a hemispherical plano-convex lens for photographing in a full 180° in all directions in front of the camera, creating a circular image having an increasing amount of distortion from the center to the periphery.
an eyepiece consisting of two plano-convex crown-glass lenses of equal focal length, placed with the convex sides facing each other and with a separation between the lenses of about two-thirds of the focal length of each.
