34^ 



Tables 368 and 369 

 TABLE 368. — Sensitometric Constants of Type Plates and Films 





Material 



Motion picture film: 



Extra fast 



Normal 



Panchromatic 



Positive 



Portrait extra fast 



Portrait normal 



Amateur film 



"Focal plane" plate 



Commercial ordinary 



Commercial orthochromatic 

 Commercial panchromatic. 



Process ordinary 



Process panchromatic 



Lantern slide plate 



.12 



• 03 



• 15 

 .10 

 .10 



.15 

 .05 



.03 



.10 



•03 



0.15 

 .16 

 .16 

 .30 

 .14 



• 15 

 .15 

 .15 

 .17 

 .17 

 .17 



• 30 

 •30 



• 34 



1.4 

 1.6 

 1.6 

 2.7 

 1.4 

 1.8 

 1.8 

 1.8 



2.2 

 2.2 

 2.2 

 30 

 3-0 

 32 



Ty 



8.5 

 6.0 

 6.0 

 1.5 

 8.5 

 6.0 

 5-5 

 5-5 

 3-5 

 3-5 

 3-5 

 1.5 

 1-5 

 i.o 



Lat. 



200 

 200 



300 

 50 



200 

 200 

 100 

 100 



75 

 75 

 75 

 25 

 25 



25 



o.on 



.020 



.017 



•33 



.on 



.020 



.025 



.012 

 .040 

 •033 

 .025 



• 33 

 .10 



• 65 



Speed 



900 

 500 

 600 



30 

 900 

 500 

 400 

 800 

 250 

 300 

 400 



30 

 100 



15 



TABLE 369. — Resolving Power, Sharpness, and Astro Gamma, Definitions 



Resolving Power. (R). The capacity of a photographic plate or film to render fine detail 

 is known as its resolving power. It is usually found by photographing a series of gratings of 

 alternate parallel transparent and opaque lines, each line of a width equal to the space 

 between the lines. The grating constant, (width of line plus width of space), is variable for 

 different line groups over a relatively wide range. Resolving power is specified by stating 

 the number of lines per mm resolvable by the material. 1 - 2 



Resolving power depends upon exposure, development time, the developing solution, the 

 spectrum composition of the exposing radiation, and the contrasts in the test object. The 

 values of resolving power given are for the optimal exposure values and optimal time of 

 development in a particular developing solution (laboratory pyrogallol). The exposing radia- 

 tion used had a spectral composition close to that of average daylight and the contrast 

 between the elements of the test object was very high (greater than 10,000). 



Sharpness. The sharpness characteristics of a photographic material is defined as the 

 differential of density (D) with respect to distance (s) in a direction perpendicular to the 

 edge of the image; sharpness (S) = dD/ds, where 5 is expressed in microns (0.001 mm). 



Images used are obtained by making a contact print of a very carefully prepared knife 

 edge. The exposing radiation is carefully collimated and incident normal to the surface. 



Sharpness of the developed image depends upon the extent to which development is 

 carried and this is specified by one value of gamma (7), dD/d log E. It is dependent upon the 

 quality of radiation. The values given in the table were obtained by exposure to light, 

 approximately equivalent to average daylight, and the exposure was so adjusted that 

 development to a gamma of unity in pyrogallol at 20°C gave an image density of unity. 

 These values of sharpness express the diffuse-density gradient (dD/ds) of the straight line 

 portion of the sharpness curve obtained by plotting diffuse density (D) as a function of the 

 distance (s) from the geometrical edge of the image. 



Astro gamma. Astro gamma is defined as the coefficient (b) of log 10 E in the Scheiner 

 equation, which gives the relation between the diameter (D) of a stellar image and the 

 exposure (£). 



D = a + b logio E 

 Since exposure (E) = intensity (/) X time (t) this equation offers a means of determining 

 the relative brightness of stars by measurement of the diameter of the stellar images ob- 

 tained under known conditions of exposure and development. 



In the table are given values of astro gamma for a group of typical photographic ma- 

 terials. These values were determined by photographing with a highly corrected lens, using 

 a magnification of 0.05, a circular aperture (diameter of 0.56 mm). Exposing radiation was 

 of daylight quality, and intensity was so adjusted that an exposure of 1 second was just 

 above the threshold value. Keeping the intensity factor constant, the exposure time was 

 increased by consecutive powers of 2 from 1 to 512 seconds. The exposed plates were de- 

 veloped to a gamma of unity in standard pyrogallol at 20°C. 



1 Mees, Proc. Roy. Soc. (London), 83. 10, 1909. 



2 Ross, Physics of the developed photographic image, New York, Van Nostrand, 1924. 



Smithsonian Tables 



