Dall-Kirkham reflecting telescope, 1960-1975.
© Science Museum / Science & Society Picture Library
Dated from 1960-1975, this miniature reflecting telescope was built and designed by the amateur astronomer, Horace Dall. Fitted with a 95.25mm main mirror, the whole telescope folds flat for a carrying pouch that will fit inside a person's pocket. The instrument uses an optical configuration now known as the Dall-Kirkham design, an adaptation of the earlier Cassegrain system first proposed in 1672. Dall conceived of his modifications in 1928 and corresponded on its merits with fellow amateur, Allan Kirkham in Oregon, America. Later the design was described in the journal, 'Scientific American' under the title of, 'Dall-Kirkham' a name that has stuck ever since.