Fixed-focus optical system and imaging apparatus
AssigneeFUJIFILM Corporation
InventorsTaro ASAMI, Takashi KUNUGISE
Life of this patent
Estimating the term…
Abstract
In a fixed-focus optical system, a first negative lens is disposed closest to an object side, the first negative lens being uncemented and concave toward an image side, a stop is disposed closer to the image side, and one or more positive lenses are arranged between the first negative lens and the stop. The fixed-focus optical system includes at least one lens pair including a negative lens that is concave toward the image side and a positive lens that is convex toward the image side, which are continuously arranged in this order from the object side, and satisfies predetermined conditional expressions. In the fixed-focus optical system, the number of positive lenses is 2 or more, and the number of negative lenses is 2 or more and 6 or less.
Claims20
A fixed-focus optical system comprising:
- a first negative lens that is uncemented and concave toward an image side, the first negative lens being disposed closest to an object side;
- a stop disposed closer to the image side than the first negative lens;
- one or more positive lenses disposed between the first negative lens and the stop;
- and
- at least one lens pair, in which a negative lens that is concave toward the image side and a paired positive lens that is convex toward the image side are continuously arranged in order from the object side,
- wherein the paired positive lens may or may not be included in the one or more positive lenses,
- wherein the number of positive lenses provided in the fixed-focus optical system is 2 or more, and the number of negative lenses provided in the fixed-focus optical system is 2 or more and 6 or less, and
- in a case where, among negative lenses arranged closer to the image side than the first negative lens, a negative lens closest to the object side is defined as a second negative lens,
- a focal length of the first negative lens is denoted by fn1,
- a focal length of the second negative lens is denoted by fn2,
- a refractive index of the first negative lens with respect to a d line is denoted by Nn1,
- a refractive index of the second negative lens with respect to the d line is denoted by Nn2,
- an Abbe number of the second negative lens based on the d line is denoted by νn2, and
- among positive lenses arranged closer to the object side than the stop, a focal length of a positive lens having a strongest refractive power is denoted by fpmax,
- Conditional Expressions (1), (2), (3), and (4) are satisfied, which are represented by
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Dependencies are inferred from the claim text.