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Artificial illuminants for use in practical photography
NOTES FROM THE RESEARCH LABORATORY, E A S T M A N K O D A K COMPANY.* A R T I F I C I A L I L L U M I N A N T S F O R USE I N P R A C T I C A L PHOTOGRAPHY. By C. E, Kenneth Mees, D.Sc.
[ABSTRACT.] ARTIFICIAL illuminants can be used in negative making for portraiture, cinematograph work, and photo-engraving. For portraiture diffused sources are necessary, and either a large source, such as that given by a bank of Cooper-Hewitt lamps, must be used or the light must be reflected from a large area. In cinematograph work about a quarter kilowatt per square foot of stage is used, the usual arrangement including the use of Cooper-Hewitt lamps overhead and at one side of the stage, and arcs in front. For photo-engraving an arc lamp is hung on each side of the copy-board, most engravers using flame carbon arcs. For printing papers the enclosed arc is used for silver papers, while for platinum the Cooper-Hewitt lamp is satisfactory. In printing fish-glue on metal it is important that a small source of light should be used in order to get sharp definition of the dots, and the printing should be as far away as possible. The following illttminants are recommended for portraiture: flame arcs, Cooper-Hewitt lamps, and nitrogen tungsten lamps; for cinematograph work, the Cooper-Hewitt, quartz arc, and flame arc; for photo-engraving, the enclosed arc and flame arc; for silver printing, the enclosed or flame arcs; for platinum printing, the Cooper-Hewitt lamp. The photographic efficiency of artificial illuminants depends upon their quality and upon their visual efficiency, but must be considered from the point of view of the materials used, which materials are of three chief kinds: ( I ) panchromatic materials sensitive to the whole spectrum and used with filters to give a rendering similar to that seen by the eye, or for color pl~otography ; (2) ordinary materials having their maximum sensitiveness in the blue-violet; (3) materials sensitive only to the ultra-violet. For panchromatic materials the efficiency of the illuminant wilI * Communicated by the Director. 48x
482
E A S T M A N KODAK CO. LABORATORY NOTES.
[J. F. I.
depend almost entirely upon its visual efficiency, while for ordinary materials the chief point o.f importance is the efficiency in the blueviolet, but, since the latitude and freedom from halation increase with shorter wave-lengths, it is better to use light sources having. their maximum near 4oo ~ rather than near 47o ~ . It is pointed out that nearly all artificial illuminants have application in some branch of photography or other. Research Laboratory, September 14, 1915. THE
RETINAL
SENSIBILITIES RELATED ENGINEERING. I
TO ILLUMINATING
B y P. G. N u t t i n g , P h . D .
THE fundamental principles of good lighting are derived primarily from the properties .of the human retina, the eye being the sole means of judging whether illumination is good or defective. Of chief importance is the magnitude .of the brightness sensa, tion as a function of the flux density of light at the retina. This cannot be directly measured, but sensibility, its derivative., may be readily determined at all working intensities and formulated in the function S = Sm"l- (I -- Sin) (B/Bo) n
For threshold sensibility Sm= 0oo022, Bo = oooooI 7 millilamberts, and n = o.49 for white light. For photometric sensibility (K6nig's data), Sm=o.oI75, Bo=o.oo9o (unit o.oo36 m.1.) and n = o . 4 5 . These formulae for sensibilities integrate into the luminous sensation scale L = K log (I + Sm(InIo " n - x))x/n
In practical engineering problems interest is centred on four chief levels of brightness. For these the important data are the foil,owing : I. 2. 3. 4.
Mean brightPhotometric ness level (millilamberts) sensibility E x t e r i o r daylight . . . IOoo o.o175 0.030 Interiors in daylight io O.123 Interiors at night . . . o.I O.OOI 0.79 Exteriors at night ..
