Compact lens system having a long back focal length and a large relative aperture

Claim 2

A compact lens system having a long back focal length and a large relative aperture comprising a first positive meniscus lens, a second positive meniscus lens, a third negative meniscus lens, a fourth cemented doublet lens component consisting of a negative lens element and a positive lens element, a fifth positive meniscus lens and a sixth positive lens and, satisfying the following conditions f.sub.5 > f.sub.6, f.sub.7 > f.sub.6 1 0.7 < d.sub.8 /d.sub.10 < 0.76 2 0.18f < d 7 +d 8 +d 9 +d 10 < 0.20 f n.sub.1, n.sub.2, n.sub.5 substantially equal to 1.8 3 wherein f represents the focal length of the entire lens system, f 5 , f 6 and f 7 denote focal lengths of the image side lens element of the fourth lens component, the fifth lens and sixth lens, d 7 , d 8 , d 10 designate the thicknesses of the two lens elements of the fourth component and the fifth lens, and n 1 , n 2 and n 5 are refractive indices of the first lens, the second lens and the image side lens element of the fourth lens component.

Claim 3

A compact lens system having a long back focal length and a large relative aperture comprising a first positive meniscus lens, a second positive meniscus lens, a third negative meniscus lens, a fourth cemented doublet lens component consisting of a negative lens element and a positive lens element, a fifth positive meniscus lens and a sixth positive lens and having following numerical data: ______________________________________ r.sub.1 = 0.8121 d.sub.1 = 0.0772 n.sub.1 = 1.8061 ν.sub.1 = 40.9 r.sub.2 = 2.9863 d.sub.2 = 0.0023 r.sub.3 = 0.4397 d.sub.3 = 0.0878 n.sub.2 = 1.8061 ν.sub.2 = 40.9 r.sub.4 = 0.6942 d.sub.4 = 0.0454 r.sub.5 = 0.8082 d.sub.5 = 0.0261 n.sub.3 = 1.78472 ν.sub.3 = 25.7 r.sub.6 = 0.2900 d.sub.6 = 0.3320 r.sub.7 = -0.3007 d.sub.7 = 0.0261 n.sub.4 = 1.78472 ν.sub.4 = 25.7 r.sub.8 = -0.7514 d.sub.8 = 0.0712 n.sub.5 = 1.8061 ν.sub.5 = 40.9 r.sub.9 = -0.4770 d.sub.9 = 0.0019 r.sub.10 = -0.80→ d.sub.10 = 0.0944 n.sub.6 = 1.713 ν.sub.6 = 53.9 r.sub.11 = -0.4347 d.sub.11 = 0.0023 r.sub.12 = 2.0815 d.sub.12 = 0.0616 n.sub.7 = 1.713 ν.sub.7 = 53.9 r.sub.13 = -1.6221 f = 1.0 f.sub.B = 0.7388 F/1.4 ______________________________________ wherein reference symbols r 1 through r 13 represent radii of curvature of respective lens surfaces, d 1 through d 12 denote thicknesses of respective lenses and distances between respective lenses, n 1 through n 7 indicate refractive indices of the lenses and ν 1 through ν 7 designate Abb's number.

Claim 4

A compact lens system having a long back focal length and a large relative aperture comprising a first positive meniscus lens, a second positive meniscus lens, a third negative meniscus lens, a fourth cemented doublet lens component consisting of a negative lens element and a positive lens element, a fifth positive meniscus lens and a sixth positive lens and having following numerical data: ______________________________________ r.sub.1 = 0.8121 d.sub.1 = 0.0772 n.sub.1 = 1.8061 ν.sub.1 = 40.9 r.sub.2 = 2.9863 d.sub.2 = 0.0023 r.sub.3 = 0.4397 d.sub.3 = 0.0878 n.sub.2 = 1.8061 ν.sub.2 = 40.9 r.sub.4 = 0.6942 d.sub.4 = 0.0454 r.sub.5 = 0.8082 d.sub.5 = 0.0261 n.sub.3 = 1.78472 ν.sub.3 = 25.7 r.sub.6 = 0.2900 d.sub.6 = 0.3320 r.sub.7 = -0.3007 d.sub.7 = 0.0261 n.sub.4 = 1.78472 ν.sub.4 = 25.7 r.sub.8 = -0.7514 d.sub.8 = 0.0712 n.sub.5 = 1.8061 ν.sub.5 = 40.9 r.sub.9 = -0.4770 d.sub.9 = 0.0019 r.sub.10 = -0.80→ d.sub.10 = 0.0944 n.sub.6 = 1.713 ν.sub.6 = 53.9 r.sub.11 = -0.4347 d.sub.11 = 0.0023 r.sub.12 = 2.0815 d.sub.12 = 0.0616 n.sub.7 = 1.713 ν.sub.7 = 53.9 r.sub.13 = -1.6221 f = 1.0 f.sub.B = 0.7388 F/1.4 ______________________________________ wherein reference symbols r 1 through r 13 represent radii of curvature of respective lens surfaces, d 1 through d 12 denote thicknesses of respective lenses and distances between respective lenses, n 1 through n 7 indicate refractive indices of the lenses and ν 1 through ν 7 designate Abb's number.

