US2592298A - Photographic reversal process using high-intensity flash exposure - Google Patents

Description

' second or less.

Patented Apr. 8, 1 952 UNITED STATES PATENT I OFFICE PHOTOGRAPHIC PROCESS USING HIGH-INTENSITY FLASH EXPOSURE Gerald I. P. Levenson, wealds tone, England, as-

signor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application February 1,1950, Serial No. 141,833. In Great Britain February 14,

2 Claims. (01. 95-5) This invention relates to photographic processes and especially to photographic reversal processes.

In Knott and Stevens U. S. Patent 2,456,953,

Kodatron Speedlamp which provides an extremely high intensity flash 1 of the order of /1o,ooo of a second or less in duration.

For example, two of these lamps, used together and provided with suitable reflectors, were used to illuminate a x 8" document having a clean white background, in an optical printer for which will develop surface latent image but not develop or develop only slightly the first formed internal latent image.

The silver halide emulsion is defined in the .Knott and Stevens patent as being of such a nature that the latent image is formed mostly inside the silver halide grains and relatively little surface latent image is formed. Emulsions of this type are also described in Davey and Knott U. S. application Serial No. 82,914, filed March 22, 1949.

Many emulsions of this type when coated on a support and used to make a direct positive image by the methods described in Knott and Stevens U. S. Patent 2,456,953 by giving an image-wise exposure of the order of /25 of a second or longer followed by a second exposure sufficiently long to obtain good contrast in the reversed image yield an image which is degraded by a comparatively heavy veil and this is particularly undesirable when the emulsion is coated on paper and the resultant light-sensitive material is used for document copying.

It is therefore an object of the present invention to provide a method for making an improved direct positive photographic image. A further object is to provide an improvement in or modification of the invention described in Knott and Stevens 2,456,953.

These objects are accomplished according to the present invention by making the first or image-wise exposure in an emulsion of the internal latent image type as described in the Knott and Stevens patent, of a duration of /1000 of a Such exposure may be made by using a high intensity light equivalent in intensity to a gas discharge lamp, for example, a

making a fullscale reproduction. A light-sensitive material was used containing a layer of emulsion as defined above which gave a reversed image of a gamma of 0.6 and a veil having a 1 reflection density of 0.25 when the-first exposure was about 30 seconds with an ordinary tungsten lamp. When using the two Kodatron lamps according to the invention, the reversed image had a gamma of 1.4 with a veil having a reflection density of 0.05.

The emulsion which I use in the present invention is of the type in which the latent image is formed mostly or entirely internally in the grains; that is to say an emulsion only few or none of whose exposed grains are developable to silver by a developing solution which cannot act as a developer for latent image inside the grainssuch a solution is Formula I (below). Whether an emulsion is of this type for the purpose of this invention 'can'be ascertained by treating it (after exposure) in developers of the kind given in Formulae I, II'and III below. It is of the type defined if it will develop in those of Formula II but will not develop or'will develop only slightly in Formula III and in Formula I.

The developer formulae above referred to are:

FORMULA I Surface developer p-I-Iydroxyphenylglycine grams 10 Sodium carbonate (cryst.) do Water to cc 1,0 0 Development time 4 minutes at 20 C.

FORMULA II "Internal developer.

Hydroquinone grams 15 N-methyl-p-aminophenyl sulphate do 15 Sodium sulphite, anhy do 50 Potassium bromide do 10 Sodium hydroxide do 25 Sodium thiosulphate (cryst.) do 20 Water to cc 1,000

Development time 3 minutes at 20 C.

Development time 4 minutes at 20 C.

As measured according to normal photographic testing technique, when a test layer of the emulsion is coated on a transparent support, for example glass, and the layer is exposed for a fixed time between ,4 and one second to a light intensity scale which gives upon full development at 20 C. in the internal developer Formula II a transmitted density which is the arithmetic means of the densities obtainable by varying only said intensity, the transmitted density so obtained is at least five times the transmitted density obtained when an identical test layer of the emulsion is exposed for the same length of time to light of the same intensity and .fully developed at 20 C. Formula I or preferably Formula III.

A further advantage of the use of an exposure of extremely brief duration is that loss of definition due to vibration in the camera is avoided, so that the camera may be made of a lighter construction than has hitherto been found necessary.

It will be understood that my invention is to be taken as limited only by the scope of the appended claims.

I claim:

l. The method of producing a reversed photographic image, which comprises exposing to a lighted object or image, for a period not exceeding 0.001 second, with a high intensity light equal in intensity to a gas discharge lamp, a layer of a light-sensitive silver halide emulsion, a test layer of which, when coated on a support and the layer exposed to a light intensity scale for a fixed time between and one second, gives upon full development at 20 C. in the following developer (II):

Hydroquinone grams l5 N-methyl-p-aminophenol sulfate ..do 15 in the surface developer 4 Sodium sulfite, anhydrous grams Potassium bromide do 10 Sodium hydroxide do 25 Sodium thiosulfate, crystals -do 20 Water to cc-.. 1,000

a transmitted density which is the arithmetic mean of the minimum and maximum densities obtainable by varying only said intensity, which density is at least five times the transmitted density obtained when an identical test layer of the emulsion is exposed for the same length of time to light of the same intensity and fully developed at 20 C. in the following developer (I):

'p-Hydroxyphenyl glycin grams 10 Sodium carbonate, crystals do Water to cc 1,000

soaking the exposed emulsion layer in a photographic developer which develops substantially only the latent image which is developable by the following developer (III):

Hydroquinone grams l2 N-methyl-p-aminophenol sulfate do 3 Sodium sulfite, crystals do 90 Potassium bromide do 4 Sodium carbonate, crystals do Water to cc 1,000

for a length of time sumcient to give no more than a negligible development of the latent image but sufficient to render the emulsion layer capable of forming surface latent image which is developable by the aforesaid developer (III), and then subjecting the emulsion layer to a uniform exposure to light to produce latent image, some of Which is developable by the aforesaid developer (III), and then developing the emulsion layer in a developer which develops the latent image which is developable by said developer (III) and gives no more than a negligible development of the negative latent image formed by the original exposure compared with the positive image which is developed.

2. The method of claim 1, in which the high intensity light is a high intensity gas discharge flash.

GERALD I. P. LEVENSON.

No references cited.

Claims (1)

1. THE METHOD OF PRODUCING A REVERSED PHOTOGRAPHIC IMAGE, WHICH COMPRISES EXPOSING TO A LIGHTED OBJECT OR IMAGE, FOR A PERIOD NOT EXCEEDING 0.001 SECOND, WITH A HIGH INTENSITY LIGHT EQUAL IN INTENSITY TO A GAS DISCHARGE LAMP, A LAYER OF A LIGHT-SENSITIVE SILVER HALIDE EMULSION, A TEST LAYER OF WHICH, WHEN COATED ON A SUPPORT AND THE LAYER EXPOSED TO A LIGHT INTENSITY SCALE FOR A FIXED TIME BETWEEN 1/100 AND ONE SECOND, GIVES UPON FULL DEVELOPMENT AT 20* C. IN THE FOLLOWING DEVELOPER (II):