The attachment lenses for the 12x zoom system are attached to the base of the system tube and are available in various magnifications. The nominal working distance of the zoom system is approximately 90 mm. The lens attachments screw onto the bottom of the zoom system and can extend the working distance to 350 mm or shorten it to 36 mm. The extending lenses (0.75X, 0.5X, and 0.25X) decrease the total magnification and increase the field of view. The shortening lenses (1.5X and 2.0X) increase the magnification and decrease the field of view. As the working distance goes from long to short, the "acquisition NA" of the system increases, resulting in an increase in resolving power.