New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1910-02-27
Do You Know? P Psfhaps You You B Do

plate without use OF the intermediate mega
tive. This IS brought about by the phenomenon
called reversal II a plate Is exposed sUftl-
Gent length OF time, so that when It IS printed
the positive gives : pleasing contrast OF Shad-
ows and lights normal exposure IS SAID to
have been produced. This normal exposure
when n midday sunlight using the largest
stop n the camera. IN general takes anywhere
from one one-hundTedth TO about one-teIlth
Of second.
# 2 plate Is exposed for Z longer time, an
abnormal exposure IS obtained II a series OF
abnormal exposures are taken. which have been
exposed respectively for one, ten twenty,
thirty and f0rtv-tlve seconds. one minute, ana
fifteen minutes. and then these plates are de-
ef0-7e,i Il IS found that N the One-second plate
he, lights are less conrrasted with the shadows
than n the normal plate In the teI1-secono
Mate the effect increases. until II the twenty
second plate . black, OF logged, negative Win
almost complete lack OF contrast IS produced
In The th1-tv-second plate however, the I1ghts
Of -Fe original object photographed begin TO Io-
pear light And IS the longer oVereNpoSureS
ere developed i Is seen that there IS 4 reversal
- q -os--I[t n parts OF the plate In hfteen-
-,7-7rl-a a--osr1re this reversal becomes com
-7le1e and IN entire positive plate IS OBTAINED
This r,oSltiye plate however, IS weaker al over
than IS the normal negative. from q PoSiliNe
Mate negative prints may be made Whlch give
. curious effect
c---77ne4 that 9 plate IS exposed for several
7,-eal,s instead OF for . fifteen minute peTloG
n this case d second reversal partially taxes
- nd the Mate when developed shows q
rr-eye--. n some parts while other parts stu
-a-7aIr the positive OF the first reversal I IS
l7747r-.1- 10 pet this second reversal complete
and i IS doubtful Il Z perfect one couId De oD-
tanned ::
WIT causes the phenomenon OF reversal Is
q case OF conjecture, but one OF the DeI'ei
F-,r,o+leees IN explanation OF this fact has been
.-7ii-a-,-t5 by q German named Luther. n the
T-s+ Mace i must be considered that q Pho1o-
e-r7lc plate has spread on Its surface q MIN OF
g5al..r1r7a which contains silver bromide Nheh
<+e 1,of7+ strikes the silver bromide, It decoH-
noses i and brornlne Is given of he geiauhe
beo-l,s This hronlIne, and thereby becomes
r7;17-f,- harder. The longer the film IS exposed
- -I7a 7-gF7+ the more brOTnIle IS gwen OF,
hence ! follows that the more broInlne the
,,e1s+;ne afsorbs the harder the gelatIne IS sure
= become. y :.
struck by light are turned biacK DV I!le oe
C-7e- Tnasmucll as the development 81 a plate
,3e,7erds on the perrnea biItv OF the him 10 the
developer IN a plate that has been exposed iYi
7f-er7 minutes the gelatIne that corresponds 10
rbe lights has been 50 hardened by the 'tDSol =
-, IF lror7ine that II Is almost 1r1lpeTVlouS 70
~ za.-..lor7e-. and hence no blaCkness appears
The yaIarIne on the shadows, however, ("h'Ch
- zen exposed long enough 10 equal the
1..,7rs n a normal platel Is less hard, allowing
~ developer TO soak IN and thereby deVeiop
r. shadows a black Thus the hnal erect -
hat II light lights and dark shadows or III
short. a positive .--.r :;
The explanation OF the second reversal =
Inc ei-7aIlar lines but IS more complicated,
- 7.1,a-afore understood only by one wen
- N the subject -Harold r RG1SFy