A wide-angle photographic objective comprises ten (10) components. In the order from the object side, the first component is a positive meniscus lens having its convex surface facing the object side, the second component is a negative meniscus lens having its convex surface facing the object side, the third component is a negative meniscus lens having its convex surface facing the object side, the fourth component is a positive lens, the fifth component is a negative meniscus lens having its convex surface facing the object side, the sixth component is a positive lens, the seventh component is a positive lens, the eighth component is a biconcave negative lens comprising a doublet, the ninth component is a positive meniscus lens having its convex surface facing the image side, and the tenth component is a positive lens.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an inverted telephoto lens type wide-angle 
photographic objective having a relatively large aperture. 
2. Description of the Prior Art 
In an inverted telephoto lens type wide-angle objective for single lens 
reflex cameras, it is usually necessary that the back focal distance be 
greater than the focal length as the angle of view is increased or the 
focal length is decreased. This in turn leads to the necessity of 
increasing the refractive power of the forward diverging group. However, 
it is difficult to correct the resulting negative distortion, spherical 
aberration and especially, coma, and the greater the aperture, the more 
difficult it has been to keep the aberrations well corrected. 
SUMMARY OF THE INVENTION 
The present invention has, for its object, to provide a wide-angle 
photographic objective having an angle of view of 84.degree. and a 
relative aperture of 1:2 and in which the aforementioned aberrations are 
well corrected. 
The invention will become fully apparent from the following detailed 
description of several embodiments thereof, taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The wide-angle photographic objective according to the present invention 
comprises, in the order from the objective side, a first component L.sub.1 
which is a positive meniscus lens haing its convex surface facing the 
object side, a second component L.sub.2 which is a negative meniscus lens 
having its convex surface facing the object side, a third component 
L.sub.3 which is a negative meniscus lens having its convex surface also 
facing the object side, a fourth component L.sub.4 which is a positive 
lens, a fifth component L.sub.5 which is a negative meniscus lens having 
its convex surface facing the object side, a sixth component L.sub.6 which 
is a positive lens, a seventh component L.sub.7 which is a positive lens, 
an eighth component L.sub.8 which is a biconcave negative lens comprising 
a doublet, a ninth component L.sub.9 which is a positive meniscus lens 
having its convex surface facing the image side, and a tength component 
L.sub.10 which is a positive lens. This wide-angle objective achieves its 
intended purpose by satisfying the following conditions: 
EQU 6.1f&lt;f.sub.1 &lt;8.0f (1) 
EQU -1.4f&lt;f.sub.2 &lt;-1.1f (2) 
EQU -2.1f&lt;f.sub.3 &lt;-1.7f (3) 
ti 2.9f&lt;f.sub.4 &lt;4.0f (4) 
EQU -5.0f&lt;f.sub.5 &lt;-2.4f (5) 
EQU 1.3f&lt;f.sub.6 &lt;1.7f (6) 
EQU 1.6f&lt;f.sub.7 1.8f (7) 
EQU -1.0f&lt;f.sub.8 &lt;-0.8f (8) 
EQU 1.3f&lt;f.sub.9 &lt;1.6f (9) 
EQU 2.0f&lt;f.sub.10 &lt;2.3f (10) 
where f represents the total focal length of the entire system, and 
f.sub.1, f.sub.2, f.sub.3, . . . f.sub.10 represent the focal lengths of 
said first, second, third, . . . and tenth components, respectively. 
Each of the above conditions will hereinafter be discussed in detail. 
Condition (1) is for keeping the balance between distortion and flatness of 
image plane. If the lower limit of this condition is exceeded, it will be 
easy to correct the negative distortion which will be created by the 
diverging system in the forward group. However, the back focal distance 
will become shorter so that the power of the diverging lens in the forward 
group must be increased, as a result of which coma will be created to such 
an extent that it will be difficult to correct it. If the upper limit is 
exceeded, the back focal distance will be easy to secure, whereas the 
negative distortion will be increased. An approach to correct this by a 
subsequent lens component will be to increase the air spaces and lens 
thicknesses in the forward group and especially, if the center thickness 
of the negative meniscus lens L.sub.1 forming the first component is 
increased, it will be possible to correct distortion alone without so much 
affecting the other aberrations to any substantial degree. However, this 
is not desirable because the diameter of the forward lens has to be 
increased. 
