Zoom lens, lens unit, camera and portable information terminal device
AssigneeRicoh Company, Ltd.
InventorKazuyasu Ohashi
Life of this patent
Estimating the term…
Abstract
A third group of lenses is constructed by subsequently arranging those four lenses from an object side to an image side which include a positive lens, a cemented lens of a positive lens and a negative lens, and a positive lens, both of a surface of the third group of the lenses nearest to the object side and a surface of the third group of the lenses nearest to the image side are so aspheric that positive refractive power becomes gradually weaker as a location of the third group of the lenses departs from an optical axis; and a following conditional formula is satisfied: −0.5<(Y′ max/R34I)<0.0 where R34I is a curvature radius of the surface of the third group of the lenses nearest to the image side, and Y′ max is a maximum image height.
Claims54
A zoom lens, comprising:
- a first group of lenses, a second group of lenses and a third group of lenses which are subsequently arranged from an object side to an image side;
- said first group of the lenses having a positive focal length, said second group of the lenses having a negative focal length and said third group of the lenses having a positive focal length;
- and
- an aperture stop provided between said second group of the lenses and said third group of the lenses, wherein
- at least said first group of the lenses and said third group of the lenses are moved in accordance with changes in magnification power as the zoom lens shifts from a wide-angle end to a telephoto end, such that an interval between said first group of the lenses and said second group of the lenses becomes gradually larger and an interval between said second group of the lenses and said third group of the lenses becomes gradually smaller,
- said third group of the lenses is constructed by subsequently arranging those four lenses from the object side to the image side which comprise a positive lens, a cemented lens of a positive lens and a negative lens, and a positive lens,
- both of a surface of said third group of the lenses nearest to the object side and a surface of said third group of the lenses nearest to the image side are so aspheric that positive refractive power becomes gradually weaker as a location of the third group of the lenses departs from an optical axis, and
- a following conditional formula is satisfied:
- −0.5<(Y′ max/R34I)<0.0
- where R34I is a curvature radius of the surface of said third group of the lenses nearest to the image side, and Y′ max is a maximum image height.
A zoom lens, comprising:
- a first group of lenses, a second group of lenses and a third group of lenses which are subsequently arranged from an object side to an image side;
- said first group of the lenses having a positive focal length, said second group of the lenses having a negative focal length and said third group of the lenses having a positive focal length;
- and
- an aperture stop provided between said second group of the lenses and said third group of the lenses, wherein
- at least said first group of the lenses and said third group of the lenses are moved in accordance with changes in magnification power as the zoom lens shifts from a wide-angle end to a telephoto end, such that an interval between said first group of the lenses and said second group of the lenses becomes gradually larger and an interval between said second group of the lenses and said third group of the lenses becomes gradually smaller,
- said second group of the lenses comprises at least two negative lenses and one positive lens, and both of a surface of said second group of the lenses nearest to the object side and a surface of said second group of the lenses nearest to the image side are so aspheric that negative refractive power becomes gradually weaker as a location of the second group of the lenses departs from an optical axis.
Dependencies are inferred from the claim text.