GB2086611A

GB2086611A - Photographic densitometer

Info

Publication number: GB2086611A
Application number: GB8131289A
Authority: GB
Original assignee: Dainippon Screen Manufacturing Co Ltd
Current assignee: Dainippon Screen Manufacturing Co Ltd
Priority date: 1980-10-23
Filing date: 1981-10-16
Publication date: 1982-05-12
Also published as: SE454808B; ES8206851A1; FR2492977B1; GB2086611B; FR2492977A1; JPS5772046A; JPS6317174B2; DE3141665A1; SE8106243L; ES506420A0

Abstract

A photographic densitometer has a converging lens 14 which directs light to an aperture 7 on which the material S being measured is placed, and a photoelectric cell 16 which is placed on or immediately adjacent the material being measured. This arrangement greatly increases the amount of light entering the photoelectric cell, thus increasing the accuracy of the measurements. A colour filter 12 can be mounted between the light source and the aperture and a diffuser e.g. opal glass 9 can be mounted between the aperture and the photoelectric cell. <IMAGE>

Description

SPECIFICATION Photographic densitometer (i) Field of the invention This invention relates to a photographic densitometer.

(ii) Description ofprior art Generally, the densitometer to measure the color density of a photograph and the ink reflection density of a printed matter may be roughly classified into three types: a transparency type, a reflection type and a combined type.

The conventional photographic densitometer consists of a table and a cantilever arm extending over the table. The table has an illuminated plate mounted on the upper surface thereof which is formed with an aperture. Contained in the table below the aperture are a heat ray absorbing filter, a condenser lens and a light source lamp in that order.

The arm has a lens barrel at its end facing the aperture. Also provided in the arm are a prism or a mirror above the lens barrel and, on the side of the prism or the mirror, a photoelectric tube concentric with the color filter. The lens barrel has an opal glass (a milky white light diffusing glass) mounted on the front end and also contains a condenser lens.

The light from the light source lamp is led through the condenser lens, the heat ray absorbing filter and the small opening of the aperture and radiated to the material placed on the illuminated plate. The light that has passed through the material is further led through the opal glass at the front end of the lens barrel, the condenser lens in the barrel, the prism in the arm and the color filter, and then enters the photoelectric cell, which converts the intensity of light into voltage and current. By the converted value of voltage and current or their derived value it is possible to know the color density and the ink reflection density of the material.

However, with the conventional photographic densitometer, the amount of light reaching the photoelectric cell is very small because the parallel light rays that have passed through the condenser lens are led through the small opening of the aperture and radiated to the material and the transmitted, diffused light is further passed through the opal glass, the condenser lens in the lens barrel and the prism of the arm until finally it enters the photoelectric cell. Therefore, an accurate measurement cannot be taken with the conventional device.

When the lamp with a great light intensity is used to make up for the deficiency in the amount of light, it may, however, cause damage to the material.

Especially when the semiconductor elements such as photodiodes or phototransistors are employed in the photoelectricity converting portion of the photoelectric cell, the insufficiency in the amount of light will be an obstacle to the accurate measurement. To converge the diffused light which has been dispersed by the opal glass, various points should be taken into consideration, such as the diffusion rate of the opal glass, the shape of the lens barrel and the degree of finish on the inner surface of the lens barrel. These factors constitute the limitation in manufacturing the photographic densitometer.

Objects of the invention An object of this invention is, therefore, to overcome the above-mentioned drawbacks experienced with the conventional devices.

Another object of this invention is to provide a photographic densitometer which greatly increases the amount of light entering the photoelectric cell even when the conventional lamp is used, thereby enabling a correct density measurement.

A still another object of this invention is to provide a photographic densitometer which is easy to manufacture.

A yet stili another object of this invention is to provide a photographic densitometer which is compact in size.

Summary ofthe invention The photographic densitometer of this invention is characterized in that the material to be measured such as a developed film is placed on the aperture, that the photoelectric cell is placed in contact with the material, and that the light from lamp is converged by the condenser lens disposed in front of the aperture and is passed through the small opening of the aperture to be radiated to the material.

Brief description of the drawings Figure 1 is a vertical cross-sectional view of the main components of conventional photographic densitometer; and Figure 2 is a vertical cross-sectional view of the main components of the photographic densitometer of the present invention.

Detailed description of the preferred embodiments Figure 1 is the vertical cross-sectional view of the main components of the conventional photographic densitometer, which is presented for comparison with the present invention. The conventional photographic densitometer consists of a table 1 and a cantilever arm 2.

The table 1 has an illuminated plate 3 mounted on the upper surface which is fitted with an aperture 7.

Below the aperture 7 are provided a heat ray absorbing filter 6, a condenser lens 5 and a lamp 4 as a light source in that order. Also provided in the table 1 is a fluorescent lamp 17 to facilitate the positioning of the material to be measured.

The arm 2 has a lens barrel 8 at its end so that it vertically extends facing the aperture 7. Provided above the vertical lens barrel 8 is a refrecting prism 11, on the side of which is installed a photoelectric tube 21. Also provided in the arm 2 is a cylinder 13, coaxial with the photoelectric tube 21, which has a plurality of equidistantly spaced color filters 12. The lens barrel 8 has an opal glass 9 at its tip and a condenser lens 10 inside of it.

