Reseau Plate
With contributions by Markus Mehring, Phill Parker, David Woods, and Eric Jones.
Last revised 21 November 2003.
The Reseau plate was engraved with a 5 x 5 grid of crosses . The intersections of the crosses were 10 mm apart and accurately calibrated to a tolerance of 0.002 mm. Except for the double-sized central cross, each of the four arms on a cross was 1 mm long and 0.02 mm wide. The crosses (also known as 'fiducials') were recorded on every exposed frame and provided a means of determining angular distances between objects in the field-of-view.
When the Hasselblad Lunar Surface Data Camera was fitted with a 60mm lens, the images of the reseau crosses on the film have an apparent separation of 10.3 degrees. With a 500mm lens fitted, the apparent separation is 1.24 degrees.
