Sky and Telescope - July 2018 - 65
p Left: In these examples two unguided images taken 30 minutes apart are layered with a "Difference" blending mode applied in Photoshop to better
show the image movement from misalignment. After performing a conventional polar alignment with the HEQ5's polar scope, stars exhibited a northsouth drift in declination (the vertical shift here) as well as an east-west drift in RA during the half hour. Middle: After using the PoleMaster mounted
on-axis to perform an alignment, the images show markedly less shift after 30 minutes. The small amount of shift in this example is left-right in right ascension, likely from the mount's tracking error, not from poor polar alignment. There was no declination drift, a testament to the accurate polar alignment.
Right: A test on another night shows the effectiveness of the PoleMaster even when mounted off-axis on the telescope tube. The software still correctly
located the mount's axis of rotation and provided an accurate final alignment with only a slight declination drift.
moving the mount to start afresh, I
tried an alignment with the PoleMaster
mounted off-axis on the telescope tube.
I performed alignments with the Windows software, and then ran a sequence
of exposures on another night after realigning using the MacOS software.
Using the PoleMaster in either mode
- on-axis or off-axis, or with the Windows or MacOS app - worked equally
well. Each method produced a much
greater accuracy with minimal image
shift in declination or right ascension
over 30 minutes compared to the visual
alignment method with the mount's
built-in polar scope. The difference was
noticeable even when imaging with
short focal-length instruments.
In a nutshell, the PoleMaster worked
as advertised, providing an accurate
polar alignment. One caveat is that
achieving the ﬁnal "Precise Pole" step
depends on the mechanical smoothness of your mount's altitude and
azimuth adjustments. As I turned, then
tightened, the HEQ5's adjustments,
the image would shift. After several
attempts to get the two markers to
exactly match, I'd say, "Good enough!"
and call it done.
That ﬁnal step in particular also
requires that your computer screen be
close to the mount, so you can inspect
the readout carefully while making the
If you shoot primarily with short-focal
length telescopes (say, under 600 mm)
on small equatorial mounts, as I often
do, I feel the PoleMaster is a luxury you
could probably live without. Certainly
I have. For many years I've eyeballed
polar alignment using my various
mounts' built-in polar scopes and have
never encountered issues with trailing
or the inability to align and stack short
exposures as long as I was auto-guiding.
I also prefer to avoid having to use
a computer at the telescope if I can
help it, to keep my ﬁeld set-up simple
and avoid dreaded "Application Not
Responding" errors. As such, I use a
stand alone autoguider that doesn't
require a computer. Still, even wideangle photographs of entire constellations with exposures of, say, 10 minutes
or more will display ﬁeld rotation in the
corners of the frame if my polar alignment isn't accurate.
But for those shooting with CCD
cameras (and for many photographers
who shoot with DSLRs) a computer has
to be present anyway, to run the main
camera and the auto-guider. In addition, as the number and length of exposures goes up, accurate polar alignment
becomes far more critical.
The PoleMaster provides a quick yet
precise method of achieving the required
accuracy, avoiding any need to perform
tedious drift alignments. The PoleMaster is ideal for those shooting with
long-focal-length Cassegrain systems,
especially on mounts that lack an onaxis polar scope such as fork mounts.
Even on a mount that includes a polar
scope, using a PoleMaster avoids having
to bend down and crane your neck to
sight through the scope. For aging astrophotographers, saving wear and tear on
necks, backs, and knees may be reason
enough to rely upon the PoleMaster. It
provides truly painless polar alignment!
■ Contributing Editor and TWAN
(twanight.org) member ALAN DYER often
photographs the night sky from his dark
location in Alberta, Canada. Visit his
website at amazingsky.com.
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