A rear conversion lens includes: a chassis including two opposite ends, the chassis including light-transmitting holes on the ends, respectively; a first coupler configured to detachably couple one of the ends of the chassis with an image field side of an image-pickup lens of a three-chip camera including three first image sensors, the image-pickup lens being designed based on an assumption that the image-pickup lens is to be used with a color-separation prism in combination; a second coupler configured to detachably couple the other end of the chassis with a single-chip color camera including a second image sensor, the second image sensor including an image field larger than an image field of the first image sensors of the three-chip camera; and an optical system including a first lens group, a second lens group, and a third lens group arranged in the chassis in this order from an object side, the first lens group having a negative compound focal length, the second lens group being configured to correct a spherical aberration, the third lens group being configured to form an image.