Conditions (2) and (3) are intended to secure a predetermined back focal 
distance. If the lower limits of these conditions are exceeded, the back 
focal distance will become ample, but the negative distortion will become 
so excessive that it will be difficult to correct it even by any other 
lens component. If the upper limit of these conditions are exceeded, it 
will be difficult to secure a predetermined back focal distance. Further, 
if the lower limit of condition (3) is exceeded, spherical aberration will 
be over-corrected and if the upper limit of condition (3) is exceeded, 
spherical aberration will be under-corrected. 
Condition (4) is necessary to maintain good symmetry of meridional coma. If 
the lower limit of this condition is exceeded, meridional coma will be 
asymmetric in the positive direction, and if the upper limit of this 
condition is exceeded, meridional coma will be asymmetric in the negative 
direction. If the correction of the asymmetry of meridional coma created 
outside the range of this condition is undertaken by any other lens 
component, bending of high-order spherical aberration will undesirably be 
caused. 
Condition (5) is necessary for the correction of spherical aberration. If 
the lower limit of this condition is exceeded, spherical aberration will 
become excessive toward the negative and in this case, the spherical 
aberration may be drawn toward the positive by decreasing the air space 
immediately behind the fifth lens component L.sub.5. However, high-order 
spherical aberrations will be created to an extent too great to be 
corrected by the other lens components, and thus a sufficiently corrected 
condition would not be maintained. If the upper limit of condition (5) is 
exceeded, spherical aberration will become excessive toward the positive, 
and the spherical aberration may be drawn toward the negative by 
increasing the air space immediately behind the fifth lens component 
L.sub.5, but again it will become difficult to eliminate high-order 
spherical aberrations. 
Conditions (6) and (7) are desirable for correcting spherical aberration 
and meridional coma. If the lower limits of these two conditions are 
exceeded, there will be a strong tendency that spherical aberration 
becomes excessive toward the negative, while meridional coma becomes 
asymmetric. If the upper limits of these conditions are exceeded, the 
exact converse will be the case. Thus, difficulties will be encountered in 
achieving sufficient correction of aberrations. 
Condition (8) is intended to suitably maintain spherical aberration and 
astigmatism. If the lower limit of this condition is exceeded, spherical 
aberration will be overcorrected in the positive direction and astigmatism 
will also be excessive in the positive direction. If the upper limit of 
this condition is exceeded, the opposite tendency will become so unusually 
excessive that it cannot be corrected by any other lens component. 
Conditions (9) and (10) are requisite for the positive lens components 
L.sub.9 and L.sub.10 forming the last part of the lens system, and these 
conditions are desirable for well maintaining spherical aberration and 
flatness of image plane. 
Numerical data for several embodiments of the present invention will be 
shown below, with the understanding that r represents the curvature radius 
of each lens surface, d the axial thickness of each lens component or the 
air space between adjacent lens components, n the refractive index of each 
lens component, .nu. the Abbe number of each lens component, and the 
suffix i in order from the object side. 
In the preferred form of the invention, the wide-angle photographic 
objective best achieves its intended purposes by also satisfying the 
following conditions: 
##EQU1## 
where r.sub.1, r.sub.2 ; r.sub.3, r.sub.4 ; r.sub.5, r.sub.6 represent the 
curvature radii of the surfaces of said first, second and third 
components, respectively, which face the object side and the image side, 
respectively, r.sub.10 represents the curvature radius of the surface of 
said fifth component which faces the image side, and r.sub.11 represents 
the curvature radius of the surface of said sixth component which faces 
the object side. 
Condition (11) is chiefly for correcting distortion and meridional plane. 
If the lower limit of this condition is exceeded, distortion will be 
excessive toward the positive while meridional plane will be excessive 
toward the negative. If the upper limit of this condition is exceeded, 
distortion and meridional plane will be excessive toward the opposite 
direction. 
Condition (12) is concerned chiefly with distortion and meridional coma. If 
the lower limit of this condition is exceeded, distortion will be 
excessive toward the positive while meridional coma will be asymmetric, 
and if the upper limit of this condition is exceeded, distortion will be 
excessive toward the negative while meridional coma will be undesirably 
asymmetric toward the opposite direction. 
Condition (13) is the condition especially concerned with spherical 
aberration and meridional coma. If the lower limit of this condition is 
exceeded, spherical aberration will be over-corrected toward the positive 
while meridional coma will be asymmetric. If the upper limit of this 
condition is exceeded, spherical aberration will be over-corrected toward 
the negative while meridional coma will be exceedingly asymmetric toward 
the opposite direction. In any case, sufficient correction of aberration 
would become difficult. 
