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Патент USA US2510592

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June 6, 1950
Filed Nov. 1a, 194e
Patented `Íune 6, 195()
Robert L. Malcom, Indianapolis, Ind., assignor to
Radio Corporation of America, a corporation
of Delaware
Application November 18, 1946, Serial No. 710,431
13 Claims. (Cl. 179-100.3)
This invention relates to photographic sound
recording systems, and particularly to a feed
recording system in which a control ñlm is used
back system which compensates for the non
ol' the film emulsion.
A still further object of the invention is to
linearity of the exposure-transmission charac
teristic of a photographic emulsion.
Feedback systems for the elimination of dis
to provide compensation for the non-linearity
provide a feedback system for a photographic
recording system in which a compensatory conn
trol ñlm is produced by the recording system for
tortion due to non-linearity of a modulating
use in the feedback system.
element, such as a galvanometer, are well-known,
Although the novel features which are believed
as evidenced by Wolfe U. S. Patent No. 2,270,367
of January 20, 1942, Singer U. S. Patent No. lU to be characteristic of this invention will be
2,292,166 of August 4, 1942, and Albin U. S.
Patent No. 2,357,623 of September 5, 1944. An
other patent pertinent to the present invention
is Blaney U. S. Patent No. 2,361,451 of October
31, 1944, which discloses and claims a method of
and system for controlling the exposure of a
film in accordance with the emulsion character
pointed out with particularity in the appended
claims, the manner of its organization and the
mode of its operation will be better understood
by referring to the following description read in
conjunction with the accompanying drawings,
forming a part hereof, in which:
Fig. 1 is a graph of a composite characteristic
between positive transmission and negative eX
posure, mirror displacement, and control film
istie of the film.
The present invention is directed to a system
of compensating for the non-linearity of the ñlm 20 density.
Fig. 2 is a diagrammatic view of a photographic
recording and feedback system embodying the
density or transmission variation in accordance
invention, and
with a control ñlm actually made on the record
Fig. 3, Fig. 4, and Fig. 5 are diagrams illus
ing system in which it is to be subsequently used.
In this manner, a particularly accurate com 25 trating the relative positions of the light beam
with respect to the- recording slit mask and con
pensation can be achieved, and the linear re
trol beam mirror.
cording range extended between more widely
Referring now to Fig. 1, the solid line curve
separated limits.
represents an exposure-transmission character
It is well-known that the negative exposure
istie having a linear portion between points A
positive transmission characteristic of a photo
and B and toe and shoulder curved portions. It
graphic emulsion has a central linear portion
is well-known that as long as the exposure is
and curved end portions. As long as the ex
between the points A and B, the light trans-`
posure varies between the limits of the linear
mitted through the ñlm will be directly propor-y
portion of a characteristic, true fidelity is ob
tained; but, when the exposure exceeds these lim 35 tional to the exposure; but, when the exposure
is less than at point A or greater than at point
its, distortion is introduced, since the transmis
B, there Will be a non-linear proportionality, as
sion does not vary linearly in accordance with
illustrated. The present invention is adapted
the exposure. By varying the exposure over the
to approach very closely the condition wherein
curved portion of the characteristic to compen
sate for the departurefrom linearity in accord 40 the straight portion A-B is extended, as shown
by the dotted lines, to permit undistorted opera
ance with the amplitude of the signal, the final
tion over the range of negative exposures be
sound record willfaithfully correspond to the
tween C and D.- Although the portion A-B may
original signal.
not be absolutely rectilinear, it may be considered
The principal object of the invention, therefore,
is to facilitate the recording of photographic 45 as such for purposes of explanation, the inven
emulsion’ by the use of a control film having a
sound records.
Another object of the invention is to provide
an improved method of and means for recording
tion, however, correcting for any departure from
rectilinearity regardless of its position> on the
The same curve may be translated into terms
A further object of the invention is to provide 60 of positive4 transmission and galvanometer mir
photographic sound records.
an improved method of and means for produc
ing a sound record having linearity over a wider
range than normal.
