Compact wide-angle objective lens

A wide-angle objective lens is comprised, from the object side, of a first lens component which is a negative meniscus lens having its convex surface facing the object side, a second lens component which is a meniscus lens having its convex surface facing the object side and having positive refractive power, a third lens component which is a cemented meniscus lens comprising a positive lens and a negative lens cemented together and having its convex surface facing the object side and having positive refractive power, a fourth lens component which is a positive meniscus lens having its concave surface facing the object side, and a fifth lens component which is a negative meniscus lens having its concave surface facing the object side. The wide-angle objective lens has a stop disposed between the second lens component and third lens component, and satisfies predetermined conditions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a wide-angle objective lens for cameras, and 
particularly to a compact, large aperture, wide-angle objective lens 
suitable for use in a 35 mm format lens shutter camera or a 35 mm format 
camera with a range finder. 
2. Related Background Art 
Biogon type, abiogon type, etc. are known as symmetrical type wide-angle 
lenses having a negative, positive, negative refractive power 
distribution. The biogon type wide-angle lens can cover a wide angle of 
view and can make distortion small. Also, its refractive power 
distribution is a negative, positive, negative refractive power 
distribution and therefore, as compared with a symmetrical type wide-angle 
lens of a positive, negative, positive refractive power distribution such 
as a topogon type wide-angle lens, the biogon type wide-angle lens has an 
advantage that the quantity of marginal light is great and moreover the 
diameters of fore and rear lenses can be made small. 
Various wide-angle lenses of negative, positive, negative construction are 
known as the developed types of the biogon type wide-angle lens. They are 
known, for example, from Japanese Utility Model Publication No. 43-30782, 
U.S. Pat. No. 3,829,198, U.S. Pat. No. 4,211,472, Japanese Laid-Open 
Patent Application No. 56-140311, etc. 
Examples in which the F-number is made small are shown in Japanese Utility 
Model Publication No. 43-30782 and U.S. Pat. No. 4,211,472 and examples 
which comprise a small number of lens components are shown in U.S. Pat. 
No. 3,829,198 and Japanese Laid-Open Patent Application No. 56-140311. 
However, the biogon type wide-angle lens generally suffers from the 
disadvantages that the total thickness of the lens system (the thickness 
from that surface of the lens which is most adjacent (nearest) to the 
object side to that surface of the lens which is most adjacent to the 
image side) is great and that the F-number is large. 
In the lens systems shown in U.S. Pat. No. 3,829,198 and Japanese Laid-Open 
Patent Application No. 56-140311, the number of lens components is small 
but the correction of spherical aberration is deficient and therefore, the 
F-number cannot provide a large aperture. They also have suffered from the 
disadvantages that the total thickness of the lens system is very great 
and that the spacing between the front unit and the rear unit of the lens 
system in which a diaphragm is placed is too narrow and therefore great 
limitations must be imposed upon the structure of an aperture stop, a 
shutter unit, a lens barrel, etc. 
In the lens system shown in Japanese Utility Model Publication No. 
43-30782, the total thickness of the lens system is very great. Moreover 
the diameters of the fore and rear lenses are great. This is against the 
desire to make the lens system compact. In the lens system shown in U.S. 
Pat. No. 4,211,472, the F-number provides a large aperture but the total 
thickness of the lens system is great, and this is against the desire to 
make the lens compact. Also, the shape of coma is bad and therefore, if 
the lens system is left in its original condition, it is necessary to 
apply a limitation to the light beam and the quantity of marginal light 
becomes very small, and this has not been preferable. 
Further, in the lens system of Japanese Laid-Open Patent Application No. 
54-70826, the symmetry of the refractive power distributions on both sides 
of a stop is destroyed, the air space between a negative lens component 
disposed on the object side and a positive lens component and the air 
space between the positive lens component and a negative lens component 
disposed on the image side are both are widened, and a wide-angle of view 
and a large aperture can be obtained. However, this lens system has the 
disadvantages that the great air spaces result in a great total thickness 
of the lens system and that the height of a ray of light passing through 
the lens component remote from the stop becomes far from the optical axis 
and therefore the effective diameter of each lens becomes large. 
Further, Gaussian type, Topogon type, etc. are known as symmetrical type 
lenses having positive, negative, positive refractive power distribution. 
