Sky & Telescope - March 2024 - 69

Left: This view of the globular star cluster M13 is reproduced from the image saved on the author's iPhone after a 15-minute exposure. A better
result is possible by using dedicated astronomical software to process the FITS file saved in the Seestar's internal memory, but it's certainly not a
requirement to get good results. Right: Because Seestar's fixed field of view is too small to capture the whole Andromeda Galaxy, M31, at once,
the author made three overlapping 7-minute exposures and stitched them together. This view is from images saved to the iPhone rather than
processing the FITS files.
10-second exposures are automatically
snapped and stacked. A countdown
" clock " and total-exposure tally keep
you informed during the stacking process.
After a minute or so even relatively
faint deep-sky objects are visible in the
displayed image. At any time during the
image updating, you can tap a button to
save the current result while the stacking
continues. And as is always the case
with deep-sky imaging, the longer the
total exposure the better the result.
Because I was mainly interested in
exploring features of the Seestar, my
first nights of testing were usually spent
making exposures of just a few minutes.
Although the individual Seestar exposures
are fixed at 10 seconds, the stacking
time can vary depending on how
much internal calculation is needed
to compensate for the image rotation
that's inherent when shooting with an
altazimuth mount, and this can also
vary depending on your target's location
in the sky. For one object near the
meridian, it took 30 minutes to accumulate
a total exposure of 20 minutes,
and 90 minutes to complete a 61-minute
exposure. For another object high in
the northeastern sky, it took 34 minutes
to complete a 20-minute exposure.
Seestar uses an internal algorithm
to decide if images are good enough
to stack. I don't know all the criteria
for rejecting an image, but there
were clearly times when an image was
rejected because its 10-second exposure
was not added to the total exposure
time. The rejection algorithm, however,
is not flawless. One night while shooting
from the deck on our house, my
stacked image was sometimes fuzzy
because slightly blurred exposures
caused by vibration as I walked around
the deck were added to the stack. The
lesson here is to always have the Seestar
sitting on a solid surface.
At first it was fascinating to stare at
my phone as images were accumulating,
but my enthusiasm faded when shooting
longer exposures (not to mention
the process being a drain on my phone's
battery). The good news is that once
the Seestar starts shooting a target you
can turn off your phone and walk away.
You don't need to maintain a phone
connection for Seestar to continuously
shoot an object. If you want to monitor
the image progress, you simply open the
app and reconnect to the Seestar. This is
also good news if you walk too far from
the Seestar while it's running, since
the Wi-Fi connection isn't particularly
t Far left: When using Seestar to view the Sun,
the app first asks to confirm that the included
solar filter is attached to the scope before automatically
pointing toward the Sun. Putting the
filter over the objective is on the honor system,
and if you confirm it's attached when it's not,
you'll almost certainly destroy the detector if
you point sunward.
t Near left: The included fitted hard foam carrying
case holds the entire Seestar setup and
weighs only 3.6 kg (less than 8 pounds) with
everything inside.
sk yand tele scope .o r g * MARCH 2024 69

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Sky & Telescope - March 2024

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