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Патент USA US3094590

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June 18, 1963
R. ROSIER
AFOCAL OPTICAL SYSTEM FOCAL LENGTH CHANGER
Filed Aug. 3, 1960
F1G.l.
3,094,580
United States Patent O?ice
3,094,580
Patented June 18, 1963
1
2
3,094,580
.AFOCAL OPTICAL SYSTEM FOCAL LENGTH
CHANGER
_
Raymond Rosier, Asnieres, France, assignor to Socrete
In order to suppress this aberration exactly the terminal
lens 2 should be detached from the front lens 1 (FIG. 2),
but the air gap which then separates the two lenses must,
in compliance with the general principle of the invention,
d’Optiqne et de Mecanique dc Haute Precision, Paris,
have its surfaces concentric and of same centre as that of
France, a French company
the front surface.
Filed Aug. 3, 1960, Ser. No. 47,165
Claims priority, application France Aug. 6, 1959
1 Claim. (CI. 88-57)
.
.
(b) The systematic use of concentric surfaces on con
ventional lenses is of course known; but if in these lenses,
the external or internal surface limiting the lenses is cor
10 rectly centered at the same point the center-image proper
This invention relates to an optical combination in
also has this same center of curvature and therefore is
cluded in the class of the “afocal systems.”
strongly curved, so much so, that a sensitive surface is
It is known that in such systems the focus, instead of
used having a spherical form, centred on the common
being positioned at a ?nite distance as in conventional
center of curvature.
lenses, are cast to the in?nite.
15
In fact, in an ordinary objective the ?nal focal length
The advantage of this disposition results from the fact
the structure which is based on the concentricity principle
that it permits in particular, when the afocal system is
of the surfaces, the image-?eld is “applied” on a sphere
?tted in front of a conventional lens adjusted to in?nity,
having for its centre the common center of curvature and
to change the focal length that is to say, in short the mag
for its radius the distance from this point to the image
nitude of the image without altering its position: in this 20 focus. In this case the common center of curvature is
way the setting of a lens on a camera with standard me
the optical center and the objective symmetry center.
chanical print or an ordinary camera is not adversely af
In the afocal combination of the present invention, the
fected by addition of the afocal system. ,,
object-focus and image being projected to the in?nity,
Of course in the case of a short shot the adjustment
the radius of the imagesphere reaches an in?nite value.
should be controlled in taking into account the presence of 25 This means that the image-?eld is ?at. Consequently the
the additional system; this can be readily obtained for
afocal system could be mounted in front of a lens without
example in keeping the lens set on in?nity and adjusting
increasing the proper aberrations of said lens.
the proper setting of the additional system (by spacing of
(c) In order to correct the physical aberrations (chro
its elements).
matisrn)
it is sufficient, according to a known process, to
According to the invention the afocal optical system in 30 divide certain
(or all) simple lenses which constitute the
cludes two elements the ?rst one thereof comprising two
afocal device into two or more lenses having the same
concentric spherical faces and back surfaces, the second
basic index as the simple lens so that the previous correc
element comprising one spherical face surface concentric
tion of the geometric aberrations may not be affected but
to the surfaces of the ?rst element and a plane rear surface.
given dispersion powers or with distinct “V” and properly
The annexed drawing shows diagrammatically an afocal 35 selected. In such case, of course, the power resulting
system according to the invention.
from the constituents should be substantially equal to the
On said drawing:
lens power before division.
FIG. 1 is a basic diagram;
The description which follows of the embodiment of
FIG. 2 is a diagram showing the two separate elements
the accompanying drawing, which is shown only as an ex
of the afocal system;
40 ample and not as a limitation, will show how the inven
FIG. 3 is a diagram showing a special embodiment of
tion can be achieved, the particularities that merge from
the afocal system.
the drawing and from the ‘text as well being, of course an
The diagram of FIG. 1 shows the afocal system com
integral part of the invention.
prising two elements 1 and 2, the radii R; and R2 of the
According to a general standard the direction in which
front surface d; and middle surface d2 having a common 45 the successive elements of the afocal system are encoun
centre C while the rear surface d;, is plane; the surface dz
tered is that of the incident propagation of light, assumed
projects the image to in?nity.
to move from left to right in the drawing. This is also
The following advantages result from the general struc
the adopted positive direction.
ture disclosed above:
The basic indexes (for helium line) of the glasses mak
(a) The aberrations which affect the luminous beams 50 ing up the afocal system elements, satisfy the inequality:
oblique on the axis are the same as the ones affecting the
beams parallel to the optical axis. In fact the secondary
axis of the ?rst such as SI of FIG. 1 cross normally, that
where n is the refraction index of the front lens, n’ the
is to say without refraction, the front surface d; and
refraction index of the next lens in the basic diagram of
middle surface d, of the additional system, which sup 55 FIG. 1.
presses, for these surfaces, any astigmatism, coma or
The concentricity of the surfaces of the afocal combi
chromatism defect. ‘In other Words, the common centre
of curvature is situated in the centre of a pupil. On the
other hand, the image from the middle surface d2 being
nation may be expressed in terms of the thickness e of the
?rst lens, its front radius R and the indexes in and n’:
projected to the in?nity, the refraction through the ter 60
minal plane surface d3 introduces no new aberration.
