Sky and Telescope - December 2017 - 60

S&T Test Report

Tracking Functions

p The included polar scope clicks into the
polar axis with a solid assurance. A separate
illuminator clips onto the front to illuminate
the field. A "Snap" port controls the camera
shutter. A micro USB port is for applying firmware updates or powering the tracker with an
external 5-volt source.

With the WiFi set to turn off, I
found the two internal AA batteries provide several hours of tracking
or panning, more than enough for 3
or 4 nights' work on warm summer
evenings. Alternatively, SAM can be
powered from an external 5-volt power
pack, such as used to charge phones,
through a micro USB port. Users need
to supply their own micro USB cable.
While the WiFi connection worked
reliably, I would have preferred if SAM
connected via Bluetooth LE, as is the
case with many other motion controllers. Connecting via Bluetooth LE is
easy, takes less power, doesn't require
switching away from your normal WiFi
network, and allows for convenient
over-the-air updates to ﬁrmware using
the mobile device itself, as it can remain
connected to the internet and to the
controller at the same time.
As it is, updating Sky-Watcher's
mount ﬁrmware currently requires
using a Windows-only application, leaving MacOS users out of luck.
60

D E C E M B E R 2 0 17 * S K Y & T E L E S C O P E

When set up as a star-tracker, the
included polar-alignment scope inserts
into the polar axis. The scope comes
with a separate bright-ﬁeld illuminator and an excellent reticle suitable
for both the northern and southern
hemispheres. The app also displays the
same reticle and the current positions
of Polaris or Sigma Octantis.
The SAM gets its location from your
mobile device, so there is no hardware
N-S motor direction switch on the
device. If it detects you are south of the
equator, it turns the motor in the opposite direction to what's needed up north.
I tested SAM only from home in Canada.
There are software options for setting the tracking rate to Sidereal, Solar,
or Lunar, and for having SAM turn at
2× or 0.5× sidereal rate, the latter useful
for some nightscape images.

I set up several exposure sequence
tests that would ﬁre the shutter while it
tracked over several hours. As a startracker, the SAM worked great. It was
easy to polar align and tracked well
when using wide-angle lenses.
Images through a 200-mm telephoto
did show some trailing, with about 60%
of 1- to 2-minute exposures displaying trailed stars. Unlike the larger Star
Adventurer, SAM has no autoguider
interface. While an optional declination
axis and counterweight are offered, I
didn't see any improvement in tracking
accuracy when using them to balance
a telephoto lens. However, this wasn't
surprising; I found the Mini's tracking
accuracy to be typical of small drives
in the $300 price class. When shooting
with focal lengths over 50 mm, it's best
to shoot lots of frames so you can pick
out the best and toss the rest later.
Even so, I would emphasize that SAM
is, after all, a "mini" mount. When
weighed down with a heavy camera and
lens, plus the optional counterweight, it
does become bouncy. I feel the unit works
best with the wide-angle lenses typically
employed in nightscape imaging.

Time-Lapse Functions
When mounted to a tripod in its timelapse orientation, SAM stands vertically
and turns left/right in azimuth for
time-lapses panning along the horizon.
SAM then remains in balance, and not
tipped over precariously as when using
repurposed star-trackers.
SAM offers three modes for taking
time-lapses: Regular, Long Exposure, and
Astro. "Regular-Exposure Time-Lapse"
is for day or twilight shots where the
camera operates on auto-exposure or
at some pre-determined shutter speed,
and at an interval (what the app
calls "Frame Period") you set.
SAM then just sends a ﬁxed
t The Mini is compatible with the same
optional accessories offered for the larger Star
Adventurer: the Equatorial Wedge, the FineTuning Assembly for declination slow motion,
and a counterweight. These aid polar alignment and shooting with heavier lenses. SAM is
shown here powered by a user-supplied battery
plugged into the USB port.

Sky and Telescope - December 2017

Table of Contents for the Digital Edition of Sky and Telescope - December 2017