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Патент USA US2404448

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July 23, 1946.
o. c. MARTIN
Original Filed June 28, 1939
2 Sheets-Sheet 1
_57.25. 2.
0275 6. MRW/v
Arme/v w
July 23, 1946.
‘0. c. MARTIN
Original Filed June 28, 1939
2 Sheets-Sheet 2
_2716. 4. `
,Fra 5.
Or/s 6. MMU/xg
Patented July 23, 1946
Y ~Otis C. .Martin, Los Angeles, Calif.; Marion 5E.
Martin administratrix ofsaid Otis C. Martin,
AOriginal `application June 28, 1939, Serial No.
Divided and this application VMarch
16, 1942, SerialvNo. 434,810
2 Claims.
My invention relates to a matrix for making
projection screens which finds particular utility
or spiral .groove ofthe requisite'cross section in
the .front 'face of'a sheet of “Lucite”
when employed for ref-photographing motion
Screens employed for the “back projection”
process oftentimes are required to‘havea size as
This application is a division of my copending Cl large-as 30 x 40 `feet and until the present‘inven
tion it has been impossible to construct a screen
application Serial No. 281,625, filed June 28, 1939,
of this size of “Lucite” which employs the de
now Patent No. 2,315,721, and entitled “Matrix
sired optical principles which are incorporated
element for making light transmitting screens,”
One of the most common uses of light trans
mitting screens for rephotographyof motion pic
tures is in connection with the process known to
the motion picture industry as “back projection.”
Back projection consists in projecting a, motion
picture of a landscape, street scene, or other
background material upon a translucent projec
tion screen. Actors participating in the enact
ment of a motion picture being filmed are po
sitioned before this screen and the actors and
the screen are photographed simultaneously so
that the completed photograph portrays the ac
tors in the environment Whichvis “back projected.”
on the translucent screen.
Considerable difficulty has been encountered in
the use of this process as regards the obtaining
of the Arequired uniformity of illumination
throughout the‘entire surface of the translucent
screen when viewed fromlthe location of the cam
era lens. The'use of a cloth screen for this proc
in the smaller sized screens.
It is an object of my invention to .provide a
novel matrix upon which liquid “Lucite” may be
cast to. provide alight transmitting screen of any
desired size having iformed integrally-therewith
va means for'redirectingthelight which is passed
v.It is also an object of my invention to >provide
a‘matrix of the characterset forth in the pre
cedingparagraph which-includes means for de
ñning a continuousspiral groove of any selected
cross section in the ‘.‘Lucite” which may be cast
It .is anadditional object of my invention to
provide afmatrixiof the character'set forth in the
preceding paragraph .which comprises a `sheet
formed by winding a nat interlocking ribbon
spirally >about itself.
Other obiectsland advantages of my invention
will'be apparentAfrom a'study ofthe following
specifications, .read :in Aconnection with the ac
ess’is unsatisfactory in that the cloth ‘absorbs too
much light kand prevents adequate exposure >of 30 companying drawings, wherein:
Fig. '1 is ‘an `elevational View illustrating the
the film used in the rephotographing camera.
appearance of a light vtransmitting yscreen con
As a result, ground glass has been usedin the
structed-byïthe matrix fof my invention;
past but has not been satisfactory due vto wthe
Fig. A.2 »is «an enlarged vfragmentary cross ysec
fact that the ground glass, While tending to clif
tional lview taken substantially .along the line
fusethe light transmitted through it, tends nev
II-II of`Fig. 1 illustrating in detail the mech
ertheless t0 transmit the greater proportion of
anism -by which the screen may be mounted in
the light in Ythe .same general direction as »was
-its frame and illustrating one type of spiral
followed by the light striking the screen. The
groove which may be provided in the‘screen face;
screen, therefore, when viewed from .the location
Fig. 3 is a plan viewof a matrix core member
of the rcamera lens displayed la Ávery bright cen
tral area, becoming increasingly darker 'as »the
edge of the screen was approached.