The positive, negative, positive symmetrical type lens is advantageous for 
large aperture, but cannot cover a wide-angle of view, and conversely, the 
aforedescribed negative, positive, negative symmetrical lens can cover a 
wide-angle of view, but has the disadvantage for large aperture. 
In the positive, negative, positive symmetrical type lens, the off-axis 
light beam passing through the lens component remote from the stop passes 
a location remote from the optical axis and therefore, when an attempt is 
made to achieve a wide-angle, the effective diameters of the front and 
rear lenses become large, and this results in the bulkiness of the optical 
system. Accordingly, when an attempt is made to achieve a wide-angle, a 
negative, positive, negative symmetrical type lens is desirable. 
Thus, it has been difficult to provide an optical system which satisfies 
the condition that a wide-angle can be achieved by a symmetrical type lens 
and the optical system is compact with a large aperture. The positive, 
negative, positive symmetrical type lens and the negative, positive, 
negative symmetrical type lens are generally of a construction 
advantageous in the correction of distortion and chromatic aberration. 
When in such symmetrical type lenses, the whole lens system is axially 
moved to effect focusing (so-called whole axial movement system), the 
fluctuation of off-axis aberration can be suppressed to a certain degree. 
However, where the whole axial movement system is used in the optical 
system as disclosed in Japanese Laid-Open Patent Application No. 54-170826 
wherein the symmetry of the refractive power arrangement of the negative, 
positive, negative symmetrical type lens is greatly destroyed in order to 
make the optical system bright, there has been a problem that the 
fluctuation of off-axis aberration becomes great. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to solve the 
above-noted problems peculiar to the prior art and to provide a 
symmetrical type wide-angle lens which realizes the small total thickness 
and great aperture of the lens system and which is compact and bright as 
well as small in distortion. 
To achieve the above object, a wide-angle objective lens according to the 
present invention comprises, in succession from the object side, a first 
lens component comprising a negative meniscus single lens having its 
convex surface facing the object side, a meniscus-shaped second lens 
component having its convex surface facing the object side and having 
positive refractive power, a stop, a third lens component comprising a 
cemented meniscus lens comprising a positive lens and a negative lens 
cemented together and having its convex surface facing the object side and 
having positive refractive power, a fourth lens component comprising a 
positive meniscus single lens having its concave surface facing the object 
side, and a fifth lens component comprising a negative meniscus single 
lens having its concave surface facing the object side, and is constructed 
into a negative, positive, negative refractive power arrangement as a 
whole, and when the focal length of said first lens component is f.sub.1 
and the focal length of said fifth lens component is f.sub.5 and the 
radius of curvature of that surface of said third lens component which is 
most adjacent to the image side is r.sub.32 and the radius of curvature of 
that surface of said fourth lens component which is most adjacent to the 
object side is r.sub.41, said wide-angle objective lens is designed to 
satisfy at least one of the following conditions: 
EQU 0 02.ltoreq..vertline.t.sub.1 /f.sub.1 .vertline..ltoreq.0.1 
EQU 0.01.ltoreq..vertline.t.sub.4 /f.sub.5 .vertline..ltoreq.0.08 
EQU -0.85.ltoreq.(r.sub.32 +r.sub.41)/(r.sub.32 -r.sub.41).ltoreq.0.90, 
where 
t.sub.1 : the air space on the optical axis from that surface of the first 
lens component which is most adjacent to the image side to that surface of 
the second lens component which is most adjacent to the object side, 
t.sub.4 : the air space on the optical axis from that surface of the fourth 
lens component which is most adjacent to the image side to that surface of 
the fifth lens component which is most adjacent to the object side. 
By constructing the objective lens as described above, it becomes possible 
to correct, in particular curvature of image field, astigmatism and coma, 
and a wide-angle lens which is compact, large aperture and high in 
performance can be realized. 
It is a further object of the present invention to provide a wide-angle 
lens which suffers little from the fluctuation of off-axis aberration 
caused by focusing and which is compact with a large aperture and covers a 
wide-angle of view. 
To achieve the above object, the present invention has a stop, and a first 
lens unit and a second lens unit that are disposed on the object side of 
the stop and on the image side of the stop respectively. The first lens 
unit and the second lens unit are designed such that, during focusing, the 
first and second lens units are moved on the optical axis toward the 
object side and the amounts of movement of the lens units on the optical 
axis differ from each other. 
