 The image formed on this ground glass can be observed directly, giving a "waist-level reflex finder," or through a redressing optical device (set of mirrors or prism) for eye-level viewing, giving an "eye-level reflex finder".With a reflex finder, you can focus the image on the ground glass and frame your picture at the same time.It is common to find a device on the center of the ground glass to help precise focusing, for example a split-image or a microprism device.