Sky & Telescope - March 2024 - 61

Higher Tool Standards
Imaging the night sky with the large sensors found in many
of today's DSLR and other deep-sky cameras, astrophotographers
often find what worked well for a smaller sensor
is inadequate to cover the real estate of larger chips. The
leading culprits are lack of precision collimation tools and a
means to evaluate and fix a tilted focuser, which can create
havoc with the star images at the very edges of your camera's
field of view.
Poor collimation produces a variety of artifacts in deepsky
images, including hot spots, an asymmetrical coma pattern,
variable focus across the frame, or a combination of all
these issues. Even the best composed and processed images
cannot make up for the appearance of distorted star images.
Additionally, the use of a matched coma corrector (a mandatory
accessory when pairing a fast Newtonian astrograph
with an APS-format or larger detector) complicates diagnosing
the problems, as improperly spaced correctors can add
their own aberrations as well. The challenge of precision
optical alignment may lead you to give up on a telescope that
has the potential to become a truly fine instrument. Standard
collimation methods are often inadequate to fully correct
these issues.
To improve your collimation precision, you'll need several
tools. Most important are a laser collimator, a 1¼- to 2-inch
eyepiece adapter, a 1¼-inch-format, perforated collimation
cap (an accessory often included with new Newtonian telescopes),
and a machinist's scale (a type of ruler). In addition,
you'll need the tools required to adjust your scope's secondary
mirror, typically a hex wrench set and a Phillips-head screwdriver.
Other household items necessary include aluminum
foil, scissors, masking tape, a fine sewing needle, and a little
white paint with a small paint brush or a white paint pen,
which you can find at most office supply stores.
REQUISITE TOOLS To supercharge your Newt's collimation, you'll
need several household items and a few telescope-specific tools. Seen
from top to bottom are a roll of aluminum foil, a Phillips-head screwdriver,
a pair of scissors, a paint marker, a laser collimator, masking tape,
a set of hex wrenches, a collimator cap, a 1¼- to 2-inch adapter, and a
machinist's scale. Not shown is the sewing needle needed to make the
collimator mask.
Supercharging a Laser Collimator
Laser collimators are a very popular tool for aligning Newtonian
reflectors and are available from a variety of distributors
such as Agena Astro (agenaastro.com), Hotech
(hotechusa.com), or Orion Telescopes & Binoculars
(telescopes.com). Most of these lasers project a roughly circular
dot a few millimeters in diameter. But they aren't all made
to the same level of precision - some are better than others.
With your laser collimator in hand, the first task is to
verify its beam is mechanically aligned with its barrel. To
do this, you'll need to place the device in a groove that
allows you to rotate the collimator to see if its projected
MASKING THE LASER Left: Construction of the aluminum-foil beam restrictor starts by cutting a ½-inch-wide strip of foil. Place the foil on a flat
surface and smooth out any wrinkles by rolling a marker or pencil across it. Center: Cut the foil to size, then add masking tape " wings " to affix the
completed mask to the laser collimator. Right: Place the foil mask on a piece of corrugated cardboard and use a sewing needle to make a tiny round
hole in the approximate center. Press straight down to avoid creating an oval-shaped aperture.
sk yand tele scope .o r g * MARCH 2024 61

http://www.agenaastro.com http://www.hotechusa.com http://www.telescopes.com http://skyandtelescope.org

Sky & Telescope - March 2024

Table of Contents for the Digital Edition of Sky & Telescope - March 2024