The use of ‘ïLucite”-(atransparent‘plasticana
terial `having a vhigh light » transmitting -efliciency
and-»afrelatively high‘ïinde'x of-re'fraction) Ihas re
sulted in the manufacture lof extremely satis
~factory. screens :in »the-smaller I'sizes, f not exceed
ing six Ifeet '1in Veither Widthor height.
`'smal-1er screensusually-either incorporatea great ‘
number of individual lens elements ~for redirect
ingthe'lightasit is'passe'd'through the trans
parent'screen'or are made in the 'form of -avplane
upon which ya 'suitable ribbon material may be
`wound to providea spiral matrix;
Fig. V‘i is lanßexplo'ded Vperspective view illus
trating the! manner in whi‘chthe endtofthe rib
bon material-may be securedtoithe core member
which isi1lustratedinFig¢3; ‘and
Fig. 5 is a fragmentary cross section asimilar
to’Fig. T2 but _illustrating thefmanner in which
the îadjacent turns ‘of ¿ribbon .material einterlo'ck
'with ‘eachother to providera Vmatrix upon which
a liquid ‘fLuoit`e”l"maylbefcast to yprovide a'screen
of the desired character.
Referring -to the drawings, SI have illustrated
inïFig. lfoneformïof screen which‘may'beeon
lWhich ` 'are formed 'by' cuttinga continuous 4scroll 55 structed accordingï'to myïinvention. The screen
y'Fresnel ~lens,'the 'individual prismatic faces of
includes a working surface or area l which is
adapted to receive a picture projected upon the
reverse side thereof by a suitable motion picture
stantially the entire screen surface which inter
sects the rays HB and Il is comprised of a Imul
tiplicity of light refracting facets comprising the
curved surfaces 9. The rays IG and Il strike
projector, which picture is ordinarily photo
graphed by a motion picture camera disposed Si the curved surfaces 9 at an acute angle and are
consequently refracted thereby, the amount of
before the screen. The working area l is bounded
refraction depending upon the angle at which
by an integral border portion 2 which includes
the rays lil and l l strike this surface.
means cooperating with suitable lacings 3 to `
It will be observed that the greater part of
support the screen structure Within any suitable
the light will strike this curved surface at such
supporting frame 4. The frame 1l is adapted
to hold the screen in a substantially vertical
plane and for this purpose may be suspended
from suitable overhead supporting structure or
may rest upon a supporting surface such as a
an angle as to cause it to be refracted in the
proper direction to enter the lens of a camera
disposed before the screen irrespective of whether
the particular groove in question is located at the
floor 5 by means 0f feet or legs 6.
It has been found that if the screen l is made
of a transparent yplastic of the type known in the
trade as “Lucite” and is provided on its front
face with a series of concentric or spiral grooves
l of the proper cross section to provide a step
cut screen surface having a plurality of light re
center of the screen or at the extreme edge there
fracting facets, light which is projected upon the
will appear as though uniformly lighted, I prefer
to make the spacing between each of the grooves
‘l’ extremely small as compared with the dimen
back of the screen by a motion picture projector
will be redirected by such facets into the objec
tive of a camera disposed before the screen.
The cross section of the grooves l may be so
chosen as to redirect substantially all of the
light which falls upon the rear face of the screen,
thus, in effect, forming a ‘Fresnel type of lens.
It has been found, however, that if the grooves ‘
’l are so constructed, the motion‘picture pro
jector which is disposed behind the screen and
the camera which is disposed in front of the
screen must be very carefully aligned >with the
axis of the lens formed by the screen and the
The screen, when lighted from behind and
viewed from the position of the motion picture
camera lens, appears to have a bright line of
light wound in spiral fashion in the same man»
ner as are the grooves l. In order that the screen
" sions of the screen.
