GB681456A - High aperture objectives - Google Patents

Abstract

681,456. Photographic objectives. BERTELE, L. J. April 28, 1950 [May 11, 1949], No. 10561/50. Class 97 (i) A high aperture objective consists of three air-spaced components of which the front component L<SP>1</SP> is a simple positive lens, the middle component is a divergent meniscus convex toward the front and the rear component is positive; the air space between the first and second components has the form of a meniscus convex toward the front and the air space between the second and rear components has the form of a converging lens with its bounding surface r<SP>6</SP> more highly curved than the other bounding surface r'. This objective is characterized in that the sum of the refractive indices for the d-line of the front component Ll and the front element L<SP>2</SP> of the second component is greater than 3.357. The rear component may comprise negative elements L<SP>5</SP> and L' and a positive element L<SP>6</SP> of refractive index at least 0.03 greater than element L<SP>6</SP>. The lens L<SP>5</SP> may be omitted. Preferably, the sum of the curvatures of surfaces r<SP>1</SP> and r<SP>3</SP> diminished by the curvature of surface r<SP>2</SP>, is between 3 and 3.9 times the reciprocal of the focal length F of the objective. The axial thickness of the middle component may be between 0.14 and 0.30 F. Adjacent elements of a compound component may be left uncemented, the surfaces thereof being treated to reduce reflection thereat. In this case, the curvatures of the adjacent surfaces differ by not more than 0.2 times the reciprocal of F. Optical data are given for four examples.