Rear converter lens and imaging apparatus

An optical system that has a negative refractive power and is mounted on an image side of a master lens so as to make a focal length of a whole system including the master lens larger than a focal length of the master lens alone, the optical system consisting of, in order from an object side:

• a first lens group that has a positive refractive power;
• a second lens group that has a negative refractive power;
• and
• a third lens group that has a positive refractive power,
• wherein the first lens group consists of a negative lens concave toward the image side and a positive lens convex toward the object side in order from the object side,
• wherein the second lens group consists of a cemented lens in which a negative lens concave toward the image side, a positive lens convex toward both sides, and a negative lens concave toward the object side are cemented in order from the object side,
• wherein the third lens group includes, closest to the object side, a cemented lens in which a positive lens convex toward the object side and a negative lens are cemented in order from the object side, a lens surface closest to an image side of the third lens group has a convex shape toward the image side.