If the lower limit of condition (14) were to be exceeded, it would be 
difficult to provide suitable symmetry of meridional coma. 
The biconvex negative component L.sub.8 is a doublet comprising a positive 
lens and a negative lens cemented together and the cemented surface 
thereof should desirably be convex with respect to the image side, and 
this would particularly be suitable for the correction of chromatic 
difference of magnification. 
By satisfying the above-described construction and conditions, it has 
become possible a wide-angle photographic objective having an angle of 
view as wide as 84.degree. and yet having a relative aperture 1:2 and 
which is compact in size and moreover, to maintain a well-balanced coma 
over the entire image field. 
______________________________________ 
Embodiment I: 
Total focal length f = 100 mm Angle of view 2.omega. = 84.degree. 
Relative aperture 1:2.0 
______________________________________ 
r.sub.1 = 346.939 
d.sub.1 = 16.61 
n.sub.1 = 1.67025 
.nu..sub.1 = 57.5 
r.sub.2 = 1632.653 
d.sub.2 = 0.78 
r.sub.3 = 193.878 
d.sub.3 = 15.84 
n.sub.2 = 1.77279 
.nu..sub.2 = 49.4 
r.sub.4 = 60.943 
d.sub.4 = 13.27 
r.sub.5 = 120.408 
d.sub.5 = 5.14 
n.sub.3 = 1.69680 
.nu..sub.3 = 55.6 
r.sub.6 = 60.310 
d.sub.6 = 14.65 
r.sub.7 = 239.559 
d.sub.7 = 27.71 
n.sub.4 = 1.66755 
.nu..sub.4 = 41.9 
r.sub.8 = -2487.845 
d.sub.8 = 0.41 
r.sub.9 = 152.959 
d.sub.9 = 4.37 
n.sub.5 = 1.69680 
.nu..sub.5 = 55.6 
r.sub.10 = 91.073 
d.sub.10 = 8.49 
r.sub.11 = 121.633 
d.sub.11 = 29.39 
n.sub.6 = 1.74950 
.nu..sub.6 = 35.0 
r.sub.12 = -906.759 
d.sub.12 = 10.49 
r.sub.13 = -1791.461 
d.sub.13 = 15.84 
n.sub.7 = 1.56384 
.nu..sub.7 = 60.8 
r.sub.14 = -90.808 
d.sub.14 = 18.61 
r.sub.15 = -112.057 
d.sub.15 = 9.51 
n.sub.8 = 1.74443 
.nu..sub.8 = 49.4 
r.sub.16 = -91.073 
d.sub.16 = 3.18 
n.sub.9 = 1.80518 
.nu..sub.9 = 25.5 
r.sub.17 = 220.816 
d.sub.17 = 5.55 
r.sub.18 = -676.045 
d.sub.18 = 13.47 
n.sub.10 = 1.7443 
.nu..sub.10 = 49.4 
r.sub.19 = -87.347 
d.sub.19 = 0.41 
r.sub.20 = 808.163 
d.sub.20 = 14.65 
n.sub.11 = 1.69680 
.nu..sub.11 = 55.6 
r.sub.21 = -190.857 
______________________________________ 
______________________________________ 
Embodiment II: 
Total focal length f = 100mm Angle of view 2.omega. = 84.degree. 