Other objects, features and effects of the present invention will become 
fully apparent from the following detailed description of the invention 
taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Some embodiments of the present invention will hereinafter be described in 
detail with reference to the accompanying drawings. 
FIGS. 1 to 8 show the lens constructions of first to eighth embodiments, 
respectively, of the present invention. The wide-angle lenses according to 
the present invention, as shown in FIGS. 1 to 8, comprise, in succession 
from the object side, a first lens component L1 comprising a negative 
meniscus single lens having its convex surface facing the object side, a 
meniscus-shaped second lens component L2 having its convex surface facing 
the object side and having positive refractive power, a third lens 
component L3 comprising a cemented meniscus lens comprising a positive 
lens and a negative lens cemented together and having its convex surface 
facing the object side and having positive refractive power, a fourth lens 
component L4 comprising a positive meniscus single lens having its concave 
surface facing the object side, a fifth lens component L5 comprising a 
negative meniscus single lens having its concave surface facing the object 
side, and a stop between the second lens component L2 and the third lens 
component L3, is constructed into a negative, positive, negative 
refractive power arrangement as a whole, and is designed to satisfy at 
least one of the following conditions: 
EQU 0.02.ltoreq..vertline.t.sub.1 /f.sub.1 .vertline..ltoreq.0.1(1) 
EQU 0.01.ltoreq..vertline.t.sub.4 /f.sub.5 .vertline..ltoreq.0.08(2) 
EQU -0.85.ltoreq.(r.sub.32 +r.sub.41)/(r.sub.32 -r.sub.41).ltoreq.0.90,(3) 
where 
t.sub.1 : the air space on the optical axis from that surface of the first 
lens component L1 which is most adjacent to the image side to that surface 
of the second lens component L2 which is most adjacent to the object side, 
t.sub.4 : the air space on the optical axis from that surface of the fourth 
lens component L4 which is most adjacent to the image side to that surface 
of the fifth lens component L5 which is most adjacent to the object side, 
f.sub.1 : the focal length of the first lens component L1, 
f.sub.5 : the focal length of the fifth lens component L5, 
r.sub.32 : the radius of curvature of that surface of the third lens 
component L3 which is most adjacent to the image side, 
r.sub.41 : the radius of curvature of that surface of the fourth lens 
component L4 which is most adjacent to the object side. 
As described above, the lens construction of the present invention is 
comprised of the first lens component L1 and the fifth lens component L5 
each having negative refractive power, and the second lens component L2, 
the third lens component L3 and the fourth lens component L4 each having 
positive refractive power, and is a negative, positive, negative 
refractive power arrangement as a whole. 
The first lens component L1 and the fifth lens component L5 each are a 
negative meniscus lens having its concave surface facing the stop S to 
sufficiently correct curvature of image field and astigmatism. By the 
negative meniscus lenses being thus used, it becomes possible to make the 
angle of view greater and increase the quantity of marginal light. 
In a lens having a great angle of view, the correction of astigmatism and 
curvature of image field is important and it is necessary that the Petzval 
sum be an appropriate value. 
Generally, in case of a lens of a negative, positive, negative refractive 
power arrangement having symmetry with respect to the stop S, as the air 
space between a lens unit adjacent to the object side and a positive lens 
unit and between a negative lens unit adjacent to the image side and the 
positive lens unit become wider, the degree of freedom of aberration 
correction increases more, and the Petzval sum can be made into an 
appropriate value. 
However, where these air spaces are made great, the Petzval sum can be made 
into an appropriate value and this is advantageous for aberration 
correction, but the diameters of the fore and rear lenses become large and 
this is not preferable. Conversely, where these air spaces are made small, 
the Petzval sum increases to the positive and the correction of negative 
astigmastism and curvature of image field becomes difficult. So, where the 
refractive power of the first lens component L1 and of the fifth lens 
component L5 is made great to alleviate the Petzval sum, it will adversely 
affect coma, and this is not preferable. 
The Petzval sum which is the cause of these problems can be improved to a 
certain degree by setting the refractive indices of the positive lens and 
the negative lens to appropriate values. 
