After first two telescopes (the ANU 40 inch and 16 inch telescopes) were completed at Siding Spring Observatory, a third telescope, a 24 inch reflector, was also ordered from Boller & Chivens. It was built on site and was commissioned in 1966 under the directorship of Olin Eggen. The telescope building also contains an aluminising plant room as well as storage areas. It has been decommissioned and is now used as office space and work rooms.
The 24 inch Telescope was an f/18 Cassegrain on an equatorial mount. RSAA astronomers Mathewson and Serkowski began taking polarimetric observations with the double channel polarimeter on the telescope in November 1966. Mathewson went on to use this telescope to compete a two year observation of 2000 stars and collect the most accurate and polarization measures ever obtained. From this he constructed the first consistent magnetic field chart of our local arm of the Milky Way.
In its later years the telescope was primarily fitted with instruments for photometry and imaging work, and used mainly for photoelectric photometry.