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Патент USA US2406702

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Aug. 27, 1946.
7 2,406,702
’ Filec1_ Oct. 27, 1944
Patented Aug. 27, 1946
Herbert W. Morreall, Jr., Binghamton, N. Y., as
signor to General Aniline & Film Corporation,
New York, N. Y., a corporation of Delaware
Application October 27, 1944, Serial No. 560,669
3 Claims.
(Cl. 95—10)
This invention pertains to the art of photo
graphic sensitometry and concerns a method and
mechanism for converting time-scale sensitome
ters adapted to produce stepped exposure strips
to a type for producing continuously modulated
exposure strips.
ously Varying or continuously modulated strips
is so shaped as to cover the steps thereby to
prevent the production of a series of distinctly
di?erent exposures each of which Varies by a
substantial‘ increment from that preceding. This
mask is curved to follow the points of the loga
rithmic steps of the exposure aperture. Accord
ingly, a logarithmically curved contour of the
exposure aperture will thereafter modulate the
light falling upon the sensitized strip and will
are rarely used, and in all cases where such strips
are employed, they are exposed in accordance
ber of independent exposures, each varying
with variations in light intensity rather than
slightly from the preceding, applying to it along
In the art of sensitometry, the use of stepped
strips has become very common while continu
cause that strip to have an in?nitely great num
its length. It will vary in density accordingly,
variations of time of exposure. For most pur
poses the stepped strips are more desirable, or at
that is, by a continuous rather than stepped
least serve very satisfactorily, but when inter 15 variation.
preting such strips in a recording instrument such
The mask is preferably attached to the ex
posure disk or cylinder, or the like, and such
as a recording densitometer, stepped strips are
far from satisfactory; and in fact, a recording
attaching means as is used is preferably of a type
instrument will give only very approximate or
to permit easy and quick conversion to and from
entirely unsatisfactory results with such strips.
one system or the other. The invention will be
Recording instruments do function very satisfac
described in detail with respect to one speci?c
torily with the continuous-type strips, but since
embodiment thereof as outlined in the accom
panying ?gures of drawing in which:
those are not now made except with intensity
Fig. 1 is a section through part of a time-scale
scale instruments, that would require a very ex
tensive conversion of existing equipment if re 25 sensitometer to which the invention has been
cording densitometers were to be employed more
Fig. 2 is a developed view of the rotating cylin
In solving the problem outlined above, a method
der, the exposure aperture therein, and the mask
and means for converting time-scale instruments
as applied thereto.
Fig. 3 is a view showing the invention as ap
of which there are a great number in use, makes 30
it possible to convert to recording-type densi
plied to a similar instrument but one having a
tometers but to expose continuously modulated
disk rather than a cylinder for timing the ex
strips on existing time-scale instruments. This
change is effected without destroying the original
Now referring to Fig. 1, so ‘much of a typical
identity of the time-scale sensitometer, and the
time-scale sensitometer has been shown as is nec
mechanism herein described may be employed for
essary for illustrating the application of the in
rapid conversion of an instrument to production
vention thereto. The instrument includes a cas
of continuous strips, and again, allows reconver
ing generally indicated by numeral It], and at the
sion of the machine to its original form.
opposite end, has a light source which is directed
Time-scale instruments, of which there are a
great number, generally function by directing
light rays against a sensitized strip of standard
shape and size, and the light falling upon the
strip is modulated lengthwise of the strip in ac
cordance with a series of exposures of varying
lengths of time. Normally, there are twenty-one
steps, each varying in accordance with a prede
termined increment of exposure time so that be
upon a re?ector or mirror II from which rays of
the light are directed upwardly through a win
, dow l2 and against a sensitized strip (not shown)
which is held in position by a platen l3. A cyl
inder or drum l4, part of which is cut away in
this view, rotates under power and at a pre
determined speed. The cylinder has an open
ing therein which is de?ned at one side by a line
out by a plane perpendicular to the axis of rota
tion for the cylinder (see Fig. 2). The opposite
ginning with the minimum exposure, each suc
ceeding step will have V2 times as much ex 50 side of the aperture is de?ned by a series of steps
indicated by numeral l5 and having points [6.
posure as that preceding. To accomplish this,
These steps, twenty-one in number according to
the light-modulating means or time-of-exposure
standard practice, are logarithmically varied, the
varying means is logarithmically stepped.
longest being adjacent the ?rst-mentioned side of
According to the invention, a mask is provided
for the stepped exposure aperture, and that mask
the aperture while the shortest step limits the
exposure at the opposite side. Part of this aper
ture is shown in Fig. 1, and since the instrument
is one well known to the art, further description
at this point is not necessary.
it may be desirable to produce similar strips mod
ulated by continuously varying the time of ex
posure-varying steps. Instead of being parallel
steps to which it is to be applied, and connecting
posure. Certain examples have been cited as to
the form which the invention may take, and ad
To effect the exposure or" a continuous type
vantages ?owing therefrom have been enumer
strip, a mask H is applied either to the inside or
ated; but it is to be understood that other con
to the outside of the rotating cylinder or drum.
structions will naturally occur to those skilled in
This mask is to be attached by a plurality of
the art and that the use of the invention is not
connecting elements [8 such as screws or some
by any means limited to only those advantages
other detachable connecting means. The mask 10 here cited. The inventive concept may be car
is so shaped that the edge or contour i9 follows
ried out in a number of ways. This application
the points l6 of the steps so that the steps them
is, therefore, not to be limited to the precise de
selves are completely covered, but the curve in
tails described but is intended to cover all varia
following the points of the steps will produce on
tions and modi?cations thereof falling within the
the sensitized strip a corresponding logarith 15 spirit of the invention and the scope of the claims.
mically varying exposure thereby to vary the
I claim:
density along the strip from. a corresponding
1. Means for converting a time-scale sensi
maximum to a corresponding minimum such as
tometer having a stepped exposure aperture to
would have been produced by the stepped aper
one adapted to produce continuously modulated
ture, but wherein all intermediate points along 20 strips, including a mask for covering the aper
‘the strip will vary continuously or by in?nitely
ture steps, and means for securing the mask in
small increments.
position over the said steps.
In Fig. 3, a modi?cation has been illustrated
2. Means for converting a time-scale sensi
in which the invention is applied to that type of
tometer having a stepped exposure aperture to
time~scale sensitometer employing an exposure 25 one adapted to produce continuously, modulated
disk 20 rather than a cylinder or drum. Here
strips, including a mask having a logarithmically
the aperture has a corresponding series of ex
curved edge aligning with points of the aperture
to a straight line at one side of the aperture,
means for securing the mask in position to cover
these steps are made up of parallel concentric 30 said steps.
arcs cut at appropriate points by radial lines
3. In a time scale sensitometer, an apertured
logarithmically spaced. A mask 2! is attached
member for permitting passage of light to a sen
by similar connecting means to one side of the
sitized layer, the aperture in said member having
disk, and corresponds to that above described in
one side thereof stepped in logarithmically in
that it covers the steps and has an exposure 35 creasing progression, and a detachable mask hav
determining contour which ‘follows. the points of
ing a continuously and logarithmically curved
the steps, i. e., is logarithmically curved.
edge aligning with points of the aperture steps,
The invention has been described as applying
and connecting means by which the said mask
to sensitometers adapted to expose the standard
is attached and detached thereby selectively to
strips, but it is to be understood that it is ap 40 permit exposures of stepped or continuous type.
plicable to any of the instruments primarily con
struoted for exposing stepped strips and on which
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