Image-forming lens having four lens elements
AssigneeFuji Photo Optical Co., Ltd.
InventorsHiroshi Yamada, Akiko Nagahara
Life of this patent
Estimating the term…
Abstract
An image-forming lens having four lens elements of refractive power, in order from the object side, of: negative, positive, positive, and negative. By making the distance from image-side surface of the first element to the image-side surface of the second lens element to be greater than or equal to 0.3 f and less than or equal to 1.5 f, where f is the focal length of the image-forming lens, an image-forming lens having an F# of approximately 2.8 and a picture angle of about 60 degrees is obtained. A diaphragm may be positioned such that the distance along the optical axis from the diaphragm to the object side of the fourth lens is less than or equal to the focal length of the image-forming lens.
Claims9
A fixed focal length image-forming retro-focus lens comprising:
- four lens elements, each an individual mass separated by air with no additional lens element between said four lens elements, said four lens elements each having a refractive power and arranged, in order from the object side, as a negative first lens element, a positive second lens element, a positive third lens element, and a negative fourth lens element;
- wherein,
- opposite surfaces of the second lens element have different curvatures and said second lens element is oriented with its stronger curvature surface on the image side;
- opposite surfaces of the third lens element have different curvatures and said third lens element is oriented with its stronger curvature surface on the image side;
- said fourth lens element is a meniscus lens having its convex surface on the image side;
- and
- said negative first lens element is the lens element having refractive power that is positioned nearest the object side of said fixed focal length image-forming retro-focus lens.
Dependencies are inferred from the claim text.