Rear attachment lens and image pickup optical system using the same
AssigneeCanon Kabushiki Kaisha
InventorJunya Ichimura
Life of this patent
Estimating the term…
Abstract
A rear attachment lens according to the aspect of the embodiments is configured to vary a focal length of a system by being attached to an image side of a master lens. The rear attachment lens includes a positive lens arranged closest to the image side in which a lens surface on the image side of the positive lens has a shape convex toward the image side. A focal length of the rear attachment lens, a magnification of the rear attachment lens when attached to the master lens, and a distance from the lens surface on the image side of the positive lens to a rear principal point position of the rear attachment lens when attached to the master lens are appropriately set.
Claims18
A rear attachment lens configured to vary a focal length of a system by being attached to an image side of a attachable to an image side of a master lens to form a system having an increased focal length as compared to a focal length of the master lens, comprising:
- a first positive lens, a first negative lens, a second positive lens, a second negative lens, a third positive lens, and a fourth positive lens arranged closest in order from an object side to the image side,
- wherein the fourth positive lens is arranged closest to the image side,
- wherein a lens surface on the image side of the fourth positive lens has a shape convex toward the image side, and
- wherein the following conditional expression is satisfied:
- |fe|/(fe×(1−βe)+np2)>9,
- where fe represents a focal length of the rear attachment lens, βe represents a magnification of the rear attachment lens when attached to the master lens, and np2 represents a distance from the lens surface on the image side of the fourth positive lens to a rear principal point position of the rear attachment lens when attached to the master lens.
An optical system, comprising:
- a master lens;
- and
- a rear attachment lens configured to vary a focal length of the system by being attached to an image side attachable to an image side of a master lens to form a system having an increased focal length as compared to a focal length of the master lens,
- wherein the rear attachment lens includes a first positive lens, a first negative lens, a second positive lens, a second negative lens, a third positive lens, and a fourth positive lens, arranged closest in order from an object side to the image side,
- wherein a lens surface on the image side of the fourth positive lens has a shape convex toward the image side, and
- wherein the following conditional expression is satisfied:
- |fe/BF|>9,
- where fe represents a focal length of the rear attachment lens, and BF represents a back focus obtained when the rear attachment lens is attached to the master lens.
Dependencies are inferred from the claim text.