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Патент USA US3045556

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' United States Patent 0 ” CC
3,045,546
Patented July 24, 1962
2
1
the convergent front member comprises a plurality of
3,045,546
convergent components of which at least one is a doublet
FOCAL LENGTH
component having a dispersive internal contact surface
and at least one is a simple component, whilst the di
OPTICAL OBJECTIVES OF VARIABLE
Gordon Henry Cook, Leicester, England, assignor to Tay
vergent second member comprises a plurality of divergent
lor, Taylor & Hobson Limited, Leicester, England, a
components of which at least one is a doublet component
having a collective internal contact surface and at least
British company
Filed Sept. 29, 1958, Ser. No. 764,006
Claims priority, application Great Britain Oct. 2, 1957
14 Claims. (CI. 88-57)
This invention relates to an optical objective for photo
graphic or other purposes, having relatively movable
one is a simple meniscus component whose rear surface
is convex to the front and has radius of curvature not
10 less than 0.33)‘; and not greater than the range of axial
members, whereby the equivalent focal length of the ob—
jective can be varied at will, whilst maintaining good
correction for the various aberrations.
movement of such divergent second member, where f2
is the equivalent focal length of such second member.
in one arrangement of such objective, the convergent
front member comprises a simple convergent component
located in front of a convergent doublet component
Desirable features in such an objective include a wide
whose front surface is convex to the front with radius
range of continuously variable focal lengths, constant
of curvature between 0.5f1 and 1.0f1 (where fl is the
equivalent focal length of the convergent front member),
focussing position throughout the range, constant relative
aperture throughout the range at any setting of the dia
phragm, a short distance ‘from front vertex to focal
plane, simplicity of construction to minimise loss of light
by absorption and reflection and also to reduce weight,
and focussing for near objects independent of focal
length.
All these desirable features have been attained by the
invention forming the subject of United States of America
patent speci?cation'No. 2,649,025, according to which
the objective comprises an axially movable divergent
at least one simple meniscus component in the divergent
second member having its rear surface convex to the front
with radius of curvature not less than 0.5f2.
In an alternative arrangement, the convergent front
member comprises a convergent doublet component lo
cated in front of a simple convergent component whose
front surface is convex to the front with radius of curva
ture between 0.4f1 and 0.813. The internal contact sur
face in such doublet component is preferably convex to
the front with radius of curvature between 0.41‘, and
member located in front of a stationary convergent rear
09h, the mean refractive index of the material of the
member and behind an axially movable convergent front 30 front element of such doublet component exceeding that
member, wherein in each operative position the equiva
of the rear element thereof by between 0.05 and 0.15.
lent focal length of the divergent combination of the
In either of such arrangements, the radius of curvature
front two members bears to that of the complete objec
tive a ratio between 8 and 13 times the reciprocal of the
vergent front member is preferably greater than 1.511,
f/number of the objective, the virtual image of a distant .
whether such surface is convex or concave to the front.
of, the rear surface of the front component of the con
object formed by such divergent combination having a
Preferably, the ratio of the equivalent focal length of
constant axial position relatively to the stationary rear
member throughout the range of variation of the equiva
the divergent combination of the front two members to
the equivalent focal length of the whole objective lies
lent focal length of the objective, the complete objective
between 3 and 8 times the reciprocal of the f/ number of
being corrected for spherical and chromatic ‘aberrations, 40 the objective.
coma, astigmatism, ?eld curvature and distortion through
The equivalent focal length h of the convergent front
out the range of variation.
member preferably lies between 1.0f2 and 1.67)‘; times the
It should be made clear that the terms “front” and
value of the expression (l+\/Q), where Q is the ratio
“rear” are herein used in accordance with the usual con
of the value of the upper limit of the range of variation
vention to relate to the sides of the objective respectively 45 of the equivalent focal length of the complete objective
nearer to and further from the longer conjugate.
to the value of the lower limit'thereof. In this case, the
The present invention has for its object to effect im
ratio of the equivalent focal length of the complete ob
provements in the variable focus objective of such prior
jective at the lower end of the range of variation thereof
patent, especially in respect of its optical properties, and >
to the f/number of the objective lies between 0.27;‘2 and
more'particularly, whilst still attaining the desirable fea 50 0.565.
tures above mentioned, to achieve increased relative aper
The rear component of the divergent second member
ture and increased angular ?eld of view and at the same
preferably consists of a divergent doublet component
time to enable the objective to focus on objects closer to
whose internal contact surface is collective and convex
the camera. These improved optical properties render
to the front with radius of curvature between 0.66)‘, and
'the objective according to the present invention highly 55 1.55, the mean refractive index of the material of the
suitable, not only for exterior use at relatively great ob
rear element of such doublet component exceeding that
ject distances, but also for studio photography or cine
of the front element of such component by between 0.15
matography or television photography.
and 0.3. Preferably, the divergent second member com
The objective according to the present invention is
prises two divergent simple meniscus components in front
corrected for spherical and chromatic aberrations, coma, 60 of a divergent doublet component, and has axial length
astigmatism, ?eld curvature and distortion throughout the
between 0.613 and 1.313.
range of variation, and comprises an axially movable di
Preferably, the ratio of the equivalent focal length f_-,
of the stationary rear member to the equivalent focal
vergent member located in front of a stationary con
length of the complete objective at the lower end of the
vergent rear member and behind an axially movable con
vergent front member, wherein throughout the range of 65 range of variation thereof lies between 1.25 and 2.5\/Q,
variation the ratio of the equivalent focal length of the
and such ratio may also conveniently lie between 0.2 and
divergent combination of the front two members to the
1.2 times the f/number of the objective.
equivalent focal length of the complete objective remains
The Petzval sum for all the surfaces of the stationary
constant and the virtual image of a distant object formed
rear member may conveniently lie between 0.3 and 4.0
by such divergent combination has a constant axial posi 70 times the equivalent power of such member.
_
tion relative to the stationary rear member, and wherein
Conveniently, the diaphragm of the objective is located
3,045,546
3
4
at or near the front surface of the stationary rear mem
Thus, the Petzval sum for all the surfaces of such
ber, and the diameters of the front two members are
made larger than is necessary to accommodate the full
axial beam. This ensures that the diaphragm will always
be the effective aperture stop of the system and that the
angle of the cone of light from the rear member to an
rear portion preferably is positive and lies between 0.25
and 0.85 times the reciprocal of the equivalent focal length
of the complete objective at the lower end of the range
of variation thereof. For distortion compensation, at
least one of the four air-exposed surfaces of such rear
axial image point will remain constant throughout the
portion should preferably be both collective and strongly
convex towards the diaphragm. For oblique colour com
range of variation, and therefore that the relative aper
ture of the objective will remain constant throughout such
pensation, such rear portion preferably includes at least
range for any one setting of the diaphragm.