Relative aperture 1:2.0 
______________________________________ 
r.sub.1 = 375.510 
d.sub.1 = 17.14 
n.sub.1 = 1.67025 
.nu..sub.1 = 57.5 
r.sub.2 = 1909.351 
d.sub.2 = 0.82 
r.sub.3 = 189.796 
d.sub.3 = 16.33 
n.sub.2 = 1.77279 
.nu..sub.2 = 49.4 
r.sub.4 = 61.633 
d.sub.4 = 13.67 
r.sub.5 = 125.367 
d.sub.5 = 5.31 
n.sub.3 = 1.69680 
.nu..sub.3 = 55.6 
r.sub.6 = 62.449 
d.sub.6 = 15.10 
r.sub.7 = 246.939 
d.sub.7 = 28.57 
n.sub.4 = 1.66755 
.nu..sub.4 = 41.9 
r.sub.8 = -2564.490 
d.sub.8 = 0.41 
r.sub.9 = 157.673 
d.sub.9 = 4.49 
n.sub.5 = 1.69680 
.nu..sub.5 = 55.6 
r.sub.10 = 93.878 
d.sub.10 = 8.69 
r.sub.11 = 124.898 
d.sub.11 = 32.24 
n.sub.6 = 1.74950 
.nu..sub.6 = 35.0 
r.sub.12 = -934.694 
d.sub.12 = 10.82 
r.sub.13 = -1846.653 
d.sub.13 = 16.33 
n.sub.7 = 1.56384 
.nu..sub.7 = 60.8 
r.sub.14 = -93.016 
d.sub.14 = 19.18 
r.sub.15 = -115.510 
d.sub.15 = 9.80 
n.sub.8 = 1.74443 
.nu..sub.8 = 49.4 
r.sub.16 = -93.878 
d.sub.16 = 3.27 
n.sub.9 = 1.80518 
.nu..sub.9 = 25.5 
r.sub.17 = 226.122 
d.sub.17 = 5.71 
r.sub.18 = -696.873 
d.sub.18 = 13.88 
n.sub.10 = 1.74443 
.nu..sub.10 = 49.4 
r.sub.19 = -92.653 
d.sub.19 = 0.41 
r.sub.20 = 612.245 
d.sub.20 = 15.10 
n.sub.11 = 1.69680 
.nu..sub.11 = 55.6 
r.sub.21 = -191.984 
______________________________________ 
______________________________________ 
Embodiment III: 
Total focal length f = 100mm Angle of view 2.omega. = 84.degree. 
Relative aperture 1:2.0 
______________________________________ 
r.sub.1 = 379.592 
d.sub.1 = 17.14 
n.sub.1 = 1.65844 
.nu..sub.1 = 50.8 
r.sub.2 = 2022.604 
d.sub.2 = 0.82 
r.sub.3 = 203.363 
d.sub.3 = 17.96 
n.sub.2 = 1.71300 
.nu..sub.2 = 53.9 
r.sub.4 = 60.163 
d.sub.4 = 13.67 
r.sub.5 = 123.061 
d.sub.5 = 5.31 
n.sub.3 = 1.69680 
.nu..sub.3 = 55.6 
r.sub.6 = 62.286 
d.sub.6 = 15.10 
r.sub.7 = 247.755 
d.sub.7 = 26.94 
n.sub.4 = 1.65844 
.nu..sub.4 = 50.8 
r.sub.8 = -2564.490 
d.sub.8 = 0.41 
r.sub.9 = 157.673 
d.sub.9 = 4.49 
n.sub.5 = 1.69680 
.nu..sub.5 = 55.6 
r.sub.10 = 93.878 
d.sub.10 = 8.98 
r.sub.11 = 125.616 
d.sub.11 = 31.43 
n.sub.6 = 1.74950 
.nu..sub.6 = 35.0 
r.sub.12 = -934.694 
d.sub.12 = 10.82 
r.sub.13 = -1846.653 
d.sub.13 = 16.33 
n.sub.7 = 1.56384 
.nu..sub.7 = 60.8 
r.sub.14 = -92.653 
d.sub.14 = 19.18 
r.sub.15 = -115.510 
d.sub.15 = 9.80 
n.sub.8 = 1.74443 
.nu..sub.8 = 49.4 
r.sub.16 = -102.041 
d.sub.16 = 3.27 
n.sub.9 = 1.80518 
.nu..sub.9 = 25.5 
r.sub.17 = 225.576 
d.sub.17 = 5.71 
r.sub.18 = -696.873 
d.sub.18 = 13.88 
n.sub.10 = 1.74443 
.nu..sub.10 = 49.4 
r.sub.19 = -92.347 
d.sub.19 = 0.41 
r.sub.20 = 612.245 
d.sub. 20 = 15.10 
n.sub.11 = 1.69680 
.nu..sub.11 = 55.6 
r.sub.21 = -193.061 
______________________________________ 
Lens constructions of several embodiments have been described above and may 
typically be represented by the lens construction of the first embodiment 
which is shown in FIG. 1. To illustrate the aberrations of a photographic 
objective in accordance with the invention, FIGS. 2A, 2B, 2C and 2D show 
the various aberrations for described Embodiment III. It will be seen that 
the various aberrations are all well corrected in the context of a small 
and bright wide-angle photographic objective, particularly having good 
symmetry in meridional coma. 
It is believed that the advantages and improved results afforded by the 
wide-angle photographic objective of the invention will be apparent from 
the foregoing detailed description of several preferred embodiments 
thereof. Various modifications and changes may be made without departing 
from the spirit and scope of the invention as sought to be defined in the 
following claims.