These LEDs were also used for TTL Electronic Focus assisted manual focus. After lightly pressing the shutter button, the photographer would turn Pentax brand manual focus lenses in the direction of whichever red arrow LED lit until the green LED lit to indicate sharp focus. Again, if both red LEDs lit, the ME F could not determine correct focus. Note that many independent manufacturer K mount lenses focus by turning in the opposite direction of Asahi Optical made lenses and that the focus direction LEDs will point the "wrong" way for them.