Registers of photographic plates taken with the Thompson Equatorial Group of Telescopes (series RGO 156/1) and 13-inch Astrographic Telescope (series RGO 156/2). Both series list the photographs taken in order of plate number, and have two separate plate number runs, representing first the Greenwich plates and then plates taken when the instruments were moved to Herstmonceux. The objects imaged are listed, along with right ascension and declination, the initials of the observer, and other information such as the plate type and exposure times. In particular, the 'remarks column' often includes comments on visibility, issues with instruments, clocks or plates (e.g. accidental breakage), or notes on adjustments.

While at Greenwich, the Thompson 26-inch Photographic Refractor was mounted on the same support as the 30-inch Reflector, where they counterbalanced each other. Made by Howard Grubb of Dublin, the telescopes were originally housed in the South Building at RO, Greenwich, and came into use at the end of 1898.

The Thompson 26-inch Refractor was used to take tens of thousands of large-scale photographs of the night sky and the faintest stars. Major programmes included photography of satellites for positional astronomy (including Neptune's satellite, Triton), stellar parallaxes, proper motions, and photometry in Kapteyn Selected Areas. The telescope was also used to photograph the asteroid Eros in 1901 and 1930-1931 for use in solar parallax determinations (see registers RGO 156/1/1 and 1/12-13). The 30-inch remained the largest telescope at Greenwich until the 1930s and was used, for example, to photograph comets, asteroids and the satellites of outer planets. Significantly, it was used in the discovery of Pasiphae, the eighth satellite of Jupiter, by Philibert Melotte in February 1908 (see register RGO 156/1/3).

The Thompson Equatorial Group registers include ticks and cross marks from a later 1965-1966 plate inventory, indicating whether the plates were still in existence by that date or not. A register from this inventory is at RGO 156/1/16.

The 13-inch Astrographic Telescope was at first used for the Carte du Ciel project, photography for which was completed in December 1909 (see register RGO 156/2/7). Many plates in these registers are marked 'Chart' or 'Cat' [Catalogue] in red. Significantly, registers RGO 156/2/1-3 include entries made by William Christies' "Lady Computers", Alice Everett (A.E.), Edith Rix (E.R./E.M.R.), and Annie Russell (A.R.), all of whom observed and took photographs with the telescope for the Carte du Ciel. In addition to star fields, objects listed as imaged in the registers include periodic comets, planets, novae, nebulae, and asteroids.

Note: While initials of observers are listed in the registers, the full names of observers can be identified by checking the introduction to the publication 'Greenwich Observations' for the relevant years.