A still further object of the invention is to
provide a feedback system for a photographic
ror displacement when such a modulating ele
ment is used, 91 Arepresenting the maximum an
gular displacement of the mirror in the direction
indicated by the positive values of the signal cur
rent, and oz, the maximum displacement in the
negative direction. The curve also shows the
variation of the transmission through the con~
trol nlm made in accordance with the invention
with displacements of the galvanometer mirror
serted between the output of amplifier 21 and the
output of ampliiier 20 is an impedance 28 which
is adjustable for varying the voltage impressed
as will be explained hereinafter.
Referring now to Fig. 2, I is a .lightsource
upon ampliñer 2| in addition to that from am
pliñer 26. The output current from amplifier 21
is of such polarity or phase that it augments
having a straight filament, the :light therefrom
being collected by a lens 2 and projected onto
the voutputcurrent from amplifier 26, while the
output currents from amplifier 2i! are phased to
a galvanometer mirror ë by a lens 5. Inter
oppose the output currents from ampliner 26.
mediate the lenses 2 and 5 is a mask 4 having 10
In normal operation of the system just de
an aperture I6 therein and an edged-1 for'forrn
scribed, vthe penumbra is vibrated across the slit
ing a penumbra of uniform intensity :.gradient.
‘8 `bytlu-ymirror '6 in accordance with the ampli
A lens 3 is so positioned as to aid in getting a
tude and frequency of a signal impressed upon
sharp image of slit I6, but does not appear in
the line of light contributing‘to 'the penumbra
ëthegalvanometer 1.33, while the light through the
aperture ¿I6 is'impressed upon the control nlm
produced by the edge I1.
Light, passing the edge I1-and fromthe mirror
6 which is vibrated by a galvanometerâ'ß, is re
iiected to a lens 1 in front of a slit maskiSLI hav
I3 for impression-on the photoelectric cell I5 in
.accordance `with the'amplitude and frequency of
the signal. When, at certain input signal levels,
galvanometer mirror S’produces an exposure on
ing a slit 8 therein. Light emerging through the 20 negative iilm Ill within the linear range, the image
slit .8 Vis projected by .a .lens A9 -onto the isound
of ¿slit :IB- is Valso ïat a - corresponding. position of
track `portion of a 4nlm Il). By .the dotted lines
~linearity.',a'long- control;stripf',»l 3. ~.Over this grange,
of the mirror 6, the limiting excursions .of the
vthe J.output vfrom gampliñer A»2li is ¿balanced 4yby lthe
mirror E are represented between .positions 91
output ¿from-'amplifierî 1, and; no _control potential
and e2, `as .shown in Fig. 1.
is developedzacrossximpedancesZß. This4v
Light through the aperture I6 is reñected by
between .A „and vZB .1 on thecurve finfFig. s1.
the mirror 5 to a stationary .mirror II where it
At'another value Vof ,inputrsignalsand .corr-e
is reiiected through a lens I2 'to -a curved surface
i3, which, during recording, vis a control ñlm.
Shown at I8 and I9,.are two mirrors, which, `when
rotated to the positions shown-by .the dotted-lines,
reflect the penumbra shadow back through aper
ture I5 which is then reflected >by the mirror 6to
the mirror II and through .lens I2Ítovcurved sur
face I3, the points 91 rand y£92 representing `the
maximum excursion limits .of the mirror, as
shown in Fig. 1. When the .mirrors .are in their
dotted line positions, thecontrol ñlmfor use .dur
ing recording is exposed in .its preparation.
To produce the control strip I3, a striplofnn~
exposed negative stock is exposed so that .from
position 91 to 92 there is a uniform lexposure
gradient. This strip is then developedand .a,-positive strip printed from it. `The positive‘ßstrip is
then placed accurately along the .surface --I3 --so
as to maintain the original register of -» exposure.