10 one internal contact between a convergent element and
Focussing for near objects is preferably effected by
a divergent element, the Abbé V number of the material
of such convergent element exceeding that of such di
axial-movement of the convergent front member inde
pendently of the second and third members.
vergent element by at least 20. It should be made clear
Conveniently, with the above described objective, use-.
ful alternative arrangements thereof may in some cir
cumstances be obtained by replacement of one stationary
rear member by another, the front two members re
maining unaltered. For this purpose, the lens mount
housing the objective may conveniently be providedwith
that the term “internal contact” as used therein is in
tended to include both an internal cemented contact sur
face and a broken contact, that is, a contact formed be
tween two surfaces differing by so little in curvature that
the contact can be assumed for all practicable purposes
to have a radius of curvature equal to the harmonic mean
means whereby two or more alternative rear members
of the radii of curvature of the two surfaces forming such
can be selectively attached to the mount in the correct
broken contact.
In the case when two alternative rear members are pro
vided for use with the same pair of movable front mem
bers, the rear member associated with the higher f/num
position relative to the front axial movable members.
It should also be mentioned that it is often practicable,
with a given example of the above described objective,
for such example to be scaled proportionally to suit
different ranges of variation of the equivalent focal length
of the complete objective, the range of variation of angu
ber and with the range of higher equivalent focal lengths
may consist of two convergent portions separated from
one another by an air space whose axial length is greater
lar ?eld covered by the objective remaining approximately
than the equivalent focal length of either of such por
tions. For example, the front portion may consist of a
the objective.
30 convergent doublet component, whilst the rear portion
Again, for example in the case of two differently sized
widely spaced therefrom may consist of two convergent
television cameras having different sensitivities and whose
doublet components.
ranges of variation of equivalent focal length are related
Four practical examples of variable focus objective ac
by a scaling factor of say 2.5, it may happen that it will
cording to the invention will now be described by way
suffice for the objective of the larger camera to have
of example with reference to the accompanying drawings,
an f/number about 2.5 times the f/number of that of
in which
the same in such scaled variants, as also the f/ number of
the smaller camera. In such case, it is possible to utilise
the same two front members for both cameras, but with
FIGURE 1 shows one example of variable focus ob
jective suitable for use in the smaller of the above-men
different rear members, giving ranges of focal length and
tioned television cameras, as well as for other uses,
also f/numbers related by the same factor, say 2.5, but 40
FIGURE 2 shows one example of variable focus ob
both covering approximately the same range of angular
jective suitable for use in the larger of such television
?eld. A typical example of this is for a television camera
having a f/ 1.8 objective with equivalent focal length
varying from 2.25 to 8.0 centimetres, and a second tele
vision camera having an f/4.5 objective with variation
of equivalent focal length from 2.25 to 8.0 inches. .
A further possibility is, by substitution of a different
rear member, to give, in any position of adjustment of
the front members, an increased equivalent focal length
of the objective, without change of image size, and there
fore with reduced angular ?eld.
Widely different types of rear member may be em
ployed, but in general it is important for the rear mem
ber to have the correct Petzval sum dependent on that
of the front two members, and to provide the correct
compensation for the residual distortion and oblique
colour aberrations of the front two members. Such dis
tortion and oblique colour compensation can most effec
tively be provided by suitable choice of the parts of the
cameras, as well as for other uses,
FIGURE 3 shows a further example which may be used
in the smaller television camera, and
FIGURE 4 shows a fourth example which may be used
in the larger television camera.
Numerical data for the example of FIGURE 1 are
given in the following table, in which R1, R2 . . . rep
resent the radii of curvature of the individual surfaces
counting from the front, the positive sign indicating that
the surface is convex to the front and the negative sign
that it is concave thereto, D1, D2 . . . represent the axial
thicknesses of the various elements, and S1, S2 . . . rep
resent the axial air separations between the components,
the table also giving the mean refractive index nd for the
d-line and the Abbé V number of the material used for
each element. The table also gives the clear diameters
for the air-exposed surfaces of the objective.
rear member furthest from the diaphragm of the objec 60 The insertion of equals (=) signs in the radius columns
of the tables, in company with plus (+) and minus (-)
tive, which as above mentioned is preferably located near
the front surface of the rear member.
Thus, the Petzval sum for all the surfaces of the rear
member preferably lies between 0.35/1‘, and 0.7/f2, and
may also lie between 0.7 and 1.4 times the positive value
of the equivalent power of the divergent combination
of the front two members in the position of adjustment
corresponding to the lower end of the range of variation
of the equivalent focal length of the objective.
Usually, the stationary rear member will include at
least six air-exposed surfaces, and the rear portion of
such- member, having the rear four of the air-exposed
surfaces, is especially important in connection with the
residual aberrations of the front two members.
signs which indicate whether the surface is convex or
concave to the front, is for conformity with the usual
Patent Office custom, and it is to be understood that these
signs are not to be interpreted wholly in their mathematical
signi?cance. This sign convention agrees with the mathe
matical sign convention required for the computation
of some of the aberrations including the primary aberra
70 tions, but different mathematical sign conventions are
required for other purposes including computation of
some of the secondary aberrations, so that a radius indi
cated for example as positive in the tables may have to be
treated as negative for some calculations as is well under<
stood in the art.
3,045,546
5
6
Example I
R2 in this doublet component is dispersive and convex
to the front with radius of curvature equal to 0.609)‘;,
[Equivalent focal length varying from F0=1.000 to Fm=3.555. Relative
the difference between the mean refractive indices of the
materials of the two elements of this component being
‘0.11. The rear surface R3 of such doublet is slightly
concave to the front with radius of curvature equal to
aperture 171.8]
Radius
Thickness or Refractive
Air Separation Index m
Abbe V
Number
Clear
Diameter
3.85f1.
R1 =+ 7. 5120
3 984
D1 =0.1693
1. 7618
26. 98
D2 =0. 7902
1.651
58. 60
R1 =+ 3. 2319
R: =-20.4139
3.721
S, =0.0056
R4 =+ 2.9246
3.248
D; =0. 3612
1. 651
58.60
R, =+ 4.7196
3.113
S2 =0. 0564 to
1.9995
R5 =+ 1.7611
1.795
D4 =0.1129
1.62344
56.22
R1 =+ 1.0395
1.524
S3 =0. 2484
Rs =+ 2. 9246
1.510
D5 =0.1129
1. 62344
56. 22
Re =+ 1.6104
1.377
S4 =0. 5757
Rm=— 1. 7367
1. 156
De =0. 0903
Rn=+ 1.3767
1. 51507
56. 35
1. 7618
26.98
I
D1 =0. 2145
R1z=+ 7.2263
D! =0. 2484
1. 717
tween the front two members is increased to the maximum
0.986
member from its initial position to increase the equiva
lent focal length F of the objective from its minimum
0.960
value F0 is given by the expression fz(F—-Fo)/\/FmFo,
0.835
‘and the forward movement of the front member from its
S6 =0. 2484
R15=— 1.1519
Rlt=— 0.6037
R11=+ 1.1519
D9 =0. 2484
1.723
37. 99
Dw=0. 1242
1. 64793
33.80
1. 6935
1.005
It will thus be seen that the front member at ?rst moves
1.063
forward and then back again, returning to its initial posi
tion again when F reaches its maximum value Fm. The
53. 39
R1u=-— 1.5956
Ss =0. 3951
R1u=+ 1.4933
Rn=— 0.9178
initial position is given by the expression
0.805
S7 =0. 3048
R1a=+ 5.9011
D11=0. 2484
air space S2 between the front two members has its lowest
value 0.0564F0, whilst the air space S5 between the rear
two members has its highest value 2.1124150. When the
objective is to be adjusted to increase its equivalent focal
length, the middle member is moved backwards towards
the stationary rear member until in the position of maxi
mum focal length Fm the air space S5 has been reduced
to O.l693Fo, and at the same time the air space S; be
value 1.9995130. The backward movement of the middle
46.0
R14=-— 5.9011
>
1.072
S5 =2.1124 to
0.1693
R13=+ 1.1519
10
’
The semi-angular ?eld covered by the objective varies
from about 191/2 degrees at minimum equivalent focal
length F0 to about 51/2 degrees at maximum equivalent
focal length Fm.
