GB2073907A

GB2073907A - Photographic process and apparatus

Info

Publication number: GB2073907A
Application number: GB8108741A
Authority: GB
Original assignee: MAINTIDE Ltd
Current assignee: MAINTIDE Ltd
Priority date: 1980-03-21
Filing date: 1981-03-20
Publication date: 1981-10-21
Also published as: GB2073907B

Abstract

Photoexposure of a direct reversal colour photographic film to an object is effected as three successive exposures through, in any order, red, green and blue filters, and the film is then developed to form a colour print. A camera for the process incorporates the three filters on a rotatable wheel mounted within the camera body and movable from outside the body.

Description

SPECIFICATION Photographic process and apparatus A photograph colour print can be made either in two stages, by exposing a colour film to form a colour negative upon development, followed by printing a colour print from the negative, or in a single stage, by exposing a direct reversal colour photographic film and developing the exposed film to form the print.

Photographic exposures are often conducted through one or more colour filters. In particular studio photography is often conducted through several filters, great care being given to choosing the correct combination of filters. Thus colour correction filters are supplied in six colour ranges (cyan, blue, red, green, yellow and magenta) with up to fifty shades in each range of colour and exposure may be effected through, for instance, six filters simultaneously.

We have now surprisingly found that when forming a colour print by photographically exposing direct reversal colour photographic film to an object and then developing the exposed film to form the print improved photographic results are obtained if the exposure is effected as three successive exposures each through a different filter, the filters used in the successive exposures being, in any order, red, green and blue filters. Successive exposures of other photographic films through different filters have of course been conducted previously for other purposes but so far as we are aware it has been never previously been conducted during exposure of direct reversal colour photographic film to form a print.

As a result of conducting successive exposures in the manner described the definition of the image in the print is clearer than by the traditional methods of exposing direct reversal paper and the colour quality can easily be better than has previously been obtainable.

In order to obtain optimum colour quality it is necessary to use high quality filters and the filters that are referred to in the studio photographic trade as photomechanical filters are best for use in the invention. Selection of the three filters out of the full range of colour correction filters is not satisfactory since the colour density is generally too weak and selection of three filters out of the range known in the studio photographic trade as Trifilters is also generally unsatisfactory as their colour tends to be rather impure. Photomechanical filters have high colour density and purity and are generally filters cut out of the centre of a large filter sheet, so as to avoid impurities near the edges of the sheet. Suitable filters are known by their Wratten numbers and are listed in the Kodak filter catalogue.A suitable red filter is TM25 Kodak catalogue 1 534288.

A suitable blue filter is 47B Kodak catalogue 1496850. A suitable green filter is 58 Kodak catalogue 1496868.

Before conducting the exposure the film must be tested for its colour reproduction qualities in conventional manner and the duration of exposure through each filter necessary to give optimum colour reproduction of a standard object under standard lighting conditions determined. In order to permit very fine control of the intensity of illumination and the duration of exposure through each filter either or both of these are preferably controlled through a computerised control system. A suitable system is the Photoclark HE310 system.

The camera in which the exposures are made can be a standard studio camera adapted by the provision of means for introducing the individual filters in succession.

Preferably the filters are within the camera body, i.e. in the dark chamber, and preferably they are mounted within a filter wheel that can be rotated, so as to bring individual filters into line of exposure, from outside the camera. In order that the camera does not move as a result of this rotation it must not move during the photoexposures and so may be sufficiently heavy to prevent movement or may be securely fixed against movement. A suitable camera is the Photoclark model Autophot 705.

The photographic film can be conventional Kodak direct reversal colour film.

The invention includes not only the method but the apparatus for use in the method.

1. A process in which a direct reversal colour photographic film is photoexposed to an object and is then developed to form a colour print and in which the photoexposure of the object is effected as three successive exposures each through a different filter, the filters used in the successive exposures being, in any order, red, green and blue filters.

