Abstract: A glass for a light guide fiber GA1 is used in a core of a fiber 10 of a light guide, and has a refractive index nd between 1.56 and 1.74. The glass for a light guide fiber GA1 has the following composition: (A) SiO2: 20 to 55 wt %, (B11) B2O3: 0 to 2.0 wt %, (B2) does not contain P2O5 and GeO2, (C1) (BaO+SrO+La2O3+Lu2O3+Ta2O5+Gd2O3+WO3): 39 to 46 wt %, (D1) ZnO: 4 to 16 wt %, (E) does not contain Al2O3, (F) does not contain ZrO2, (G) does not contain PbO and As2O3, (H1) (Na2O+K2O): 4 to 10 wt %, (I) Sb2O3: 0 to 0.050 wt %, and (J1) (Na2SO4+K2SO4): 0.32 to 0.78 wt %.

Abstract: An endoscope objective lens includes, in sequence from an object side, a front group which includes a negative first lens having a concave surface faces at image side, a filter, and a positive second lens having a convex surface at the object side and a flat surface or concave surface at the image side; an aperture stop; and a back group which includes a positive third lens having a convex surface at the image side, and a combined lens formed of a plano-convex lens or a biconvex lens and a negative meniscus lens, and satisfies the Conditional Expression (1) and (2): n3>??3/12+5.5,??(1) 2.0>df/Ih>1.5.

Abstract: A glass for a light guide fiber GA1 is used in a core of a fiber 10 of a light guide, and has a refractive index nd between 1.56 and 1.74. The glass for a light guide fiber GA1 has the following composition: (A) SiO2: 20 to 55 wt %, (B11) B2O3: 0 to 2.0 wt %, (B2) does not contain P2O5 and GeO2, (C1) (BaO+SrO+La2O3+Lu2O3+Ta2O3+Gd2O3+WO3): 39 to 46 wt %, (D1) ZnO: 4 to 16 wt %, (E) does not contain Al2O3, (F) does not contain ZrO2, (G) does not contain PbO and As2O3, (H1) (Na2O+K2O): 4 to 10 wt %, (I1) Sb2O3: 0.001 to 0.010 wt %, and (J1) (Na2SO4+K2SO4): 0.32 to 0.78 wt %.

Abstract: Provided is a simple-structured endoscope objective lens suitable for a compact, high-resolution image acquisition element. Provided is an objective lens constituted of a first negative lens, a second positive lens, an aperture stop, a third positive lens, and a joined lens arranged in that order from an object side, the joined lens being formed of a fourth positive lens and a fifth negative lens and satisfying the expressions (1) and (2), and the objective lens satisfies the expression (3): nn?2.0??(1) 12<(?p??n)<34??(2) 1.52<(f23/fl)<1.75??(3) where nn, ?p, ?n, f23 and fl denote a refractive index at d-line of the fifth lens, an Abbe number of the fourth lens, an Abbe number of the fifth lens, a combined focal length of the second lens and the third lens, and a focal length of the entire, respectively.

Abstract: An endoscope objective lens includes, in sequence from an object side, a front group which includes a negative first lens having a concave surface faces at image side, a filter, and a positive second lens having a convex surface at the object side and a flat surface or concave surface at the image side; an aperture stop; and a back group which includes a positive third lens having a convex surface at the image side, and a combined lens formed of a plano-convex lens or a biconvex lens and a negative meniscus lens, and satisfies the Conditional Expression (1) and (2): n3>?v3/12+5.5,??(1) 2.0>df/Ih>1.5.

Abstract: Provided is a simple-structured endoscope objective lens suitable for a compact, high-resolution image acquisition element. Provided is an objective lens constituted of a first negative lens, a second positive lens, an aperture stop, a third positive lens, and a joined lens arranged in that order from an object side, the joined lens being formed of a fourth positive lens and a fifth negative lens and satisfying the expressions (1) and (2), and the objective lens satisfies the expression (3): nn?2.0??(1) 12<(?p??n)<34??(2) 1.52<(f23/fl)<1.75??(3) where nn, ?p, ?n, f23 and fl denote a refractive index at d-line of the fifth lens, an Abbe number of the fourth lens, an Abbe number of the fifth lens, a combined focal length of the second lens and the third lens, and a focal length of the entire, respectively.