The Claude glass was an early pocket lens, sans camera, that 18th century men and women would hold aloft to regard the scene over their shoulder.
Its technology is reminiscent of the types of filters and effects one can choose from with Instagram and Hipstamatic: the blackened mirror reduced to tonal values of the image in its reflection and its convex shape brought more of the scene into center, rendering a tidy snapshot of a larger expanse. [Kottke]
