These three early Photomic heads required Nikon F-mount lenses with a meter coupling shoe ("rabbit ears", see above). Rabbit ear lenses required a special mounting procedure. After mounting, the lens aperture ring must be turned back and forth to the smallest aperture (largest f-stop number) and then to the largest aperture (smallest f-stop number) to ensure that the lens and the head couple properly (Nippon Kogaku called it indexing the maximum aperture of the lens—users called it the Nikon Shuffle!) and meter correctly. This system seems unwieldy to today's photographers, but it was second nature to Nikon and Nikkormat camera using photographers of the 1960s and 1970s.