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Патент USA US2407347

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2,407,347
Patented Sept. 10, 1946
UNITED STATES PATENT OFFICE
2,407,347
OBJECTIVE
Lawrence T. Sachtleben, Indianapolis, Ind., as
signor to Radio Corporation of America, a cor
poration of Delaware
Application June 27, 1944, Serial No. 542,309
8 Claims. (Cl. 88-57)
This invention relates to an objective and,
somewhat exaggerated. The drawing also shows
more particularly, to one adapted to be used in
the path of a pair of tangential or meridional
rays a and b through the margin of the full
an optical system for reproducing sound from
?lm.
Sound tracks having a width up to .200” are,
in many respects, more desirable than tracks of
the standard Width of approximately .100", par
ticularly because of the proportionate gain in
light output and improved signal-to-noise ratio
aperture of the diaphragm to the edge of the
0
image ?eld, as well as a corresponding marginal
ray M of an axial pencil. The table which is
included in the drawing gives the actual speci
- ?cation of said embodiment.
The objective comprises four lenses spaced
obtainable therewith. A substantial increase in 10 from each other along the optical axis of the
e?iciency may be obtained in a system for re
system. In the drawing, the light is regarded
producing sound from wide-track ?lm by in
as passing from left to right, as indicated by
creasing the working numerical aperture of the
arrows, and the lenses are numbered L1 to L4
objective.
in that order, the lens L1 being regarded as the
It is an object of the invention to provide an 15 front lens. The thicknesses of these four lenses
improved objective adapted for use in the re
are indicated by the reference characters T1 to
production of sound tracks on ?lm having a
T4, the eight surfaces and their radii of curva
Width up to .200".
ture by the reference characters R1 to R3, and
Another object of the invention is to provide
the separations between the four lenses by the
an improved, highly corrected objective capable 20 reference characters S1 to S3, all in the same
of operating satisfactorily at an effective speed
order. A diaphragm which may have a diam
of f/2.0.
eter of .267" is located between the two inner
A further object of the invention is to pro
lenses at a distance of .015" from the vertex of
vide an improved objective which has a ?at ?eld,
surface R5.
a working numerical aperture of 0.25 at a mag 25
In the reproduction of sound from ?lm, cesium
ni?cation of 1/5, and minimum focus in the
photocells are ordinarily employed. Such cells
orange part of the spectrum.
are particularly sensitive to red light, and this
A further object of the invention is to pro
is ordinarily derived from a tungsten lamp. One
vide an improved objective which is highly cor
requirement of the objective, therefore, is that
rected for spherical and chromatic aberration,
it should have minimum focus for light of that
astigmatism, ?atness of ?eld, coma and dis 30 color. For practical reasons of design, the A’
tortion.
'
and D lines of the spectrum are united, giving
Another object of the invention is to provide
minimum focus in the orange part of the spec
an improved objective in which, in addition to
trum. For maximum e?lciency, it is also de
sired to maintain the effective speed of the objec
the characteristics before mentioned,‘ there is no
vignetting over the useful ?eld.
tive at f/2.0. A further requirement is that
These objects are achieved by employing a
the magni?cation should be 1A; from the slit (not
four-lens, axially air-spaced objective wherein
shown), from which the light passes to the ob
the two inner, negative lenses are of glass of
jective to the ?lm on which the image of the
higher index of refraction than has been cus
slit is formed.
tomary in prior art objectives of this type, and
To meet these requirements without undue
by selecting such thicknesses for the lenses, such
curvature, the ‘two inner or intermediate lenses
curvatures for the lens surfaces, and such sepa
are made of extra dense ?int glass having an in
rations between the lenses (all of which are de
dex of refraction of 1.72 for light of the D line
of the spectrum, and of 1.70555 for light of the
scribed in detail hereinafter), as are suf?cient
substantially to correct the various aberrations
A’ line of the spectrum. Of these two lenses, the
to which the objective would otherwise be subject.
front intermediate lens is bi-concave and the
The invention may be better understood from
rear intermediate lens is of concave meniscus
a consideration of the following description
form. The two outer lenses are of dense barium
thereof, when read in conjunction with the ac
crown glass, having indices of refraction of
companying drawing, the single ?gure of which 50 1.61088 and 1.60411 for the D and A’ lines of the
is a view in meridian section of a preferred em
spectrum, respectively. The front lens of the
bodiment of the invention. This view is drawn
two outer lenses is bi-convex, and the rear lens
generally to a scale of approximately 6.5:1; but
equi-convex. It was found that departure of
to make the view clearer, the curvatures, thick
the rear lens from the equi-convex form in
nesses and separations of the lenses have been 55 creased spherical over-correction in the- tan
a
I
2,407,347
gential fans at the edge of the ?eld. This form
is also of value because it is not possible in as
sembly to make a mistake by turning the lens
the wrong way, and it therefore provides ease
of assembly.
