Sky & Telescope - March 2024 - 72

ASTRONOMER'S WORKBENCH by Jerry Oltion
Make
a Solar
Finder
How to point out the obvious
WITH THE UPCOMING total solar
eclipse on April 8th, many people in
North America are dusting off their
solar filters or making new ones so they
can safely view the event through their
telescopes. (For advice on how to build
your own filter, check out my article in
S&T: June 2017, p. 38.)
One problem you'll quickly discover
when you put that filter on your
telescope is how difficult it is to aim the
scope at the Sun. You'd think it would
be easy, given that the Sun is right
there in the sky, but it's not. The Sun is
too bright to look directly at without a
protective filter. And at only ½° across,
it doesn't appear in a filtered view until
you're right on it. (You won't see a
gradual brightening of the field as you
get close, because solar filters are too
dense for that.)
In order to aim reliably at the Sun,
you need a solar finder. I wrote about
several types back in
2017, too (S&T: July
2017, p. 72), but I've
since become fond of
another simple design
that I only mentioned
in passing then.
This design is
made from a short
piece of PVC pipe.
One-inch-diameter
works well, but pretty
much anything will
do. Cut a piece three
to five inches long.
Put a cap on one end,
with a hole drilled in
the center of the cap. You can use an
end cap designed for the pipe size you're
working with, or any opaque material
will do. Cardboard works fine. For the
one pictured below, I made a circle cut
from a sheet of white PVC plastic and
glued it to the front of the pipe.
The hole in the center of the cap
allows a beam of sunlight to enter the
tube. You can make it any size you
want, within reason. (I used a #43 drill
bit for mine.) If you put a translucent
screen on the back of the tube, that
beam will fall on the screen when the
body of the finder is pointed at the Sun.
Thin paper works okay for the
screen, but depending on its density it
might be a little too opaque to be ideal.
I found a piece of plastic shopping bag
Steve Edberg cut the
rear end of his finder at an
angle to make the screen
viewable from the side.
to be perfect for the
task. California ATM
Steve Edberg made
his from a piece cut
out of a report folder
made from translucent
plastic.
Steve added one
further refinement to
his finder that I like
quite a bit: He cut the
rear of the tube at an
angle in order to view
the finder from the side or from above.
No hunkering down necessary!
Steve uses tool clips to mount his
solar finder to the body of his optical
finder. Note that if you do this, you
must cap the lens of the optical finder -
it can be dangerous without the cap, not
to mention the finder's crosshairs will
melt away.
I built a dovetail foot for my solar
finder so it completely replaces the optical
finderscope. That also lets me move
the solar finder onto any scope that has
a universal dovetail mount, provided I
have a solar filter for that scope.
You'll be tempted to put a center
dot on your projection screen, and you
should certainly dot it, but the odds
that you'll need it exactly on-center
pLeft: This simple solar finder uses a short piece of PVC pipe with an opaque cap on front, with a hole in the cap to allow a narrow beam of sunlight
through. Right: The rear of the finder uses a thin piece of white plastic shopping bag for a screen. Note that the index mark isn't on-center. That's
because the dovetail bracket that holds the finder isn't perfectly aligned with the telescope's optical axis.
72 MARCH 2024 * SKY & TELESCOPE
FRONT AND REAR VIEWS OF THE FINDER: JERRY OLTION (2);
SOLAR FINDER WITH ANGLED SCREEN: STEVE EDBERG

Sky & Telescope - March 2024

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