To expose the original negative, l„the .mirror 6» is
uniformly moved between its -twoiextreme posi
tions 61 and 62. The mirrors -I8 and-ISiare-then
sponding , angular ¿displacementfof .the 4galvancm
eter mirror, _the :resulting-'effective»exposure ,at
.negative I0 maybe such;that it> fails tofreach the
,condition of linear ,opacity afterfdevelopment'of
the negative. Thus,v.while perfectlydinearemul
sion .system would ;give.;linear ¿positivetransmis
sionfor linear exposure, the »emulsion‘beingfcon
sidered .will .b_e _assumed ¿give .lessthan the
requisitetransmission '-_through its positive. fAt
.thisvpositionof y'mirror-¿n the imagefoñslit IB isat
a position of corresponding non-,linearity-ialong
.the .surfaceof control strip y[3,resultingîinäan-:out
putv current ¿from amplifier 20 i-that fis -gless „than
thatifromfamplifler -2».1. Due to >»thisf_laclcof bal
ance, ~there .is developed across .impedance-¿28, .a
current >that .augments :the «._output .from ampli
ner-26. Theputput fromfampliñer 2| being-.thus
increased, the galvanometer „tends Vtin-.assume ,a
position _» providing =more »illuminationifor „the `ex
posure of.ne_gativer.-l0. Whenmirrorß has --ad
vanced to a position whereby the fimvager- of slit
IB has .reached such Ta point alonggcontrol- strip
returned to their normal operating positions, 50 I 3 Vthat' balance .tends . .be restoredîindmpedance
shown by the solid lines. The _positive »strip 'de
2-8, «the feedback .potential tendsytoßease increas
veloped from the negative 'is then place'dat I3,
the slit i6 being sharply focused thereon. The
.Whenthe `exposure .ofñlm ».lûfoccurs’infaregion
recording system is now ready for use ’in »con
where the >¿positiver transmission ¿is _greater ...than
junction with the remainder of the system which 55 that .indicated .by „linear conditions, >the .output
will now be described.
Light, emerging through the positive strip I3,
of ,amplifier ZILeXceeds lthat of ampliñeráü ,and
the lunbalance >’potential .developed :across «impe
is projected by lens Ill onto the photoelectriccell
dance 28 v.tends to oppose kthe 'input V„to 4amplifier
I5 connected to an amplifier 2D havinglow phase
2|, vthereby resultingr in a tendencyfor'the .illu
distortion. The input signal to the galvanometer 60 mination ofexposure `toV-bereduced.
3d arrives'at terminals 24 from any suitable sig
By proper selection-.ofthe
nal generating device,.such as amicrophone ora
current derivedfromfimpedance .28, kit `is Ipossible
sound reproducer, the signal’beingimpressedup
to approach, at will, the condition ofloverallnega
on an amplifier 26.
tive exposure-„positive transmission¿characteris
Amplifier 26 has .one out
put over conductors 32, 33, and 3.4 to amplifier 65 tic --with ,any type Aof .emulsion ordinarily used.
2l which >is connected over conductors `35 tothe
galvanometer 3l), anda second output over v'con-
This is- because the controlled strip -`
ductors 3? and 38 to amplifier 21, conductors `31
and `-thereafter used- therein. `By .making .the di
mensions of the control Ȗlm I3 Yandthe imageof
and 33 »having a, resistor Yor :potentiometer 29
made .with .the »recording :system .justcdescribed
therein for controlling the amplitudeoffthe signal 70 slit i5 very large with respect-.tothe average,- grain
impressed upon amplifier 2.1. That is, .the at
size,.ground noise ~will~be minimized.
tenuator 29 is so adjusted thattheoutput of yam
.In Figs. 3,
`and 5, ¿three _positions :of Y thge
pliner 21 balances, or ¿isfequal to, theoutput of
penumbra shadow, shown graduated :fromflight
amplifier 20 when lthe image fof slitfIB -isinífocus
at the atop ï.to fdark .at .the r.lcxottorrn .aref'shown im
on the linearportion of the control strip I3. `In 76 pressed positions `on-ïthe.-~slit 8 and .the
means in accordance With the variation in density
of said second film to compensate for the non
linear characteristic of said emulsion, said cir
cuit including a detector of said second beamand
îfiirror Il together with an image 25 of the aper
ture >I6 thereon. As the mirror 6 vibrates through
out its excursion, the penumbra will travel across
the slitr 8, While the image of aperture I6 will
aconnection to said vibrating means.
move across the mirror Il. Therefore, regard
2. A sound recording system comprising a
source of light, means for forming said light into
less of Whether a high or low intensity light is
being passed by the slit 8, a constant intensity
two beams, one of said beams having a uniformly
light image 25 is being projected on the control
ñlm strip I3 which is modified in intensity by the
density of the film control strip, as shown in Fig.
1, which corresponds to the emulsion character
istic of the original film.
