A wide aperture tele-photo-lens

摘要

818,807. Telephoto lenses. SCHNEIDER, M. C. June 24, 1957 [Aug. 7, 1956], No. 19774/57. Class 97(1) The positive part of the lens on the object side of the diaphragm comprises a front simple lens and a rear doublet, the negative part of the lens on the image side of the diaphragm comprises two simple lenses, the focal length f of the positive part is such that 0.85FfF (where F is the equivalent focal length) and the back focal length of the positive part is less than 0.65F. Preferably, the air gap between the front and rear parts of the lens lies between 0.4 times the total axial length of the lens and 0.4F. Also the ratio of the radii of the front and rear surfaces r 3 and r 5 of the doublet is preferably not greater than 1.3. and the refractive index difference in this doublet should not exceed 0.15. Optical data are given for two examples, one of which is shown.