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Tuesday, June 04, 2013

The Yukon’s Northern Lights – Behind the Scenes

The Yukon’s Northern Lights – Behind the Scenes:
A guest post by Phil Hart – author of the Shooting Stars eBook (use code DPSTARS for a 25% discount).
My three favourite things in the world are mountains, aurora and snow. In early 2012 I got all three of them in spades when I spent nine weeks in the frozen north of Canada’s Yukon Territory.
With four cameras and dozens of lenses, tripods and a truck full of extreme cold weather gear, I journeyed across the Yukon and chased every gap in the clouds I could find. Three terabytes and a long learning curve later, this video is short, fast and high-impact two minute compilation of some of the best footage I captured during my aurora adventures.
In this post, let me share some of the ‘behind the scenes’ work that went into producing it. First the video, which you really do have to watch in full-screen with the lights down and the music up!

The Yukon’s Northern Lights from Phil Hart on Vimeo.

Camera Gear

Cameras: 2 * Canon 5D Mark II and a Canon 1100D (aka Rebel T3).
Lenses: Canon 24mm f1.4L (I & II) and 14mm f2.8L with the full-frame cameras and Canon 10-22mm f3.5-5.6 and 15-85mm f3.5-5.6 with the cropped sensor camera.
Tripods: Various Manfrotto and Induro tripods with mainly ball-heads. The grease in the Manfrotto heads froze at around -25 ºC (~15 ºF) but were still workable.
Remote Releases: I was using both programmable and simpler push-button cable releases. Most often I simply had the camera in Manual mode, set with a particular aperture, ISO and exposure duration. With the camera set to Continuous Shooting mode (aka Sports mode) I could lock the button down on the cable release and the camera would fire off a long sequence of images with the same setting (and almost no gap in between) until I came back to stop the sequence (or the battery ran flat).
Dew Heaters: Dew is a common problem for night sky photography, but in sub-arctic climates like that in the Yukon, the air is so dry that it is less of a problem (although it forms as frost, not dew with the temperature well below freezing). Some nights when the cameras were running on long sequences, I did need a little protection from frost on the lenses, and was generally using little 2-inch heater straps from from Dew-Not.
Power Supplies: 12 volt lithium-ion batteries to power dew-heaters, motion control (below) and also one of the cameras via a DC-power adapter for long all-night sequences. Lithium-ion is about the only type of widely available battery-chemistry that can cope with extremely cold temperatures. While their capacity did drop, I could still get 1 hour of continuous operation out of my Canon 5D Mark II even at temperatures down to -40 degrees and a very respectable 2 hours at milder temperatures of -15 ºC (~0 ºF).

Setting Up Gear in the Cold

Exposure Settings

The aurora can vary enormously in brightness. When it is quiet, it can be as faint or fainter than the Milky Way, requiring 30 seconds with a high ISO setting (~1600-3200) to capture it nicely (like the final aurora sequences in the video). However, when it is bright it can be as bright as the Full Moon. On those few nights of the greatest aurora storms (like the two main sequences in the video), exposures of just 2-4 seconds can be enough (still with the aperture wide open and a high ISO).
The other challenge with aurora is how fast it can move. Generally there is a balance here with the brightness. Faint aurora displays are usually also quiet in terms of movement, so longer exposures do not blur out too much of the movement. The fast moving auroras also tend to be bright, and the curtains and rays move rapidly, enough to cause them to blur significantly even in 8-10 second exposures. So it’s important to keep carefully balancing the trade-off in this regard. You get more experienced at this quite quickly, but fast lenses also help a lot, which is why I particularly valued the 24mm f1.4 lenses I was using extensively during this trip for images like this one:

Fast and Bright Aurora: 2 second exposure with 24mm lens at f1.4, ISO3200.

Focus

Focus at night is difficult already, but with timelapse you have the additional complexity of often incorporating some foreground elements without the daytime luxury of stopping the lens down to provide high depth-of-field. In most cases this can be avoided by trying to work with large foreground elements that can be kept a couple of meters away from the camera. Although focus on the stars and the foreground is not perfectly the same, at this distance the difference is not significant enough for most people to notice or object to. The eye is also a lot more forgiving of these kind of compromises in video than it is high with a large format still image.