Thresh-
old (nail-
Relative sensibility
lilamberts) Threshold Contrast Glare
0.35 o.o17 o.oo14 O.OOOI I
I 21 251 3090
I 59 143o
223o0
I 200 18o0o
160000
1Abstract of a paper delivered at the Washington Convention of the Illuminating Engineering Society.
[ABSTRACT.] ARTIFICIAL illuminants can be used in negative making for portraiture, cinematograph work, and photo-engraving. For portraiture diffused sources are necessary, and either a large source, such as that given by a bank of Cooper-Hewitt lamps, must be used or the light must be reflected from a large area. In cinematograph work about a quarter kilowatt per square foot of stage is used, the usual arrangement including the use of Cooper-Hewitt lamps overhead and at one side of the stage, and arcs in front. For photo-engraving an arc lamp is hung on each side of the copy-board, most engravers using flame carbon arcs. For printing papers the enclosed arc is used for silver papers, while for platinum the Cooper-Hewitt lamp is satisfactory. In printing fish-glue on metal it is important that a small source of light should be used in order to get sharp definition of the dots, and the printing should be as far away as possible. The following illttminants are recommended for portraiture: flame arcs, Cooper-Hewitt lamps, and nitrogen tungsten lamps; for cinematograph work, the Cooper-Hewitt, quartz arc, and flame arc; for photo-engraving, the enclosed arc and flame arc; for silver printing, the enclosed or flame arcs; for platinum printing, the Cooper-Hewitt lamp. The photographic efficiency of artificial illuminants depends upon their quality and upon their visual efficiency, but must be considered from the point of view of the materials used, which materials are of three chief kinds: ( I ) panchromatic materials sensitive to the whole spectrum and used with filters to give a rendering similar to that seen by the eye, or for color pl~otography ; (2) ordinary materials having their maximum sensitiveness in the blue-violet; (3) materials sensitive only to the ultra-violet. For panchromatic materials the efficiency of the illuminant wilI * Communicated by the Director. 48x
482
E A S T M A N KODAK CO. LABORATORY NOTES.
[J. F. I.
depend almost entirely upon its visual efficiency, while for ordinary materials the chief point o.f importance is the efficiency in the blueviolet, but, since the latitude and freedom from halation increase with shorter wave-lengths, it is better to use light sources having. their maximum near 4oo ~ rather than near 47o ~ . It is pointed out that nearly all artificial illuminants have application in some branch of photography or other. Research Laboratory, September 14, 1915. THE
RETINAL
SENSIBILITIES RELATED ENGINEERING. I
TO ILLUMINATING
B y P. G. N u t t i n g , P h . D .
THE fundamental principles of good lighting are derived primarily from the properties .of the human retina, the eye being the sole means of judging whether illumination is good or defective. Of chief importance is the magnitude .of the brightness sensa, tion as a function of the flux density of light at the retina. This cannot be directly measured, but sensibility, its derivative., may be readily determined at all working intensities and formulated in the function S = Sm"l- (I -- Sin) (B/Bo) n
For threshold sensibility Sm= 0oo022, Bo = oooooI 7 millilamberts, and n = o.49 for white light. For photometric sensibility (K6nig's data), Sm=o.oI75, Bo=o.oo9o (unit o.oo36 m.1.) and n = o . 4 5 . These formulae for sensibilities integrate into the luminous sensation scale L = K log (I + Sm(InIo " n - x))x/n
In practical engineering problems interest is centred on four chief levels of brightness. For these the important data are the foil,owing : I. 2. 3. 4.
Mean brightPhotometric ness level (millilamberts) sensibility E x t e r i o r daylight . . . IOoo o.o175 0.030 Interiors in daylight io O.123 Interiors at night . . . o.I O.OOI 0.79 Exteriors at night ..
Thresh-
old (nail-
Relative sensibility
lilamberts) Threshold Contrast Glare
0.35 o.o17 o.oo14 O.OOOI I
I 21 251 3090
I 59 143o
223o0
I 200 18o0o
160000
1Abstract of a paper delivered at the Washington Convention of the Illuminating Engineering Society.