Claim 5

A compact lens system having a long back focal length and a large relative aperture comprising a first positive meniscus lens, a second positive meniscus lens, a third negative meniscus lens, a fourth cemented doublet lens component consisting of a negative lens element and a positive lens element, a fifth positive meniscus lens and a sixth positive lens and having following numerical data: ______________________________________ r.sub.1 = 0.8616 d.sub.1 = 0.0740 n.sub.1 = 1.8061 ν.sub.1 = 40.9 r.sub.2 = 3.0764 d.sub.2 = 0.0023 r.sub.3 = 0.4190 d.sub.3 = 0.0879 n.sub.2 = 1.8061 ν.sub.2 = 40.9 r.sub.4 = 0.6568 d.sub.4 = 0.0454 r.sub.5 = 0.7284 d.sub.5 = 0.0261 n.sub.3 = 1.78472 ν.sub.3 = 25.7 r.sub.6 = 0.2785 d.sub.6 = 0.3447 r.sub.7 = -0.2912 d.sub.7 = 0.0265 n.sub.4 = 1.78472 ν.sub.4 = 25.7 r.sub.8 = -0.7232 d.sub.8 = 0.0676 n.sub.5 = 1.8061 ν.sub.5 = 40.9 r.sub.9 = -0.4339 d.sub.9 = 0.0019 r.sub.10 = -0.7859 d.sub.10 = 0.0919 n.sub.6 = 1.713 ν.sub.6 = 53.9 r.sub.11 = -0.4251 d.sub.11 = 0.0023 r.sub.12 = 1.8635 d.sub.12 = 0.0577 n.sub.7 = 1.713 ν.sub.7 = 53.9 r.sub.13 = -2.2793 f = 1.0 f.sub.B = 0.7391 F/1.4 ______________________________________ wherein reference symbols r 1 through r 13 represent radii of curvature of respective lens surfaces, d 1 through d 12 denote thicknesses of respective lenses and distances between respective lenses, n 1 through n 7 indicate refractive indices of the lenses and ν 1 through ν 7 designate Abbe's number.

Claim 6

A compact lens system having a long back focal length and a large relative aperture comprising a first positive meniscus lens, a second positive meniscus lens, a third negative meniscus lens, a fourth cemented doublet lens component consisting of a negative lens element and a positive lens element, a fifth positive meniscus lens and a sixth positive lens and having following numerical data: ______________________________________ r.sub.1 = 0.8616 d.sub.1 = 0.0740 n.sub.1 = 1.8061 ν.sub.1 = 40.9 r.sub.2 = 3.0764 d.sub.2 = 0.0023 r.sub.3 = 0.4190 d.sub.3 = 0.0879 n.sub.2 = 1.8061 ν.sub.2 = 40.9 r.sub.4 = 0.6568 d.sub.4 = 0.0454 r.sub.5 = 0.7284 d.sub.5 = 0.0261 n.sub.3 = 1.78472 ν.sub.3 = 25.7 r.sub.6 = 0.2785 d.sub.6 = 0.3447 r.sub.7 = -0.2912 d.sub.7 = 0.0265 n.sub.4 = 1.78472 ν.sub.4 = 25.7 r.sub.8 = -0.7232 d.sub.8 = 0.0676 n.sub.5 = 1.8061 ν.sub.5 = 40.9 r.sub.9 = -0.4339 d.sub.9 = 0.0019 r.sub.10 = -0.7859 d.sub.10 = 0.0919 n.sub.6 = 1.713 ν.sub.6 = 53.9 r.sub.11 = -0.4251 d.sub.11 = 0.0023 r.sub.12 = 1.8635 d.sub.12 = 0.0577 n.sub.7 = 1.713 ν.sub.7 = 53.9 r.sub.13 = -2.2793 f = 1.0 f.sub.B = 0.7391 F/1.4 ______________________________________ wherein reference symbols r 1 through r 13 represent radii of curvature of respective lens surfaces, d 1 through d 12 denote thicknesses of respective lenses and distances between respective lenses, n 1 through n 7 indicate refractive indices of the lenses and ν 1 through ν 7 designate Abbe's number.