In the position of adjustment giving the lowest value
F0 of the equivalent focal length of the objective, the
1.209
Du=0. 5080
1. 6968
55. 61
D1s=0. 1129
1. 70035
30. 28
most forward position of the front member occurs when
F'q/FmFo so that ‘at the time the front member has ad
vanced (as indicated at c) by about 0.59F0, from its
initial position. In this way the overall length of the ob
jective is kept short throughout the range of variation.
In this example, the equivalent focal length f1 of the
During these movements the conjugate, distances of
convergent front member in front of the air space S2 is 40 the middle member (that is the distances from its nodal
5.3067150. The equivalent focal length f2 of the divergent
points of the image of the object formed by the front
second member between the air spaces S2 and S5 is _ member and of the virtual image of such image formed
1.4337F0 so that the ratio of F0 to the f/number of the
by the middle member) vary; the ratio of such conjugate
objective is equal to 0.3913. The equivalent focal length
distances being the magni?cation produced by the middle
)3 of the convergent stationary rear member behind the
member. Thus, if M0 and Mm are the values of such
air space S5 is 1.6917Fo so that the ratio fa/Fo is equal
magni?cation corresponding respectively to the minimum
to 0.94 times the f/number of the objective.
'
and maximum focal lengths F0 and Fm, then
The equivalent focal length of the divergent combina
Mm/ M02Fm/ F0
tion of the front two members varies between 2.8143170
and 10.0065Fo. The ratio of this focal length to the
The arrangement is such that this magni?cation passes
equivalent focal length F of the whole objective remains
through unity when FWFmFO, so that in fact
constant throughout the whole range of variation and is
equal to 2.8143, which is 5.0657 times the reciprocal of
the f/number, 1.8, of the objective.
Since the virtual image of the object formed by the
The ratio f1/f2 is 3.701, which is 1.283 times the ex
combination of the front two members occupies the same
pression (1+\/Q), where Q is equal to Fm/Fo and Fm/Fo
position relatively to the stationary rear member in all
is 3.555. It will be noticed that the ratio f3/F0 is greater
positions of adjustment (that is, the algebraic sum of the
back focal length of this combination and the separation
than 1.25 and less than 2.5\/Q, that is 4.714.
The divergent second member between the air spaces 60 between the middle member and the rear member re
mains constant in all positions), such image in the ex
S2 and S5 consists of two simple meniscus divergent com
ample being 4.8573F0 in front of the surface R13, the po
ponents located in front of a doublet divergent component,
sition of the image thereof formed by the stationary rear
whose internal surface is collective with radius R11 equal
R”: m
1. 119
member likewise remains the same, so that the image
to 0.9615, the difference between the mean refractive
indices of the materials of the two elements of this doublet 65 plane A of ‘the whole objective remains ?xed in position
throughout the adjustment, the back focal distance a from
being 0.247. The radii of curvature of the rear surfaces
R7 and R9 of the two simple components are respectively
0.7251‘2 and 1.123f2. The range of movement of this
divergent member is l.943lFo. The overall axial length
of this member between the air spaces S2 and S5 is
1.3547F0 or 0.945192.
the rear surface R20 to such image plane A being 1.1056Fo.
The size of the image however increases as the equivalent
focal length increases, and the ratio of the maximum
image size to the minimum image size is clearly. equal
to Fm/Fo.
In the foregoing description of the movements, it has
The convergent front member consists of a convergent
been assumed that the object position remains unchanged,
doublet component in front of a simple convergent com
for example at in?nity, and it will be clear that for a
ponent whose front surface R4 is convex to the front
with radius equal to 0.5 5 1 f1. ' The internal contact surface 75 ?xed object position the resultant image position remains
3,045, 546
7
8
?xed, the effect of the adjustments being to_alte?r__the___s_ige
also equal to 0.532/f2 and to —-l.04 times the equivalent
power of the divergent combination of the front two
members, at the lower end of the range of focal length
variation, such power being —0.3554/F0.
v_lf_t_h_e imageJ'l'fT however, the object position changes;~
a furtl?adj'ustment will be necessary in order to retain;
the same resultant image position for all object positions];
This can be simply achieved by an additional movement
of the front member independgngiluo_f_ the mlddw
rear meglhers/ Taking'th'e position (or ~faMthTé'FFETnge of
The individual Petzval curvatures of the surfaces of
the rear portion of the stationary rear member (such rear
portion comprising a convergent simple component fol
lowed by a convergent doublet component) are respec
positions) of the front member corresponds to an in
?nitely distant object as the standard, the necessary fur
tively for R18 +0.069/Fo, for R19 +0.257/Fo, for R20
ther adjustment of the front member for focussing for 10 +0.275/F0, for R21 —0.00l/F0 and for R22 zero, so that
a near object consists of a forward movement of such
member through a distance equal to f12/ (ll-f1) , where d is
the distance of the object in front of the front nodal point
of the front member in its position of adjustment. Since
the Petzval sum for this rear portion is 0.6/F0. The sur
face R20 is both collective and strongly convex to the
front and contributes largely towards compensation of
the residual distortion error of the front two members.
this expression is independent of the equivalent focal 15 The Abbé V number difference across the cemented sur
length F of the whole objective, it will be clear that with
each and any additional adjustment of the front member
to suit a particular object distance, the main movements
to vary the focal length and alter the image size can still
be effected without altering the resultant image position.
face R21 in the doublet component amounts to 25.33, and
thus contributes largely towards compensation of the
residual oblique colour error of the front two members.
Numerical data for the alternative example of variable
focus objective shown in FIGURE 2 are set forth in the
following table.
This arises from the fact that in any one position of the
Example 11
middle member, the additional movement of the front
[Equivalent focal length varying from F0: 1.000 to Fm: 3.555.
member to suit object distance is such that the image of
Relative aperture 174.5]
the object formed by the front member always occupies
the same position relatively to the middle member. In 25
other words, throughout the whole range of both adjust
ments, the position of the virtual image of the object
formed by the combination of the front two members
remains constant relatively to the stationary rear member.
