The Cadence of the Moving Sky


Saturn, Mars and the Milky Way over the Bow River

Saturn, Mars and the Milky Way appeared in the twilight over the Bow River.

I shot this scene on August 24 from the viewpoint at Blackfoot Crossing Historical Park, overlooking the Bow River. Mars appears between Saturn above and Antares below, in a line of objects west of the Milky Way.

The valley below is the traditional meeting place of the Blackfoot Nation, and the site of the signing of Treaty Seven between Chief Crowfoot and Colonel MacLeod of the North West Mounted Police in 1877.

The image is a panorama of two images, each 20-second exposures at f/2 and ISO 1600 with the 24mm lens. I shot them just prior to shooting time-lapses of the moving sky, using two cameras to create a comparison pair of videos, to illustrate the choices in setting the cadence when shooting time-lapses.

The movies, embedded here, will be in the next edition of my Nightscapes and Time-Lapse ebook, with the current version linked to below. The text explains what the videos are showing.

 

Choose Your Style

When shooting frames destined for a time-lapse movie we have a choice:

  • Shoot fewer but longer exposures at slower ISOs and/or smaller apertures.

OR …

  • Shoot lots of short exposures at high ISOs and/or wide apertures.

 

The former yields greater depth of field; the latter produces more noise. But with time-lapses, the variations also affect the mood of a movie in playback.

This comparison shows a pair of movies, both rendered at 30 frames per second:

Clip #1 was taken over 2 hours using 20-second exposures, all at ISO 2000 and f/2 with 1-second intervals. The result was 300 frames.

Clip #2 was taken over 1 hour using 5-second exposures also at f/2 and 1-second intervals, but at ISO 8000. The result was 600 frames: twice as many frames in half the time.

Clip #1 shows fast sky motion. Clip #2 shows slow motion.

Clip #2 exhibits enough noise that I couldn’t bring out the dark foreground as well as in Clip #1. Clip 2 exhibits a slower, more graceful motion. And it better “time-resolves” fast-moving content such as cars and aircraft.

Which is better? It depends …

Long = Fast

The movie taken at a longer, slower cadence (using longer exposures) and requiring 2 hours to capture 300 frames resulted in fast, dramatic sky motion when played back. Two hours of sky motion are being compressed into 10 seconds of playback at 30 frames per second. You might like that if you want a dramatic, high-energy feel.

Short = Slow

By comparison, the movie that packed 600 frames into just an hour of shooting (by using short exposures taken at fast apertures or fast ISOs) produced a movie where the sky moves very slowly during its 10 seconds of playback, also at 30 frames per second. You might like that if you want a slow, peaceful mood to your movies.

So, if you want your movie to have a slow, quiet feel, shoot lots of short exposures. But, if you want your movie to have a fast, high-energy feel, shoot long exposures.

As an aside – all purchasers of the current edition of my ebook will get the updated version free of charge via the iBooks Store once it is published later this year. 

— Alan, August 26, 2016 / © 2016 Alan Dyer / AmazingSky.com

 

Moon and Twilight Planets over the Bow River


Moon with Antares, Mars & Saturn over Bow River

The waxing Moon shines between Saturn and Mars over the waters of the Bow River.

It was a beautiful autumn evening for watching the twilight showing of the crescent Moon accompanied by Saturn (at right of centre) and the pairing of Mars (at left, above) with his rival red star, Antares in Scorpius (at left, below).

The river is the Bow, with its headwaters at Bow Glacier in Banff.

To shoot this scene I drove to the grounds of the Blackfoot Crossing Historical Park south of Cluny, Alberta to take advantage of its viewpoint overlooking the Bow River and the heart of the traditional Siksika First Nations tribal lands.

It was here, in the valley below, that Treaty Seven was signed between Chief Crowfoot and Colonel James Macleod in September 1877. Today, a beautiful interpretive centre sits on the hillside at the heart of Blackfoot country.

– Alan, September 28, 2014 / © 2014 Alan Dyer

 

Rainbow at Blackfoot Crossing


Rainbow at Blackfoot Crossing #2

A low rainbow shines beneath a retreating thunderstorm at Blackfoot Crossing Historical Park.

On my way home from Waterton Lakes I drove through a thunderstorm, then watched it retreat and the Sun break through in the west. I was hoping for a rainbow in the east, and sure enough, one appeared.

With the Sun still high in the late afternoon sky, the rainbow was low, with just a small arc appearing above the horizon.

By good luck, I was passing the hilltop Blackfoot Crossing Historical Park, a beautiful museum interpreting the history of the Siksika Nation, and a great place to look out over the prairie.

These photos look down a line of rock cairns running from the interpretive centre to the hilltop cemetery in the distance, below the arc of the bow.

Rainbow at Blackfoot Crossing #1

This wider angle image gives the context, with the bow at the bottom of the thundercloud, and fresh blue sky above.

I love the mountains but it’s nice to be back home on the prairies where we can see the wide horizon.

– Alan, July 20, 2014 / © 2014 Alan Dyer