An in-line microscope introduces illumination into the system before the objective and aligns it with the optical axis. The "in-line" name actually refers to the type of illumination and is also known by other names such as axial, co-axial, through-the-objective, vertical, and incident brightfield. The clear difference from other types of illumination is that in this case the light is transmitted through the objective. An infinity-corrected system is used for this type of microscope. Since the light between the objective and secondary lens is collimated, the separation between these lenses can be adjusted to accept a beamsplitter that will introduce horizontally aligned input light and redirect it vertically down to the objective. This type of illumination is very efficient for high power objectives that need to evenly illuminate an opaque object, such as a semiconductor wafer. Since this type of system is very sensitive to mounting with objective powers 20X and higher, we recommend using a vibration isolation platform. For proper focusing, a rack and pinion movement is always suggested for the system.