The sun. [volume] (New York [N.Y.]) 1833-1916, 1914-07-26

crayon to take up gum and oil. with all
their limitations in drawing?
The art of photography lies in rem
dering the gradations Of light. shading
and shadow in their infinite delicacy.
The mechanical part Of This rendering
| Is done by the lens; thus the brilliant
rays of light reflected from "A dewdrop
are focused on their proper spot in the
picture and appear on the focusing
screen with all their brillianCy; the
| feeble rays Of light reflected from some
! shadow are focused on their spot in the
picture and fall on the screen with
feeble genlleness In this way the pic
| tur" is mechanically reproduced on the
| focusing screen.
| The lens Is covered. a sensitive plate.
a sheet Il glass coated with "A thin layer
of gelatine containing minute PARTED -
| of bromide of silver. is substituted for
the focusing screen; the lens is uncov-
red; the picture is allowed 10 fall on the
sensitive place for a few moments; the
lens is again covered and the exposure
| has been made.
Now no one seems to know the exact
eject that the light produces on the
! particles of silver, and So. If | avoid
scientific language and write in plain,
non scientific English, ! must be par
doncd.
The practical action of the light strik-
! ing the sensitive film j. very similar to
| the blow from a prlZefghter's fist.
| When the light strikes the film hard it
bruises deeply; when il strikes the film
gently the bruisc Is on the surface. This
simile may be carried still further; for
the light bruise does not show at once.
but grows black as soon as the plate is
placed in the developer.
Again, a single sharp blow does not
| bruise the face deeply; but let a second
blow fall on the same spot, and the bow
seems to sink in, and the bruise be-
comes serious. In the same way the
| evening light during an exposure of
| one second may not bruise the shadow
! portions of the film sufficiently; but let
"A second blow be struck by another eX-
| posture Of one second and the blow viii
| sink in. In practice such blow IL
struck by one exposure of two seconds
| duration.
In an undercXposurc the violent rays
of light reflected from the dewdrop
bruise the film, the gentle light re-
fected from a shadow fails 10 make "A
bruise and leave n mark.
In a correct exposure the rays from
/ the dewdrop hruise deeply, Will" the
/ shadow rays have time to keep on strik-
/ ing until they bruiSc the surface of the
/ film.
/ In an overeXposure the light batters
| away at the Him until II is heavily
| bruised all over,
The secret Of development. like the
secret of exposure, lies in the fact that
/ the film has thickness.
In exposure the thickness of the film
| prevents the light from penetrating too
far into the ge,atine; IN development
the thickness of the film prevents the
developer from circulating freely
| through the depths of The film, As the
delicate gradatiuns Of the high lights
lie far down in the him th"s" must be
reached and developed.
Sow most developers rapidly become
worn out with the labor OF hlackcning
the light struck silver; and the moment
"A developer becomes worn out II ceases
to act The silver Particles which are
near the surface of the gclatine are safe
enough. for the bulk of tn" developer
Is flowing TO and Fl" over them ana con-
| tlnually bringing fresh developer into
contact with them; but tn" silver par
ticles which lie deep down in the film
have no such generous supply. When
the first dose of developer. which has
been sucked down into tn" depths OF
the high lights has become exhausted
the silver particles can attract fr"Sh ue-
voloper only as IT clrcu'at's tHr'us"
the gelatlnc,