Radius
R1 =+2.9578
The two movements can readily be eifected by a suitable 30
R1 =+1.2724
mechanism interlinking the movement of the middle
R3 =—8.0370
member with that of a carriage on which the front mem
R4 =+1.1514
ber is adjustably mounted.
In order to maintain constant relative aperture through
out the range of movement and also to avoid objectionable 35
vignetting of the oblique rays, the clear diameters of all
the surfaces of the front two members are made greater
than is necessary to accommodate the full axial beam for
all settings of the iris diaphragm, which thus alone de
termines the relative aperture in all positions of adjust
ment. In the example, the iris diaphragm is located
0.0564170 in front of the surface R13 and has maximum
diameter of 0.952170. The clear diameters of the indi
vidual surfaces in the example are speci?ed in the table
of data given above, these values being well in excess of 45
the full diameter of the axial beam. Thus, for instance,
Thickness or Refractive Abbe V
Air Separation Index n4 Number
Clear
Diameter
1. 569
D1 =0.0667
1.7618
26. 98
Dz =0.3111
1.651
58. 60
1.465
51 =0.0022
1.279
Ds =0.1422
1. 651
58.60
Rs =+1.8581
1.226
Sr =0.0222 to
0.7872
R6 =+0.6933
R1 =+0.4093
D4 =0.0444
1.6234
56. 22
0.707
0.600
83 =0.0978
Rt =+1.1514
0.594
D: =0.0444
1.6234
56.22
R9 =+0.6340
'
0. 542
S4 =0.2267
R1o= -0.6837
R1|=+0.5420
0. 455
De =0.0356
1. 5151
56.35
D1 =0.0844
1.7618
26.98
Rn=+2.8450
0. 388
S5 =0.8316 to
0.0667
Rit=+1.5650
the maximum diameter of the axial beam at the surface
R14=—0.4601
R1 varies during the adjustment from 0.556Fo to 1.976Fo,
Rr5= —0.8424
0.388
D; =0.1333
1.5151
56. 35
Do =0.0667
1. 7283
28.66
0. 405
st =2.1112
the clear diameter of such surface being 3.984150. At
R.t=+2.3003
0~ 984
D1o=0.2222
1. 5075
61.16
the surface R5, whose clear diameter is 3.1l3F0, the axial
Rn=—1.0337
beam diameter varies from 0.494Fo to 1.752F0. For the
Du =0.0667
1.70035
30. 28
Ris=-4.3350
1. 014
surface R6, having clear diameter 1.795F0, the axial beam
S7 =0
diameter varies from 0.487130 to 0.997Fo.v For the sur
Rm=+0.8386
,
>
1.041
D12=0.2667
1. 5097
64. 44
face Rm, having clear diameter 1.072F0, the axial beam
Rz0=—2.3003
.
55
diameter varies from 0.544F0 to 0.930Fo.
D1a=0.0667
1. 70035
30. 28
Rzr=+9.8290
_
0.986
In this ?rst example, the stationary rear member has
four components, of which the ?rst is simple and conver
In this second example, the iris diaphragm B, which
gent, the second is a divergent doublet, the third is simple
has a maximum diameter 0.381F0, is located 0.0222Fo in ‘
and convergent and the fourth is a convergent doublet.
The objective is well~corrected throughout the range of 60 front of the front surface R18 of the rear member, and
the virtual image of the object formed by the divergent
variation for the usual primary aberrations and also for
combination of the front two members is located 1.8901F0
secondary aberrations. It is to be appreciated, however,
in front of the diaphragm. The back \focal distance a
that the number and arrangement of the components of
from the rear surface R21 to the image plane A is 0.596Fo
the rear member may be considerably modi?ed, inde
and remains constant in all positions of adjustment. The
pendently of the two front members, according to cir
semi-angular ?eld covered is the same as in the ?rst
cumstances.
example, varying from 191/2 degrees at minimum equiva
In the above example, the Petzval sum for the surfaces
lent focal length F0 to 51/2 degrees at maximum equiva
of the movable convergent front member is +0.116/F0,
lent focal length Fm. The equivalent focal length f1 of
that for the movable divergent second , member
the front member is 2.0892130 and that of the divergent
is --0.447/F0, that for the stationary convergent rear
second member f2 is 0.5644Fo, so that the ratio of F0 to
member is +0.371/F0, and that for the complete objec
tive is +0.040/F0. Since the equivalent power of the
rear member is 0.591/Fo, its Petzval sum is 0.63 times
such power. The Petzval sum of the rear member is
the f/number in this example is 0.3913. The equivalent
focal length f3 of the stationary rear member is 3.1585 F0,
so that the ratio fa/Fo is equal to 0.713 times the f/num
ber of the objective.
3,045,546
10
for the smaller camera. In the ?rst example above de
As in the ?rst example the ratio f1/f2 is 3.701 or
1.283 (l+\/Q). The ratio fa/Fo is again greater than
1.25 and less than 2.5\/Q, Q being again equal to 3.555.
The ratio of the equivalent focal length of the divergent
scribed, where the equivalent focal length f; of the rear
member is materially smaller than the combined equiv
alent focal length of the front two members, when the
rear member of the objective is replaced by an alternative
rear member whose equivalent focal length is about 2.5
times that of the rear member given in the table, without
combination of the front two members to that of the
whole objective is again constant and is equal to 1.108,
which is 4.986 times the reciprocal of the f/ number (4.5)
of the objective.
altering the front two members, the minimum and maxi
,
mum equivalent focal lengths of the two alternative com
In the example of FIGURE 2, the rear member com
prises two widely spaced convergent portions, the front
10
plete objectives thus obtained are respectively related by
a factor of approximately 2.5, the angular ?elds covered
by the two objectives are the same and the f/numbers of
the two objectives are related by a factor of approxi
mately 2.5. Now if the data in the second table above set
forth are scaled up by a factor of about 2.5, it will be
realised that the data given for the front two members
two portions of the rear member are each less than the
become identical with that given for the front two mem
axial air space between them.
_
bers in the ?rst table, so that the examples of FIGURES
The individual Petzval curvatures of the surfaces of
1 and 2 constitute two alternative complete objectives of
the rear portion of the rear member are respectively, for
above-described kind, the rear member of the second
R1‘, 0.146/F°, for R17 -o.073/F0, for R18 +O.095/F0, 20 the
example
being and alternative rear member for the same
for R1,, +0.403/F0, for R20 —O.032/F0, and for R21
front two members. The two alternative complete ob—
—0.042/Fo, so that the Petzval sum forlall the surfaces
. jectives are respectively suitable for use in the two televi
of such rear portion is positive and equal to 0.497/Fo.
sion cameras above mentioned, the objective of the ?rst
The Petzval sum of the whole rear member is positive and
equal to 0.958/Fo, which equals 0.540/7‘2 or 1.07 times 25 example being suitable for the smaller camera and the ob
jective of the second example being suitable for the
the equivalent power (0.903/F0) of the divergent com
larger camera.
