Sky & Telescope - October 2022 - 66

S&T Test Report
diagrams, quality photographs, and
tables. This seemed like a lot for such a
relatively simple device until I realized
that 27 pages were devoted to using
Vixen's optional polar-alignment scope.
This is a $374.95 accessory, which I did
not test but which I expect from past
experiences with Vixen polar-alignment
scopes will work very well.
Another reason for the large manual
is that it also offers an introduction to
starscape photography with all the basics
briefly covered and charming but spot-on
advice such as having warm clothing
available for cold nights and keeping a
plastic bag handy to cover equipment in
case of a sudden rain shower.
Heading Outside
Most of my night-sky testing was
done with an aging Nikon D700 DSLR
camera attached to the Polarie U via
a heavy-duty ball head. On my first
night outside I mounted the setup on a
mid-weight tripod (the Star D clone of
the Tiltall for those " veteran " photographers
among us), attached a 50-mm
lens to the camera, and eyeballed the
polar alignment with the Polarie U's
peep sight. (This alignment was not
as casual as I make it sound here, but
more about that in a minute.) Not
surprisingly, exposures ranging from a
few seconds up to 2 minutes all showed
perfectly pinpoint stars - something
The ball head mounting block can be
removed from the Polarie U to reveal two sets
of tapped holes that do-it-yourselfers could
use to attach their own custom setups to the
drive base.
ary camera. This amounted to less than
4 arcminutes of tracking error in right
ascension over the three-hour period.
This review isn't about photographic
I'd expect from even the most rudimentary
camera trackers. The real test
of the Polarie U's tracking accuracy
required longer exposures, which aren't
practical in my suburban sky. So I
switched tactics.
I changed to a 200-mm lens and set
the camera's internal intervalometer
to shoot 30-second exposures every
5 minutes for three hours. The 36
individual images were then stacked
with the freeware program Startrails
(startrails.de) that registers image
frames rather than stars to effectively
show how much the stars trailed over
the course of three hours.
The first result wasn't just good, it
was astoundingly good. In three hours
the Polarie U's tracking was so accurate
that stars trailed less than they did in a
15-second exposure made with a stationprojects,
but I suspect that many readers,
like me, will dream up interesting things
to do with a camera that accurately
tracks the sky unattended for an entire
night. Following short-period variable
stars, for example, or perhaps shooting
a time-lapse sequence of a solar or lunar
eclipse (the Polarie U has selectable
tracking rates for the Sun and Moon as
well as the usual sidereal rate for stars).
Polar Alignment
According to the user manual the Polarie
U's peep sight has an 8.9° field of view -
a value that seems rather precise given
that the peep sight is merely a 37-mmlong
plastic tube with a 9-mm internal
diameter. Furthermore, when I held my
eye at the end of the tube I could view
the whole 15°-long handle of the Big
Dipper, which matches the field of view I
calculated with a quick bit of trigonometry.
That 8.9° field is accurate if your eye
were positioned about 20 mm back from
the peep sight - a comfortable distance
for someone wearing eyeglasses.
pDescribed in the accompanying text, the peep sight's changing apparent field of view that occurs as your eye is moved back from the sight can be
used to advantage in polar aligning the Polarie U.
66 OCTOBER 2022 * SKY & TELESCOPE

http://www.startrails.de

Sky & Telescope - October 2022

Table of Contents for the Digital Edition of Sky & Telescope - October 2022