The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1900-03-16

J great differences, according to the size
and position of the windows and the
color Of the glass. that the time re-
quired varies from less fhan minute
10 three or four hours. or even more.
subjects including a large proportion
or sea and sky require, as a rule, very
short exposures. The time Of exposure
in the case Of portraits varies very
much, and depends on the conditions
Of Hshtng, and also on the character
OF the effect desired.
The light is most active, and the ex-
posures required are shortest in June.
and on bright day the activity of the
light remains practically the same be-
tween a. m and p. m, and it is
equally active in May and July from
10 a. m. TO : p. m. In spring and au-
tumn longer exposures are required,
and in winter the time must be from
three to ten times as long as in June,
according TO the hour Of the day. The
Light is least active IN December, and
the exposure required becomes shorter
and shorter as we approach June, and
afterward becomes longer and longer
until the maximum is again reached in
December. The light increases in
brightness from early morning until
midday, when it attains a maximum,
and then falls off again until sunset,
the falling OF being considerably more
rapid in winter than in summer. In
very early morning and toward sunset
the exposures are always long, espec-
tally if the light is at all yellow.
When the sun is shining and there are
white clouds in the sky opposite the
sun, the exposures needed are shorter,
other things being equal, than when
the sky is perfectly cloudless. A cloud
actually in front of the sun, of course,
lengthena the necessary exposure very
considerably, and the same is true. in
a smaller degree, OF light clouds that
do not completely obscure the sun. Rain
clears the atmosphere Of dust. etc. and.
other things being equal, less EXP S5ure
Is required after a shower.
1t will be clear that the estimation of
correct exposure requires Judgment and
experience The conditions are never
constant, and hence numerical tables
are only very approximate, although
they afford some assistance at the begin
ming. Not much help can be obtained
from actinometers, because they only
measure the intensity of the light
where the photographer is standing,
while what We ought to measure is the
intensity of the light reflected from the
different parts of the subject. Now and
again, and especially when dealing with
, interiors; they will tell us that the light
is much yellower and less active than
we should otherwise have believed.
The photographer must learn TO rely
upon his own judgment, guided by the
nature of the subject, with a special re-
gard to the proportion and depth of the
shadows; the apparent brightness of
the image on the ground glass. the time
Of year, the time of day and the char
acter of the light, especially with re-
gard to the presence Of .cloudS-eYen
light ones-between the sun and the
earth. Brightness TO the eye is not nee
eSsarily a measure of activity on the
Photographic plate, and. as already
pointed out, any yellowness- even
though slight-in the light lengthens
considerably the time of exposure re-
quired. Sufficient exposure should al
ways be given for the dark parts Of the
subject; the brightly Illuminated parts
will take care of themselves. The ex-
posure given will also depend on the
character Of the results required; very
short exposures increase the contrast,
and long exposures reduce the contrast.
If. therefore, you consider that the con-
trast of light and shade in the subject
is too strong for pictorial effect, give a
longer exposure, and vice versa. For
example, a view including whitewashed
cottages or other brilliantly lighted OBJ
jects, together with foliage, will require
q comparatively long exposure if harsh
contrasts in the negative are to be
avoided.