_
\bination of the front two members in the minimum focal
The following table sets for the numerical data for
length position. The surface R19 is both collective and
the rear member of Example II in terms of the same basic
strongly convex towards the diaphragm of the objective
and thus largely contributes towards compensation for 30 unit as the table for Example I, i.e. the minimum equiv
alent focal length F0 of Example I.
the residual distortion error of the front two members.
portion consisting of a convergent doublet component
having equivalent focal length 1.38%, whilst the rear
portion consists of two convergent doublet components,
whose combined equivalent focal length is 1.52F0. It
will ‘be noticed that the equivalent focal lengths of the 15
The Abbé V number difference across the cemented sur
face R1», is 30.88 and that across the cemented surface R20
is 34.16, such differences, especially the latter, largely con
Radius
Thickness or Refractive Abbe V
Air Separation Index nd Number
Clear
Diameter
tributing towards correction of the residual oblique colour
S5 =2.1124 to
error of the front two members. The movements of the
front two members are the same as those described for
the ?rst example but on a reduced scale, the maximum
forward movement of the front member being indicated
at 0 (‘approximately 0.241%) whilst the front and rear
surfaces of the divergent second member in its rearmost
position are indicated by broken lines.
It will be observed that the components of the ?rst
and second members in the second example are arranged
0.1693
Rl3=+ 3.9752
0.985
D; =0.3387
1. 51507
56. 35
DD =0.1693
1. 72830
28. 66
Ru=~ 1.1687
Rl5=-‘ 2.1397
'
7
.
1.028
SB =5.3625
Rm=+ 5.8428
2.500
Dw=0.5645
R11=-— 2.6255
D11=0.l693
R1s=~1l.0l09
-
1. 50749
61.16
1. 70035
30. 28
‘
2. 576
S7 =0
in the same manner as in the ?rst example, and further
more that the radii of curvature of individual surfaces of
Rm=+ 2.1301
the front member have the same relationships with the
equivalent focal length f1 of such member in each exam
ple, as have also the radii of curvatures of surfaces in
R21=+24.9657
_
2. 645
Di:=0.6774
1. 50970
64. 44
D1a=O.1693
1. 70035
30. 28
R2o=— 5.8428
2. 504
the second member with the equivalent focal length f2. 50
The data in this table completely describes the alterna
It will be clear that the objective in either of the two
tive rear member for the objective of Example I, which is
above-described examples may be proportionately scaled
suitable for the smaller television camera, to provide an
dimensionally to suit various requirements. For exam
alternative objective suitable for the larger television
ple, the objective in either example may be scaled dimen~
camera. It will be clear that in‘ these alternative objec
sionally to have a minimum equivalent focal length F0 of 55 tives, the rear members are not related simply by a scaling
1 centimetre and a maximum equivalent focal length Fm
factor since, when one of such rear members is dimen
of 3.555 centimetres, or alternatively the objective may
sionally scaled, its degree of aberration correction is also
be scaled so that F0 is equal to 1 inch and Fm is equal
similarly scaled, whilst the requirement is that the aber
to 3.555 inches. In the former case, the ?gures in the
ration correction aiforded by each rear member should
table for such example are indicative of measurements in 60 be the same since the alternative objectives employ iden
centimetres and in the latter case such ?gures are indica
tical movable members and the aberration corrections of
tive of measurements in inches. The scaling factor for
the rear member must compensate for the residual aberra->
the complete objective in this instance is 2.54, that is, the
tions of the front members. One advantage of modifying
ratio 1 inch to l centimetre. When the complete objec
the rear member only of the objective for the smaller
tive is scaled in this manner not only the angular ?eld 65 camera to suit the larger camera is that the larger camera
covered by the objective remains unaltered, but also the
f/number of the objective is unaltered.
will be able to focus on objects equally as close to the
camera as will the smaller camera, whereas the scaling up
of the whole objective results in a corresponding scaling
It may sometimes be the case, for example with two
differently sized television cameras having different sensi
up of this minimum focussing distance. It will be ap
tivities, that in addition to such cameras requiring variable 70 parent in the above described circumstances, that instead
focus objectives whose minimum and maximum equiv
of providing two complete objectives, one for each cam
era, it may often be convenient to provide interchange
able rear members in the mount housing the movable
example of approximately 2.5, the larger camera need
members, such complete mount being suitable for use in
only be provided with an objective having an f/number
of about 2.5 times the f/number of the objective needed 75 either one of the cameras. For convenience, FIGURES
alent focal lengths are related by a scaling factor, for
3,046,546
11
1 and 2. have been drawn to scales which make the size
of the front two members the same in each ?gure in
order to make clear the interchangeability of the rear
In this example, the back focal length a from the sur
face R22 to the rear focal plane A of the objective is
l.3577F0. The iris diaphragm B is located as near the
members.
front surface R13 of the rear member as is practicable.
This means that in terms of the minimum
equivalent focal ‘length F0 respectively of Examples I
and II, the scale of FIGURE 2 is approximately 2.5 times
the scale of FIGURE 1 since the minimum equivalent
The equivalent focal length h of the convergent front
member in front of the air space S2 is 5.5227170. The
equivalent focal length f2 of the divergent member be
focal length F0 of such examples are related by this
tween the air spaces S2 and S5 is 1.4338F0
factor.
ratio of F0 to the f/number (1.9) of the
It should be mentioned, however, that when the rear 10 0.365f2. The equivalent focal length is of
member of one objective is replaced by another rear
gent stationary rear member behind the air
member, so as to give an alternative objective having an
1.4649Fo so that the ratio fa/Fo is equal to
increased equivalent focal length (in any position of ad
justment of the front members) and approximately the
same angular ?eld, the Petzval sum of the rear member
should not be reduced and the ratio of such sum to the
equivalent power of the rear member will therefore in
crease in approximately the same proportion as the
increase in the equivalent focal length. Conversely, a
so that the
objective is
the conver
space S.,, is
0.771 times
the f/number of the objective.
The equivalent focal length of the divergent combina
tion of the front two members varies between 2.9291F0
and lO.4l46Fo. The ratio of this focal length to the
equivalent focal length F of the Whole objective remains
constant throughout the whole range of variation and
is equal to 2.9291, which is 5.565 times the reciprocal
substitution of a more powerful rear member to provide 20 of the f/number (1.9) of the objective.
an alternative objective of reduced equivalent focal length
would reduce such ratio.
In a further variant of either of the above described
complete objectives, the equivalent focal length of the
whole objective may be increased, in any position of ad
justment, by appropriate change of rear member, without
changing the image size. This results in smaller angular
?elds of view and in these circumstances it is permissible
to reduce the Petzval sum of the whole objective or to
make such sum negative. Small changes of this kind can
be achieved by merely scaling the rear member and mak
ing relatively minor dimensional changes to re-balance
the aberrations.
A further example of variable focus objective is shown
in FIGURE 3 and numerical data for such example are
given in the following table,
Example III
that is 4.714.
