Zoom lens unit, imaging device, and monitoring video camera
AssigneeRicoh Company, Ltd.
InventorKazuyasu Ohashi
Life of this patent
Estimating the term…
Abstract
A zoom lens unit includes, in order from an object side to an image side, a first lens group having positive refractive power and a focus function, a second lens group having negative refractive power, which moves when changing a magnification, a third lens group which moves when changing a magnification, and a fourth lens group having positive refractive power, which is fixed when changing a magnification, wherein the following condition (1) is fulfilled: |M2W·M3W·M4W|<0.14 (1) where M2W represents an imaging magnification of the second lens group at a wide-angle end, M3W represents an imaging magnification.the third lens group at the wide-angle end, and M4W represents an imaging magnification of the fourth lens group at the wide-angle end.
Claims11
A zoom lens system comprising, in order from an object side to an image side:
- a first lens group having positive refractive power and a focus function;
- a second lens group having negative refractive power, which moves when changing a magnification;
- a third lens group which moves when changing a magnification;
- and
- a fourth lens group having positive refractive power, which is fixed when changing a magnification, wherein
- the following condition (1) is fulfilled:
- |M2W·M3W·M4W|<0.14 (1)
- where M2W represents an imaging magnification of the second lens group at a wide-angle end, M3W represents an imaging magnification of the third lens group at the wide-angle end, and M4W represents an imaging magnification of the fourth lens group at the wide-angle end,
- the fourth lens group includes, in order from the object side, three positive lenses, and
- each of the three positive lenses fulfills the following conditions (7), (8):
- 75 <νd<96 (7)
- θC.A′<0.000667·νd+0.300 (8)
- where vd represents Abbe number of a lens material, and θC,A′ represents a partial dispersion ratio of the lens material, in this case, θC,A′=(nC−nA′)/(nF−nC), and nF, nC, nA′ are refractive indexes relative to F-line, C-line and A′-line of the lens material, respectively.
A zoom lens system comprising, in order from an object side to an image side:
- a first lens group having positive refractive power and a focus function;
- a second lens group having negative refractive power, which moves when changing a magnification;
- a third lens group which moves when changing a magnification;
- and
- a fourth lens group having positive refractive power, which is fixed when changing a magnification, wherein
- the following condition (1) is fulfilled:
- |M2W·M3W·M4W|<0.14 (1)
- where M2W represents an imaging magnification of the second lens group at a wide-angle end, M3W represents an imaging magnification of the third lens group at the wide-angle end, and M4W represents an imaging magnification of the fourth lens group at the wide-angle end, and
- the fourth lens group includes a plurality of positive lenses with each of the positive lenses fulfilling the following conditions (5), (6):
- α>110×10−7/° C. (5)
- dn/dt<−4×10−6/° C. (6)
- where α is a linear expansion coefficient of a lens material in a temperature range including 20° C., and dn/dt represents a temperature coefficient of a relative refractive index of a lens material in a range from 20° C. to 40° C.
Dependencies are inferred from the claim text.