According to the present invention, in the symmetrical type wide-angle lens 
as disclosed in Japanese Utility Model Publication No. 43-30782, it 
becomes possible to divide the cemented positive lens disposed rearwardly 
of the stop into two lens components L3 and L4, effect the correction of 
spherical aberration by that surface r.sub.32 of the third lens component 
L3 which is most adjacent to the image side and that surface r.sub.41 of 
the fourth lens component L4 which is most adjacent to the object side, 
and make the F-number small. Further, since the cemented positive lens is 
divided into two lens components, the degree of freedom of aberration 
correction increases and it is possible to correct curvature of image 
field and astigmatism better. 
The aforementioned conditional expressions of the present invention will 
hereinafter be described in detail. 
Conditional expressions (1) and (2) are conditions regarding the correction 
of astigmatism and curvature of image field and compactness. 
If the lower limit of conditional expression (1) is exceeded, the following 
two cases 1 and 2 are conceivable. 
1 A case where the air space t.sub.1 between the first lens component L1 
and the second lens component L2 is small; and 
2 A case where the focal length f.sub.1 of the first lens component L1 is 
great. 
In case 1, positive distortion increases and the correction of spherical 
aberration becomes impossible, and the F-number cannot be made small. In 
case 2, the Petzval sum increases to the positive and therefore, the 
correction of negative astigmastism and curvature of image field becomes 
impossible. 
On the other hand, if the upper limit of conditional expression (1) is 
exceeded, the following two cases 3 and 4 are conceivable. 
3 A case where the air space t.sub.1 between the first lens component L1 
and the second lens component L2 is great; and 
4 A case where the focal length f.sub.1 of the first lens component L1 is 
small. 
In case 3, there is an advantage in aberration correction, but the diameter 
of the fore lens and the total thickness of the lens system become great 
and this is against the desire for compactness, and thus is not 
preferable. In case 4, Petzval sum decreases, but the coma under the 
principal ray increases to the negative in a portion which is great in the 
angle of view, and this is not preferable. 
If the lower limit of conditional expression (2) is exceeded, the following 
two cases 5 and 6 are conceivable. 
5 A case where the air space t.sub.4 between the fourth lens component L4 
and the fifth lens component L5 is small; and 
6 A case where the focal length f.sub.5 of the fifth lens component L5 is 
great. 
In case 5, the correction of spherical aberration becomes impossible and 
the F-number cannot be made small. In case 6, the Petzval sum increases to 
the positive and the correction of negative astigmatism and curvature of 
image field becomes impossible, and a good image plane cannot be obtained. 
On the other hand, if the upper limit of conditional expression (2) is 
exceeded, the following two cases 7 and 8 are conceivable. 
7 A case where the air space t.sub.4 between the fourth lens component L4 
and the fifth lens component L5 is great; and 
8 A case where the focal length f.sub.5 of the fifth lens component L5 is 
small. 
In case 7, the degree of freedom with which the Petzval sum is made into an 
appropriate value increases and this is advantageous in correcting 
astigmatism and curvature of image field, but the total thickness of the 
lens system becomes great and this is against the desire for compactness, 
and thus is not preferable. In case 8, the correction of spherical 
aberration becomes impossible and further, the fluctuation of the coma 
above the principal ray by the angle of view becomes great and this is not 
preferable. 
Conditional expression (3) is a condition regarding the shape of the air 
space between the third lens component L3 and the fourth lens component 
L4, and is concerned with coma, curvature of image field and astigmatism. 
If the upper limit of conditional expression (3) is exceeded, the Petzval 
sum will increase to the positive and cannot be made into an appropriate 
value and the correction of astigmatism and curvature of image field will 
become difficult, and a good image plane cannot be obtained. Also, the 
shape of coma will exhibit a sharp tendency toward inner coma, and this is 
not preferable. 
If conversely, the lower limit of conditional expression (3) is exceeded, a 
good Petzval sum will be obtained, but aberrations of high orders will 
occur in a portion which is great in the angle of view and astigmatism 
will become great. Also, the shape of coma will exhibit a great tendency 
toward outer coma, and this is not preferable. 
It is desirable that in order to correct spherical aberration, curvature of 
image field and astigmatism and to form the lens compactly, the wide-angle 
lens according to the present invention be designed to further satisfy the 
following conditions: 
EQU 0.20.ltoreq..vertline.r.sub.42 /f.vertline..ltoreq.0.55 (4) 
EQU 0.40.ltoreq.D/f.ltoreq.1.00, (5) 
where 
f: the focal length of the entire lens system, 
r.sub.42 : the radius of curvature of that surface of the fourth lens 
component L4 which is most adjacent to the image side, 
D: total thickness of the lens system. Conditional expression (4) is 
concerned with the correction of spherical aberration. 
