Improvements in the Production of Photographic Negatives.
Year: 1893

page_text: Date of Application, 30th Aug., 1893
Complete Specification Left, 30th June, 1894-Accepted, 25th Aug.. 1894
PROVISIONAL SPECIFICATION.
Improvements in the Production of Photographic Negatives.
I, Dr. EUGEN ALBERT, of 55 Schwabinger Landstrasse, Munich, in the Empire
of Germany, do hereby declare the nature of this invention to be as follows:-
It is a matter of common knowledge that autotype negatives are made by placing
a screen in front of the sensitive plate. The half-tones of the original are thereby
divided into lines or points, and the essential requirements are that the negative
itself must contain no half-tones, but only complete opacities and pure trans-
parencies, and that the area of the opacities for all half tones of the original must
grow from 0 to ∞, i.e. in the negative narrow opacities must correspond to the deep
tones, and narrow transparencies to the light tones, of the original. This difference
in the size of the opacities and transparencies is regulated by the power of
solarization possessed by silver salts (ie. the power of propagating the action of
light laterally on the sensitive plate), by the size of the lens opening, by the
distance of the screen from the sensitive plate, by the focus of the lens, and by the
extent of the reduction from the original which is being photographed. The larger
the lens opening, the further the screen from the sensitive plate, and the nearer the
screen and sensitive plate are to the lens, the more obtuse is the angle at which
the rays of light fall upon the sensitive plate; that is to say, since the rays of light
must pass through the screen before falling upon the sensitive plate, and as some
rays pass obliquely through the screen, those portions of the negative which
correspond to the light tones of the original must show very broad, and, owing to the
strong light, thorough, opacities, and only narrow transparencies. This detrimental
action moreover takes place all over the negative with the result that in those
portions of the negative which correspond to the deep tones of the original there is
not the necessary strength and narrowness in the opacities, but they are broad,
woolly, and too weak, as the feeble light reflected by the deep tones has spread itself
over a larger area.
With a smaller lens opening (in fact under conditions the opposite of those
mentioned above, i.e. when the light rays fall upon the sensitive plate at the acutest
possible angle) firm, clean cut opacities are obtained in the dark tones, but quite
inadequate lights, as the power of solarization is insufficient to prolong the action
of the light far enough laterally when the screen is of the customary, and for
printing purposes necessary, size of 3 to 5 lines to the millimetre.
The advantages of large and small lens openings may be combined if the different
points of the lens opening stand in different relation to one another in accordance
with the principle of the angle of incidence as above explained. If, instead of a
stop with a round opening, a stop is used with for example a slit and the slit
is placed at first parallel to the direction of the lines of the screen, and afterwards
at right angles to their direction, then in the first case practically only the power
of solarization acts (the narrower the slit the more precise is the action); the length
of the slit, i.e. the size of the stop is, so far as sharpness is concerned, without
influence; and in the second case, the longer the slit the stronger are the opacities
in the lights, because the angle of incidence of the rays of light is more obtuse.
It is clear therefore that it is possible to make correct autotype negatives by
regulating the slit stop in its relation to the direction of the screen lines, and by
means of variously shaped stops that exclude the rays of light which act
letrimentally.

