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 popular telescopes. The Dob rage brought on what many referred to as “aperture fever.”
The basic Dobsonian mount carries a Newtonian reflector with its concave primary mirror and flat 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 tracking 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 concrete column tubing or metal became impractical due to weight. This led to the truss tube: a set of rigid poles to connect 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 secondary mirror and focuser. This design, and the use of innovative connectors, means the telescope quickly disassembles into the rocker box, the mirror box, the secondary cage assembly, and the truss tubes.
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