5
three-fourths of. the focal length of the objec
bending the lens L2 excessively, it was found nec
comprising in order from front to rear in the
direction of incident light, a bi-convex lens, a bi
conoave lens, a meniscus concave lens and an
To prevent spherical undercorrection without
cident light. and the focal length of said equi-con
vex lens being more than one-half and less than
tive as a whole.
2. A four-lens, axially air-spaced objective
essary to reduce the spacing S: between the two
inner lenses. From the data of the preferred
equi-convex lens, the outer lenses being of equal
embodiment, it will be seen that the spacing S2 is 10 thickness and of the same dense barium crown
.0606" for a focal length of the objective of .550",
glass having an index of refraction of less than
which is equivalent to a ratio of somewhat less
1.7, and the inner lenses being of equal thick
than .115 times the focal length, while the radius
ness and of the same dense ?int glass having an
of curvature Ra of the front surface of the lens
index of refraction of greater than 1.7, the axial
L2 is .4564, which is equivalent to a ratio of more 15 separation between the two inner lenses being
than .82 times the focal length. In this embodi
less than .115 times the focal length of the ob—
ment, R3 is more than seven times S2. An in
jective, the surface of said bi-concave lens hav
creased bending of the lens L2 would have required
ing the shorter radius of curvature and the sur
an increase of the spacing S1, but in the preferred
face of said meniscus concave lens having the
embodiment the ratio between S: and S1 was 20 greater radius of curvature being disposed to
maintained at 2:1.
wards the incident light.
In the preferred embodiment, the focal length
3. A four-lens, axially air-spaced objective
of the equi-convex lens L4, as derived from the
comprising in order from front to rear in the
data contained in this speci?cation and the ac
direction of incident light, a bi-convex lens, a
companying drawing, was 0.36368" for the A’ line 25 bi-concave lens, a meniscus concave lens and an
of the spectrum, for which the objective was
equi-convex lens, the outer lenses being of equal
' originally designed. As before stated, the focal
thickness and of the same dense barium crown
length of the objective as a whole, in the preferred
glass having an index of refraction of less than
embodiment, was 0.550", giving a ratio of the focal
1.7, and the inner lenses being of equal thickness length of L4 to that of the objective as a whole 30 and of the same dense ?int glass having an index
of .66124. In general, this ratio should be more
of refraction of greater than 1.7, the radius of
than .5 and less than .75".
' curvature of the front surface of the bi-concave
It was found that coma and ?eld curvature re
lens being greater than .82 times the focal
sponded to bending of lenses L1 and In more
length of the objective, the surface of said bi
than to any other changes in the system, and the 35 concave lens having the shorter radius of curva
?attest ?eld consistent with removal of coma at
ture ‘and the surface of said meniscus concave
the margin of the ?eld was obtained when the
lens having the greater radius of curvature be
radii R1 and R2 were approximately in the ratio
ing disposed towards the incident light.
2:5, and the radii R5 and Re were approximately
4. A four-lens, axially air-spaced objective
in the ratio 14:5. Chromatic correction was es 40 comprising in order from front to rear in the
tablished for each crown and ?int pair separately,
direction of incident light, a bi-convex lens, a
as this practice tends to hold transverse or lateral
bi-concave lens, a meniscus concave lens and an
color aberration to a minimum.
equi-convex lens, said meniscus lens having its
With the objective constructed as here de
concave surface facing said equi-convex lens, the
scribed, it was found that there was no vignetting - outer lenses being of equal thickness and of the
up to an angular semi-?eld of 8° 39', measured
same dense barium crown glass having an index
from the second principal point. The ?eld was
of refraction of less than 1.7, and the inner lenses
strongly ?attened, astigmatism was slightly over
being of equal thickness and of the same dense
corrected, and spherical aberration slightly under
?int glass having an index of refraction of greater
corrected.
