Objective lens system for endoscopes

An objective lens system for endoscopes comprising, in order from the object side:

• a front lens unit having a negative refractive power, an aperture stop, and a rear lens unit having a positive refractive power;
• wherein said rear lens unit includes a graded refractive index lens component, and wherein said graded refractive index lens component satisfies the following conditions (15) and (7) when a refractive index and an Abbe's number are approximated by formulae (1) through (5) shown below:
• N.sub.d (r)=N.sub.0.sbsb.d +N.sub.1.sbsb.d r.sup.2 +N.sub.2.sbsb.d r.sup.4 +N.sub.3.sbsb.d r.sup.6 ( 1)
• N.sub.F (r)=N.sub.0.sbsb.F +N.sub.1.sbsb.F r.sup.2 +N.sub.2.sbsb.F r.sup.4 +N.sub.3.sbsb.F r.sup.6 ( 2)
• N.sub.C (r)=N.sub.0.sbsb.C +N.sub.1.sbsb.C r.sup.2 +N.sub.2.sbsb.C r.sup.4 +N.sub.3.sbsb.C r.sup.6 ( 3)
• .nu..sub.0.sbsb.d =(1-N.sub.0.sbsb.d)/(N.sub.0.sbsb.F -N.sub.0.sbsb.C)(4)
• .nu..sub.1.sbsb.d =N.sub.1.sbsb.d /(N.sub.1.sbsb.F -N.sub.1.sbsb.C)(5)
• N.sub.1.sbsb.d >0 (15)
• 0.ltoreq..nu..sub.0.sbsb.d .ltoreq..nu..sub.1.sbsb.d ( 7)
• wherein the reference symbols N.sub.d (r), N.sub.F (r) and N.sub.C (r) represent refractive index of said graded refractive index lens component for the d-line, F-line and C-line respectively when a distance as measured in the radial direction from an optical axis is designated by r, the reference symbols N.sub.0.sbsb.d, N.sub.1.sbsb.d, N.sub.2.sbsb.d and N.sub.3.sbsb.d denote refractive index distribution coefficients for the d-line, the reference symbols N.sub.0.sbsb.F, N.sub.1 F, N.sub.2 F and N.sub.3.sbsb.F represents refractive index distribution coefficients for the F-line, the reference symbols N.sub.0.sbsb.C, N.sub.1.sbsb.C, N.sub.2.sbsb.C and N.sub.3.sbsb.C designate refractive index distribution coefficients for the C-line, and the reference symbols .nu..sub.0.sbsb.d and .nu..sub.1.sbsb.d denote Abbe's numbers.

An objective lens system for endoscopes comprising, in order from the object side:

