Sky & Telescope - June 2019 - 68

Imaging Tips

tt A MATTER OF
BALANCE Ensuring your
equipment is balanced properly on your mount will go a long
way toward reducing tracking
errors. Adjust the weight of
the telescope tube first on the
declination axis, then check
the right ascension by sliding a
counterweight on the shaft.
t CABLE MANAGEMENT Secure any dangling cables close
to the telescope and mount so
that they don't snag during an
exposure or while slewing to
another target.

both directions, your scope is in balance in that axis. If not,
then adjust the position of the scope forward or backward
in its tube rings or along the dovetail plate to balance it.
Tighten everything up and then move to the right ascension
(RA) axis. Loosen the RA clutch and simply slide the counterweights on the shaft to balance the scope in RA.
Balancing on a fork mount is similar, though you may
need to add counterweights to a rail attached to your telescope tube if there aren't accommodations to shift the position of the tube.
Once you have your payload properly balanced, be sure
everything is locked down and then test the mount's performance in a guided image. You should also repeat the test with
a target on the opposite side of the meridian.
Some mount manufacturers recommend that you keep
q PERFECT EVERY TIME Once you've solved all your guiding issues,
you're more likely to produce a steady stream of excellent data ready for
processing. The author recorded this colorful image of IC 410 (left) and
IC 405 through the same equipment as the photo on pages 64-65.

the RA axis very slightly unbalanced towards the east side for
long exposures. This ensures that the RA worm gear is always
engaged as the mount tracks the motion of your target. If
you ﬁnd unbalancing the mount helps, ﬁrst ﬁnd perfect balance as described above. Then use a very small weight (just
an ounce or two will usually do) that can be attached to the
telescope or the counterweight shaft as needed, depending on
where your target lies.
Ensure any cables connecting your equipment to the
control computer are bundled neatly and secure them to the
telescope in a manner that minimizes any stresses that could
change as the telescope tracks the sky.

If You Don't Succeed
The best-laid plans don't always work as expected, so if you still
end up with slightly trailed stars in your exposures, you can
turn to tools that can repair misshapen stars after the fact.
For example, PixInsight's Deconvolution tool has a Motion
Blur PSF mode that can signiﬁcantly reduce star elongation
when you input the length and angle of the trailing in your
image. There's also a powerful plug-in script for Maxim DL
that can repair elongated stars (https://is.gd/trailﬁx). Just
be aware that no after-the-fact ﬁ x will produce as high a
resolution in your image as does preventing the problem from
happening in the ﬁrst place. Remember that if stars are elongated, any non-stellar objects in the image are also smeared,
and they can't be repaired as easily as the stars.
You may have heard it said that "Good data never goes
bad." You can always reprocess good images as your processing skills improve and your artistic tastes change over time.
Unfortunately, the reverse is also true: Bad data never gets
better. That's why it's worth spending the time to get your
imaging system performing at its best before your next clear,
moonless night. There's nothing quite as satisfying as sitting
at the computer on a perfect night watching while each subexposure downloads and displays tight, round stars.

¢ RON BRECHER images the night sky from his backyard
observatory in Guelph, Ontario.
68

J U N E 2 019 * SK Y & TELESCOPE

https://www.is.gd/trailfix

Sky & Telescope - June 2019

Table of Contents for the Digital Edition of Sky & Telescope - June 2019