Objective lens system for endoscope

• US 5,587,839 A
• Filed: 10/17/1995
• Issued: 12/24/1996
• Est. Priority Date: 10/18/1994
• Status: Expired due to Fees

• Current Assignee: Fuji Photo Optical Co. Ltd (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Optical Co. Ltd (Fujifilm Holdings Corporation)
• Inventors: Miyano, Hitoshi, Yamamoto, Chikara
• Primary Examiner(s): Sugarman, Scott J.
• Application Number:
  US08/544,003
• Time in Patent Office: 434 Days
• Field of Search: 359/656, 359/657, 359/658, 359/659, 359/660, 359/783
• US Class Current: 359/660
• CPC Class Codes: G02B 23/243 Objectives for endoscopes
• CPC Class Codes: G02B 9/34 having four components only

Abstract

An objective lens system for an endoscope includes first to fifth lens elements L₁ to L₅ arranged in this order from the front to the rear. An aperture stop is disposed between the second and third lens elements L₂ and L₃. The first lens element L₁ is a negative lens concave to the rear, the second lens element L₂ is a positive lens having a flat surface facing rearward, the third lens element L₃ is a positive lens having a flat surface facing forward, the fourth lens element L₄ is a positive lens having a flat surface facing forward and the fifth lens element L₅ is a negative meniscus lens. The fourth and fifth lens elements L₄ and L₅ are cemented together to form a cemented lens having a positive refracting power. The following formulae (1) to (3) are satisfied,

0.75<|f.sub.1 ×Bf/f.sup.2 |<1.45   (1)

D.sub.i <|R.sub.i |                      (2)

υ.sub.2 <45                                        (3)

wherein f₁ represents the focal length of the first lens element L₁, Bf represents the back focal length of the overall objective lens system, f represents the combined focal length of the overall objective lens system, D_i represents the central thickness of an lens element L_i having a convex face, R_i represents the radius of curvature of the convex face of an lens element L_i having a convex face and υ₂ represents the Abbe'"'"'s number of the second lens element L₂.

Claims

1. An objective lens system for an endoscope comprising first to fifth lens elements L₁ to L₅ arranged in this order from the front to the rear and an aperture stop disposed between the second and third lens elements L₂ and L₃, the first lens element L₁ being a negative lens concave to the rear, the second lens element L₂ being a positive lens having a flat surface facing rearward, the third lens element L₃ being a positive lens having a flat surface facing forward, the fourth lens element L₄ being a positive lens having a flat surface facing forward, the fifth lens element L₅ being a negative meniscus lens, the fourth and fifth lens elements L₄ and L₅ being cemented together to form a cemented lens having a positive refracting power wherein the following formulae (1) to (3) are satisfied,

View Dependent Claims (2)

2. An objective lens system as defined in claim 1 in the following formula (4) is further satisfied