Bifocal optical system

• US 5,013,142 A
• Filed: 12/12/1989
• Issued: 05/07/1991
• Est. Priority Date: 12/16/1988
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Perrin, Jean-Claude, Rollin, Joel
• Primary Examiner(s): Dzierzynski, Paul M.
• Application Number:
  US07/449,638
• Time in Patent Office: 511 Days
• Field of Search: 350/449, 350/450, 350/422, 350/427, 350/423
• US Class Current: 359/674
• CPC Class Codes: G02B 15/10 by adding a part, e.g. close-up attachment

Abstract

The bifocal optical system is formed in the long focal length mode by an objective having fixed lenses L1, L2, L3, L4 to which, for obtaining the short focal length, a group of movable lenses L5, L6, L7, L8 is added. The lenses L5, L6, L7 and L8 are accommodated in a holder (MB) which is rotatable around an axis YY'"'"' which extends parallel to the optical axis XX'"'"', thereby enabling very wide tolerances in the positioning of the movable holder.

Claims

1. A bifocal optical system, having a long focal length LF and a short focal length SF and comprising an objective with fixed lenses arranged in a front group and a rear group, and an intermediate group in a movable holder for insertion between the front and rear groups, characterized in that the front group having a focal length LF/γ

is convergent and comprises three lenses, the rear group is convergent and includes a lens having a magnification γ

in that the movable holder is rotatable around an axis parallel to the system optical axis, and in the intermediate group is convergent constituted by four lenses and has a magnification of γ

'"'"'=SF/LF.

2. A bifocal optical system as claimed in claim 1, for use in a mixed day/night vision device having at the front side a controllable iris for dosing the illumination of the day channel relative to the night channel, characterized in that in addition it includes an diaphragm which forms an integral part of the movable holder for preserving the illumination of the night channel during the switch to the short focal length, the diaphragm being positioned near the front group.

3. A bifocal optical system as claimed in claim 1, for used in a mixed day/night vision device, characterized in that the front group has a small relative aperture, the intermediate group has a magnification value γ

'"'"' near utility, whilst the rear group has a magnification γ

=γ

'"'"'/2.

4. A bifocal optical system as claimed in claim 1, characterized in that, in the short focal length situation, the lenses forming the system are realised and adjusted in accordance with the following value Table, in which the work "radius" indicates the radius of curvature of the denoted surface, the words "subsequent thickness" indicate the spacing to be allowed between said denoted surface and the subsequent denoted surface, which spacing is measured along the optical axis, "radius" and "subsequent thickness" being expressed in millimeters:

space="preserve" listing-type="tabular">______________________________________ N.sup.O of the Subsequent Subsequent surface Radius material thickness ______________________________________ 2 45.073 BALF5 8.581 3 -1090.367 AIR 5.637 4 39.611 LAK21 5.680 5 84.688 AIR 8.787 6 -293.757 SF6 13.064 7 21.752 AIR 6.693 8 -33.773 SK5 6.865 9 47.715 AIR 2.703 10 45.052 SF6 4.881 11 25.250 AIR 1.092 12 29.141 SK11 6.104 13 -120.174 AIR 1.102 14 113.326 FK3 3.379 15 -37.859 AIR 17.093 16 87.406 BAF4 3.426 17 -64.601 AIR 40.945 ______________________________________