2. A process according to claim 1 in which each photoexposure is through a single photomechanical filter.

3. A process according to claim 1 or claim 2 in which the duration of exposure of the film through each filter is selected based on the duration shown to give optimum colour reproduction in that film of a standard object under standard lighting conditions.

4. A process according to any preceding claim in which the filters are mounted within the camera on means for introducing the filters in succession into the line of exposure.

5. A process according to claim 4 in which the filters are mounted within the camera on a wheel that can be rotated from outside the camera, without movement of the camera, so as to bring the individual filters into the line of exposure.

6. A camera having red, green and blue filters mounted within it and means for intro

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Photographic process and apparatus A photograph colour print can be made either in two stages, by exposing a colour film to form a colour negative upon development, followed by printing a colour print from the negative, or in a single stage, by exposing a direct reversal colour photographic film and developing the exposed film to form the print. Photographic exposures are often conducted through one or more colour filters. In particular studio photography is often conducted through several filters, great care being given to choosing the correct combination of filters. Thus colour correction filters are supplied in six colour ranges (cyan, blue, red, green, yellow and magenta) with up to fifty shades in each range of colour and exposure may be effected through, for instance, six filters simultaneously. We have now surprisingly found that when forming a colour print by photographically exposing direct reversal colour photographic film to an object and then developing the exposed film to form the print improved photographic results are obtained if the exposure is effected as three successive exposures each through a different filter, the filters used in the successive exposures being, in any order, red, green and blue filters. Successive exposures of other photographic films through different filters have of course been conducted previously for other purposes but so far as we are aware it has been never previously been conducted during exposure of direct reversal colour photographic film to form a print. As a result of conducting successive exposures in the manner described the definition of the image in the print is clearer than by the traditional methods of exposing direct reversal paper and the colour quality can easily be better than has previously been obtainable. In order to obtain optimum colour quality it is necessary to use high quality filters and the filters that are referred to in the studio photographic trade as photomechanical filters are best for use in the invention. Selection of the three filters out of the full range of colour correction filters is not satisfactory since the colour density is generally too weak and selection of three filters out of the range known in the studio photographic trade as Trifilters is also generally unsatisfactory as their colour tends to be rather impure. Photomechanical filters have high colour density and purity and are generally filters cut out of the centre of a large filter sheet, so as to avoid impurities near the edges of the sheet. Suitable filters are known by their Wratten numbers and are listed in the Kodak filter catalogue.A suitable red filter is TM25 Kodak catalogue 1 534288. A suitable blue filter is 47B Kodak catalogue 1496850. A suitable green filter is 58 Kodak catalogue 1496868. Before conducting the exposure the film must be tested for its colour reproduction qualities in conventional manner and the duration of exposure through each filter necessary to give optimum colour reproduction of a standard object under standard lighting conditions determined. In order to permit very fine control of the intensity of illumination and the duration of exposure through each filter either or both of these are preferably controlled through a computerised control system. A suitable system is the Photoclark HE310 system. The camera in which the exposures are made can be a standard studio camera adapted by the provision of means for introducing the individual filters in succession. Preferably the filters are within the camera body, i.e. in the dark chamber, and preferably they are mounted within a filter wheel that can be rotated, so as to bring individual filters into line of exposure, from outside the camera. In order that the camera does not move as a result of this rotation it must not move during the photoexposures and so may be sufficiently heavy to prevent movement or may be securely fixed against movement. A suitable camera is the Photoclark model Autophot 705. The photographic film can be conventional Kodak direct reversal colour film. The invention includes not only the method but the apparatus for use in the method. CLAIMS

6. A camera having red, green and blue filters mounted within it and means for intro ducing the filters in succession into the line of exposure.

7. A camera according to claim 6 in which the filters are mounted on a wheel that can be rotated from outside the camera, without mcvement of the camera, so as to bring the individual filters into the line of exposure.

8. A camera according to claim 6 or claim 7 in which the filters are photomechanical filters.

9. A camera according to any of ciaims 6 to 8 loaded with direct reversal colour photographic film.