Clifton Tuttle

Experimental Determination of Photographic Density

The fact that various instruments used to determine photographic density yield different results makes it desirable that some one method should be chosen as a standard. This method should produce results which are in keeping with the implications of the Hurter and Driffield definition of photographic density. A study has been made, extending some of the previous work of Tuttle, of the factors responsible for discrepancies between the readings of existing densitometers, and it is concluded that the integrating sphere densitometer is best suited to serve as a standard instrument. The relations existing between its readings and those of other densitometers are given and it it is shown that these relations are valid for a wide range of photographic materials of varying grain size. Toy’s experiments to determine contact printing densities have been repeated with somewhat different results. Certain effects connected with opal densitometers and reported by Bull and Cartwright have been explained. The dependence of photographic density upon orientation of the photographic sample, that is, whether the emulsion side or base side acts as first surface, is shown. Thin metallic films on glass have been suggested to serve as standard densities. It is shown that such films are not suitable for this purpose since their optical properties are quite different from those of the photographic density.

A Recording Physical Densitometer

The principal schemes of photoelectric control which may be applied in the design of a recording physical densitometer are: (1) The direct reading method in which the response of the cell to the light passed by the density is used to move the recording stylus. (2) The constant response method in which the cell indicates the attainment of a predetermined intensity level for the light passed consecutively through the density and a light-modulating system to which the recording stylus is linked. (3a) The intensity matching method in which equality of intensity between two beams, one passing through the density and the other passing through a light-modulating system, is indicated by a single cell exposed alternately to the two beams. (3b) An intensity matching system like (3a) in which equality of intensity of the two beams is indicated by equality of response of two cells one in each beam. The merits and shortcomings of each method are discussed and upon the basis of this discussion the last method (3b) is selected as most nearly fulfilling the specifications of an instrument for the sensitometric department of the Eastman Kodak Company Laboratories. Details of the design of this recording densitometer are explained at some length. The chief items of interest are the beam-splitter, the light-modulator, and the photoelectric control system. A discussion of the performance of this instrument and the variables which influence the performance concludes the paper.

Densitometry and Photographic Printing. Illumination of the Negative and Its Effect upon Density

The nature of the photographic image is such that the value of density is dependent upon the optical system in which the image is employed. Light-scatter by the embedded silver particles has been thoroughly discussed in the literature of photography, but, for the most part only the extreme systems of densitometry—“diffuse” and “specular” have been considered. This paper summarizes the previous conclusions and extends the discussion to certain intermediate optical systems of practical importance.

An Intensity-Scale Sensitometer that Works at Intensity-Time Levels Used in Practical Photography*

A new intensity-scale sensitometer capable of producing a top maximum exposure of about 100 meter-candle-seconds in 1/50 second has been designed and built. The instrument exposes twenty steps, one step at a time. The individual steps are the same size as those produced by the IIb instrument. Every effort has been made to make this sensitometer reproducible to specifications and free from variability with age and use. Instead of the absorbing step tablet ordinarily found in high intensity instruments of the variable-intensity type, this sensitometer produces its exposure series by the interposition of metal diaphragms in an optical system. The size of these diaphragms was determined by computation and the results have been checked experimentally.

A Method for the Measurement of Flatness of Polished Surfaces

An optical method providing for the rapid inspection of extended surfaces is described. Two beams of parallel light are reflected by the sample through a cylindrical lens to form an astigmatic image of the source. If this image is a single line the surface is flat within the accuracy of the instrument. Radii of curvature in tested samples of the order of forty feet can be readily detected. An inspection device for testing glass to be used for photographic purposes is now in service.

An Experimental Investigation of Projection Screen Brightness: I. Choice of the Average Observer * -->

An account is given of an experimental device by means of which an observer is enabled to control and select the brightness at which he wishes pictures to be projected. Data are given for the selections of thirteen individuals on five typical motion picture prints. It is concluded that (1) the average selected brightness is about 30 foot-lamberts; (2) individual observers differ by a factor of 3; (3) a border brightness of 0.05 foot-lambert is preferable to a dark border.

Negative Illumination in Projection Printing

Diffusion in the illumination of a negative to be printed by projection affects the image contrast, the print graininess, the delineation of scratches, and the quantity of light available for printing. These four factors are discussed separately and, from the quantitative results obtained, certain general conclusions regarding the required amount of diffusion for a given type of enlarger are drawn.

Note on the Evaluation of Photographic Speed from Sensitometric Data

A method of ascertaining the gradient speed of a photographic material without the use of special gradient measuring instruments is pointed out. The derived formula shows the relation which must exist between density and log exposure at the value of exposure which is the reciprocal of the speed.

Motion Photomicrographs of the Progress of Development of a Photographic Image

An account was recently published by E. P. Wightman and one of us 1 concerning the development of silver bromide grains. Motion photomicrographs of the progress of development were made at that time by E. P. Wightman, using a four mm. water immersion objective immersed in a drop of dilute developer placed on a single-grain layer plate. The optical resolution obtainable by this method leaves much to be desired, and the presence of so much liquid between the objective and object slide gives rise to difficulties resulting from vibration and striation. Recently, a method has been devised which permits the use of a 1.8 mm, oil immersion objective. The consequent resolution is considerably enhanced and the difficulties of the former method are minimized.