JANUARY, 1936

Pressure Effect on Sensitivity of Different Photographic FilmsNY TSI-ZM AND LUi TA-YUAN, Institute of Physics, National Academy of Peiping

(Received August 12, 1935)

The effect of pressure on photographic sensitivity isstudied with the monochromatic radiations of a quartzmercury arc for four different films of Eastman KodakCompany; namely, Kodalith film, motion picture positivefilm, commercial film, and portrait film. The quantityE/EC, where E is the illumination actually used when theemulsion is under pressure, and E the illumination whichwould be required to produce the same optical density

when the emulsion is under no pressure, is a function ofpressure only and, for pressures greater than 250 kg/cm2,E/E is a linear function of the pressure. The variation ofE/Ec with the wave-length of the radiations is very similarto that of the contrast for all the films studied. It is pointedout that the pressure effect on photographic sensitivitymay be closely related to the absorption properties of theemulsion.

INTRODUCTION

THE application of pressure to a photographicemulsion during exposure prevents the

formation of latent image to a great extent andthus reduces its sensitivity.' To characterize thiseffect, one of us2 has introduced a quantityE/Ee, e being the illumination which wouldproduce, on an emulsion without being subjectto any pressure, the same optical density as thatproduced by illumination E on the same emulsionunder a pressure p with equal time of exposure.E is always less than E and may be called inphotography the effective illumination of Eunder pressure p. The quantity E/BC is a functionof pressure only, and for p greater than acertain value, the ratio E/E is a linear functionof the pressure.

It has also been shown3 that the effect ofpressure on photographic sensitivity varies verymuch with the wave-length of the radiation used.It diminishes, in general, with the wave-length.For the yellow or green light a pressure of lessthan one hundred kilograms per square centi-meter is sufficient to produce a marked effect,while for the radiation 3131A, we have to applymore than one thousand kilograms per squarecentimeter in order to make the effect justobservable.

The pressure effect on photographic sensitivity

'P. E. Poindexter, J. Opt. Soc. Am. 2, 59 (1931).2 Ny Tsi-Z6 and Tsien Ling-Chao, Comptes rendus 194,

1644 (1932); Science et industries photographiques (2),4, 1 (1933).

3 Ny Tsi-Z6 and Tsien Ling-Chao, Comptes rendus 196,107 (1933).

differs from one kind of film to another. 4 It isproposed in the present paper to investigatesystematically this effect upon materials differingwidely in characteristics, and to correlate it, ifpossible, with the known properties of thedifferent films, so as to throw some light on thenature of this effect.

EXPERIMENTAL ARRANGEMENT AND METHOD

The experimental arrangement is schemati-cally shown in Fig. 1. The light of a quartzmercury lamp is projected by a quartz condenserC on the slit S of a Leiss monochromator.- Afterentering the slit S, the light is rendered parallelby the spherical mirror M, passes through aCornu prism P at minimum deviation, is re-flected by a Wadsworth plane mirror M, and

URFQ

-1D

FIG. 1

4 Ny Tsi-Z6 and Tsien Ling-Chao, Chinese J. Phys. 1,66 (1934).

5 C. Leiss, Zeits. f. Physik 72, 822 (1931).

26

J. . . A. VOLUME 26

SENSITIVITY OF PHOTOGRAPHIC FILMS

I..

a'

-.5

I ; .z .3 4.Ioj ~ /17 l

Loq E

FIG. 2. d log E and d' log E curves of positive filmunder a pressure of 716 kg/cm 2 for 5791-70A, E/BE= 1.38.

finally converged by a second spherical mirrorM2 on the slit S2. On rotating, as a whole, theprism and the mirror M which remains alwaysparallel to the base of the prism, any line of themercury lamp can be brought before the slit S2.The beam of monochromatic light through S2 isthen totally reflected upwards by a quartzprism T.