If the upper limit value of conditional expression (4) is exceeded, it will 
become impossible to correct positive spherical aberration, and this is 
not preferable. 
If conversely, the lower limit value of conditional expression (4) is 
exceeded, it will become impossible to correct negative spherical 
aberration, and this is not preferable. 
Now, the wide-angle lens of the present invention is characterized in that, 
as compared with popular symmetrical type wide-angle lenses, its back 
focal length differs little, but the total thickness of the lens is very 
small. This makes it possible to make the lens barrel into the sunk barrel 
type to thereby contain it compactly when the lens of the present 
invention is used in a compact lens shutter camera or a camera with a 
range finder, and it is more realistic and effective to make the total 
thickness of the lens system small than to shorten the back focal length. 
So, conditional expression (5) sets a condition for prescribing the total 
thickness of the lens system, i.e., the length from that surface of the 
first lens component L1 which is most adjacent to the object side to that 
surface of the fifth lens component L5 which is not adjacent to the image 
side. 
If the lower limit value of conditional expression (5) is exceeded, the 
difference in height between the on-axis ray and the off-axis ray will 
become small in the lens far from the stop S and the degree of freedom 
will be deficient and thus, it will become impossible to correct the 
on-axis aberration and the off-axis aberration independently of each 
other. 
If conversely, the upper limit value of conditional expression (5) is 
exceeded, the Petzval sum can be made into an appropriate value and a 
better image plane performance will be obtained, but this is against the 
desire for compactness and is therefore against an object of the present 
invention. 
Also, it is desirable that in order to correct curvature of image field and 
astigmatism better, the first lens component L1, the third lens component 
L3 and the fifth lens component L5 be designed to satisfy the following 
conditions: 
EQU 0.04&lt;N.sub.31 -N.sub.32 &lt;0.25 (6) 
EQU N.sub.1 &lt;1.70 (7) 
EQU N.sub.5 &lt;1.70, (8) 
where 
N.sub.31 : the refractive index of the positive lens L3 disposed on the 
object side in the third lens component L3 for d-line, the refractive 
index of the negative 
N.sub.32 : the refractive index of the negative lens disposed on the image 
side in the third lens component L3 for d-line, 
N.sub.1 : the refractive index of the first lens 
component L1 for d-line, 
N.sub.5 : the refractive index of the fifth lens component L5 for d-line. 
Conditional expression (6) represents the difference between the refractive 
indices of the position lens disposed on the object side in the third lens 
component L3 and the negative lens disposed on the image side in the third 
lens component L3 for d-line. 
If the lower limit value of conditional expression (6) is exceeded, the 
Petzval sum will increase to the positive and therefore, it will become 
impossible to correct negative curvature of image field and astigmatism. 
If conversely, the upper limit value of conditional expression (6) is 
exceeded, a better Petzval sum will be obtained, but aberrations of high 
orders will occur in a portion which is great in the angle of view and 
astigmatic difference will be created, and this is not preferable. 
Conditional expressions (7) and (8) are concerned with curvature of image 
field and astigmatism. 
If the upper limit values of these conditional expressions are exceeded, 
the Petzval sum will increase to the positive and therefore, the 
correction of curvature of image field and negative astigmatism will 
become impossible and a good image plane will not be obtained. 
Another embodiment of the present invention has a first lens unit and a 
second lens unit disposed with a stop interposed therebetween, on the 
object side of the stop and on the image side of the stop, respectively, 
said first lens unit comprising, in succession from the object side, a 
first lens component of negative refractive power and a second lens 
component of positive refractive power, said second lens unit comprising a 
third lens component of positive refractive power and a fourth lens 
component of negative refractive power, said first lens unit and said 
second lens unit being designed such that during focusing, they are moved 
on the optical axis toward the object side and the amounts of movement of 
said lens units on the optical axis differ from each other. 
