NAPM IT3.110 : 0

Foreword
1 Scope
2 Definitions
3 Aperture markings
4 Tolerances for f-numbers for photographic lenses
5 Methods for measuring effective entrance pupil and
    focal length
TABLES
1 F-number series
2 Tolerances of measured f-numbers
FIGURES
1 Focal length of a photographic lens
2 Schematic layout of telecentric projection system
    apparatus
3 Schematic layout of apparatus for measuring the focal
    length (Method 1)
4 Schematic layout of apparatus for measuring the focal
    length (Method 2)

Defines related properties of photographic lenses affecting the illuminance at the center of the image. Specifying all types of lenses in still cameras, with tolerances for stop numbers. Includes entrance pupil, relative aperture, focal length, aperture stop, giving methods for determinations and measurements.