The system may also be used in push-pull
class B variable density systems by using two
varying intensity gradient, and the other of said
beams being of constant intensity, a film emul
sion having a non-linear exposure-transmission
characteristic, means having a variation in densi
ty corresponding to said exposure-transmission
characteristicr and means for simultaneously vi
directionally opposed and laterally displaced 15 brating both of said beams, said varying inten
penumbra and light slit channels. Properly ad
justed, this system and method of feedback also
tends to reduce distortion eñects introduced at
any point in the feedback loop, such as ampliñer
2i and galvanometer 3€), the latter including re 20
flected mechanical properties. To provide the
least possible delay distortion at all frequencies
sity beam being impressed upon said film emul
sion in accordance with the amplitude and fre
quency of a signal being recorded, and said beam
of constant intensity being vibrated over said
means having a density varying in accordance
with the exposure-transmission characteristic of
said emulsion`
3. A sound recording system in accordance
with claim 2, in which a detecting means for
rier currents may be used and all gain be effected
by wide band amplification at these high frequen 25 light passing through said means having a den
in the range being recorded, high frequency car
cies, with power detectors forming the output
circuits to the various loads.
Should it be economically desirable to accom
sity varying in accordance with the exposure
transmission characteristic of said emulsion is
Y provided together with a feedback system be
tween said detecting means and said vibrating
plish vdynamic control of film exposure with less
means for varying the portion of said varyingfin
equipment than that already described, the elec 30 tensity
beam impressed on said emulsion in ac
trical portions of this system may be simplified
cordance with'the variations in density of said
varying density means.
4. A sound recording system in accordance
from the photoelectric cell as a degeneration fac
2, in which a feedback circuit is pro
tor directly into the amplifier channel that drives 35 vided claim
between said constant intensity beam and
the galvanometer. This eliminates the balancing
said vibrating means for varying the actuation
arrangement. In this event, it is only necessary to
of said vibrating means in accordance with the
consider the exposure characteristics of the film
position of said constant intensity light beam on
emulsions used, together with the conditions of
said variable density means, said circuit includ
feedback, and to compute the variable manner 40 ing
a light-to-current translator for detecting
in which the progressive exposure characteristic
in intensity of said beam.
shall proceed along the length of the control strip
5. The method of sound recording comprising
negative. Alternatively, the control strip may be
generating a light beam of uniformly varying in
computed and laid out as a variable area mask
gradient and a light beam of constant
so that various lengths of the image of the con
cross-section and constant intensity, simultane
trol light slit -are presented to the condenser lens
ously vibrating said beams, impressing said beam
photoelectric cell combination. When this is
of varying intensity on a light sensitive emulsion
done, there is the advantage that this element
accordance with the amplitude and frequency
of the system, namely, the control strip, intro
50 of a signal being recorded, and varying the im
duces no background noise.
pression of said beam on said emulsion in ac
It is also possible to obtain the compensation
with the position of said constant in
current from a separate system using a galva
tensity beam.
nometer as nearly identical as possible to the
6. The method of compensating for the non
one in the actual recording channel, thus provid
considerably and satisfactory operational stability
may be retained by applying the amplified current
ing conversion apparatus for existing systems. 55 linearity of the exposure-transmission character
This auxiliary galvanometer would, of course, be
actuated by amplified signal current obtained
ahead of that point in the circuit at Which de
istic of a film emulsion during recording compris
ing producing two light beams, one of said beams
having a uniformly varying intensity gradient,
and the other of said beams having a constant
00 intensity, impressing portions of said beam of
I claim:
varying intensity on a film emulsion in accordance
l. A sound recording system comprising a
with the amplitude and frequency of a signal
source of light, means for forming said light into
recorded, and simultaneously Varying the
a beam having a uniformly varying intensity
position of said constant intensity beam over a
gradient, a slit mask having a slit therein, means
for vibrating said light beam across said slit, a 65 surface varying in light transmission in accord
ance with the variation in the exposure-trans
ñlm having an emulsion thereon, said emulsion
mission characteristic of said emulsion.
having a non-linear exposure-transmission char
7. The method in accordance with claim 6
acteristic, a second film having a density varia
which includes generating a current from said
tion varying in accordance with the exposure
transmission characteristic of said emulsion, 70 constant intensity beam as modified by trans
generation is introduced.
means for forming said light into a second beam
having a uniform intensity throughout its cross
sectional area, said vibrating means vibrating
said second beam over said second ñlm, and a
mission through said surface for varying the
position of said varying intensity beam.
