The present invention provides variable spot size illuminators that provide a light spot on a treatment plane by utilizing a zoom lens to direct light received from an image of a light source formed on an intermediate image plane onto the treatment plane. The zoom lens allows varying the size of the treatment spot while ensuring that the treatment spot exhibits parfocality. An illuminator of the invention can be utilized for performing a number of ophthalmic surgical procedures, such as, photocoagulation, transpupillary thermal therapy, and photodynamic therapy.