Magnification changing lens
AssigneeCanon Kabushiki Kaisha
InventorsHiroki Nakayama, Keiji Ikemori
Life of this patent
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Abstract
This specification discloses a magnification changing lens which has, in succession from the object side, a first lens unit of negative refractive power, a second lens unit of positive refractive power, a third lens unit of negative refractive power and a fourth lens unit of positive or negative refractive power and in which at least the second and third lens unit are moved toward the object side to thereby accomplish the magnification change from the wide angle end to the telephoto end. This magnification changing lens particularly satisfies the following condition: 0.13<bf.multidot.min/fw<0.7, where bf.multidot.min is the shortest distance of the back focus in the whole magnification change range and fw is the focal length of the entire system at the wide angle end.
Claims28
A magnification changing lens comprising in succession from an object side:
- a first lens unit having a negative refractive power;
- a second lens unit having a positive refractive power;
- a third lens unit having a negative refractive power;
- and
- the last lens unit;
- wherein said second lens unit and said third lens unit are moved toward the object side during magnification change from wide angle end to telephoto end, and unit spacing between said first lens unit and said second lens unit and unit spacing between said second lens unit and said third lens unit at the telephoto end are smaller and unit spacing between said third lens unit and said last lens unit at the telephoto end is greater than at the wide angle end.
A magnification changing lens comprising in succession from an object side:
- a first lens unit having a negative refractive power;
- a second lens unit having a positive refractive power;
- a third lens unit having a negative refractive power;
- and
- the last lens unit;
- wherein a magnification change from wide angle end to telephoto end is accomplished by moving at least said second lens unit and said third lens unit toward the object side, and when the shortest distance of a back focus in the whole magnification change range is bf.multidot.min and focal length of the entire system at the wide angle end is fw, following condition is satisfied:
- 0.13<bf.multidot.min/fw<0.7.
Dependencies are inferred from the claim text.