Sky & Telescope - January 2025 - 72

ASTRONOMER'S WORKBENCH by Jerry Oltion
The Salad Bowl
Telescope
An artist builds a Dobsonian . . . sort of.
MOST OF YOU KNOW Cindy Krach for
her stunning lunar sketches that illustrated
two of my feature articles (S&T:
Sept. 2022, p. 20 and July 2024, p. 34).
She's also the coordinator of the Astronomical
League's Sketching Observing
Program (https://is.gd/ALsketching).
You'd probably guess that I met her
because of her sketching, but that's not
actually the case. It was her enthusiasm
for telescope making that initially
kindled our friendship.
Cindy is one of only a handful of
people I know of who have built a trackball
mount for a ball scope. That's how
we met, with her asking me for information
about my design. Then over the
years she became interested in grinding
her own mirror and building a scope for
it. She chose an 8-inch blank and set to
work, using a glass tool to hog it out to
f/5 and fine-grind it, then pitch to polish
and parabolize it.
Not surprisingly, parabolizing her
first mirror proved a challenge. Cindy
got close several times and messed it up
several times, as almost all new mirror
makers do until we learn the nuances of
parabolizing. She would gamely take it
back to a spherical figure and try again,
and she would send me progress reports
with Ronchigrams she took through a
homemade tester. I watched one series
of Ronchigrams draw closer and closer
to the ideal pattern until I finally told
her, " Stop there and star test. "
That meant building a star-testing
rig. Cindy first tried to mount the mirror
deep inside a longer-focal-ratio commercial
scope tube, but that proved too
awkward to collimate. Other attempts
at building a skeletal OTA proved
equally unusable. So she set out to build
the actual scope that would house her
homemade mirror.
Cindy is an artist, so not surprisingly,
she didn't settle for plywood and
cardboard. She kept an eye out for more
interesting materials that might do, and
one of the first things she found was a
pCindy Krach built this beautiful as well as
functional 8-inch Dobsonian telescope.
deep, laminated-wood salad bowl that
was just the right diameter at the bottom
to hold the mirror. Not long after, she
found laminated cutting boards that
she used to make moon-shaped altitude
bearings. More cutting boards provided
the secondary ring and the base for the
mirror bowl and struts to rest on.
Of course, these non-traditional
materials meant she had to custom-fit
everything, often rethinking things
that didn't go right the first time. I got
emails like, " I managed to move the
bowl by butchering the center hole. I'll
probably throw a few screws into the
bottom to hold it in place. Can't be seen
which is good 'cos it ain't pretty. " Many
times it felt like she took two steps
backward for every step forward. And
sure enough, one day I got an email that
started with, " Today I almost gave up
on the scope. " My heart stopped until
I read the next sentence: " But after
stamping my feet and saying a lot of bad
words, I figured it out. "
That was pretty much the story all the
pLeft: Cindy used a gorgeous hardwood bowl and cutting boards for the mirror enclosure, its
base, the altitude bearings, and the secondary ring. Right: The focuser mounts on slotted angle
brackets for adjustability.
72 JANUARY 2025 * SKY & TELESCOPE
way to the end, with some surprisingly
innovative ideas along the way. Cindy
bought a commercial focuser, but rather
ALL IMAGES COURTESY OF CINDY KRACH

https://www.is.gd/ALsketching

Sky & Telescope - January 2025

Table of Contents for the Digital Edition of Sky & Telescope - January 2025