'
The divergent member between the air spaces 8,, and
S5 consists of two simple meniscus divergent components
located in front of a doublet divergent component, whose
internal contact surface R11 is collective, the radii of
30 curvature of the rear surfaces R7 and R9 of such simple
components respectively being equal to 0.823f2 and
0.81813. The range of movement of this divergent mem
ber is 1.943130. The convergent front member consists
of a simple convergent component in front of a conver
gent doublet, whose internal contact surface R4 is dis
persive. The front surface R3 of the doublet component
of the front member has a radius of curvature equal
to 0.68413.
Equivalent focal length varying from F0=1.0O0 to Fm=3.555. Relative
aperture f/1.9]
Radius
The ratio fl/fg
is 3.851, which is 1.335 times the expression (1—|—\/Q),
where Q is Fm/FO which equals 3.555. It will be no
ticed that f3/F0 is greater than 1.25 and less than 2.5\/ Q,
Thickness or Refractive Abbé V
Air Separation Index 11.1 Number
Clear
Diameter
.
The semi-angular ?eld covered by the objective in the
example of FIGURE 3 varies from about 191/2 degrees
at minimum equivalent focal length F0 to about 51/: de
grees at maximum equivalent focal length Fm.
The movements of the two front members follow the
same general laws as those for the ?rst example de
R1 =+ 6.2363
4.144
D1 =0. 3584
R, =+22. 0600
1. 6510
58.60
'
4.095
Si =0. 0036
R3 =+ 3.7771
3. 794
D2 =0. 1433
1. 7484
27. 85
D; =0. 7885
1. 6510
58. 60
R4 =+ 2.1724
R5 =+12. 1838
3. 319
S2 =0.0358 to
1. 9790
R5 =+ 1.7767
'
D4 =0. 1076
1. 7200
1.816
50. 31
R1 =+ 1.1802
1.588
S; =0.2151
Ra =+ 1.9188
1. 515
D5 =0.1076
1. 7200
D5 =0. 0860
1.5076
61.16
D1 =0. 2151
1. 7484
27.85
0.858
by an additional movement of the convergent front mem
0.823
ber alone, the arrangement being such that the image
plane remains in the same position for all object dis
adjustment. Focussing on near objects is again effected
0. 0364
Rl3==+ 0.9260
1. 7170
47. 90
R14=—27. 9977
85 =0. 2267
R1s=— 1.0929
'
0.722
D9 =0.1693
1.7230
37.99
D1o=0.0948
1. 6535
33. 48
R1s= - 0.5385
R11=+ 0.9452
0.696
S1 =0. 1037
R|s=+ 8. 4198
0.844
Dii=0. 0903
1. 7003
30. 28
D12=0. 3386
1. 6910
54. 80
R?=+ 0. 9935
Rzu=-— 1.4814
1.019
Si =0. 0034
Rz1=+ 1.2972
1.109
D13=0. 1919
R2Z= —46. 1968
highest value, and the air space 8,, decreases from its
1.146
S5 =1.9796 to
D5 =0. 2171
The
maximum forward movement of the front member is
indicated at c and is about 0.591%. During this move
ment the air space S2 increases from its lowest to its
namely 4.655F0 in front of the surface R13, in all posi
tions of adjustment, so that the image plane A of the‘
whole objective remains ?xed in position throughout the
R1|=+ 1. 3227
R1z=+ 8.8900
50 and then moves back again to its initial position.
1- 224
1.349
S4 =0. 5018
Rm=— 1.5832‘
moves backwards toward the stationary rear member,
while the convergent front member at ?rst moves forward
highest to its lowest value. The virtual image of the
object formed by the front two members occupies the
same position relatively to the stationary rear member,
50.31
Rn =+ 1.1716
scribed, so that during the variation of the equivalent
focal length of the objective-from its minimum value F0
to its maximum value Fm, the divergent second member
1.6910
54. 80
1. 099
tances.
As mentioned in connection with the ?rst example, in
order to retain constant relative aperture throughout the
range of movements and also to avoid objectionable
vignetting of oblique rays, the clear diameters of all
the surfaces of the front two members are made greater
than is necessary to accommodate the full axial beam
for all settings of the iris diagphram, which thus alone
determines the effective aperture in all positions of ad
justment. Thus, in the example of FIGURE 3, the maxi—
75 mum diameter of the full axial beam respectively at the
3,045,546
13
14
front surface R1 and at the rear surface R5 of the
front member varies from 0.526F0 to 1.871Fo and from
virtual image formed by the combination of the front
two members is located 1.833F0 in front of the dia
phragm. The back focal length a from the surface R20
to the rear focal plane A of the objective is 0.9118F0.
0.446F0 to 1.594F0 during the movements, but the actual
clear diameters of these surfaces R1 and R5 are respec
tively 4.144Fo and 3.319130. The maximum diameter of 5
1.816F0 and 1.146F0.
As shown in FIGURE 3, the stationary rear member
has four components of which the ?rst is simple and con
vergent, the second is a divergent doublet, the third is a
convergent doublet and the fourth is simple and con
The angular ?eld covered is the same as in Example
111, varying from about'19l/z degrees at minimum equiva
lent focal length F0 to 51/2 degrees at maximum equiva
lent focal length Fm.
The equivalent focal length f1 of the convergent front
the axial beam respectively at the front surface R6 and
at the rear surface R12 of the middle member varies from
0.441F0 to 0.903F0 and from 0.482Fo to 0.831110, the actual
clear diameters of these surfaces R6 and R12 being
10 member is 2.1743F0 and that of the divergent second
member is 0.5 645E) so that the ratio of F0 to the f/num
ber (4.8) is 0.36913. The equivalent focal length )3 ofv
the stationary rear member is 1.4555F0 so that fa/Fo
equals 0.303 times the f/number of the objective.
vergent. The objective of the example is well-corrected 15
The ratio of fl/fz is 0.385, the same as in the ex
throughout the range of variation for the usual primary
ample of FIGURE 3, whilst the ratio of f3/Fo is again
aberrations and also for secondary aberrations.
greater than 1.25 and less than 2.5\/6, where Q is
In this third example, the Petzval sum for the surfaces
equal to F,,,/ F0 which equals 3.557.
of the movable convergent front member is 0.1l1/F0, that
The Petzval sum of the rear member is positive and
for the movable divergent second member is —0.450/F0, 20 equal to 0.9827/Fo or 0.555/f2, whilst the individual
that for the stationary convergent rear member is
0.354/F0, and that for the complete objective is 0.015/F0.
Petzval curvatures of the surfaces of the rear portion
of the rear member are respectively, for Rm —0.037/F0,
The Petzval sum of the rear member is thus 0.52 times
fO-r R17
for R18
for R19
its equivalent power, or —1.04 times the equivalent power
+0.284/F0 and for R20 zero, so that the Petzval sum for
of the divergent combination of the front two members 25 such rear portion is 0.436/F0.
at the lower end of the range of focal length variation.
The movements of the front two members in Example
Such Petzval sum is also equal to 0.507/1‘2.
