72 PHOTOGRAPHIC FACTS AND FORMULAS 
The numbers in the table are multipliers of the calculated 
exposure. 
VARIATION OF ENLARGING EXPOSURES FROM THEORETI- 
cAL.—Mr. Watkins also gives the table for enlarging: 
Enlarging 
Diameters Thin Neg. Medium Neg. Dense Neg. 
Equal size 1 os a 
ly, ly 3 6 
2 2 44 o 
2% gS 6 12 
3 4 8 16 
+ 6% 12yY% 25 
y 9 18 36 
These numbers are multipliers, as in the last table. 
The numbers of diameters of enlargement are found by 
dividing the length of one side of the enlargement by the 
length of the same side of the negative. 
THe EFrrect oF ALTITUDE ON ExposuRE.—Variations in 
exposure due to variations in altitude, or distance above sea 
level, are negligible in ordinary work, that is to say, unless 
the altitude exceeds 5000 ft., when three-quarters of the cal- 
culated exposure should be given. Over 10,000 ft., half the 
regular time would be sufficient. This is for near objects. 
Panoramic views from mountain tops require panchromatic 
plates and special filters to cut out haze, as in aerial exposures. 
SHUTTER SPEEDS FoR Movinec Opjects.—The following 
are approximately the slowest speeds of the shutter which will 
give a sharp image. The object is assumed to be 25 feet 
distant from the lens and to move diagonally across the field 
of the lens: 
eople walking ini streetiseenesi isi Sisal cajewn 1/10 sec. 
Animals and people walking slowly ............ LAL 
People walking three miles per hour ........... 1/50) \* 
