ISO 00005-1:2009 pdf free download – Photography and graphic technology一 Density measurements一 Part 1: Geometry and functional notation.
5 Instrument representation
Every instrument used to perform optical density measurements of a specimen typically has three components:
— an illuminator to project radiant flux onto the specimen,
a reference plane at which the specimen is placed, and
a receiver to measure the radiant flux from the specimen.
These components are shown schematically in Figure 1 for a general instrument. The illuminator consists of a source for providing radiant flux, and a director, which directs the radiant flux from the source onto the reference plane. Likewise, the receiver consists of a collector, which guides the radiant flux from the reference plane to the detector, which is a device that converts radiant flux into a measurable signal. Examples of sources are incandescent and arc lamps, while examples of detectors are photodiodes and photomultiplier tubes. The central axes, marginal rays, and chief rays of the illuminator and receiver are also shown in Figure 1 as dashed, thin, and thick lines, respectively.
The illuminator and receiver are optical systems with aperture and field stops. These stops determine the illuminator and receiver beams, which are the collections of rays that can pass through the systems. The images of the aperture stops as viewed from the reference plane are the pupils. The illuminator axis is the central axis of the illuminator beam, and is usually the optical axis of the illuminator, although it could also be the centroid of the distribution of rays within the beam. The illuminator axis has an angle of illumination with respect to the normal of the reference plane. Likewise, the receiver axis is the central axis of the receiver beam and has an angle of observation (or viewing) with respect to the normal of the reference plane. The intersections of the illuminator and receiver beams with the reference plane are the illuminator and receiver regions, respectively.
7 Description of geometry
The description of the geometry starts with the type of geometry, which applies to both the illuminator and receiver and depends upon their axes. The types of geometry are
— directional,
— annular, and
— hemispherical.
For the directional geometry, the axis has one fixed anormal angle and one fixed azimuthal angle. For the annular geometry, the axis has one fixed anormal angle and all azimuthal angles. For the hemispherical geometry, there is no defined axis. Specific cases of the directional geometry are the circumferential geometry, in which there are more than one discrete fixed azimuthal angles, and the uniplanar geometry, in which the illuminator and receiver axes and the normal to the reference plane are in the same plane.
In many cases, the illuminator and receiver beams can be adequately described in terms of cones. Figure 3 (which is an extension of Figure 2) shows the coordinate system and necessary conventions. The half-angle of a beam is designated ic(using subscripts “i” for incident, “r” for reflected, and “t” for transmitted) and it is the angle from the central axis of the beam to the edge with apex at the centre of the sampling aperture. For the directional geometry, the half-angle is rotationally symmetric about the axis. For the annular geometry, the half-angle is confined to the anormal direction. For the hemispherical geometry, there is no half-angle.