8. The method in accordance with claim 6
which includes generating a current from said
feedback circuit adapted to vary said vibrating 75 constant intensity beam as modiñed by trans
mission îthrough :said smëfacefand "utilizing .said
currentiformodifyingllthe impression of: said y.var-y
«ing intensityâbeamronasaid- emulsion.
ï9.l'12he method lof compensating -for the nonh
linearity of the ¿exposure-transmission = character
:istic »fof »a v¿ñlmvnemnlsion r'during recording com~
nlm-means funpmjectingisaidaanstaat: intensity
'beamïtoßsai’diseeondïñlm;fandJ meansïïfor1 élir'riinat
iin‘g p:said «varying-:intensity beam ¿from said -ñrs’t
»film ‘and ïpro'j acting it-lìto# sai‘d Vsecond-’film 'iin‘st'ead
'of ßsaiidfcens'tant iintensityîbearn.
`12. Y l~A ’system
»accordance ?îwith l«claim ' K11, Aiin
uprising generating two ilíghtfbeams, one of »said
‘beams v¿having :a uniformly varying .intensity
‘which `>->said hiíibrating «means
fa galvanometer
-mirror and said'ilastmention'e `meansfcomprïises
gradient, "and Athe :Sather-»Eef :said “beams bei-ng »of
îlígl'htkieñeòtors, one îof »which ishp‘osîtione'd víin ¿the
'constant size and .intensity,>projecting 4portions
@of-said ¿var-ying intensity-beam to a ïñlm 'emulsion
`having ~amori-linear îexposureltransmission»char
iacteristic, :the .portion fof :said lb'eam being-pro
jected :at ¿any Ainstant Vdepending »upon ‘the ïampli
vtud'e :ofltheïsig'nal being recorded, 'varying the i
rinten-sity of. saidv 'constant intensity 'beamfin ac
cordance 'with Lthe‘por-tionloff'the varyingin'tensity
lbe‘am ’Seeing-»impressed Lupen said emulsion, and
:controlling the-'portion Ao'f saidvvar-iable 'intensity
:beam impressed :on said emulsion ïby .the -Ñaria
rtions 2in saîdfconstantfintens'ity beam.
10. The method in accordance with c1aim'9,
¿in Wlhichfsaid last ymentioned `controlling supple
'ments the 'variation ,of 4said variable intensity
'beam‘by the>anip1itude of said signal.
A¿11..Asound recording vsystemYcomprising-a light
îsource, .means 'for 'fform‘ing :a
beam'sffro‘m said source, one'of
Aa .uniformly'varyìngsiintensity
-other .of‘said kbeams'lnaving a,
plurality >of light
gradient, 'and the
‘constant `size and
'path-:of fsaid 'variable Yintensity `beam Aafter »tie
'ñe'ctie-nífby said-mirror.
13. A system in accordance:Withfclaim T11, iin
whichis'aid~ilast lmention‘ed?means includes alight
fdene‘ctor îde'fiecting .said :varying :intensity beam
ifromfzsa'id Vibrating means Landia Sdeflectorréinter
'mediate 'said ligïlitfs'ource ¿and >said¿beam forming
imeans ëfor :zfnrther -iienecting ¿said varying fin
"Theföllowing Ireferences are of record lin 'the
‘íìle of «this ïpatent':
Hansen ________-_-___ Jan.’ 118, '1938
:'Albershein ,_ __ ____ __' Apr. .30, V-1940
»Underhill ________ __ -Dec. 130, 11941
»Hal-1_.“` __________ __ »June @16,1942
intensity, Vmeans ifor :simultaneously vibrating
«Singer f_.____r________ Aug. -4, >1942
said beams, ;a íñrst fìlm,zsa-i'd Vvibrating lmeans ‘be
¿Albi-n __»___-_____v__.__ Septö, 111944
ing adapted to impress different portions iof‘said
Ávary-ing >intensity beam .on said ñlm, :a second
Blane'y -»__-_____-._____ Oct. 311, 1944
.Albin __ _____ ________ May 22,»1-945
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