At the heart of the modern fluorescence microscope is the reflected light vertical illuminator, which is sandwiched between the observation viewing tubes and the nosepiece carrying the objectives, as illustrated in Figure 6. The illuminator is designed to direct light generated by a high-intensity source (such as an arc-discharge lamp) onto the specimen by first focusing the light through the microscope objective on the lateral specimen focal plane and then using that same objective to capture the light being emitted by the specimen. This type of illumination strategy has several advantages. The microscope objective, which acts first by serving as a well-corrected condenser, next gathers image-forming fluorescence emission for transmission to the eyepieces or camera detection system. As such, the objective is always in correct alignment. Furthermore, most of the excitation light that is scattered or reflected by the specimen (over a 360-degree angle) travels away from the objective front lens element, rather than being projected directly into the glass, as is the case in transmitted fluorescence illumination. Finally, the specimen area being illuminated is restricted to the same area that is being observed, and both illumination and light collection can utilize the full numerical aperture of the objective.