Réseau plate

A Réseau plate is a transparent sheet of glass or plastic engraved with a grid of crosshatches called fiducial markers.

When the frame is exposed the fiducial markers scatter incoming light, creating a permanent shadow on the negative.

[2] Fiducial markers are generally unnecessary for digital cameras because the physical pixel structure of the sensor itself inherently provides a source of geometric reference.

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 60 mm lens, the images of the Réseau crosses on the film have an apparent separation of 10.3 degrees.