ISO 5-2:2009 pdf free download – Photography and graphic technology一 Density measurements一 Part 2: Geometric conditions for transmittance density.
In combinations a) and d) of Figure 2, the diaphragm is part of the receiver, and the illuminator region (i.e. the area over which the specimen is illuminated) shall be larger than the size of the diaphragm. In combinations b) and c) of Figure 2, the diaphragm is part of the illuminator, and the receiver region (i.e. the area over which the specimen is viewed) shall be larger than the size of the diaphragm.
The size and shape of the sampling aperture is not critical
— if no dimension is so large that the influx and efflux geometric conditions vary materially over the sampling aperture, or
— if no dimension is so small that the granularity of the film, the finite specimen thickness, diffraction effects, or the halftone dot structure is significant.
In the case of periodic halftone screens, the diameter of a circular sampling aperture should not be less than 15 times the screen width; it shall not be less than 10 times the screen width that corresponds to the lower limit for the screen ruling for which the instrument is recommended by the manufacturer. The area of noncircular sampling apertures shall not be smaller than that required for circular sampling apertures.
Measurements on areas less than 0,5 mm diameter border on, or involve, micro-densitometry and are subject to special considerations not dealt with in this part of ISO 5. The angle from the centre of the optical component limiting the directional distribution to the edge of the sampling aperture shall not be greater than 1 0 The angle from the centre of the sampling aperture to the edge of the optical component limiting the directional distribution shall not be greater than 10°.
NOTE 2 Density measurements are sensitive to variations in the reflectance factor and surface polish of the diffuser because of the effects on the inter-reflections that occur between it and the specimen.
NOTE 3 Such a distribution has often been produced by the use of a plate of opal glass to diffuse the incident radiant flux, or to integrate the transmitted radiant flux, but the use of opal glass is not required if the specified optical conditions are met by other means.
NOTE 4 Opal glass is a material consisting of very small colourless particles embedded in a clear glass matrix, It is
available in two forms:
— flashed opal, which consists of a thin layer carried by a clear glass substrate, and
— pot opal, which has diffusing particles throughout its entire thickness.
6.4 Directional distribution
6.4.1 General
The ideal angular distribution of radiance from the illuminator (influx) or of responsivity of the receiver (efflux) shall be uniform for angles within the cone defined by the illuminator or receiver axis and half-angle, and zero for angles outside the cone.
The realized angular distribution shall be uniform to within 10 % within the cone and less than 2 % of the maximum of the cone distribution outside the cone.
6.4.2 Determination of illuminator radiance distribution
The illuminator radiance distribution can be determined by placing a receiver having uniform angular response over a conic distribution with a half-angle of 2° at the centre of the sampling aperture. Anormal angles are scanned with the receiver both inside and outside the ideal influx cone, and the signal from the scanned receiver is recorded at each angle. The signal at any angle within the influx cone shall be at least 90 % of the maximum signal recorded. Outside the influx cone, the signal shall be less than 2 % of the maximum signal recorded within the influx cone.