Geometrical optics / by Archibald Stanley Percival.

  • Percival, A. S. (Archibald Stanley), 1862-
Date:
1913
Catalogue details

Licence: In copyright

Credit: Geometrical optics / by Archibald Stanley Percival. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    CHAPTER VI. LENSES. Any refracting medium bounded by two curved surfaces which form arcs of spheres is known as a spherical lens; the axis of the lens is the line joining the centres of the spheres, and that part of the axis lying between the two surfaces gives the thickness of the lens. Thus in Fig. 31 the surface A is the arc of a sphere that has its centre at Ci, and the surface B is the arc of another sphere that has its centre at C2: the axis of the lens is the line joining Cx and C2, and the thickness of the lens is the length of the line AB. These are the only definitions we shall require for the present. It will be apparent that if one of the surfaces be plane, it may be regarded as a spherical surface of which the radius is infinite. Thin Lenses. Thin Axial Pencils.—The conjugate focal distances of an axial pencil of a thin lens can be very easily determined from the formula that we have already found for a single spherical surface. It should be noted that the term centric is no longer equivalent to the term axial, as an oblique pencil that passed through the centre of one spherical surface would not pass through the centre of m