In previous blog
posts, I’ve written about taking still pictures of the night sky, and how to
take time exposures in daylight. Now, let’s look at the ten basic steps for capturing
the motion of the stars:
1.
Leave
town. I typically drive 1 to 2 hours north of the city to get away from its ‘light
dome’.
2.
Make sure
you have a sturdy tripod for your DSLR.
3.
Use as
wide-angle a lens as you can get. For a full frame sensor, consider using
anywhere from 14mm to 18mm focal length. For APS-C sensors (ie. Canon Rebel or
equivalent), a 10 to 12 mm focal length will work. Camera brand lenses can be
outrageously expensive, so consider much cheaper but still good third party
brands like Rokinon or Tokina.
4.
Consider
getting an intervalometer, or at least a wired shutter release for your camera.
Either one will cost you less than $20 on eBay.
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| Intervalometer |
5.
If the air
temperature is expected to drop below the dew point, be ready to clear
condensation off your lens. You could use a microfibre cloth between shots, buy
a battery operated fan at the dollar store to keep the air moving across the
front of the lens, or look into some form of lens warmer.
6.
Set your
ISO to about 3200 and your shooting mode to Manual. Since you want to keep
exposure to less than 30 seconds to prevent the stars from creating noticeable
trails on each frame you shoot, select a value between 20 and 30 seconds and set
aperture to maximum (ie. f/2.8). I use f/4 with success, but it might force the
choice of 30 seconds over 20 seconds. You may also want to use a fixed White
Balance mode instead of Auto, but I generally have not found Auto to be a
problem.
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| Normal Infinity Focus Setting |
7.
If your
lens has a focus scale, set it to the vertical bar near the infinity mark, but
not at the infinity mark. Take a test shot and zoom in on the playback to see
if you have optimal focus. If not, tweak it very slightly and re-check. The
actual infinity focus point varies slightly with focal length, so leave the
lens at your intended focal length when setting the focus point, and only zoom
in on the playback to verify it.
8.
If using
an intervalometer, set your camera to Bulb (may be found in Manual mode
settings or may be a separate mode depending on the camera). Set the
intervalometer shutter ‘on’ time to 20 to
30 seconds (depending on your test shots), set its interval between shutter
actuations to something like 5 seconds (to allow you to wipe condensation off
the lens between shots), and set the number of frames to about 150. I normally
shoot with RAW+JPEG, but you may want to consider doing such a long sequence in
JPEG only to conserve memory card space. Elapsed time will be close to an hour
and a half, so bring a coffee flask!
9.
If using a
simple wired shutter release, set the camera to burst or continuous mode
instead of single shot mode. You will not use Bulb mode in this case. Instead,
select either 20 or 30 seconds for your shutter speed in Manual mode. When
ready to start, use the lock on the wired release to hold the shutter button on.
The camera will take one shot immediately after the other with no breather in
between. This will get the sequence over with more quickly than when using an
intervalometer with a 5 second breather, but you won’t have an opportunity to
clean off condensation between shots. Depending on the camera, you may also
have to manually keep track of the number of shots taken.
10.
Find an
interesting object on earth that you can anchor your shots to. Put it in the
lowe part of your frame, about a third of the way in from the edge. You can
have it silhouette against the sky, or use a flashlight to do a little light
painting. In a sequence, however, you may want to forget the light painting
because it is difficult to make the object look uniformly lit in all 150 or so
frames. Now, consider putting Polaris somewhere in your shots, so you can see
the stars rotate around it in your final sequence.
That takes care of the capture portion. Now for the post-production
steps:
1.
I import
all 150 frames (images) into Lightroom. Then, if corrections for exposure,
white balance, etc. are needed, you can make the changes to one frame and sync
the changes to all 150. Similarly, I have set up a custom crop mode in Lightroom
for 16x9, so that the resultant video will frame properly on television. Again,
I can crop one and sync-crop all the others.
2.
A sidebar
on ‘stuck’ pixels: You are going to notice that there will be bright spots on
all frames, which don’t move with the stars. These are generally due to the
long exposures and the number of such exposures, which result in heating up of
the sensor. If these are left alone, it will look weird once you put all the
stars in motion, since stuck pixels don’t move. You could use the camera’s long
exposure noise reduction feature to mitigate this, but you will be out there
for three hours instead of one and a half hours capturing the 150 frames. My
approach is to use the clone brush in Lightroom on one frame and sync to all
other frames.This is the most time-intensive and frustrating part of the
process due to thenumber of stuck pixels my camera produces, and the way you
clone them out may adversely affect other frames once you sync. There is a bit
of an art to it, and I could write a whole treatise on it. But not now.
3.
Once I’ve
cleaned up all the frames, I export them from Lightroom as TIFF files. At this
point, you may want to decide if you simply want to make a video clip of the
stars rotating around Polaris, or create progressively longer and longer star
trails as they rotate. For the latter, you could use StarStax. This software
creates another set of files in which the star trails get progressively longer.
This is done by ticking a checkbox in the settings menu to force it to save a
file every time it adds another file to the sequence. If you don’t check the
box, it will only create one file that consists of all 150 frames forming a
single long trail for each star.
4.
Now to put
things in motion. There are a number of software packages that can accomplish
this, but I use my Corel VideoStudio video editor. In that software, you simply
right-click on an empty timeline and select the time lapse option(‘Insert Photo
for Time-lapse/Strobe’). You then tell it where your frames are and how long
you want to make the clip (I generally start with about 10 seconds), and the
frames load onto the timeline. If you want to have the stars rotate without
making trails, use the files you exported out of Lightroom. On the other hand,
if you want the stars to create progressively longer star trails, use the files
created by StarStax.
5.
Now you
can create a finished video (Share tab in Corel). I prefer to save mine in .mp4
format. Have a look at my two samples on YouTube. One is without StarStax
(Milky Way video) and the other is with StarStax (observatory video). I hope these inspire you to try out this fun
technique.
