Both parties took similar 13-inch astrographic lenses of 11 feet 3 inches focal length.
That taken to Sobral came from the Astrographic Telescope at Greenwich, as depicted in the photograph above by the London Stereoscopic and Photographic Company c.1896, From the Greenwich Astrographic Catalogue, Volume 1, (HMSO, 1904)
The object glass taken to Principe came from the Astrographic Telescope at Oxford. The object glasses were attached on arrival to hollow steel tubes (made by Harvey & Co.), with the lens at one end and the photographic plate holder at the other and then mounted horizontally so that the sunlight could be reflected into them by a 16 inch diameter flat mirror.
The flat mirror or coelostat, was slowly rotated to follow the Sun, using a clock driven by a heavy weight, that ran for about half an hour before the weight had to be rewound. Both astrographic lenses were stopped down to 8 inches diameter to improve their image quality.
The Greenwich Sobral group, also took a 4 inch diameter lens with a focal length of 19 feet, loaned to them by Father Cortie. This was fed by an 8 inch diameter coelostat loaned by the Royal Irish Academy. The Greenwich group also took a 3½ inch Detached Telescope (R.O. No. 3) and the Eros Micrometer.
Mounting the telescope horizontally avoids the need to transport and align a heavy equatorial mount and makes it easier to keep the apparatus cool and free of wind shake, but the flat coelostat mirror introduces an extra optical element, capable of spoiling the image quality.