A rear conversion lens, which may include a plurality of lenses may be disposed at a side of master lenses facing an image side for varying a focal length, and may include: a first lens having a positive refractive power; a second lens having a biconcave shape; a third lens having a positive refractive power; a fourth lens having a positive refractive power; and a fifth lens having a negative refractive power. The first to fifth lenses may be sequentially arranged in a direction from an object side to the image side.