Figure 2 is the longitudinal cross section of the main components of the photographic densitometer of this invention. This photographic densitometer consists of a table 1 and a cantilever arm 2 extending overthetable 1.

The table 1 has an illuminated plate 3 on its upper surface which has an aperture 7 with a small opening 27 formed at an almost central part thereof.

Below the aperture 7 are provided a condenser lens 14 and a flat reflecting mirror 18 in that order. The reflecting mirror 18 is fixed in the frame at the angle of 45on. On the reflection side of the mirror 18, a color filter 12, a heat ray absorbing filter 6, a condenser lens 5 and a lamp 4 as a light source are provided in that order.

The condenser lens 5 is arranged so that the light source lamp 4 is at the focal point of the lens. The condenser lens 14 is so arranged that when the photoelectric cell 15 is placed in contact with the material S to be measured which is on the illuminated plate 3, the semiconductor photoelectric cell 16 is positioned at the focal point of the lens.

The color filter 12 can be changed by turning the knob 20. That is, several kinds of color filter are attached to the periphery of the disk 22. The knob 20 is secured to the end of a shaft (not shown) of the disk 22 and it is turned until the desired color filter 12 comes in frontofthe mirror 18.

Also provided in the table 1 is a fluorescent lamp 17 which is turned on only to adjust position of the material S placed on the plate 3 so that the part of the material S which is to be measured is aligned with the aperture 7.

The arm 2 has a photoelectric cell 15 attached vertically movable to the front end thereof. The photoelectric cell 15 has at its front end a photoelectric conversion element 16 formed of semiconductors such as photodiode or phototransistor. The arm also has an opal glass 9 in front of the photoelectric conversion element 16. The opal glass may be replaced with other opal member formed of resin. If no opal glass or resin opal member is not provided, the amount of light received by the photoelectric conversion element 16 will be increased.

The arm 2 is provided with a lever 19 to move up and down the photoelectric cell 15. When the lever 19 is rotated downward to the horizontal position as shown by the two-dot chain line, the photoelectric cell 15 is lowered to come into contact with the upper surface of the material S on the illuminated plate 3.

When the photographic density of the material S is to be measured, the lever 19 is first rotated up to the position shown by the solid line to lift the photoelectric cell 15 from the plate 3 and at the same time the fluorescent lamp 17 is lighted. Next, the material S is placed on the plate 3 and then adjusted so that the part of the material S to be measured is aligned immediately above the small opening 27 of the aperture 7. After this, the lever 19 is lowered to the horizontal position shown with the two-dot chain line to cause the photoelectric cell 15 to lower and come into contact with the material S.

The fluorescent lamp 17 is turned offhand the light source lamp 4 is lighted. The light radiated from the lamp 4 passes through the condenser lens 5, the heat ray absorbing filter 6 and the color filter 12 and reaches the reflecting mirror 18, as shown by the arrow. The light then is reflected by the mirror 18 vertically upward until it is converged by the condenser lens 14. The converged light ray passes through the opening 27 of the aperture 7 and reaches the material S.

The light that has passed through the material S futher passes through the opal glass 9. The transmitted light immediately is introduced into the semiconductor photoelectric conversion element 16 of the photoelectric cell 15 where it is converted into voltage or current whose value or derived value is displayed on the indicator not shown.

As explained in the above, since with this invention the photoelectric cell 15 is placed in contact with the material on the aperture 7, the light from the lamp 4 is converged by the condenser lens 14 disposed in front of the aperture 7 and radiated against the material, and since the light transmitted through the material S is introduced through the opal glass 16 into the photoelectric cell 15, the amount of light entering the photoelectric cell 15 is approximately 1000 times greater than that of the conventional photographic densitometer shown in Figure 1. Therefore, with the photographic densitometer of this invention, it is possible to take very accurate measurement as compared with the conventional densitometer.

In addition, since the photographic densitometer of this invention can employ the lamp 4 which radiates a smaller amount of light than that of conventional device, the possibility of damaging the material S is greatly reduced.

Furthermore, since this invention makes it possible to omit the lens barrel 8 and the prism 10 which are used with the conventional devices, the accuracy of measurement is improved and the size of the densitometer as a whole becomes small.

Claims

1. A photographic densitometer, comprising a condenser lens disposed in front of an aperture to converge the light radiated from the light source lamp and a photoelectric converter placed in contact with the material to be measured which is placed on the aperture.

2. A photographic densitometer as set forth in claim 1,wherein a colorfilteris provided between the light source lamp and the aperture.

3. A photographic densitometer as setforth in claim 1, wherein the photoelectric converter has a milky white light diffusing member such as an opal glass or opal resin which is mounted immediately in front of the photoelectric conversion element incorporated in the coverter.

4. A photographic densitometer as set forth in claim 3, wherein the photoelectric converter is mounted vertically movable on the arm extending over the table.

5. A photographic densitometer as set forth in claim 2, wherein the aperture is formed in the illuminated plate on the upper surface of the table and the condenser lens to converge the light from the light source lamp is provided immediately below the aperture.

6. A photographic densitometer substantially as hereinbefore described with reference to and as shown by Figure 2 of the accompanying drawings.