The photographic film was placed on top of aquartz plate Q with its sensitive layer next tothe plate. The pressure was applied by means ofa lever and weights W which forced the wellflattened base of a steel cylinder R against theback of the film F. The light from the slit S2which was about 65 cm from the film wasconfined, by means of the two diaphragms D, toa beam circular in cross section having a diameterof 14 mm on the quartz plate Q while theflattened base of the cylinder had a diameter of5 mm and was approximately concentric withthe beam of light. To avoid reflection and otherpossible effects due to direct contact, a sheet ofblack paper or an exposed and developed filmwas interposed between the base of the metallic

cylinder R and the photographic film underinvestigation.

The experiment was performed on one film,either with the same pressure but differentradiation, or with the same radiation but differ-ent pressures. For a certain radiation and onegiven pressure, five normal exposures of equaltime with different intensities were always made,the intensity of illumination being varied bymeans of screens inserted in the path of light.These screens consisted of exposed and developedphotographic sensitive layer between two quartzplates, and their densities had been previouslycalibrated.

The measurement of the densities at thecenter and the rim of the photographic imageswith a Moll microphotometer permits one totrace the two curves d log E and d' log E inFig. 2, which are parallel to each other. Thetranslation parallel to the axis of abscissa bring-ing about the coincidence of the curve d withthe curve d' measures the quantity log E/E 6 andconsequently the ratio E/E,.

The time of exposure varied from ten secondsto three minutes according to the intensity ofthe different mercury lines and to the sensitivityof the different films.

RESULTS

Four different films of Eastman Kodak Com-pany 6 were used in this experiment. They are:Kodalith film, motion picture positive film,commercial film, and portrait film. They repre-sent a very wide range in speed and grain sizefrequency characteristics. All these films havetheir maximum sensitivity at about 4600A, andthe portrait film has another secondary maximumat 5600A.

The pyro developer (formula D-90) recom-mended by Eastman Kodak Company was used.The temperature of the developer and the timeof development were kept constant throughoutour experiment so that the contrast y of eachfilm for different radiations of the mercury arccan be measured and compared.

The results obtained with these four films for

I These films were supplied to us through the kindnessof Dr. Loyd A. Jones, to whom we express here ourheartiest thanks and appreciation.

.S .6

27

NY TSI-ZE AND L TA-YUAN

FIG. 3. Eastman regular Kodalith film.

TABLE I.

E/EPRESSURE p 57911 5460 4917 4358 4047 3650 3341 3131A

(kg/cm2) 5770

EASTMAN REGULAR KODALITn FILM H AND D SPEED: 10/i =0.525.208 1.11 1.11 1.11 1.32 1.27 1.06 N335 1.15 1.14 1.14 1.36 1.29 1.07 No462 1.18 1.17 1.17 1.38 1.32 1.09 effect716 1.24 1.22 1.22 1.43 1.35 1.12 1.02970 1.29 1.28 1.27 1.47 1.38 1.14 1.02

1224 1.35 1.33 1.32 1.52 1.42 1.17 1.03

EASTMAN CIN, POSITIVE FILM H AND D SPEED: 10/i =50.208 1.23 1.19 1.19 1.19 1.17 1.02 No335 1.28 1.25 1.26 1.25 1.20 1.03 effect462 1.31 1.28 1.28 1.29 1.21 1.05 1.02716 1.38 1.35 1.34 1.34 1.25 1.08 1.04970 1.46 1.41 1.41 1.41 1.28 1.11 1.05

1224 1.53 1.48 1.48 1.47 1.32 1.13 1.07

EASTMAN COMMIIERCIAL FILM H AND D SPEED: 10/i =269.208 1.25 1.23 1.21 1.13 1.06 1.02462 1.33 1.31 1.30 1.22 1.14 1.05 No716 1.40 1.37 1.35 1.28 1.16 1.07 eft970 1.45 1.44 1.39 1.32 1.20 1.09 efec

1224 1.50 1.48 1.44 1.36 1.27 1.11

EASTMAN SUPER-SPEED PORTRAIT FILM H AND D SPEED: 10/i =646.208 1.41 1.41 1.21 1.17 1.09 1.04335 1.54 1.54 1.30 1.24 1.12 1.06462 1.64 1.63 1.38 1.31 1.16 1.08 1.03716 1.76 1.76 1.50 1.40 1.21 1.11 1.04970 1.90 1.90 1.58 1.47 1.27 1.16 1.06