The present invention as a whole is of a negative, positive, negative 
refractive power arrangement. The first lens component of negative 
refractive power in the first lens unit disposed at a location remote from 
the stop and the fourth lens component of negative refractive power in the 
second lens unit are negative meniscus lenses having their concave 
surfaces facing the stop in order to sufficiently correct curvature of 
image field and astigmatism. The use of the negative meniscus lenses leads 
to the achievement of a wider angle and the provision of the action of 
increasing the quantity of marginal light. 
The present invention makes the first lens unit and the second lens unit 
take their share of the correction of on-axis aberration and the 
correction of off-axis aberration. Specifically, there are the following 
two kinds of sharing: 
(a) To achieve a wide-angle and yet make the refractive power of the first 
lens unit small in the positive, thereby correcting the off-axis 
aberration well with the first lens unit, and make the refractive power of 
the second lens unit great in the positive and divide the positive lens 
component in the second lens unit into two lens components, thereby 
correcting the on-axis aberration well with the second lens unit and 
making the optical system bright. 
(b) To achieve a wide-angle and yet make the refractive power of the second 
lens unit small in the positive, thereby correcting the off-axis 
aberration well with the second lens unit, and make the refractive power 
of the first lens unit great in the positive and divide the positive lens 
component in the first lens unit into two lens components, thereby 
correcting the on-axis aberration well with the first lens unit and making 
the optical system bright. 
In the present invention, as described in items (a) and (b) above, the lens 
units forward and rearward of the stop S are made to take their share of 
the correction of the on-axis aberration and the correction of the 
off-axis correction to thereby enable the optical system to be bright, but 
correspondingly thereto, the symmetry of the refractive power on both 
sides of the stop is destroyed. Therefore, when focusing is effected by 
the use of the whole axial movement system, it becomes impossible to 
suppress the fluctuation of the off-axis aberration well. 
So, the fluctuation of the off-axis aberration, when focusing is effected 
by the use of the whole axial movement system, will hereinafter be 
considered with respect to the following two types of optical systems in 
which the refractive power distribution on both sides of the stop is 
asymmetrical, 
(I) Petrofocus Type; and 
(II) Telephoto Type. 
In the case of (I) above, the refractive power arrangement on both sides of 
the stop is negative and positive and the pupil magnification exceeds 1. 
Therefore, when the object position moves from the infinity state to a 
short distance, positive astigmatism occurs. 
In the case of (II) above, the refractive power arrangement on both sides 
of the stop is positive and negative and the pupil magnification is 
smaller than 1. Therefore, when the object position moves from the 
infinity state to a short distance, negative astigmatism occurs. 
In the present embodiment, when focusing by the whole axial movement is 
effected, the construction of item (a) above corresponds to (I) above, and 
when the object position moves from the infinity state to a short 
distance, positive astigmatism occurs. According to the definition of the 
third-order aberration coefficient in Lens Designing Method by Yoshiya 
Matsui, the third-order aberration coefficient III of the second lens unit 
exhibits the positive (+). Therefore, if the amount of axial movement of 
the second lens unit is made small relative to the amount of axial 
movement of the first lens unit, positive astigmatism could be suppressed 
well and the fluctuation of off-axis aberration caused during focusing 
could be suppressed. 
Conversely, the construction of item (b) above corresponds to (II) above, 
and when the object position moves from the infinity state to a short 
distance, negative astigmatism occurs. At this time, the third-order 
aberration coefficient III of the second lens unit exhibits the negative 
(-). Therefore, if the amount of axial movement of the second lens unit is 
made great relative to the amount of axial movement of the first lens 
unit, the fluctuation of off-axis aberration caused during focusing could 
be alleviated. 
As described above, the present invention effects focusing by the use of 
the so-called floating system that makes the amounts of axial movement of 
the first lens unit and the second lens unit different from each other 
during focusing, thereby enabling the fluctuation of off-axis aberration 
caused by focusing to be suppressed well. 
In the present invention, it is desirable that with the above-described 
construction, the following conditional expression (9) or (10) be 
satisfied. 
EQU 0&lt;.DELTA..multidot..phi./(.phi..sub.a -.phi..sub.b)&lt;0.2 (9) 
EQU 0.3&lt;.vertline..phi.1/.phi..vertline.&lt;0.95 (10) 
where 
.phi..sub.a : the refractive power of the first lens unit, 
.phi..sub.b : the refractive power of the second lens unit, 
.phi.: the refractive power of the whole lens system, 
.DELTA.: an amount defined by the following equation: 
EQU .DELTA.=(.delta.1-.delta.2)/.delta.2 
when the amount of movement of the first lens unit during focusing is 
.delta.1 and the amount of movement of the second lens unit is .delta.2, 
.phi.1: the refractive power of the first lens component. 
