Embodiments of the invention include an optical system and an optical system module, coupled to a distal end of a fluorescence emission endoscope apparatus, an optical waveguide-based fluorescence emission endoscopy system, and a method for remotely-controlled, multi-magnification imaging of a target or fluorescence emission collection from a target with a fluorescence emission endoscope apparatus. An exemplary system includes an objective lens disposed in a distal end of an endoscope apparatus. The lens is adapted to transmit both a visible target illumination and a fluorescence-emission-inducing target illumination as well as fluorescence-emission and visible light from the target. The system can thus simultaneously provide low magnification, large field of view imaging and high magnification, high-resolution multiphoton imaging with a single lens system.