• a front lens unit having a negative refractive power, an aperture stop, and a rear lens unit having a positive refractive power;
• wherein said rear lens unit includes a graded refractive index lens component, and wherein said graded refractive index lens component satisfies the following conditions (6) and (7) when a refractive index and an Abbe's number of said graded refractive index lens component are approximated by formulae (1) through (5) mentioned-below:
• N.sub.d (r)=N.sub.0.sbsb.d +N.sub.1.sbsb.d r.sup.2 +N.sub.2.sbsb.d r.sup.4 +N.sub.3.sbsb.d r.sup.6 ( 1)
• N.sub.F (r)=N.sub.0.sbsb.F +N.sub.1.sbsb.F r.sup.2 +N.sub.2.sbsb.F r.sup.4 +N.sub.3.sbsb.F r.sup.6 ( 2)
• N.sub.C (r)=N.sub.0.sbsb.C +N.sub.1.sbsb.C r.sup.2 +N.sub.2.sbsb.C r.sup.4 +N.sub.3.sbsb.C r.sup.6 ( 3)
• .nu..sub.0.sbsb.d =(1-N.sub.0.sbsb.d)/(N.sub.0.sbsb.F -N.sub.0.sbsb.C)(4)
• .nu..sub.1.sbsb.d =N.sub.1.sbsb.d /(N.sub.1.sbsb.F -N.sub.1.sbsb.C)(5)
• N.sub.1.sbsb.d>
• 0 (6)
• 0.ltoreq..nu..sub.0.sbsb.d .ltoreq..nu..sub.1.sbsb.d ( 7)
• wherein the reference symbol N.sub.d (r), N.sub.F (r) and N.sub.C (r) represent refractive index of said graded refractive index lens component for the d-line, F-line and C-line respectively when a distance as measured from an optical axis in the radial direction is designated by r, the reference symbols N.sub.0.sbsb.d, N.sub.1.sbsb.d, N.sub.2.sbsb.d and N.sub.3.sbsb.d denote refractive index distribution coefficients for the d-line, the reference symbols N.sub.0.sbsb.F, N.sub.1.sbsb.F, N.sub.2.sbsb.F and N.sub.3.sbsb.F represent refractive index distribution coefficients for the F-line, the reference symbols N.sub.0.sbsb.C, N.sub.1.sbsb.C, N.sub.2.sbsb.C and N.sub.3.sbsb.C designate refractive index distribution coefficients for the C-line, and the reference symbols .nu..sub.0.sbsb.d and .nu..sub.1.sbsb.d denote Abbe's numbers.

An objective lens system for endoscopes comprising, in order from the object side:

• a front lens unit having a negative refractive power, an aperture stop, and a rear lens unit having a positive refractive power;
• wherein said rear lens unit includes a graded refractive index lens component, and wherein said graded refractive index lens component satisfies the following conditions (15) and (7) when a refractive index and Abbe's number of said graded refractive index lens component are approximated by the formulae (1) through (5) shown below:
• N.sub.d (r)=N.sub.0.sbsb.d +N.sub.1.sbsb.d r.sup.2 +N.sub.2.sbsb.d r.sup.4 +N.sub.3.sbsb.d r.sup.6 ( 1)
• N.sub.F (r)=N.sub.0.sbsb.F +N.sub.1.sbsb.F r.sup.2 +N.sub.2.sbsb.F r.sup.4 +N.sub.3.sbsb.F r.sup.6 ( 2)
• N.sub.C (r)=N.sub.0.sbsb.C +N.sub.1.sbsb.C r.sup.2 +N.sub.2.sbsb.C r.sup.4 +N.sub.3.sbsb.C r.sup.6 ( 3)
• .nu..sub.0.sbsb.d =(1-N.sub.0.sbsb.d)/(N.sub.0.sbsb.F -N.sub.0.sbsb.C)(4)
• .nu..sub.1.sbsb.d =N.sub.1.sbsb.d /(N.sub.1.sbsb.F -N.sub.1.sbsb.C)(5)
• N.sub.1.sbsb.d >0 (15)
• 0.ltoreq..nu..sub.0.sbsb.d .ltoreq..nu..sub.1.sbsb.d ( 7)
• wherein the reference symbols N.sub.d (r) , N.sub.F (r) and N.sub.C (r) represent refractive indices for the d-line, F-line and C-line respectively when a distance as measured from an optical axis in the radial direction is designated by r, the reference symbols N.sub.0.sbsb.d, N.sub.1.sbsb.d, N.sub.2.sbsb.d and N.sub.3.sbsb.d denote refractive index distribution coefficients for the d-line, the reference symbols N.sub.0.sbsb.F, N.sub.1.sbsb.F, N.sub.2.sbsb.F and N.sub.3.sbsb.F represent refractive index distribution coefficients for the F-line, the reference symbols N.sub.0.sbsb.C, N.sub.1.sbsb.C, N.sub.2.sbsb.C and N.sub.3.sbsb.C designate refractive index distribution coefficients for the C-line, and the reference symbols .nu..sub.0.sbsb.d and .nu..sub.1.sbsb.d denote Abbe's numbers.