Lens system and imaging apparatus

A lens system for imaging consisting, in order from an object side, of a first lens group that has negative refractive power, a second lens group that has positive refractive power, a third lens group that has positive refractive power, a stop, and a fourth lens group that has positive refractive power,

• wherein the third lens group includes, at a position closest to an image plane side, a cemented lens disposed on the object side of the stop and including an image plane side-surface with a surface that is concave on the object side,
• the fourth lens group includes, at a position closest to the object side, a cemented lens disposed closest to the image plane side of the stop and including an object side surface with a surface that is concave on the image plane side, and
• during focusing from infinity to a closest distance, a distance between the first lens group and the second lens group along an optical axis increases, a distance between the second lens group and the third lens group along the optical axis decreases, and the fourth lens group and the stop disposed on the object side of the fourth lens group are fixed with respect to the image plane, and
• a radius of curvature g3er of the surface that is concave on the object side and the radius of curvature g4fr of the surface that is concave on the image surface side satisfy a following condition:
• 2.5<|g4fr/g3er|≤4.0.