50 than 1.7, the radius of curvature of the front
Therehas thus been described a highly cor
surface of the bi-concave lens being at least seven
rected objective particularly adapted for use in
times as great as the axial separation between the
the reproduction of sound from wide-track ?lm.
two inner lenses, said radius of curvature also
The objective has a ?at ?eld, a working numer
being greater than .82 times the focal length of
ical aperture of 0.25 at a magni?cation of 1/5, and 55 the objective, the surface of said bi-concave
lens having the shorter radius of curvature and
minimum focus in the region of the 0 line of the
the surface of said meniscus concave lens hav
spectrum with no vignetting over the useful
?eld.
I claim as my invention:
1. A four-lens, axially air-spaced objective
comprising in order from front to rear in the
direction of incident light, a. bi-convex lens, a
bi-concave lens, a meniscus concave lens and an
equi-convex lens, the outer lenses being of equal
ing the greater radius of curvature being disposed
towards the incident light.
5. A four-lens, axially air-spaced objective
comprising in order from front to rear in the
direction of incident light, a bi-convex lens, a
bi-concave lens, a meniscus concave lens and an
equi-convex lens, saidv meniscus lens having its
thickness and of the same dense barium crown 65 concave surface facing said equi-convex lens, the
outer lenses being of equal thickness and of the
glass having an index of refraction of less than
same dense barium crown glass having an index
1.7, and the inner lenses being of equal thickness
of refraction of less than 1.7, and the inner
and of the same dense ?int glass having an index
lenses being of equal thickness and of the same
of refraction of greater than 1.7, the axial sep
aration between the two inner lenses being double 70 dense ?int glass having an index of refraction of
greater than 1.7, the ratio of the radii of curva
the axial separation between the two front lenses.
ture of the front and rear surfaces of said bi-con
the surface of said bi-concave- lens having the
vex lens being of the order of 2:5, the axial sep
shorter radius of curvature and the surface of
said meniscus concave‘lens having the greater ra
aration between the two inner lenses being less
dius of curvature being disposed towards the in 75 than .115 times the focal length of the objective,
Search Root
2,407,347
5
6
the surface of said bi-concave lens having the
shorter radius of curvature and the surface of
equi-convex lens, the outer lenses being of equal
said meniscus concave lens having the greater
glass having an index of refraction of less than
1.7, and the inner lenses being of equal thick
radius of curvature being disposed towards the
incident light.
6. A four-lens, axially air-spaced objective
thickness and of the same dense barium crown
ness and of the same dense ?int glass having an
index of refraction of greater than 1.7, the di?er
comprising in order from front to rear in the
ence between the radii of curvature of the front
direction of incident light, a bi-convex lens, a
and rear surfaces of said bi-concave lens being
bi-concave lens, a meniscus concave lens and an
less than twenty times the focal length of the ob
equi-convex lens, said meniscus lens having its 10 jective, the surface of said bi-concave lens hav
concave surface facing said equi-convex lens, the
ing the shorter radius of curvature and the sur
outer lenses being of equal thickness and of the
face of said meniscus concave lens having the
same dense barium crown glass having an index
greater radius of curvature being disposed towards
of refraction of less than 1.7, and the inner lenses
the incident light.
being of equal thickness and of the same dense [5
8. A four-lens, axially air-spaced objective
?int glass having an index of refraction of great
comprising in order from front to rear in the
er than 1.7, the ratio of the radii of curvature
direction of incident light, a bi-convex lens, a
of the front and rear surfaces of the meniscus
bi-concave lens, a meniscus concave lens and an
concave lens being of the order of 14:5, the focal
equi-convex lens, each of the outer lenses hav
length of said equi-convex lens ‘being more than
ing a thickness of approximately .2 and being of
one-half and less than three-fourths of the focal
length of the objective as a whole, the surface of
said bi-concave lens having the shorter radius
of curvature and the surface of said meniscus
concave lens having the greater radius of cur 25
vature being disposed towards the incident light.
7. A four-lens, axially air-spaced objective
the same dense barium crown glass having an
index of refraction of less than 1.7 each,‘ of the‘
inner lenses having a thickness of approximately
.045 and being of the same dense ?int glass having
an index of refraction of greater than 1.7, the ax
ial separation between said lenses in said order be
ing, respectively, .055, .110 and .044, all dimensions
comprising in order from front to rear in the
being calculated in decimals of the focal length
direction of incident light, a bi-convex lens, a
of the ‘objective.
bi-concave lens, a meniscus concave lens and an 30
LAWRENCE T. SACH'I'LEBEN.
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