Wide angle zoom lens of long back focal distance
AssigneeCanon Kabushiki Kaisha
InventorAkihiko Shiraishi
Life of this patent
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Abstract
A wide angle zoom lens of increased back focal distance comprising, from front to rear, a first lens unit of negative power, a second lens unit of positive power, and a third lens unit of positive power, the first and second lens units axially moving in differential relation to effect zooming, while holding the third lens unit stationary, and satisfying the following conditions: 2.0.ltoreq..vertline.f.sub.1 /f.sub.W .vertline..ltoreq.3.2 0.33.ltoreq..vertline.f.sub.1 /f.sub.2 .vertline..ltoreq.0.8 where f.sub.1 and f.sub.2 are the focal lengths of the first and second lens units, respectively, and f.sub.W is the shortest focal length of the entire lens system.
Claims7
A wide angle zoom lens of long back focal distance comprising, from front to rear, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power, said third lens unit remaining stationary during zooming, and said first and said second lens units being axially moved to effect zooming, and satisfying the following conditions:
- 2.0.ltoreq..vertline.f.sub.1 /f.sub.W .vertline..ltoreq.3.2
- 0.33.ltoreq..vertline.f.sub.1 /f.sub.2 .vertline..ltoreq.0.8
- where f.sub.W is the shortest focal length of the entire lens system, f.sub.1 is the focal length of said first lens unit, and f.sub.2 is the focal length of said second lens unit.
A wide angle zoom lens of long back focal distance comprising, from front to rear, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power, said third lens unit remaining stationary during zooming, and said first and said second lens units being axially moved to effect zooming, wherein said second lens unit comprises, from front to rear, a positive lens, a meniscus lens of forward concavity in said second lens unit that has the largest thickness of the lenses of said second lens unit, a negative meniscus lens and a biconvex lens, and an aperture stop is positioned adjacent said positive lens in said second lens unit.
Dependencies are inferred from the claim text.