Distance scale
you may find in the following situations that it is easier to set focus manually for a specific distance:
To use scale: With focus mode set to M, estimate the distance to your subject, and turn focusing ring to align corresponding figure on distance scale with index line.

Infrared index
For proper focus when using infrared films, focus subject as usual and attach a filter, if desired. With focus mode switch at M, turn focusing ring until distance shown opposite the distance index aligns with the small red dot.

Film-to-mount distance
This value is used when determining total film-to-subject distance, as when taking photographs at high magnifications. The distance between the film plane at the rear of the camera and the front surface of the lens mount is 44.6mm.