Sky and Telescope - February 2017 - 70

Astronomer's Workbench by Jerry Oltion

The Craig Daniels
Dogson Telescope

º Learn more about the Dogson on Craig's
website at http://tinyurl.com/gmsm87k

And now for something completely different.

the scope simple, Craig eliminated the
traditional focuser. Instead, he focuses
by moving the primary mirror up and
down the "tube" on a sled. (Sound
familiar? Schmidt-Cassegrains and
Maksutovs do this.)
Since Craig lives near the coast,
he doesn't leave his primary mirror
exposed to the salt-laden air. It's easily
removed through a trap door in the
side of the scope for storage in a sealed,
desiccated plastic container.
All this would simply make an oddlooking Dobsonian if it were mounted
on a traditional alt-azimuth rocker
and ground board, but Craig opted for
simple and direct here, too. Inspired
by the stability of classic mounts like
Hadley's, Herschel's, and Lord Rosse's
telescopes, and especially F. J. Sellers's
1920s design, Craig decided to set the
back end of his scope on the ground
and prop the front end on a stick. An

S Above: Craig Daniels with his Dogson telescope. Right: The top end of the Dogson holds the
eyepiece, setting circles, split-pupil finder, and swing-out camera mount.

70

F E B R U A R Y 2 0 1 7 * SK Y & TELESCOPE

S The inside of the Dogson, showing the
primary mirror sled.

early articulated "dog-leg" prop lent the
Dogson its name.
To use the scope, Craig simply sets
the back end on the ground, aims the
front end at his target, and adjusts slowmotion altitude via coarse threads at
the top of the foreleg. Gentle sideways
tugs adjust for azimuth.
Says Craig, "The Dogsonian design
eliminates bearings, counterweights, and
weight. It's also easier for an amateur
astronomer to build, since weight distribution and eyepiece hole location aren't
critical. Adding accessory items to ﬂat
surfaces is fairly easy. For considerations
of operation, transport, and storage, this
is a one-piece, one-handle design."
For aiming, Craig uses several
options, starting with open sights
near the top of the scope, which he
says "eliminates that time-honored
tradition of groveling on the ground
to sight up the OTA." From there he
uses a split-pupil ﬁnder. Indeed, Craig's
split-pupil ﬁnder was the inspiration for
mine, featured in this space (S&T: June
2013, p. 66). Craig is kind of a gadget

CR AIG DA NIELS (3)

WHAT WOULD YOU GET if you took
practically every convention in telescope making and stood it on its ear?
Something that looks and functions
remarkably like the "Dogson" created
by Oregon ATM Craig Daniels.
Craig didn't set out to make the antiDob. His goal was to produce a simpleto-build, easy-to-use, modest-aperture
scope that would break neither the bank
nor the back of the person carrying it
out the door for an evening's observing.
He started with a 6-inch f/8.3 mirror.
Why f/8? Because at long focal lengths a
6" mirror can remain spherical and still
be well within ¼-wave accuracy. Spherical mirrors are way easier to produce
than parabolic mirrors, so that gives a
ﬁrst-timer a leg up right away.
The "tube" is a wooden box. Boxes
are easier to build than tubes or trusses.
In order to keep the secondary mirror small and keep the upper end of
http://www.tinyurl.com/gmsm87k
Sky and Telescope - February 2017

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