ABSTRACT
The maximum aperture of a lens is always quoted as one of its prime specifications. The focal length and field angle of view (FOV) of a lens largely determine the useful maximum aperture attainable at reasonable cost. Large apertures allow recording in dim light with fast film without supplementary illumination or the recording of fast transient events such as oscilloscope traces with high writing speed. Large-aperture lenses are in general much bulkier, heavier and more costly than counterparts with only 0.5 or 1 stop less aperture. A problem common with large-aperture lenses, more so when FOV is increased, is that of vignetting, and the peripheral image can be significantly less bright than on-axis. A special application for large-aperture, high-performance lenses is that of transferring the image output of an image intensifier coupled to an X-ray fluoroscope on to film or video with minimal light losses, especially those of vignetting.
