of his horses and observatory to show the effect of each filter on the colours recorded by the camera. Since almost all celestial photographs are taken at the very edge of the camera’s capabilities, adjustments in image editing software such as Photoshop become a necessity.

The reciprocity characteristics of silver based material vary by maker and product. In 1998 Terry predicted film would still be in use a decade later and much improved. Time proved this prediction wrong thanks to the rapid pace in DSLR evolution combined with dramatic price reductions. His last sky photograph on film was taken April 28, 2002.

Many people are introduced to astronomy through star parties. A group of amateur astronomers set up their telescopes in a park or other large area and invite the general public to join in and take a peek through the telescopes. Terry mentioned a camp ground where he participates each year in astronomy nights teaching others about the wonders of the night sky.

You can begin enjoying astronomy with a pair of binoculars and a star chart. These will let you identify many of the brighter objects in the night sky. A DSLR and normal lens mounted on a tripod can be used to record objects using exposures of up to 30 seconds. The rotation of the earth will blur objects during exposures longer than 30 seconds, or taken with a telephoto lens unless an equatorial mount is used. This motor driven device when correctly oriented, cancels out the rotation of the earth, allowing the camera to stay focussed on the same spot in the sky through out exposures up to five minutes duration. To photograph objects emitting energy beyond the visible spectrum, the filter in front of the camera sensor must be replaced with one that captures a wider spectrum.

In choosing a lens, look for one with the least chromatic and coma defects. Terry photographed the big dipper with a Sigma 8mm f/3.5 fish-eye lens (wide open at 30 seconds). The image shows the big dipper and north star exactly as they appear to the naked eye. This lens is excellent with no coma or colour fringing, but it does have the severe curvature of field common to fish-eye lenses, which seems to wrap the horizon around the stars. Terry pointed out that a lens with the correction of the Sigma fish-eye and no curvature would be very expensive.

Either a camera lens or telescope can be used on a DSLR. Surprisingly, an apochromatic telescope is less expensive than an apochromatic camera lens of the same focal length (the telescope, with its fixed aperture is mechanically simpler). An astronomical telescope equivalent to a 400mm f/4 telephoto lens costs about $600. Terry mentioned William Optics, who advertise in his SkyNews magazine as a good source for equipment. The necessary companion equatorial mount is more expensive than the telescope (about $1,000). Terry estimated to equip a back yard observatory like his would take some $15,000 plus the cost of materials and labour for the building.

Light pollution is a big and growing problem. As populated areas add more artificial lighting, the excess light escapes into the atmosphere and reflects off moisture in the air, making a light haze that obscures much of the sky. As the world becomes more urbanized and wired, the places that work well for astronomy shrink to spots that are remote and thinly populated. Properly designed street, highway, and area lights along with a conservationist attitude towards lighting would help us recover our wonderful star filled dark sky.

During the evening, Terry showed many personal night sky shots taken with a variety of lenses and telescopes. He showed the night sky from his house during the August 2003 southern Ontario power blackout and the same scene taken the next night when the power had been restored. Together, these two images make a powerful statement about light pollution and were published around the world.

The audience was asked to name the brightest star (not a planet) in the night sky. Terry noted that most people suggest it is Polaris, the north star which is actually the 28th brightest star. This belief stems from misinformation in the Walt Disney movie, Pinocchio. The correct answer is Sirius, the dog star in the constellation Canis Major - near the constellation of Orion, the hunter.

Terry's pictures of the aurora borealis taken at his home show many of the colours created by this physical phenomena. The effect is caused by the interaction of solar winds created by sun spot activity with the earth’s magnetic filed. Visit the Aurora (astonomy) page on the Wikipedia web site for more information.

Terry wrapped up his talk with pictures taken on his expeditions to Australia and to some of the world’s largest telescopes at the ESO facility in Chile’s Atacama desert. The La Silla Paranal Observatory is the largest on earth. Nearby is an underground hotel with a stunning lobby garden that adds humidity to the living quarters. Fourteen European countries participate in the ESO.

If you happen to come across a star party, or have a chance to visit the David Dunlap Observatory, don’t pass it by - there is magic in the stars and objects of the night sky, things almost completely hidden from those of us who live in large cities. If you would like more information about astronomy and astrophotography, check out Terry’s books or the latest issue of SkyNews. As photographers, you might wish to accept the difficult challenge of capturing an elusive object in the night sky!

Usual Light Pollution

Blackout, Aug 2003

Equatorial Mount

La Silla Paranal

Desert Hotel

La Silla Paranal

These are just a few of the amazing photos taken by Terry and shown during his talk