Calgary Lights Up

I’m getting the hang of shooting demanding day-to-night time-lapse movies!

For this clip I shot over 2.5 hours, using a fish-eye lens, to create a sequence suitable for projection in a digital planetarium dome.

But the trick with these day-to-night sequences is getting a smooth transition in exposures, which can range over 12 to 16 f-stops, from short snapshot exposures with the lens stopped all the way down at the start before sunset, to long 8-second exposures with the lens wide open at night, plus the camera’s ISO speed increasing from a slow ISO 100 to a faster ISO 400 or more at select points through the sequence as well.

The secret to doing this is a control box called the Little Bramper, an intervalometer that fires the shutter automatically at set intervals but also gradually ramps the exposure time a tad longer with each successive exposure. This was my third time out with the Bramper, and I more or less got it right this time!

While the Bramper does a great job running the camera, it still takes a lot of manual oversight to control its ramping rate so the exposures don’t get too long and overexpose the scene, or fail to get long enough to track the darkening sky.

At several points in the sequence it is also necessary to quickly (in one exposure cycle) half the exposure time, while at the same time opening up the lens a stop, or doubling the ISO, so that the ever-lengthening exposure doesn’t get too long and collide with the interval between exposures. In this case, shots were taken about 12 seconds apart, so the maximum exposure for each frame couldn’t be much more than 8 to 10 seconds.

The end result of the work is a time-lapse movie that shows the setting Sun, then the lights of Calgary coming on as the sky darkens. Clouds lit by the yellow glow of streetlights move in, then blow away again to reveal a few stars in the urban sky.

— Alan, October 16, 2011 / Movie © 2011 Alan Dyer

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