BS ISO 6:1993 download free.1993 Photography — Black-and-white pictorial still camera negative film/process systems — Determination of ISO speed.
Introduction
Black-and-white films will generally provide excellent results in several different developers and processing conditions. At the same time, it is realized that the speed of a film depends on the process used. Therefore, BS ISO 6 specifies a method for determining the photographic speed of filmlprocess combinations. This means a particular film may have several ISO speeds associated with it depending on the processes used. For this reason, it is important that manufacturers indicate the processing conditions for which ISO speed values are quoted.
BS ISO 6 recognizes that black-and-white films do not generally have a unique speed if several different processes are recommended. This conflicts with the tradition of associating a specific speed value with a particular product. In the future, the process used for determining speed values should be unequivocally described to avoid misinterpretation. Since users often do not know how these films will be processed. manufacturers have an obligation to provide a speed value for this situation which will ensure good results. Usually they will take advantage of the overexposure tonal latitude of the film and give it a conservative speed value to protect users from underexposure effects in case the film is put through a process which yields low speed.
It is recognized that the speed at which a film can be exposed is dependent on the extent of development, scene luminance range, subject matter, printing paper, etc. BS ISO 6 specifies that film/process speed is determined when the film is processed to obtain a specified contrast level. The relative ISO speed ranking of various films in different process systems will generally differ. The ISO speeds will provide correct exposures for average scenes with exposure meters conforming to ISO 2720 or ISO 2721 when the film is processed as specified in this International Standard.
1 Scope
BS ISO 6 specifies the method for determining the ISO speed of black-and-white negative camera films used for pictorial still photography.
BS ISO 6 applies to films processed in conventional chemicals and equipment. but also to those processed using special procedures such as those involving activators or heat for development.
BS ISO 6 does not apply to motion-picture, aerial photography, graphic arts, radiographic or micrographic applications, nor to negatives produced in diffusion transfer systems.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of BS ISO 6. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of JEC and ISO maintain registers of currently valid International Standards.
ISO 5-2:1991, Photography — Density measurements — Part 2: Geometric conditions for transmission density.
ISO 5-3:1984, Photography — Density measurements — Part 3: Spectral conditions. ISO 7589:1984, Photography — Ilium inants for sensilometry — Specifications for daylight and incandescent tungsten.
3 Definitions
For the purposes of this International Standard, the following definitions apply.
exposure, H
the time integral of illuminance on the film, measured in lux seconds
amounts of exposure are often expressed in logarithmic terms (1og1011)
3.2
speed
a quantitative measure of the response of the photographic material to radiant energy for the specified conditions of exposure, processing and image measurement
4 Sampling and storage
In determining the ISO speed of a product, it is important that the evaluated samples yield the average results obtained by users. This will require evaluating several different batches periodically under the conditions specified in BS ISO 6. Prior to evaluation, the samples shall he stored according to the manufacturers’ recommendations for a length of time to simulate the average age at which the product is normally used. Several independent evaluations shall be made to ensure the proper calibration of equipment and processes. The basic objective in selecting and storing samples as described above is to ensure the film characteristics are representative of those obtained by a photographer at the time of use.
If stepped increments are used, the
base 10 logarithm of the exposure increment shall not be greater than 0,20. The width and length of a single step shall be adequate to obtain a uniform density within the reading aperture specified for den sitom etry.
If a continuous variable modulator is used, the base 10 logarithm of the change in exposure with distance along the test strip shall be uniform and not be greater than 0,04 per millimetre.
5.3.6 Exposure time
The exposure time shall be between 5 s and 1/1 000 s corresponding to the usage practice for the particular film tested. Since the speed of film is dependent on exposure time because of reciprocity law failure, the exposure time used for determining ISO speed should be specified in use instructions.
5.4 Processing
5.4.1 conditioning of specimens In the time interval between exposure and processing, the specimens shall be kept at 23 °C ± 2 °C and at a relative humidity
of (50 ± 5) %. The processing shall be completed in not less than 5 days and not more than 10 days after exposure for general-purpose films, and not less than 4 hours and not more than 7 days after exposure for professional films.
5.4.2 Processing specifications
The only processing specification required in BS ISO 6 is that the density difference between points m and n shall be 0,80 (see 5.6.3 and Figure 1). No additional processing specifications are included in recognition of the wide range of chemicals and equipment used in processing black-and-white films. ISO speeds provided by film manufacturers generally apply to films when they are processed in accordance with their recommendations to produce the photographic characteristics specified for the process.
Process information shall be available from film manufacturers or others who quote ISO speed. This shall specify the chemicals, time, temperatures, agitation equipment and procedure used for each of the processing steps and any additional information required to obtain the sensitometric results described.
The values for speed obtained using various processing procedures can differ significantly. Although different speeds for a particular film can be achieved by varying the process, other sensitometric and physical changes can also accompany the speed changes. Generally, processes which yield higher ISO speed will also increase the graininess of the negative and the final print.
Since ISO speed is dependent on the exposing and processing conditions, these should be indicated when quoting ISO speed values.
6.3 Accuracy
The calibration of the equipment and processes involved in determining film speed shall be adequate to ensure that the error in log10 11m is less than 0,05.
7 Product marking and labelling
Speed of a product, determined in accordance with this International Standard and expressed on the scales of Table 1, may be designated ISO speed and denoted in one of the following forms:
a) by its arithmetic speed, e.g. ISO 100;
b) by its logarithmic speed, e.g. ISO 210;
c) by both its arithmetic and its logarithmic
speed, e.g. ISO 100/21°.
However, since the speed is dependent on the illuminant, exposure time and process used, these conditions should be clearly indicated whenever practical when quoting values to avoid misinterpretation.