page_text: I wish it to be understood that I do not confine myself to any particular shape
of stop but I may use stops of various shapes constructed on the principle hereinabove
explained, that is to say, to exclude detrimental rays of light.
Dated this 30th day of August 1893.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in the Production of Photographic Negatives.
I, Dr. EUGEN ALBERT, of 55 Schwabinger Landstrasse, Munich, in the Empire
of Germany, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by
the following statement :-
This invention has for its object to provide improved 'forms of stops for use in
the production of screens and of autotype negatives, such stops being characterized
by the fact that they exclude the rays of light which would act detrimentally on
the screen or negative.
The principles underlying the construction of my improved stops may be explained
as follows.
If the lens of a camera is focussed on a smooth white surface, and if in front of
the sensitive plate in the dark slide (and at a small distance from said plate) an
opaque plate is placed (for example a second glass plate covered with tin foil) in
which opaque plate a small transparent spot about of a millimetre in diameter is
provided, it is clear that, after exposing the sensitive plate and developing it, a small
round point will appear on the negative. The roundness of the form and the size of
the point are not so much caused by the fact that the hole in the tin foil is round,
as by the circular form of the lens or its stop.
A small stop gives a smaller black point than does a large stop, if the exposures
are equal. If the exposure with the smaller stop be prolonged, the size of the
point on the negative would be increased by the solarization of light (i.e. the power
of silver salts to propagate the action of light laterally on the sensitive plate). If
in place of a stop with a circular opening, having for example a diameter of
4 centimetres, a stop is used with a diametrical slit in it 4 centimetres long and
one centimetre broad, hereafter termed the "slit stop," the result on the negative is
no longer a round point but a correspondingly small and narrow line in a direction
parallel to that of the slit in the stop.
If in place of the above mentioned opaque plate, a screen, such as is usually
employed for the purpose of process work, is used, and a reproduction of it is
made with the above mentioned slit stop, a result is obtained totally different from
that obtained with a round stop, and this result is dependent upon the direction of
the slit. For simplicity's sake the case of a single line, not crossed, screen will be
considered.
If the slit is parallel to the direction of the lines of the screen, the reproduction
will consist of sharp lines, the breadth of each of which is dependent upon the
duration of the exposure, and the breadth of the slit; the density being regulated
by the length of the slit.
But if the slit is turned through 90 degrees so that it is at right angles to the
direction of the lines of the screen, the result will be a series of lines so absolutely
blurred and insufficiently dense that it is often difficult to recognise them.
If two parallel slits are made in the stop, and placed parallel to the direction of

page_text: the lines of the screen, then, subject to the distance of these slits from one another,
two lines instead of one for each line of the screen will appear on the sensitive
plate, and the number of lines of the original screen will be doubled, or the lines
will touch and the middle appear dark.
The explanation of the above is simply this, that all portions of the lens opening
which lie on either side of an imaginary line bisecting it and parallel to the lines
of the screen transmit light through the screen on to the sensitive plate at an angle
which increases proportionately to their distance from the imaginary line, whereas
all parts of the stop in the imaginary line or lying near it are without any side
dispersion so far as their passage through the screen is concerned.
Although the slit stop makes possible the preparation of any form of screen, still
its importance for such work is not so great as for the preparation of process block
negatives. In the autotype or process negatives the tones of the original are split
up into points and lines by placing the screen in front of the sensitive plate; and
it is to be noticed in the first place that the negative itself must contain no half
tones but only opacities and pure transparencies, and the reproduction of the various
tones of the original is solely effected by the greater or smaller area of the
opacities and transparencies, which therefore must range from 0 to infinity, i.e. the
narrow opacities of the negative must correspond to the deep tones, and the small
transparencies must correspond to the light tones, of the original.
This variety in the area of the opacities and transparencies is regulated by
the power of solarization possessed by the silver salts, by the size of the stop, by
the distance of the screen from the sensitive plate, by the focus of the lens, and
lastly by the degree to which the original is to be reduced in the reproduction.
The larger the stop, the further the screen from the sensitive plate, and the
nearer the screen and the sensitive plate are to the lens the more obtuse is the
angle at which a given part of the rays of light strike the sensitive plate.
The result is that in those parts of the negative which correspond to the lights of
the original, the screen expands, and in consequence of the strong light is well
covered, and, being partly assisted by solarization, narrow pointed transparencies
are therefore formed in the lights. This expansion takes place in all parts of the
negative, with the difference, however, that in those parts which correspond to the
deep tones of the original, broad, woolly, weak points appear, because the weakness
of the light reflected from the shadows of the original precludes good density.
With a smaller lens opening and under conditions diametrically opposed to those
before mentioned (i.e. if the light rays fall upon the sensitive plate at the acutest
possible angle) in those parts of the negative which correspond to the deep tones
of the original, small, well-covered, clean cut points are obtained, but the parts
corresponding to the high lights of the original are inadequately closed, because the
solarization is insufficient to propagate the influence of the light laterally to the
required extent.
From the knowledge that, only those portions of the stop opening transmit oblique
light to the sensitive plate which lie on either side of an imaginary middle line
parallel to the lines of the screen (or in the case of crossed screens, those which
are further from the middle point) as above explained, one is able to construct
stops which are totally different from those generally used, and which are charac-
terized by their power of eliminating all light which would act in a way detrimental
to the production of screens or of autotype negatives.
The forms which such stops can take are very numerous and their general
characteristics are that the opening is not circular or that they have more than one
opening.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
For the production of screens and autotype negatives, stops which contain more

page_text: than one opening or which contain one opening which is not circular, for the purpose
specified.
Dated this 30th day of June 1894.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.