Sky and Telescope - November 2015 - 64

Moving Pictures

Batch-Processing RAW ﬁles

COMPOSING Composition is important! Take care to level the camera and
compose the scene, following classic rules of composition. For example, the "rule
of thirds" suggests horizons and centers of interest should lie along and at the
intersections of lines that divide the scene into thirds.

While it's tempting to shoot just JPG images for timelapses, the card space you save doesn't make up for the
loss of image quality. Shoot in RAW format. A 16- to
32-gig card will hold enough RAW ﬁles for two to four
sequences, depending on your camera's sensor size. If
you really need to save space, shoot in one of the "sRaw"
(RAW size small) formats that produce smaller images,
if the option is available in your camera.
When processing time-lapse sequences, Adobe Lightroom works well. Or, as an alternative, you can use Adobe
Bridge and its Adobe Camera Raw utility, which is identical to the Develop module in Lightroom.
Pick a representative frame from the sequence and
process it to look as good as possible.
Once one image is processed, it's a simple matter to
right-click the processed image, select copy settings,
then select all your other frames and paste the saved settings into all the other images in the sequence.

Assemble Your Movie
ADDING CAMERA MOTION

Time-lapse videos on the web
often contain sequences in which
the camera gradually moves across
or through a scene. These cinematic moves are created with specialized "motion-control" devices.
Each rotates a camera around an
axis, along a dolly rail, or both,
shifting its position in increments
between each exposure.
An excellent choice for astronomers is Sky-Watcher's AllView
Mount, a very sturdy Go To

telescope mount. As a bonus, it
oﬀers a time-lapse mode, providing two-axis (pan and tilt) motion
control, all while ﬁring the camera
shutter in sync with its incremental motion steps.
Get more serious about timelapse imaging and you can choose
from a host of dedicated motioncontrol units. I use models from
Dynamic Perception, eMotimo,
Radian, and Rhino and can attest
to their eﬀectiveness.

Now you need to assemble those frames into a movie.
Each RAW frame from your DSLR is likely 5,000 or more
pixels-wide. Unless you're producing a movie for the
4K video standard, those frame sizes are far too large to
be practical. To create a playable movie, you ﬁrst need
to export the processed RAW frames into a folder of
downsized "intermediates" - usually a set of JPGs, to
satisfy the needs of most movie-assembly programs. For
HD-format videos, reduce the intermediate images to a
width of 1,920 pixels.
You then have a few choices for turning the intermediate JPGs into a movie ﬁle. Any recent version of Adobe
Photoshop can do the job. First, switch to its Motion
Workspace (using the pull-down menu at top-right of
the screen) to reveal a movie timeline. Now select Open
and navigate to your folder of intermediate JPGs. Select
the ﬁrst frame, and in the Open dialog box check "Open
Image Sequence." Photoshop then strings the frames
into a movie. You can then export the ﬁnal movie using
the pull-down menu File > Export > Render Video.
An alternative is to use a third-party assembly program. I like the MacOS program Sequence. But for Macs
there is also Time Lapse Assembler, Microprojects' TimeLapse, and QuickTime 7 Pro. Microsoft Windows users can
also assemble their frames into a movie using use Quicktime Pro, StarTrails.de, Time-Lapse Tool, or Virtual Dub.

Pursuing the "Holy Grail"
PANNING MOTION Dedicated motion-control units are all "shoot-moveshoot" devices, controlling the shutter to synchronize exposures and movement. The device moves the camera only when the shutter is closed, during
the few seconds between exposures. From left to right in the image above,
these are the Dynamic Perception Stage Zero dolly, the Sky-Watcher AllView
mount, and the eMotimo TB3 pan/tilt device.

November 2015 sky & telescope

Time-lapses are easiest when you start them after dark.
The exposure time for the ﬁrst frame will likely work
ﬁne for the rest of the night. Later, in processing, one
setting will work when applied to all the frames.
But if the Moon sets or rises during the shoot, the
scene brightness will change. Even more tricky is shoot-

http://www.StarTrails.de

Sky and Telescope - November 2015

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