PHOTOMETRY

Abstract: A photometer head (2) having a base plate (4) on which are mounted two housing portions (6, 8). Wall sections of the housing portions (6, 8) are spaced apart to form a gap (10) therebetween, the base plate (4) forming a bottom of the gap (10). A light source (14) and light-sensitive device (16) are also provided.

Description: PHOTOMETRY The present invention relates to photometry. It relates in particular to densitometry for measuring optical densities of, for example, photographic materials. In photographic processing apparatus, such as used for X—ray materials, it is necessary to monitor the activity of processing solutions and if necessary replenish such solutions. A well-known technique for performing such a monitoring operation is to produce a process control strip of photographic material on which a series of graduated exposures have been produced, Known as step wedges. The densities of such wedges are then measured in a densitometer so as to provide an indication of the state of the processing solutions in which the strip has been processed, and hence an indication of the need for replenishment. US-A-3623418 shows a densitometer having a measuring light source and photocell accommodated in different housing portions between which a strip is moved from a supply spool to a take-up spool. The arrangement shown in US-A-3623418 requires that the strip be of sufficient length to enable the use of the spools. If, however, the strip were very short, for example about 15 cm long, it would not be possible to use such an arrangement. In accordance with the present invention there is provided a photometer head comprising a base plate on which are mounted two housing portions, a wall section of one housing portion being spaced from a wall section of the other housing portion so as to form a gap therebetween and the base plate forming a bottom of said gap, there being provided a light source and light—sensitive means. In accordance with the present invention there is also provided a densitometer comprising a photometer head according to the present invention and signal receiving means for manipulating signals received from the light—sensitive means. In accordance with the present invention there is further provided a photographic processing apparatus comprising a photometer head according to the present invention, signal receiving means for manipulating signals received from the light—sensitive means and means for controlling replenishment of a processing solution in the apparatus. In accordance with the present invention there is still further provided a method of measuring the density of a strip of material which comprises passing the strip through the gap of a photometer head according to the present invention. In accordance with the present invention there is still further provided a method of controlling replenishment of a processing solution in a photographic process comprising measuring the density of a strip of photographic material according to the method set out in the immediately preceding paragraph and replenishing the solution in accordance with the information obtained from such density measurement. The present invention will now be described, by way of example, with reference to the single Figure of the accompanying drawing which is a perspective view of a photometer head of the present invention, with a strip of material to be measured being indicated by broken lines. The following description is directed in particular to photographic material. It is emphasised, however, that the apparatus and method are also applicable to other suitable materials. Furthermore, the description is directed to optical density measurements, whereas use of the photometer head in the measurement of other optical characteristics is also contemplated. A photometer head 2 is provided with a base plate 4 on which are mounted housing portions 6 and 8. The housing portions 6 and 8 are spaced from each other to form a gap 10 which has a tapered entry portion 12 at one end of the head 2. In housing portion 6 is provided a light source, such as one or more ED's (light—emitting diodes) or one or more incandescent lamps, which is shown in a representative manner by the numeral 14. In housing portion 8 is provided a light-sensitive device, such as one or more photodiodes, which is shown in a representative manner by the numeral 16. The light source 14 and light—sensitive device 16 are optically aligned with one another. The light—sensitive device 16 is preferably resiliently urged by springs (not shown) towards the light source 14. If desired, the light source 14 could be similarly resiliently urged. This has the effect of resiliently positioning a strip of material passing through the gap 10. As an alternative to the light—sensitive device 16 and light source 14 being resiliently urged, they can be in fixed positions and plush provided along one or both opposing edges of the gap 10, so as to provide for resiliently positioning a strip of material passing through the gap 10. In operation of the device a strip 18 of film to be measured is moved through the gap 10 in the direction of arrow A with its lower (as viewed in the Figure) longitudinal edge abutted against the upper (as viewed in the Figure) surface of the base plate 4. The tapered entry portion 12 is to facilitate moving the strip 18 into the gap 10. Movement of the strip 18 between the light source 14 and light—sensitive device 16 modifies the light received by the light-sensitive device 16 in accordance with the density of the strip 18. Signals representative of the density are produced and passed by means of connection 20 to a computer (not shown) for required manipulation. Such manipulation of the signals by a computer may include producing a plot of density against time. In the case of a step wedge, this would be in a series of steps. Each step on the step wedge could have a marker, perhaps sensed by a further light—sensitive device, to indicate to the computer which part of the step wedge is being measured. The computer could convert the plot of density against time into a plot of density against log E (exposure). Control parameters such as minimum density, maximum density, slope and speed could be calculated in the normal manner. The device is particularly useful as a desk-top unit for measuring the film densities of step wedges provided on process control strips. As the step wedges are always arranged at the same distance from one of the longitudinal edges of the process control strips used, the photometer head 2 Is so arranged that during use the longitudinal edge of the sample adjacent to the step wedge contacts the upper surface of the base plate 4. Compared to the arrangement in a conventional densitometer having a large table surface and a lowerable photometer head, the arrangement provided by the photometer head 2 offers the advantage that the individual step fields need not carefully be aligned with respect to the photometer head 2 so as to avoid measuring errors; it will be sufficient to move the sample by hand in correct orientation (standing upright) through the photometer head 2. If there is provided means for resiliently positioning the strip 18, a one—hand measuring operation is possible. It is emphasised, however, that the strip could be driven through the gap 10 by a motor—driven arrangement (not shown). The apparatus described above could be used for black-and— hite and/or colour measurements by utilising an appropriate light source, such as, for example, appropriately coloured LED's, or incandescent lamps with one or more suitable filters. As an alternative to the light source 14 and light—sensitive device 16 facing each other as described above, for measuring light transmittance, they could in fact be adjacent one another on the same side of the gap 10 for measurement of light reflection. The densitometer described above can be utilised in a photographic processing apparatus for monitoring the state of the processing solutions and indicating whether their replenishment is necessary.