Motion Control

Vixen Polarie: A compact little mount designed for taking tracked long-exposures of the stars but which can also be easily used as a simple panning mount when the motorized axis is pointed vertically.
Dynamic Perception Stage Zero Dolly: A six-foot long aluminium dolly rail with controller, used to provide the sliding sequences in the video. The LCD screen on this was very difficult to read and slow to update in extreme cold conditions.
Custom controller: Developed jointly with Fred Vanderhaven, this provided pan/tilt motion control and almost fully automated day-to-night twilight exposure control. It was only used for two of the clips in this video and the functionality in that case was similar to the Vixen Polarie.
One of the strongest sequences in the video (as the music really kicks in) has the camera moving in between two trees, with aurora on the left and moonrise on the right. Here is the scene as that sequence was being captured:

Dynamic Perception Dolly in Action
And here is a still from the resulting image sequence:

Still image from sequence captured on Dynamic Perception Dolly as shown in previous image

Image Processing and Video Editing

My workflow for editing timelapse video from the RAW image sequences has improved a lot, but it is still a very time-consuming process. And while I am very experienced at using Lightroom and Photoshop to process astrophotography images, I am still a relative beginner at video editing.
I do the most significant development of the RAW files in Lightroom, choosing one frame that is representative of the sequence and then sync the settings across all the images so that they have the same processing. In some cases, where there is a big change in brightness (which happens a lot with aurora) I use Gunther Wegner’s LRTimelapse software to interpolate development settings between keyframes in the sequence, to cope with large changes.
After saving the settings to the Metadata for the images, I then I import the sequences into Adobe After Effects, and use that to render the sequence of RAW files to a loss-less intermediate video file. One of the most common effects I apply in After Effects is to use the Neat Video noise reduction plug-in. This has a ‘neat’ temporal noise reduction algorithm which compares changes between frames to help reduce noise (which varies between frames) without smearing out real detail (which is constant, but perhaps moving between frames). The Neat Video plug-in makes a significant difference to the quality of the end-result.
The other plug-in that I made some use of is the Granite Bay Deflicker plug-in. This was essential for smoothing out flicker that is present in the evening and morning twilight sequences, and was also used in the moonset clip.
The final video was compiled from the individual sequences using Adobe Premier Pro.

Composition: Reflections and Mountains

Many classic and beautiful images of the northern lights involve reflections in the foreground. The problem for me was that there is very little open water anywhere in the Yukon in the back half of winter, with the temperature having dropped as cold as -40 ºC (~40 ºF). The only place I found was an artificial deep water outlet from Fish Lake, near the capital Whitehorse. The night that I was there the aurora was very quiet but I did manage to capture a short sequence late in the night.

Fish Lake Aurora Reflections
Aside from that, one of my favourite locations was along Annie Lake Road which offered a nice mix of trees, open areas and mountain views as well. In this image, the reflections are in some relatively clean flat ice that had been cleared of snow by wind and some early spring sunshine during the day.

Annie Lake Aurora Reflections in Ice
One of the reasons I was keen to be in the Yukon rather than the even more desolate and flat Northwest Territories (where the weather and aurora prospects may be better) is the more interesting terrain. However, with very few roads and even less open in winter getting access to interesting locations was quite a challenge.
The image below is the most spectacular mountain view I captured (technically in the northern part of British Columbia), looking south from the road between Haines Junction and Haines Alaska. However, except on the biggest storm nights, the aurora was generally viewed to the north. So I never saw aurora over these mountains but they did make for a great sunrise sequences to end the video with. Aside from that, my favourite mountain location was way up north in Tombstone Park, which you can see in the image of ‘fast and bright aurora’ above.

Mountains viewed from the Haines Alaska Road

Music

Timelapse videos without music can still be interesting to watch, but are hardly captivating. Good music brings them alive, although it’s hard to suit everyone’s tastes. There are several online sites offering stock audio clips, but the images and the story flow so much stronger with music that is composed and produced to match the visuals. In this case, I again set my talented friend Dean Roberts (of ‘The Dirt Floor‘) the challenge of recording music for the video. Aside from watching the video the previous day, he recorded and edited the track for this in one (long) day. I hope you enjoy the rockin’ soundtrack he came up with.
If you’ve read this far and not watched the video yet, have a look – I know you’ll enjoy it! And if you’ve got a taste for aurora, you can read more about my adventures in the Yukon and see more videos on my blog: philhart.com/tag/yukon-aurora
Post originally from: Digital Photography Tips.



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The Yukon’s Northern Lights – Behind the Scenes