It has been found that a
center to center distance between each of the
adjacent grooves 'l of less than île of an inch
gives excellent results. I have found that a screen
of this type of almost any desired size may be
conveniently constructed by molding or by cast
ing a suitable liquid plastic upon a corrugated
matrix surface and allowing the plastic to set or
A novel and convenient way of forming such a
matrix surface is illustrated in Figs. 3, 4 and 5.
distance between the screen and the projector
For this purpose, I prepare a matrix surface hav
and between the screen and the camera must
ing a closely Wound spiral ridge thereon, it hav
be verycarefully adjusted in terms of the effec
ing been found that a closely wound spiral very
tive focal length of the screen. For this rea
closely approaches the desired concentric ar
son it is preferred to make the grooves l of a. 40 rangement. The spiral matrix may be readily
cross section approaching those which may be
formed by employing a core member l2 which
employed in a true Fresnel type of lens but dif
has cut in the upper surface thereof a spiral
fering therefrom by a sufficient amount to avoid
groove i3, the cross section of which is so ad
the aforementioned difficulties arising from the
justed as to provide a spirally wound ridge I4
substantially optically perfect screen.
I accordingly prefer to form the grooves with
a'contour such as that illustrated in Fig. ‘2 com
prising a substantially planesurface 8 which is
disposed at a slight angle to a line normal to the
having the same cross section as the desired cross
section of the groove l. The outermost turn of
the ridge lli is preferably cut abruptly along
the vertical plane passing through the center of
the core Piece l2 to provide an end face l5 such
as that illustrated in Fig. 4. A corresponding
wards the objective of the projector which is
and similar end i6 of a strip of ribbon material
disposed behind the screen. The other face 9
Il may be placed in contact With the end l5
of the groove l is preferably made curved in cross
and secured to the bodylof the core member l2
section, the lowermost part which defines the
by means of a pin IB.
bottom of the groove 'l being disposed substan- .'
The pin lâ may be passed through a hole i9
tially parallel to the front face of the screen
provided in the ribbon Il and into a correspond
I and the part which intersects the front sur
ing hole 2li provided in the edge of the core mem
. face ofthe screen being disposed at a consider
ber l2. The ribbon material Il is then wound
screen surface so as to be directed generally to- i
able angle thereto.
The angle at which the surface 9 intersects
the front face of the screen is controlled by the
camera and projector angle which is subtended
by the screen, it being found that an angle of
substantially 60° at the intersection of the face
9 with the front surface of the screen is sufli
cient to accommodate the total camera angle ofy
about the core member I2 so as to form a con
tinuation of the spiral ridge lll. It will be ob
served that the second turn of the ribbon ma
terial Il covers the head of the pin I8 toprevent
it from coming out of the holes I9 and 20 in
which it is received so that after the ribbon Il
is wound one full turn it will remain secured
to the core member I2. The ribbon ll is then
approximately 40°.
wound about the core member l2 in spiral fash
It will be observed that with this construc
ion until a sheet having a diameter greater than
tion, the light which is projected upon the rear
surface of the Screen by the motion picture pro 70 the diagonal of the screen to be manufactured
is thus formed.
jector will strike the screen at an angle some
The strip material I1 is preferably formed of
what in the fashion indicated by arrows Ill and
a relatively soft metal having little, if any, re
li in Fig. 2. It will be observed that the di
silience so that after it is wound in the spiral
rection of these >arrows is substantially parallel
to the direction of the plane _face 8 so that sub 75 form it will not exert any great force in tend
ing to straighten out and destroy such spiral
therein so that there is formed a substantially
integral border portion 2 comprising the canvas
strip 3U impregnated with overlying layers 3l of
plastic material. The border portion 2 then may
be provided with the required cross sectional con-l C1 be perforated at intervals along its length to pro
vide openings 32 through which the lacings 3
tour in any suitable manner such as by rolling
may be passed.
or extruding or drawing through dies.
