Utilisation d'un boîtier reflex : Mise au point par la méthode de Foucault

The described procedure is applicable to small field photographs of faint objects. The traditional method, which uses a Foucault knife-edge test method, is explained. The described method replaces the sighting lens of the reflex camera with a clear piece of glass inscribed with a single reticulation. A converging lens is used to focus light from the star or other object on the intersection, and accurate positioning is assured by adjustment until the shadow on the mirror is appropriately centered.