Several factors determine the performance level of the instrument.
Instrumental factors governing the throughput are the transmission characteristics of the fiber optics, quality of the prism mountings, optical axis alignment of the fiber at the telescope and in the spectrograph, focal ratio degradation within the fibers, grating efficiency, camera throughput and vignetting, presence of central obstructions, detector efficiency, and quality of the coatings on the various optical components within the spectrograph and telescope. Environmental factors that can impact the peak instrumental performance include seeing, image quality and focus, atmospheric transparency, and external stresses on the fiber cable. Additional factors that can vary efficiency between target fields arise from astrometry errors and fiber positioning errors.