Consequently, the only defect to be considered is the
As regards the magni?cation of the system, an elemen
spherical aberration. In the hereafter disclosed embodi
tary calculation shows that it is simply expressed by n’.
mcnt this defect would be over-corrected should no cor
The numeral data of the embodiment which follows
rective steps be taken.
65 were determined with regard to the above, by the require
3,094,580
3
ments of the spherical and chromatic corrections and by
economy.
In the basic diagram ‘of FIG. 1, the thickness of the
?rst lens, being due to the concentricity of its radii of
curvature R1 and R2 is equal to their difference. This
part is comparatively thick (if the radii R1 and R2 are
almost equal the second lens would be the thicker of
the two).
Either lens thus represents a considerable amount of
material and there is advantage in production not to cut 10
them from a ‘glass as costly glass having the basic index
type n=1.8 and for v==45.5 for index required with a
high value to satisfy the n>n’ condition.
Consequently the costly material has been used for the
?rst and for the ?fth lens, L1 ‘and L5, both being relatively 15
Radli 0t
Thlcknesses
curvature
ordistances
Lens 1 _______________ __
n4
0
er: 7
1.8
45. 5
ea= 2
1. 62025
36. 2
“=34. 964
1. 62025
60. 2
u: 4
1. 62025
36. 2
es= 2
1.8
45. 5
1. 50050
6|). 7
Rz= w
Lens 2 _______________ .s
Rs = +33
Lens 3 _______________ ..
R4 =+20
Lens 4 _______________ . _
R5: on
Lens 5 _______________ ..
R5 = +15. 49
as: 0. 54
R1=14. 95
Lens 6 _______________ ._
e1: 3
R8: in
where nd is the index of refraction and v is the dispersive
power of the glass of the lenses.
What I claim is:
In an afocal optical lens system, a focal length changer
having six lens elements including a lens unit formed by
?ve of said lens elements having two concentric spherical
thin (FIG. 3).
It is necessary to chromatize and this function is pro
vided by the assembly of connected lenses L2, L3, L4
which constitute a plate with ?at and parallel faces for a
given radiation. These three elements are made up of
glasses having the same basic index (1.62025) for the
helium line dl but with distinct dispersions. Thus if the
surfaces, ‘one front and one rear, the sixth lens element
lens L3 is comparatively bulky it is at least made of a
being separated from said lens unit by an ‘air space and
much less costly material than the lens with a high index.
comprising one front spherical surface concentric to the
An ‘additional advantage is ‘provided by the following 25 surfaces of said lens unit and a plane rear surface, said
fact: this glass is substantially clearer which is all the more
lens unit including two thin terminal lens elements in
contact over adjacent parallel plane surfaces, the lens
interesting as the element is thicker.
The data (radius of curvature, thicknesses and spac
system being substantially in accordance with the follow
ings) for the lenses of the combination of the example,
30 ing table:
were determined while taking into account the structural
modi?cations made to the basic diagram for correction
Radii of
curvature
of aberrations due to the necessity for making the system
afocal. Consequently, the basic radiation, an oblique in
clined pupillary ray at angle a to the optical axis (FIG.
3) and normal to the ?rst surface of the system, refracts 35
by crossing the second surface, crosses without deviation
R2 = cu
the third and fourth surfaces and comes out of the ?fth
surface in a parallel direction to that of incidence and
directed towards the center common to the sixth and
Rs= +33
R4 = +20
seventh surfaces and forms at emergence from the eighth 40
surface an angle 6 the sinus thereof being equal to the
angle a sinus multiplied by the refraction index n’ (which
is also, as already mentioned, the magnifying value).
The afocal system so de?ned is designed for mounting
on the front of a camera lens opened at 1:28, with a
nominal focal length of 50 mm. for the 24 x 36 mm. size.
The resulting combination constitutes an objective of a
focal length of about 75 mm. Naturally the lens workin g
lengths have been amply designed to allow for a free
passage of the pupillary beam coaxially to a full opening 50
R5: m
Ru= +1549
R1=14.95
Thieknesses
or distances
na
v
:1 =7
l. 8
45. 5
ez=2
1. 62025
36. 2
ea=34. 964
1.62025
60. 2
64 =4
1.62025
36. 2
“=2
1. 8
45. 5
I. 50050
60. 7
cu =0.54
ei=3
R! = :2:
wherein R is the radius of a spherical surface of a lens
element, e indicates the thickness of an element of the
system and the thickness of an air space measured along
the axis of the system, nd is the index of refraction of a
in order not to reduce the comparative opening of the
complete combination and to avoid any troublesome dia
lens element and v is the dispersive power of the glass
of the lenses, all the dimensions being measured in like
phragrnation of the oblique beams cooperating with form~
linear units.
References Cited in the ?le of this patent
UNITED STATES PATENTS
ing and illuminance of the margin areas of the total ?eld.
It is to be understood that any embodiment designed for
applying this device to another size of camera lens or on
a visual instrument having an optical formula, with dif
ferent numeral data but complying with thg general con
ditions stated above is included within the scope of the
present invention.
60
874,049
2,522,390
2,785,604
Borsch ______________ __ Dec. 17, 1907
McCarthy ____________ __ Sept. 12, 1950
Blaisse et a1 __________ __ Mar. 19, 1957
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