A blink comparator was a viewing apparatus used by astronomers to find differences between two photographs of the night sky shot using optical telescopes such as astrographs. It permitted rapidly switching from viewing one photograph to viewing the other, "blinking" back and forth between the two taken of the same area of the sky at different times. This allowed the user to more easily spot objects in the night sky that changed position. It was also sometimes known as a blink microscope.

In photographs taken a few days apart, rapidly moving objects such as asteroids and comets would stand out, because they would appear to be jumping back and forth between two positions, while all the other fixed stars stood still. Photographs taken at longer intervals could be used to detect stars with large proper motion, or variable stars, or to distinguish binary stars from optical doubles.

The Projection Blink Comparator (PROBLICOM), invented by amateur astronomer Ben Mayer, was a low-cost version of the professional tool. It consisted of two slide projectors with a rotating occulting disk that alternately blocked the images from the projectors. This tool allowed amateur astronomers to contribute to some phases of serious research.

This instrument is significant for its association with the Sydney Observatory.

Noel Svensson, Powerhouse Volunteer, February, 2008

Mr H. F. Pinnock was appointed to the staff of the New South Wales University of Technology in 1951 where part of his duty was to maintain the instruments at the Observatory. In 1954 he was appointed to work full time in the workshop of the Observatory and this capacity to service instruments and make new ones.

Noel Svensson, Powerhouse Volunteer, February, 2008

Blink comparator, metal / glass, used and made at Sydney Observatory, made by H. F. Pinnock, Sydney 1951 - 1963

Made: 1956 - 1963

H10185

1956 - 1963