Claims: CLAIMS 1. A photometer head comprising a base plate on which are mounted two housing portions, a wall section of one housing portion being spaced from 5 a wall section of the other housing portion so as to form a gap therebetween and the base plate forming a bottom of said gap, there being provided a light source and light—sensitive means. 2. A photometer head according to claim 1 ° wherein the light source is mounted in one of the housing portions and the light—sensitive means is mounted in the other of the housing portions. 3. A photometer head according to claim 1 wherein the light source and light—sensitive means 5 are mounted in the same housing portion. 4. A photometer head according to claim 1, 2 or 3 wherein at least one of the light source and the light—sensitive means is resiliently urged toward said gap. 0 5. A photometer head according to claim 4 wherein the light source and/or light—sensitive means are or is resiliently urged by one or more springs. 6. A photometer head according to claim 1, 2 or 3 comprising a plush mounted on one or both 5 sides of said gap for resiliently positioning a strip of material passed therebetween. 7. A photometer head according to any one of the preceding claims wherein an entry end of said gap is of a tapered configuration. ° 8. A photometer head according to any one of the preceding claims wherein the light source comprises one or more light—emitting diodes. 9. A photometer head according to any one of claims 1 to 7 wherein the light source comprises 5 one or more incandescent lamps. 10. A photometer head according to claim 9 wherein said lamp or lamps is or are provided with one or more suitable filters. 11. A photometer head according to any one of the preceding claims wherein the light—sensitive means comprises one or more photodiodes. 12. A photometer head according to any one of the preceding claims further comprising drive means for moving a strip of material through said gap. 13. A densitometer comprising a photometer head according to any one of claims 1 to 12 and signal receiving means for manipulating signals received from the light—sensitive means. 14. A densitometer according to claim 13 wherein the signal receiving means comprises a computer. 15. A photographic processing apparatus comprising a photometer head according to any one of claims 1 to 12, signal receiving means for manipulating signals received from the light—sensitive means and means for controlling replenishment of a processing solution in the apparatus. 16. A method of measuring the density of a strip of material which comprises passing the strip through the gap of a photometer head according to any one of claims 1 to 10. 17. A method of controlling replenishment of a processing solution in a photographic process comprising measuring the density of a strip of photographic material according to the method of claim 15 or 16 and replenishing the solution in accordance with the information obtained from such density measurement.

Inventors: GREEN ANDREW, GREEN, ANDREW
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1988
Main classification: G03D3
IPC codes: G01N21, G03D3