December 27, 2011

2nd Annual Christmas At The Yurt - Star Trails

The Jensen clan spent Christmas weekend at a Yurt up in the mountains.  We had a pretty fantastic time.
While we were miles away from civilization, I decided to take advantage of the lack of light pollution for some star trails.  

This first image was created on our first night, and is a composite of 40 images, all shot with a 4 minute exposure at f/4.0 and ISO 400.
For those of you that are mathematically challenged, that is a total of 160 minutes, or about 2 1/2 hours.
I could have done a single exposure for the same amount of time, but the end result would have been dramatically different.

For starters, the noise that would have been created from that long of an exposure would have been ridiculous.
The Canon in-camera long exposure noise reduction is pretty fantastic, but it would still require some pretty heavy work in post processing.
In the end, the results would not be this clean.  The second issue that would be created is that the ambient light would have accumulated
over the course of the exposure, illuminating the foreground.  The foreground elements weren't strong enough to be included in the image and the
noise that would have been created from the long exposure would have been difficult to deal with.

I like the combination of the silhouettes and the bit of open snow that make up the foreground.  It adds some interest,and gives a better
sense of place to the image.  As a side note, had I wanted to illuminate a foreground element, I could have used my flash or a flashlight
to paint the objects during one of the frames.  If you try this, make sure you do the painting in the first or last frame so that you can eliminate
them from your stack if you need to.  If you paint one of the frames in the middle, you are stuck with it as you
will end up with gaps in your trails if you remove the frame.

This second image was shot on our last morning at the Yurt.  Because this was shot in the early morning, I did things a little differently.  I knew the rising sun would cause the light to change rapidly, so I elected to use much shorter exposure times so that I could eliminate frames in my stack as needed as they became to bright.  Also, I chose a different composition that included the Yurt.  Because of this, I wanted the foreground to be illuminated.  Though I shot about 45 frames at 30 Seconds, f/2.8 and ISO 320, my final stack included only 24.  Though I could have just as easily shot a 12 minute exposure with minimal noise issues, the rapidly changing light made the margin for error pretty slim.  Chances are that I would have ended up with junk.  Having multiple frames, I had the flexibility to cut frames based on the need to balance the light from the sunrise with the star trails.
I'm pretty pleased with the end results.

All of the images were shot in RAW and converted to jpeg in Lightroom.  Both images were stacked in CS5 using the free action from
After stacking, the PSD files were taken back to Lightroom for final touch ups.

By the way, while shooting the first image, the temperature was around 7°.  In an effort to help keep things a little less chilly and to prolong battery life,
I improvised a coat for my gear with my spare toque and  some hand warmers.

This last image was taken with the Canon G12,
all others were created using the Canon 1D Mk IV and the Canon 16-35mm f/2.8L lens.

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