Sky & Telescope - October 2022 - 67

Nevertheless, this byproduct of
changing perspective provides an
advantage when polar aligning with the
peep sight. Polaris is currently 0.64°
from the celestial pole offset in roughly
the direction of Mirfak (Alpha Persei).
By placing my eye about 400 mm (16
inches) back from the peep sight, the
apparent field of view shrinks to 1.3°
(twice the offset amount). And if I place
Polaris at the very edge of the peep
sight's field in the direction of Mirfak,
then the field center should be close
to the celestial pole. That's what I did
on my first night out with the Polarie
U, and even I was surprised by how
accurate the polar alignment ended up
being. It was also beneficial that I did
the alignment with my camera already
attached to the Polarie U, since most
tripods will flex at least a little when a
heavy camera is added, slightly throwing
off the alignment.
Additional Features
Among the Polarie U's advanced features
is an autoguider port that only
controls the right-ascension drive. I
didn't test it, but with autoguiders
becoming smaller and lighter it's not
unreasonable that there are applications
in which autoguiding will be useful
with a tracking mount as small as the
Polarie U - when shooting with long
telephoto lenses, for example.
The unit also has a 3-mm coaxial
port for connecting a camera's shutter
release. This port is operated via the
Polarie U app, which users can download
for iOS (Apple), Android, and
Amazon Kindle Fire devices. The app
connects to the Polarie U via Wi-Fi, and
I tested it on my iPhone 11. Camera
control only works while the app is
actively connected to the Polarie U -
you can't program information into the
tracker for later playback.
One feature of the app lets you make
sets of up to three bracketed exposures
at user-set intervals while the unit is
tracking. This would be very handy for
making a series of time-lapse exposures
for, say, a lunar eclipse. My Nikon DSLR
cameras have a similar built-in feature,
but they are limited to exposures that
The smartphone app described in the text
can control a camera's shutter as well as the
direction and speed of the Polarie U's rotation.
can be manually set on the camera (in
my case no longer than 30 seconds). By
setting the camera shutter to Bulb, I can
use the Polarie U app to automatically
make the much longer exposures that
are often needed for astrophotography.
The app also lets you set a custom
tracking speed for the Polarie U that
ranges from zero to 10× sidereal rate
(up to 2½° per minute). This is mostly
for photographers who use the Polarie U
for panning motion during time-lapse
photography. This works by panning the
mount and having it stop moving when
shooting exposures. Assembling images
taken this way into a time-lapse video
shows the rotation of the night sky as
the scene slowly pans.
The Polarie U can do everything that
astrophotographers shooting wide-field
images would likely ever want. But
its accurate tracking got me thinking
about all the excellent photos I've seen
lately made with conventional telephoto
lenses in the 135- to 300-mm range.
With such a setup properly balanced on
the Polarie U (like the example on page
65), it would be easy to make hours'
worth of short exposures that could be
stacked to create deep images. As an
afterthought (and to prove this point to
myself), I combined the exposures made
for several of my tracking-accuracy tests
mentioned earlier with the freeware
program DeepSkyStacker (deepskystacker.free.fr).
This produced surprisingly
deep images (albeit of a nondescript
star field surrounding Arcturus)
given they were made from my backyard
with a camera and settings that I had
never intended to record faint stars.
The Polarie U proved to be a first-rate
camera tracker for wide-field astrophotography,
but I also think that people
who own one will start coming up with
a lot of projects that go well beyond
simple starscape photography. It's a
sweet little device.
¢ DENNIS DI CICCO lives under the
ever-increasing light pollution of Boston's
western suburbs.
sk yand tele scope .o r g * OCTOBER 2022 67
http://deepskystacker.free.fr http://deepskystacker.free.fr http://skyandtelescope.org
Sky & Telescope - October 2022

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