IV are the same as those described for Example II, the
The individual Petzval curvatures of the rear portion
maximum forward movement of the front member being
I of the rear member are respectively for R18 0.049/F0,
approximately 0.24F0 as indicated at c, and the front
and rear surfaces of the divergent second member in its
30
for
and R19
for —0.003/Fo,
R22 0.009/F0,
£01‘soR20that the Petzval
fOl' R21
sum for all
rearmost position being indicated by broken lines.
surfaces of such rear portion is 0.646/F0.
As with Examples I and II, it will be realised that if
A fourth example of variable focus objective is shown
the data for the fourth example are scaled up by a factor
in FIGURE 4 and numerical data for such example are
of approximately 2,5, the data for the front two members
set forth 111 the following table.
35 are identical in each of Examples III and IV, so that the
rear member of FIGURE 4 constitutes an alternative rear
Example IV
member for the same two front members, the scales of
FIGURES 3 and 4, in terms of the minimum equivalent
[Equivalent focal length varying from Fo=1.000 to Fm=3.557. Relativ
aperture f/4.8]
Radius
focal lengths F0 respectively of Examples “III and IV,
Thickness or Refractive Abbé V
Air Separation Index nd Number
Clear
Diameter
40 being related in the same manner as those of FIGURES l
and 2. The complete objective of FIGURE 3 is thus
suitable for use in the smaller of the television cameras
Ri=+2.4552
D1=0.1411
R2=+8.6850
1. 6510
58. 60
R4=+0.8553
Ri=+-1.7968
Dr=0.0564
1. 7484
27.85
Da=0.3104
1. 6510
58. 60
D4=0.0423
R1=+0.4646
Ds=0.0423
Ro=+0.4613
1. 7200
50. 31
De=0.0339
R1i=+0.5207
0.715
1. 7200
60. 31
1. 7484
Ru=— 1.1286
60. 42
Ds=0.0444
1.7000
41. 18
R1s= —-0.9453
Ds =0. 2821
1. 5190
60. 42
D9 =0. 1129
1.7000
41. 18
0.840
0.869
1. 390
Dl0=0- 1693
1. 6258
35.74
Dii=0. 3950
1. 5097
04. 44
Ri7=+ 1. 6123
~
0. 331
1. 5190
Diameter
R15: —26. 2462
0. 451
Da=0.l111
Clear
Number
85 =1. 8057
27. 85
‘
Abbé V
Index m
Ri5=— 2.4012
61. 16
St=0.8238 to
0.0588
Ru= —0.4443
55
.
D7=0.0847
Refractive
Rri=+ 3.2245
0. 482
1. 5076
Thickness or
Air Separation
S5 =2. 0925
to 0.1493
0. 596
0. 531
Rn=+3.5000
R1a=+1.2695
50
0. 625
S4=0.1976
Rio= —0.6233
imum equivalent focal length F0 for Example III.
Radius
Sa=0.0847
Ra=+0.7554
The following table sets forth the numerical data for
the rear member of Example IV in terms of the min
1. 404
1.307
S2=0.0l41 to
0.7791
Rs=+0.6995
suitable for use in the larger of such cameras.
1.612
Sr=+0.0014
Ra=+1.4870
above mentioned whilst the objective of FIGURE 4 is
1. 631
60
R|s=—- 3. 2562
1. 515'
S1 =1. 8057
Rw=+ 3. 03956
2.070
D12=0. 2821
Ram
0. 342
w
1. 5151
56. 35
2. 063
Sa=0.7109
Rm= —10.3331
R11=+0.6348
R18='-1.2820
0. 547
D1u=0.0667
1. 6258
35. 74
D11=0.1555
1. 5097
64. 44
‘
D12=0.1111
R2o= -=
1. 5151
‘It should further be mentioned, however, that by con
trast with the rear member of Example III, the rear mem
0. 696
Sr=0.7109
Rn=+1.1967
65
0‘ 815
56. 35
0. 812
In this example, the iris diaphragm B is located 0.044F0
in front of the front surface R13 of the rear member,
ber of Example IV has only three components, two con
vergent doublets in front of a simple convergent compo
nent. It will thus be appreciated that the number and
70 arrangement of the components of the rear member may
be considerably modi?ed, independently of the two axial
ly movable members, according to circumstances. When
correction for some or all secondary aberrations can be
sacri?ced the rear member may be simpli?ed. Thus, in
given position of adjustment remains unchanged. The 75 comparing the alternative rear members of FIGURES l,
so that its position relative to the front members in any
3,045,546
16
15
2, 3 and 4, it may be mentioned that when a high degree
of correction is required the slightly more simple design
of FIGURE 4 is less satisfactory than the other designs,
?rstly because the rear member of FIGURE 4 has a small
er collective power remote from the diaphragm so that
the distortion produced by the front members cannot
be as well counteracted as in the other rear members, and
front member being greater than 1.5 times the equivalent
focal length f1 of such front member.
3. An optical objective as claimed in claim 1 in which
the convergent front member comprises a convergent
doublet component and a simple convergent component
located in front of such doublet component, the front sur
face of such doublet component being convex to the front
with radius of curvature between 0.5 and 1.0 times the
secondly because the lesser number of surfaces remote
equivalent focal length (h) of the convergent front mem
from the diaphragm in the rear member of FIGURE 4
does not permit lateral chromatic aberration produced by 10 ber, at least one simple meniscus component in the di
the front members to be as well counteracted as in the
vergent second member having its rear surface convex to
other rear members.
the front with radius of curvature not less than 0.5f2 while
the radius of curvature of the rear surface of the front
component of the convergent front member is greater than
It will, however, be clear that what
, ever the arrangement of the rear member, such member
should in each case alford aberration correction generally
equal and opposite to the aberrations of the axially mov
able members so that the complete objective is corrected
with respect to the diaphragm.
What I claim as my invention and desire to secure by
Letters Patent is:
'
1. An optical objective of variable focal length cor- rected for spherical and chromatic aberrations, coma,
astigmatism, ?eld curvature and distortion throughout
1.5 times the equivalent focal length f1 of such front
member.
'
4. An optical objective as claimed in claim 1 in which
the Petzval sum for all the surfaces of the stationary
rear member lies between 0.7 and 1.4 times the positive
value of the equivalent power of the divergent combina
tion of the front two members in the position of adjust
ment corresponding to the lower end of the range of
rear member including at least six air-exposed surfaces
and a divergent combination constituted by an axially
variation of the equivalent focal length of the objective,
such Petzval sum also lying between 0.35/f2 and 0.7/f2
and between 0.3 and 4.0, times the equivalent power of
movable divergent member located in front of the station
the rear member.
the range of variation, comprising a stationary convergent
ary rear member and an axially movable convergent mem
ber located in front of such axially movable divergent
member, the ratio of the equivalent focal length of the
5. An optical objective as claimed in claim 1 in which
the Petzval sum for all surfaces included in the rear
portion of such stationary rear member (that is the
divergent combination of the front two members to the 30 portion having the rear four of the air-exposed surfaces
equivalent focal length of the complete objective remain
of such member) is positive and lies between 0.25 and
ing constant and the virtual image of a distant object
formed by such divergent combination having a constant
axial position relative to the stationary rear member
of the complete objective at the lower end of the range
of variation thereof.
