Sky & Telescope - August 2020 - 61

seeing it can be extremely difﬁcult, so don't be discouraged.
To gauge focus, use areas of high contrast on your target,
such as the Cassini Division in Saturn's rings, albedo features
on the Martian surface, and small storms in Jupiter's belts.
Venus, Mercury, and even Mars can be difﬁcult to focus when
they're far from Earth and feature small disks, but the sunward limb is often a good spot to use to judge whether you're
in focus or not. Simply take your time and practice. The more
you do it, the better you'll get at it.
When you start recording video, you'll typically be operating your camera at about 30 to 80 frames per second or
more, depending on the brightness of your target, capturing
a minimum of 1,000 frames for a single image stack. Your
camera's frame rate is a balance between the exposure length
and gain settings, which are partially dictated by the brightness of the planet. Regardless, try to keep the camera's gain
setting well below its maximum. Setting the gain to about
70% is a good starting point, then adjust your exposure until
the planet is bright but not over-exposed on the screen. If you
use FireCapture, be sure the histogram of the image does not
go above about 80%. Also, ensure that the gamma setting is
at its default value.

Video Reduction
This stage is perhaps the most fun part of the whole process,
as you ﬁnally get to see what surprises your video sequences
have in store. Currently there are two popular choices for
stacking your planetary videos: RegiStax 6 (astronomie.be/
registax) and Autostakkert! 3 (autostakkert.com). While
both do an admiral job, RegiStax 6 includes powerful Wavelet
sharpening, which works extremely well, and I often stack
my videos in Autostakkert! 3 and then sharpen the resulting
image in RegiStax 6.
Both programs will stack your videos in basically the same
way. (A tutorial on using Autostakkert! appeared in the September 2016 issue of Sky & Telescope, page 68.) Each program

SX SPECIALIZED CONTROL While
most planetary cameras come with control
software, a better option is the freeware
FireCapture (ﬁrecapture.de), which controls
cameras, focusers, and filter wheels while
offering many additional features helpful for
planetary photography.

sorts and aligns all the frames in
an image sequence using a choice of
alignment modes - single-point and
multipoint alignment. Single-point
alignment works well on small planetary targets such as Mercury, Venus,
and Mars (when they're just a few
arcseconds across) as well as Uranus
and Neptune. Multipoint alignment
permits you to select multiple points
to monitor, and the program will stack the best areas around
each point, producing a superior result on larger planets like
Jupiter, Saturn, Mars, and Venus, and also on lunar close-ups.
Once the software has aligned your video frames, you'll
need to determine how many individual frames to stack -
the greater the number, the better the signal-to-noise ratio

STACKING FRAMES
Autostakkert! 3
is a free program that
can stack your videos
and requires very little
user input.

sk yandtelescope.org * AUGUST 2 02 0

http://www.firecapture.de http://www.astronomie.be/registax http://www.astronomie.be/registax http://www.autostakkert.com http://www.skyandtelescope.org

Sky & Telescope - August 2020

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