1224 2.02 2.03 1.69 1.57 1.32 1.21 1.08 1.03

different radiations under different pressures aregiven in Table I. With as abscissa and E/Eeas ordinates, we obtain for each film a family ofcurves (Figs. 3-6), which are rectilinear for pgreater than 250 kg/cm2 . The portrait film,which is the fastest among the four films studied,has a greater pressure effect than the others; butthe positive film, of which the H. and D. speedis about five times smaller than that of thecommercial film and a hundred times greaterthan that of the Kodalith film, has an effectnearly equal to these two. It is thereby inferredthat the effect of pressure on the sensitivity isnot simply related to the speed or the grain sizefrequency characteristics of the emulsion. This

/E, - 191-7° AAI S S ,5'I A

t4 1l53 A

L.3 X m 4047 A

Z. 1 r >3 650 A

I.. L. " _ 7$b (dl `,0 l oe)

FIG. 4. Eastman Cin6 positive film.

FIG. 5. Eastman commercial film.

.3 4401 A

345 A

5- M- 13 A 4,/ .03 L ;0 7E E. j s l A' o

FIG. 6. Eastman super-speed portrait film.

is in agreement with the results7 relative to theZeiss-Ikon orthochromatic film and the Agfaultrarapid isochromatic film.

The effect of pressure on photographic sensi-tivity diminishes with the wave-length of theradiation used, except in the case of Kodalithfilm which presents a maximum effect at 4358A.This pecularity of the Kodalith film may beapproached with the fact that this film presents

7 Cf. Ny Tsi-Z6 and Tsien Ling-Chao, Chinese J. Phys.1, 66 (1934). These two films are both very rapid, but theZeiss-Ikon orthochromatic film shows a pressure effectgreater than that of the portrait film, while the Agfaisochrome film shows an effect even smaller than that ofthe Kodalith film.

28

SENSITIVITY OF PHOTOGRAPHIC FILMS

45

3.5

3',1

'.6

'.5

FIG. 7. Eastman regular Kodalith film.

1.3

X.'

I.',

.9

.8

.7

FIG. 8. Eastman Cin6 positive film.

FIG. 1 1.

FIG. 9. Eastman commercial film.

FIG. 10. Eastman super-speed portrait film.

also a maximum contrast in the neighborhoodof 4358A.

To bring out this point more prominent weplot E/Ee against X (Figs. 7-10) for each pressurewith the data given in Table I. Values of gammaof different radiations for various films deter-mined at the same time as E/E 5 from thecharacteristic curves of Fig. 2 are shown inFig. 11.

The E/E-X and y-X curves for each filmare very similar in form. Hence it seems to usthat the variation of pressure effect on sensitivitywith wave-length will be closely related to the

variation of gamma with the wave-length andconsequently to the absorption properties of thephotographic sensitive layer for different radia-tions.

In fact, Fabry and Buisson5 have pointed outthe great absorption of the sensitive layer forthe ultraviolet and established for the contrast:

where m is the absorption coefficient of theemulsion for the radiation considered and m'that of the completely reduced emulsion for thevisible radiations used in the ordinary measure-ment of optical density. It follows that under theaction of ultraviolet, the sensitive layer of aphotographic plate of film is only superficiallyaffected, while for the visible light, the photo-graphic impression is produced throughout thewhole thickness. By the similarity of the generalform of the curves E/E--A and y-X, we aretherefore inclined to admit that the pressurewould affect the internal layers of the emulsionmore than the surface layer. It seems easy toaccount for this experimental result on a crystal-cracking hypothesis of latent image formation;that is, the pressure prevents the vibrationalresponse of the molecules to the radiation,especially the molecules in the deep layers ofthe emulsion.

8 Fabry and Buisson, Rev. d'optique 3, 19 (1924).

!o5;J c 114 F

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