The 77854 Monochromator Fiber Adapter holds the rectangular end of the "Large Slit" Fiber Bundles at the input of Model MS257™ Oriel^® Monochromators. The fiber replaces the slit. This fiber adapter does not require a fixed slit holder for mounting. It couples directly to the aperture of the monochromator. When used at the input, much of the light from the fiber overfills the grating and is lost. This is especially true for glass bundles. Even so, the simplicity and convenience of this technique ensures its application when there is plenty of light, and stray light is not a major concern. When this isn’t the case, use the 77358 Adapter. When you use the 77854 fiber slit at the output, the bundle accepts all the light, which falls on the "fiber slit." Be sure to choose a matching input fixed slit, or set the variable slit to match the "fiber slit."