Astronomy

This telescope

offers top-notch

construction and

high-quality optics,

and is easy to set up

and use, as well.

text and images by

Mike Reynolds

60 ASTRONOMY • JANUARY 2018

12 -inch Tr u s s

Tube Dobsonian

Explore Scientific’s

weight. This led to the truss

tube: a set of rigid poles to con-

nect the lower part of the Dob

— referred to as the rocker box,

which contains the primary

mirror — to the Dob’s upper

cage, which holds the second-

ary mirror and focuser. This

design, and the use of innova-

tive connectors, means the tele-

scope quickly disassembles into

the rocker box, the mirror box,

the secondary cage assembly,

and the truss tubes.

Opening it up

Explore Scientific, known for

its apochromatic refractors and

wide-field eyepieces, has

entered the market with three

new Dobsonian telescopes. The

trio features a number of traits

standard to most Dobs along

with a few surprises.

The Explore Scientific

12-inch Truss Tube Dobsonian

arrived in one box. This was

the first surprise; previously

reviewed Dobs have always

needed at least two boxes. I

appreciated that the included

user manual was well-written,

and even contained pictures!

Assembly of the telescope

was easy, and this would hold

true even for a beginner. I

found the construction solid,

from the mirror box to the sec-

ondary mirror cage. The fin-

ishes appear nice and should

last through many an observ-

ing session. The weight of the

T

he Dobsonian,

John Dobson’s sidewalk

telescope mount design

more commonly

referred to as a Dob, has

evolved significantly since its

first commercial introduction

in the 1980s. Many of us

remember the blue tube Coulter

Optical Dobsonian telescopes,

the first of which contained a

13.1-inch primary mirror.

Soon, amateur telescope

makers and companies began

producing larger and more

innovative Dobs. The simplicity

of the mount, coupled with a

large mirror, made them popu-

lar telescopes. The Dob rage

brought on what many referred

to as “aperture fever.”

The basic Dobsonian mount

carries a Newtonian ref lector

with its concave primary mir-

ror and f lat secondary mirror

mounted at a 45° angle to the

primary. As the Dob evolved

over the years, innovations

such as shorter focal lengths for

the big scopes, primary mirror

cooling fans, equatorial track-

ing tables (an accessory that

serves as a motor drive), and

numerous others appeared.

Truss tube Dobs were also

one of these early innovations,

brought on by need and by

mirror-size evolution. As the

primaries became larger, solid

tubes of either cardboard con-

crete column tubing or metal

became impractical due to

Explore

Scientific’s

12-inch Truss

Tube Dobsonian

offers a large

aperture at a

reasonable cost.