Patent ID: 7821720

Claim:
An endoscope objective lens, comprising: a negative lens group, G 1 ; a positive lens group, G 2 ; a stop, S, placed between the negative lens group, G 1 , and the positive lens group, G 2 ; an optical filter, F, placed between the positive lens group, G 2 , and an image plane, IP; and a tunable filter, TF, for performing multi-spectral imaging or hyperspectral imaging, wherein all of the following conditions (1) to (4) are satisfied: 0.5 ≦EFL≦ 1.4 mm, and −4 ≦F 1 /EFL≦− 1.2, and 1.1 ≦F 2 /EFL≦ 1.9 (1) F#≦4.2 (2) EPD≧ 0.4 mm, and 0.4 ≧EPD/Dia≧ 0.2 (3) FFOV≧120° (4) and wherein, EFL is the effective focal length of the objective lens, F1 is the effective focal length of the negative lens group, G 1 , F2 is the effective focal length of the positive lens group, G 2 , F# is the f number of the objective lens, EPD is the entrance pupil diameter of the objective lens, Dia is the maximum diameter of the objective lens, and FFOV is the full field of view of the objective lens.