0.85 times the reciprocal of the equivalent focal length
6. An optical objective as claimed in claim 1 in which
throughout the range of variation, and the convergent 35
the stationary rear member consists of two convergent
front member comprisingla plurality of convergent com
portions separated vby an air space whose axial length is
ponents including at least one simple component and at
greater than the equivalent focal length of either of such
least one doublet component having a dispersive internal
portions, while the ratio of the equivalent, focal length
contact surface which is convex to the front, the differ
ence between the refractive indices of the materials of 40 f3 of the stationary rear member to the equivalent focal
length of the complete objective at the lower end of the
the two elements of such doublet component of the front
range of variation thereof lies vbetween 0.2 and 1.2 times
member lying between 0.05 and 0.15, while the divergent
second member comprises a plurality of divergent com
ponents including a dirergent doublet rear component
the f/ number of the objective.
.
7. An optical objective as claimed in claim 1, in which
having a collective internal contact surface which is con 45 at least one of the four rear air-exposed surfaces of the
stationary rear member is ‘both collective and strongly
vex to the front with radius of curvature lying between
convex towards the diaphragm of the objective, whilst
0.665 and 1.573, where f; is the equivalent focal length
the rear portion of the stationary rear member (that is
of the second member, the mean refractive index of the
the portion having the rear four of the air-exposed sur
material of the rear element of such doublet component
of the second member exceeding that of the material of 50 faces of such member) includes at least one internal
contact between a convergent elementand a divergent
the front element of such component by between 0.15 and
element, the Abbe V number of the material of such
0.3, and the plurality of divergent components of the di
convergent element exceeding that of such divergent ele
vergent second member also including at least one di
ment by at least 20.
vergent simple meniscus component which has a rear sur
8. An optical objective as claimed in claim‘ 1, in which
face convex to the front with radius of curvature not less 55
the diaphragm of the objective is located at or near the
than 0.33 f2 and not greater than the range of axial move
front surface of the stationary rear member, and the
ment of such divergent second member, while the overall
diameters of the front two members are made larger than
axial length of the divergent second member lies between
is necessary to accommodate the full axial beam, so that
0.6f2 and l.3f2, the ratio of the equivalent focal length of
the relative aperture of the objective is determined solely
60
the divergent combination of the front two members to
by
the diaphragm and therefore remains constant
the equivalent focal length of the whole objective lying
throughout the range of variation.
between 3 and 8 times the reciprocal of the f/ number of
9. An optical objective as claimed in claim 1 including
the objective.
a lens mount for housing the objective and means carried
2. An optical objective as claimed in claim 1 in which
by the lens mount for axially moving the front member
the convergent front member comprises a convergent
independently of the second and third members to ef
doublet component and a simple convergent component
located behind such doublet component, the front sur
face of such simple component being convex to the front
with radius of curvature between 0.4)‘1 and 08h, where fl
is the equivalent focal length of the convergent front
member while the internal contact surface in such doublet
component is convex to the front with radius of curvature
between 0.4)‘; and 09h, the radius of curvature of the
rear surface of the front component of the convergent
fect focussing for near objects.
10. An optical objective as claimed in claim 1 includ
ing a lens mount for housing the objective, and means
carried vby the lens mount whereby alternative rear
members can be selectively attached to the mount in the
correct position relative to the front axially movable mem
bers.
11. An optical objective of variable focal length cor
rected for spherical and chromatic aberrations, coma,
'
7 3,045,546
17
18
astigmatism. ?eld curvature and distortion throughout
the range of variation, comprising a stationary convergent
tionary rear member lies between 0.3/f3 and 4.0/f3, where
f;, is the equivalent focal length of such stationary rear
rear member, and a divergent combination constituted by
an axially movable divergent member located in front of
member, the ratio of such equivalent focal length f3
to the equivalent focal length of the complete objective
at the lower end of the range of variation thereof lying
the stationary rear member and an axially movable con
between 0.2 and 1.2 times the f/number of the objective.
vergent member located in front of such axially movable
13. An optical objective as claimed in claim 11 in
divergent member, the ratio of the equivalent focal length
which the ratio of the equivalent focal length of the di
of the divergent combination of the front two members
vergent combination of the front two members to the
to the equivalent focal length of the complete objective
equivalent focal length of the whole objective lies be
remaining constant and the virtual image of a distant
object formed by such divergent combination having a 10 tween 3 and 8 times the reciprocal of the f/number of
the objective while the overall axial length of the di
constant axial position relative to the stationary rear
vergent second member lies between 0.6f2 and 1.3f2.
member throughout the range of variation, the convergent
14. An optical objective as claimed in claim 11, in
front member comprising a convergent doublet corn
which the equivalent focal length 1‘; of the convergent front
ponent whose internal contact surface is dispersive and
convex to the front with radius of curvature between 15 member lies between 1.0;‘2 and 1.67f2 times the value of the
0.4]‘1 and 0.9)‘1 and a simple convergent component
expression (1+x/Q), Where Q is the ratio of the value of
which is located behind such doublet component and
the upper limit of the range of variation of the equiva
has its front surface convex to the front with radius of
lent focal length of the complete objective to the value
curvature between 0.4)‘1 and 1.0f1, Where fl is the equiva
of the lower limit thereof, the ratio of the equivalent
lent focal length of the convergent front member, while 20 focal length of the complete objective at the lower end of
the divergent second member comprises a divergent dou
the range of variation thereof to the f/number of the
blet component whose internal contact surface is col
objective lying between 0.27f2 and 0.56f2.
,
lective and convex to the front with radius of curvature
between 0.66f2 and 1.5]‘2 and at least one simple divergent
meniscus component which is located in front of such 25
doublet component and has its rear surface convex to
the front with radius of curvature not less than 0.33;‘2
and not greater than the range of axial movement of
such divergent second member, where f2 is the equiva
lent focal length of the divergent second member, the 30
stationary convergent rear member including at least six
air-exposed surfaces, the Petzval sum for all surfaces
included in the rear portion of such rear member (that
is the portion having the rear four of the air-exposed
surfaces of such member) being positive and lying be 35
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,165,341
2,649,025
2,741,155
2,746,350
2,843,016
2,844,996
2,847,907
2,937,572
tween 0.25 and 0.85 times the reciprocal of the equiva
Capstaff et a1. ________ __ July
Cook ______________ __ Aug.
Hopkins ____________ __ Apr.
Hopkins ____________ __ May
Reiss ______________ __ July
11,
18,
10,
22,
15,
Klemt ______________ __ July 29,
Angenieux __________ __ Aug. 19,
1939
1953
1956
1956
1958
1958
1958
Yamaji ____________ __ May 24, 1960
FOREIGN PATENTS
7
lent focal length of the complete objective at the lower
end of the range of variation thereof.
12. An optical objective as claimed in claim 11, in
which the Petzval sum for all the surfaces of the sta 40
381,662
856,897
1,080,099
Great Britain _________ .._ Oct. 13, 1932
France ______________ __ Apr. 1, 1940
France ______________ __ May 26, 1954
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