A Serrurier truss

Truss

In architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in...

is used in telescope

Telescope

A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

 tube assembly construction. The design was created in 1935 by engineer Mark U. Serrurier

Mark Serrurier

Mark Serrurier is the son of Dutch-born electrical engineer, Iwan Serrurier, who created the Moviola in 1924 which became the technology used for film editing. Mark was a graduate of Caltech and went on to work on designs for the Mt. Palomar 200 inch Hale telescope...

 when he was working on the Mt. Palomar

Palomar Observatory

Palomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology...

 200 in (5.1 m) Hale telescope

Hale telescope

The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in California, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation, he orchestrated the planning, design, and construction of the observatory, but did not live to see its commissioning...

. The design solves the problem of truss flexing by supporting the primary objective

Objective (optics)

In an optical instrument, the objective is the optical element that gathers light from the object being observed and focuses the light rays to produce a real image. Objectives can be single lenses or mirrors, or combinations of several optical elements. They are used in microscopes, telescopes,...

 mirror and the secondary mirror by two sets of opposing trusses before and after the declination

Declination

In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...

 pivot. The trusses are designed to have an equal amount of flexure, which allows the optics to stay on a common optical axis

Optical axis

An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens or microscope.The optical axis is an imaginary line that defines the path along which light propagates through the system...

. When flexing the "top" truss resists tension and the "bottom" truss resists compression. This has the effect of keeping the optical elements parallel to each other. The net result is all of the optical elements stay in collimation regardless of the orientation of the telescope.
Certain designs used by amateur telescope makers

Amateur telescope making

Amateur telescope making is the activity of building telescopes as a hobby, as opposed to being a paid professional. Amateur telescope makers build their instruments for personal enjoyment of a technical challenge, as a way to obtain an inexpensive or personally customized telescope, or as a...

, specifically truss tube Dobsonians that use a single truss, are sometimes called "Serrurier truss" designs. These single truss designs are used for their rigidity and do perform the function of keeping the optical elements parallel, but since they lack the opposing truss that keeps optics on the same optical axis so are not technically a "Serrurier truss".

Other examples of Serrurier truss designs: