Lens system
A lens system includes, in order from an object side, a first lens group with positive refractive power, a second lens group with negative refractive power that moves during zooming, a third lens group with positive refractive power, and a fourth lens group with positive refractive power that moves during zooming and focusing adjustments. The first lens group includes a lens with positive refractive power and an Abbe number vd 1 x that satisfies a following condition (vd 1 x >80). The second lens group includes a lens with positive refractive power and an Abbe number vd 2 x and two lenses with negative refractive power and Abbe numbers vd 2 y and vd 2 z respectively, the Abbe numbers Vd 2 x , Vd 2 y and Vd 2 z satisfying following conditions (vd 2 x , vd 2 y , vd 2 z <23). The third lens group includes a plurality of lenses with positive refractive power, an average vd 3 a of the Abbe numbers of the plurality of lenses with positive refractive power satisfies a following condition (77.5<vd 3 a <82.5), and a sum ndts of thermo-optical coefficients of the plurality of lenses with positive refractive power in a temperature range of 40° C. to 60° C. satisfies a following condition (−12.8×10 −6 <ndts<−2.4×10 −6 ).
1. A lens system comprising, in order from an object side:
a first lens group with positive refractive power;
a second lens group with negative refractive power that moves during zooming;
a third lens group with positive refractive power; and
a fourth lens group with positive refractive power that moves during zooming and focusing adjustments,
wherein the first lens group includes a lens with positive refractive power and an Abbe number vd 1 x that satisfies a following condition,
the second lens group includes a lens with positive refractive power and an Abbe number vd 2 x and two lenses with negative refractive power and Abbe numbers vd 2 y and vd 2 z respectively, the Abbe numbers Vd 2 x , Vd 2 y and Vd 2 z satisfying following conditions, and
the third lens group includes a plurality of lenses with positive refractive power, an average vd 3 a of the Abbe numbers of the plurality of lenses with positive refractive power satisfies a following condition, and a sum ndts of thermo-optical coefficients of the plurality of lenses with positive refractive power in a temperature range of 40° C. to 60° C. satisfies a following condition,
vd 1 x> 80
vd 2 x, vd 2 y, vd 2 z< 23
77.5 <vd 3 a< 82.5
−12.8×10 −6 <ndts<− 2.4×10 −6 .
2. The lens system according to claim 1 ,
wherein the sum ndts of the thermo-optical coefficients of the plurality of lenses with positive refractive power in the third lens group satisfies a condition whereby −8.6×10 −6 <ndts<−2.4×10 −6 .
3. The lens system according to claim 1 ,
wherein the plurality of lenses with positive refractive power in the third lens group include lenses with both positive and negative thermo-optical coefficients.
4. The lens system according to claim 1 ,
wherein the third lens group consists of two lenses with positive refractive power and one lens with negative refractive power.
5. The lens system according to claim 1 ,
wherein the second lens group includes a cemented lens that includes the lens with positive refractive power and one of the two lenses with negative refractive power.
6. The lens system according to claim 1 ,
wherein the Abbe number vd 1 x satisfies a condition whereby vd 1 x >90.
7. The lens system according to claim 1 ,
wherein the first lens group includes a cemented lens includes the lens with positive refractive power and a lens with negative refractive power.
8. The lens system according to claim 1 ,
wherein the fourth lens group consists of a single lens with positive refractive power.
9. An imaging apparatus comprising:
a lens system according to claim 1 ; and
an image pickup element.
10. The lens system according to claim 1 ,
wherein the lens system consists of the first lens group, the second lens group, the third lens group and the fourth lens group.