N O T E S F R O M T H E R F ~ E A R C H L A B O R A T O R Y , E A S T - M A N K O D A K C O M P A N Y . *

T H E E F F E C T S O F B R I G H T N E S S ON VISION.

By Dr. P. G. Nutfing.t

[Abstract]

THE eye adapts itself readily to a range of brightness f rom about lO .6 millilamberts (absolute threshold) up to about 50 iamberts, which is a litt'le brighter than white paper in direct sun- light. This adaptation is in the nature of an automatically vary- ing sensibility. Numerical data on this variation in sensibility have been obtained for the whole range of adaptation and are given below.

The three kinds of sensibility of more interest at any bright- ness level are ( I ) the lowest visible low light (2) , the lowest perceptible contrast and (3) the highest tolerable highlight or

Our data are Threshold, Discrimination and Glare Sensibility. given in the accompanying table and figure.

4

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/ ,~) i , : N, il ,

/ "(, )( )( k, - 6 - d - 4 -a - z - / o ~ / z d ~ J

Z.06 hELD ~ E / c r n ~ s , B (ML )

7

6

"4

2.

* Communicated by the Director. t Communication No. 38 from the Research Laboratory of the Eastman

Kodak Company.

53~

532 EASTMAN KODAK COMPANY NOTES. [J. F. I.

TABLE--VIsuAL SENS[TOMETRIC DATA. Field Different Discrimina- Threshold Glare Limi t

Brightness Frac t ion t ion Factor Limi t ml. O.OOOOO1

O.OO(X)I

O.OOOI

O.OOI

O.OI

0 . I

I.O

IO.0

IO0.0

1,000.0

I0,O00.O

ROCHESTER, N . Y., Sept. 21, I916.

(i.oo) I.O 0.0o00oo93 2o.~ (0.66) 1.5 0.0oooo42 4o.7 0.395 2.5 0.o00o19 89.0 o.2o4 4.5 0.00o087 186.o o.078 12 .8 o.ooo39 4oo.0 o.037o 27.o o.o0174 81o.o

I. o.o2o8 48.2 o.oo81 1.66 o.o174 57-5 0.036 3,47 o.o172 .58.1 0.28 7.25 0.o240 41.7 2.I5 14.45 (0.048) (20.9) (232.0) 30,90

P R O P O R T I O N A L REDUCERS,* By Kenneth Huse and Adolph H. Nietz.

[Abstract]

Photographic reducing solutions may be divided into three classes : (x) those which attack the highest densities most, (2) those which attack the lowest densities most, and (3) those which reduce all densities in the same proportion.

Norman Deck has recently suggested that by the use of a mixture of potassium permanganate and ammonium persulphate a satisfactory proportional reducer could be obtained, belonging to the third class. This has suggested the present investigatio!a on reducers generally and espe~cially on the best formula for a mixture of potassium permanganate and ammonium persulphate to give proportiona~l reduction.

Sensitometric strips of various plates were exposed, devel- oped and reduced in. a thermostat under an aecurateIy controlled condition, the plates being first developed, fixed, washed and dried and then, after measurement, reduced, dried and read again. The percentage of the original density removed by reduction from each step of exposure was plotted against the logarithm of the exposure. The results show that persulphate is the only reducer which removes a greater percentage of the higher densities; and that all others tried, including some which have been supposed to 'work proportionally, really reduce the lower densities most,

* Communication No. 39 from the Research Laboratory of the Eastman Kodak Company.