The 400mm and 600mm lenses are too heavy and cumbersome to mount alongside a standard small to medium refractor, unless, of course, one has a really substantial observatory-housed equatorial mounting
In his search for a portable equatorial mounting
capable of handling the load presented by a large instrument, he was inspired by Willie Koorts' website to explore designs of this type.
To cure the annoying shakes of an undersize German equatorial mounting
(or to further improve the stability of a well-proportioned one), generations of amateurs have installed a brace between the upper end of the telescope tube and the declination axle or counterweight shaft of its mounting.
Usually optical telescopes have been hung in what is called an equatorial mounting
, with one rotation axis parallel to the plane of the celestial equator and the other parallel to theline between the celestial north and south poles.