TESSAR TYPE PHOTOGRAPHIC LENS PLACED BEHIND APERTURE

摘要

PURPOSE:To reduce Petzval and make possible well correction of curvature of field and astigmatism in the Tessar type photographic lens of 3-group 4-element constitution having brightness of about F2.8 at around 60 deg. of angle of view and has an aperture on the image side of the lens. CONSTITUTION:The axial face spacing D3 of a negative lens being mainly the second group is made relatively thicker than before, whereby proximate disposition of the faces R3 and R1 and the use of a relatively low refractive glass for the second group while correcting spherical aberrations and coma aberrations are made possible. Conditions (1) and (2) indicate this range and beyond the lower limits of both formulas, it is not possible to reduce Petzval sum. In addition, coma aberrations are well corrected by increasing the radius of curvature of the face R3 according to the thickness of the axial face spacing D3, disposing moderably large refracting power to the face R6 by decreasing the radius of curvature of the junction face R6 and increasing the refractive index difference of N3 and N4 and decreasing the axial spacing D4, namely, by conditions (3) thru (6).