Image: Bond-1922 - Fig 1

Description: Figure 1 from Bond's paper describing an improvement to Wood's fish-eye pail apparatus of 1906. Original caption follows:  The lens in its original form consists of a glass hemisphere L (fig. 1) of radius r. The light is incident on the plane face, which is covered by a thin screen S, except for a small circular aperture at the centre. It will be seen that a ray incident in the plane of the outer face of the lens will be refracted at the critical angle. Furthermore, all refracted rays will arrive almost normally at the hemispherical face of the lens, and will subsequently converge to form an image, which, for objects at infinity, will lie on part of a sphere III, concentric with the hemispherical face of the lens and of radius rμ/(μ–1), where μ is the refractive index of the lens. The emergent cone of rays will in practice have a total angle of slightly less than 90°; and if the aperture in the screen S is small enough, the whole image will be sufficiently in focus on a flat plate PP placed at a distance from the plane face of the lens equal to the mean distance of the various portions of the true image III from this plane face.  The screen S should be covered on the outer side by a plane plate of glass G, the whole being cemented together. This arrangement avoids the finite thickness of the screen S, preventing some or all of the light incident at fairly oblique angles from entering the lens.  It will be seen that the photographic plate should be placed at a distance h from the plane face of the lens of about 2.5r (i.e. rather less than μr/(μ–1)).
Title: Bond-1922 - Fig 1
Credit: W.N. Bond (Nov 1922), "A Wide Angle Lens for Cloud Recording", Philosophical Magazine.
Author: W.N. Bond
Usage Terms: Public domain
License: Public domain
Attribution Required?: No