Simple power-variable finder
AssigneeFuji Photo Optical Co., Ltd.
InventorKazunori Ohno
Life of this patent
Estimating the term…
Abstract
A small-size, inexpensive, simple power-variable finder comprises, successively from the object side, a negative first lens group G1, a positive second lens group G2, and a negative third lens group G3. As the second lens group G2 is moved along the optical axis X, zooming is carried out. Field masks M1 to M3 are disposed at predetermined positions. The finder satisfies the following conditional expressions (1) to (3): −1.3<f2/f1<−1.0 (1) 1.6<f3/f1<2.2 (2) −2.4<DT/f1<−1.7 (3) where fi is the focal length of the i-th lens group, and DT is the distance on the optical axis between the surface closest to the object in the first lens group G1 and the surface closest to an eye in the third lens group G3.
Claims10
A power-variable finder comprising, successively from an object side, a first lens group having a negative refracting power, a second lens group, movable on an optical axis, having a positive refracting power, and a third lens group having a negative refracting power;
- said finder satisfying the following conditional expressions (1) to (3):
- −1.3<f2/f1<−1.0 (1)
- 1.6<f3/f1<2.2 (2)
- −2.4<DT/f1<−1.7 (3)
- where
- f1 is the focal length of the first lens group;
- f2 is the focal length of the second lens group;
- f3 is the focal length of the third lens group;
- and
- DT is the distance on the optical axis between the surface closest to the object in the first lens group and the surface closest to an eye in the third lens group, and
- wherein said first lens group consists of a single negative lens having at least one aspheric surface and having a concave surface directed onto the eye side, said second lens group consists of a single biconvex lens having at least one aspheric surface, and said third lens group consists of a single negative lens.
Dependencies are inferred from the claim text.