Inner-focus-type lens
AssigneeFuji Photo Optical Co., Ltd.
InventorYou Kitahara
Life of this patent
Estimating the term…
Abstract
An inner-focus-type lens is formed of three lens groups of positive, negative and positive refractive power, respectively, in order from the object side. The first lens group is formed of four lens elements of positive, positive, negative and negative refractive power, in order from the object side. The second lens group has at least one each of a positive lens element and a negative lens element and is moved along the optical axis in order to focus the inner-focus-type lens. The third lens group has a stop and at least one each of a positive lens element and a negative lens element. Preferably, various conditions are satisfied in order to provide a compact lens that has a large back focus and which favorably corrects various aberrations so as to provide a high quality image.
Claims17
An inner-focus-type lens comprising three lens groups of positive, negative and positive refractive power, respectively, in order from the object side, as follows:
- a first lens group formed of four lens elements of positive, positive, negative and negative refractive power, respectively, in order from the object side;
- a second lens group having at least one each of a positive lens element and a negative lens element, said second lens group being moved along the optical axis in order to focus the inner-focus-type lens;
- and
- a third lens group that includes a stop nearest the object side, and at least one each of a positive lens element and a negative lens element;
- wherein the following conditions are satisfied:
- 0.6<f1/f<0.7
- −1.0<f2/f<−0.5
- 0.7<f3/f<1.6
- where
- f1 is the focal length of the first lens group,
- f is the focal length of the inner-focus-type lens when focused at infinity,
- f2 is the focal length of the second lens group, and
- f3 is the focal length of the third lens group.
An inner-focus-type lens comprising three lens groups of positive, negative and positive refractive power, respectively, in order from the object side, as follows:
- a first lens group formed of four lens elements of positive, positive, negative and negative refractive power, respectively, in order from the object side;
- a second lens group having at least one each of a positive lens element and a negative lens element, said second lens group being moved along the optical axis in order to focus the inner-focus-type lens;
- and
- a third lens group that includes a stop nearest the object side, and at least one each of a positive lens element and a negative lens element.
Dependencies are inferred from the claim text.