Sky & Telescope - February 2024 - 75

also better suited for finding your way
under light-polluted skies. Some observers
mount several progressively larger
finders on their telescopes to make hunting
down faint objects easier.
There are several types of finderscopes,
including straight-through, rightangle,
and even corrected-image finders.
Some finders are even built directly into
the telescope using the main optic as the
finder, but those are rare these days (see
page 84). Straight-through finderscopes
used to be the default aimer that came
with a new telescope, but their view
often doesn't exactly match the orientation
you are seeing the sky, which led
to a lot of confusion for beginners. A
typical straight-through refractor finderscope
produces an inverted image of the
sky, making it appear upside down.
You can even mount a laser pointer
to function as a finder, though some
observers consider these to be inconsiderate
to others on the stargazing field.
No matter the design, the key to a
good finder is that it includes the capability
to adjust its pointing in order to be
accurately aligned with the optical axis
of the main telescope. Most reflex sights
and finderscopes come with a mounting
bracket that permits adjustments in two
axes for this purpose. Larger finderscopes
often include brackets with a pair of
rings having three screws mounted at
120° intervals to adjust the pointing.
Aligning your finder should be done
in daylight, at a place where you can
readily see a distant target in your main
telescope as well as the crosshairs, red
dot, or projected bullseye in the finder.
Start by locating a distinct, far-away
object to focus on. Most telescopes are
designed to come to focus on objects far
in the distance, so a hilltop cell tower or
antenna on a faraway building should
suffice. Put your alignment target in
the field of your telescope using the
lowest-power eyepiece you own - most
commercial scopes include a 25-mm
or another wide-angle equivalent. The
lower power you use, the easier this
part will be. It may take some slewing
around until you land that recognizable
target in the field of the eyepiece.
Once you've found and centered the
target, tighten any clutches if needed,
ensuring the scope's pointing doesn't
slip, and then move on to adjusting the
finder. Without moving the scope, use
the adjustment screws on the finder (or
its bracket) until your target is centered.
Here's a useful tip for observers with
an optical finderscope: Turn the device
in its bracket so that the crosshairs are
lined up with the directions that your
telescope moves. For example, if you are
aligning a finder on a Dobsonian telescope
or any alt-azimuth mount, make
the crosshairs point left/right, up/down.
If your scope is mounted on an equatorial
mount, be sure the finder's crosshairs
are oriented to the right ascension
and declination axes. You can determine
these directions by nudging the scope
slightly.
After you've aligned the finder with
your lowest-power eyepiece, switch to
a high-power ocular and fine-tune the
pointing again. It will be off slightly, but
not nearly as much as when you began
the process.
With your finder set to your main
telescope, it then becomes easy to track
down objects in your main telescope,
or simply to align your Go To system
at the start of the night to do the work
for you. The best type of finder is really
whatever is most comfortable for you. ¢
SCOPES AND SIGHTS Top: Not so long
ago, every telescope came with a finderscope,
like the Meade ETX125 seen at top,
with a 24-mm right-angle finder conveniently
located to the right of the main scope's eyepiece.
Above: Most commercial telescopes
today come equipped with a reflex sight.
MULTIPLE FINDERS Some observers mount additional finders for different uses. The author
keeps a solar finder (top) on his favorite refractor in addition to a reflex sight, so his scope is
always ready for both day and night use.
sk yand tele scope .o r g * FEBRUARY 2024 75

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Sky & Telescope - February 2024

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