Excerpt from 'Photographic Charting of the Heavens', by R. L. J. Ellery, from the Proceedings of the Royal Society of Victoria, 1892

'The particular parts of the zones to be photographed on a night are arranged beforehand, and the guide stars for each plate selected. The dome being opened up and the driving clock set going, the observer sets the instrument on the guide star, and as soon as the telescope is found to be steadily following, an assistant brings the plate holder armed with a photographic plate and inserts it into the plate holder frame of the telescope. The time of exposure being previously settled upon, the observer as soon as all goes quite steadily, opens the exposing shutter, keeping his eye constantly on the guide star, which is now bisected at the cross of the spider webs. The time of opening the shutter is noted, and at the expiration of the fixed time of exposure, as shown by an astronomical clock in the observing room, the assistant warns the observer, who instantly closes the shutter. During the whole time, ten, twenty, forty or sixty minutes' exposure, the observer has to rigorously watch the star and spider webs, and check, by means of the accelerator and retarder hand key, any tendency to leave the intersection, and absolutely to keep the intersection bisecting the star during the whole exposure. Any failure in this respect results in the photographic images of the stars being elongated or oval, instead of round, making them difficult for measurement. One plate being thus exposed it is removed, and the instrument set on the next guide star, and so on. All changing of plates has of course to be done in the dark room, and the observing room itself must be kept moderately dark during the exposure. The development of the plates with us is usually done on the following day.' R. L. J. Ellery, 1892

Bibliography
Ellery, R.L.J. , 'Photographic Charting of the Heavens', Proceedings of the Royal Society of Victoria, Volume 4, Part 1, Stillwell and Co., London, 1892

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