It has been found lthat if the completed screen
I have found it desirable to provide a means
including the b‘ody portion I and the border por
for securing adjacent turns of the ribbon mate
I have found that solder or a similar
alloy composed chiefly of lead and tin .provides
the desired characteristics. The strip I1 may
rial I1 to each other to prevent relative move 10 tion 2 be slightly heated as by placing the assem
bly in the sun and then laced tightly within the
ment between these turns. For this purpose I
frame 4 While in a heated condition, the subse
provide a recess 2| having a rectangular cross
quent lowering of the temperature will cause the
section and extending longitudinally the full
screen to shrink and be pulled by the lacings 3
length of the ribbon I1. The recess 2I is adapted
to receive a corresponding tongue or ridge 22 15 very tightly into a true plane surface.
From the foregoing, it will appear that I have
formed upon the opposite f-ace of the strip I1.
provided a novel matrix for constructing a light
It will be seen that as the strip is Wound spirally,
transmitting screen which is very efficient and iS
adjacent turns are held against relative move
capable of many and diverse applications in the
ment by the tongue 22 entering the groove 2|.
The entire matrix surface thus formed may be 20 motion picture industry. Furthermore, I have
provided a novel matrix upon which liquid plastic
secured to a fiat supporting surface or table 23
material may be cast to provide such a screen.
by providing upon the lower edge of the ribbon a
While I have shown and described the prderred
downwardly depending tongue portion 24 yand b'y
embodiment of my invention, I do not desire to
providing in this tongue portion at spaced inter
vals along the length of the strip I1 openings 2-5. 25 be limited to any of the details of construction
A wire 26 or similar securing means may be
shown or described herein, except as defined in
passed through the openings 25 and through suit
the appended claims.
able openings 21 provided in the table 23 so as
to hold the entire matrix structure thereon.
After the matrix has been assembled and secured .
I claim:
l. In a matrix for forming a light transmitting
screen of the type employing a grooved screen
surface defining a plurality of facets for refract
ing light received from a projector disposed on
to its supporting surface 23, the rough rectan
gular outline of the screen I may be defined by a
temporary retaining wall 28 formed of Wax, clay,
or similar material. Within this retaining wall
is then poured, sprayed or otherwise introduced
one side of said screen into a camera disposed
on the other side thereof, the combination of: a
matrix body comprising a thin metal tape wound
a liquid plastic material 29 which is capable of
in spiral fashion about itself, adjacent turns of
one side of said screen into a camera disposed
said spiral lying in contact with each other, said
air-setting or hardening. After the plastic ma
tape having a pre-formed edge portion of a cross
terial 29 has set, the retaining walls 28 may be
section congruent With said grooves for forming
destroyed and the entire sheet may be removed
40 a matrix surface having a plurality of substan
from the matrix surface.
tially concentric ridges thereon.
The sheet thus formed Will be roughly rectan
2. In a matrix for forming a light transmitting
gular in shape and will have formed upon its
screen of the type employing a grooved screen
front face the previously mentioned spiral grooves
surface defining a plurality of facets for refract
1. The sheet may then be trimmed to the de
sired size and suspended for use in any suitable 45 ing light received from a projector disposed on
I have found that a convenient way of
on the other side thereof, the combination of: a
suspending the screen I thus formed within the
matrix body comprising a thin metal tape Wound
frame 4 is to employ the aforementioned border
in spiral fashion about itself, adjacent turns of
portion 2. This b'order may be formed in the
manner indicated in Fig. 2 by taking a strip of 50 said spiral lying in contact with each other; an
edge portion on said tape having a cross section
canvas 30 or other similar strong and porous ma
congruent with said grooves for forming a matrix
terial and folding it back upon itself with one
surface having a plurality of substantially con
edge of the strip disposed upon the upper surface
centric ridges thereon; a longitudinally extending
of the screen body and the other edge disposed
upon the lower surface of the screen body. Liq 55 tongue formed on one side of said tape; and a
longitudinally extending groove formed in the
uid plastic material may then be poured over the
other side of said tape for receiving the tongue on
canvas 30 to completely impregnate the same and
an adjacent turn of said spiral to hold said ad
to act as an adhesive to secure the canvas strip
jacent turns against relative movement toward
3U to the screen I. The application of pressure
at the point where the canvas overlies the screen 60 and away from said surface.
body will result in the canvas being imbedded
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