Magnification-variable optical system, optical apparatus, and method for manufacturing magnification-variable optical system

A magnification-variable optical system comprising:

• a first lens group having negative refractive power and including, sequentially from an object side, a negative lens, a negative lens, a negative lens, and a positive lens;
• and
• a rear group including at least one lens group disposed on an image side of the first lens group, wherein
• a distance between lens groups adjacent to each other changes at magnification change,
• all lens groups move in an optical axis direction at magnification change, and
• the following conditional expressions are satisfied:
• 100.00 mm2<fw×(−f1)/Fnow<165.00 mm2
• N1n≤3
• 100.00°<2ωw
• where
• fw:
• focal length of the magnification-variable optical system in a wide-angle state,
• f1:
• focal length of the first lens group,
• Fnow:
• maximum aperture of the magnification-variable optical system in a state of focusing at infinity in the wide-angle state,
• N1n:
• number of negative lenses included in the first lens group, and
• 2ωw:
• full angle of view of the magnification-variable optical system in the wide-angle state.

A method for manufacturing a magnification-variable optical system including a first lens group and a rear group, the first lens group having negative refractive power and including, sequentially from an object side, a negative lens, a negative lens, a negative lens, and a positive lens, the rear group including at least one lens group disposed on an image side of the first lens group, the method for manufacturing the magnification-variable optical system comprising:

• disposing the lens groups so that a distance between lens groups adjacent to each other changes at magnification change;
• disposing the lens groups so that all lens groups move in an optical axis direction at magnification change;
• and
• further comprising one of the following features A or B,
• the feature A comprising,
• satisfying the following conditional expressions:
• 80.00<v1n
• 1.05<nL2/nL1
• where
• v1n:
• Abbe number of a medium of at least one negative lens included in the first lens group at a d line,
• nL1:
• refractive index of a medium of a lens at a d line, the lens being closest to an object side in the first lens group, and
• nL2:
• refractive index of a medium of another lens at a d line, the lens being second closest to the object side in the first lens group,
• the feature B comprising,
• satisfying the following conditional expressions:
• 100.00 mm2<fw×(−f1)/Fnow<1/65.00 mm2
• N1n≤3
• 100.00° <2ωw
• where
• fw:
• focal length of the magnification-variable optical system in a wide-angle state,
• f1:
• focal length of the first lens group,
• Fnow:
• maximum aperture of the magnification-variable optical system in a state of focusing at infinity in the wide-angle state,
• N1n:
• number of negative lenses included in the first lens group, and
• 2ωw:
• full angle of view of the magnification-variable optical system in the wide-angle state.