Conditional expression (9) is a condition for suppressing the fluctuation 
of aberration in short distance focusing very well. 
If the upper limit value of conditional expression (9) is exceeded, the 
correction of the fluctuation of off-axis aberration caused by focusing 
will become excessive. If conversely, the lower limit value of conditional 
expression (9) is exceeded, the correction of the fluctuation of off-axis 
aberration caused by focusing will become deficient. Accordingly, it is 
preferable that the range of this condition be satisfied. 
Conditional expression (10) is a condition for achieving the balance of the 
shortening of the full length and the effective diameter of the front 
lens. 
If the upper limit value of conditional expression (10) is exceeded, the 
refractive power of the first lens component will become great to the 
negative and therefore, the diverging action will become strong and the 
back focal length will become too great. If conversely, the lower limit 
value of conditional expression (10) is exceeded, the refractive power of 
the first lens component will become small to the negative and the height 
of the ray of off-axis light passing through the first lens component will 
become far from the optical axis, and if an attempt is made to obtain the 
amount of marginal light, the effective diameter of the front lens will 
become great, which will lead to the bulkiness of the optical system, and 
this is not preferable. 
The lens constructions of the embodiments of the present invention will 
hereinafter be described in greater detail. 
All of Embodiments 1 to 7, as shown in FIGS. 1 to 7, are lens systems of 
two groups G1 and G2 constituting is a lens of five-unit seven-component 
construction comprising, in succession from the object side, a first lens 
component L1 which is a negative meniscus lens having its convex surface 
facing the object side, a second lens component L2 which is a cemented 
positive meniscus lens comprising a biconvex lens and a biconcave lens, a 
stop S, a third lens component L3 which is a cemented positive meniscus 
lens comprised of a biconvex lens and a biconcave lens, a fourth lens 
component L4 which is a positive meniscus lens having its concave surface 
facing the object side, and a fifth lens component L5 which is a negative 
meniscus lens having its concave surface facing the object side. 
Also, Embodiment 8, as shown in FIG. 8, is a lens of five-unit 
six-component construction comprising, in succession from the object side, 
a first lens component L1 which is a negative meniscus lens having its 
convex surface facing the object side, a second lens component L2 which is 
a positive meniscus lens having its convex surface facing the object side, 
a stop S, a third lens component L3 which is a cemented positive meniscus 
lens comprised of a biconvex lens and a biconcave lens, a fourth lens 
component L4 which is a positive meniscus lens having its concave surface 
facing the object side, and a fifth lens component L5 which is a negative 
meniscus lens having its concave surface facing the object side. 
The numerical data of the respective embodiments of the present invention 
will be shown in Tables 1 to 8 below. In these tables, f represents the 
focal length, F.sub.NO represents F-number and 2.omega. represents the 
angle of view. The numbers at the left end represent the order from the 
object side, r represents the radius of curvature of each lens surface, d 
represents the spacing between adjacent lens surfaces, and the refractive 
index n and Abbe number .nu. are values for d-line (.lambda.=587.6 nm). 
TABLE 1 
______________________________________ 
(Numerical Data of Embodiment 1) 
f = 28.9 
F.sub.NO = 2.88 
2.omega. = 73.8.degree. 
r d n .upsilon. 
______________________________________ 
1 17.100 1.50 1.54739 
53.5 
2 9.282 2.70 
3 12.910 3.90 1.84042 
43.3 
4 -60.183 1.10 1.62588 
35.7 
5 14.650 5.00 
6 50.105 3.30 1.79668 
45.4 
7 -10.659 1.00 1.67270 
32.2 
8 43.956 1.40 
9 -36.842 3.00 1.79668 
45.4 
10 -13.025 1.50 
11 -9.805 1.50 1.58144 
40.8 
12 -14.846 20.83 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
(1) .vertline.t.sub.1 /f.sub.1 .vertline.=0.068 
(2) .vertline.t.sub.4 /f.sub.5 .vertline.=0.027 
(3) (r.sub.32 +r.sub.41)/(r.sub.32 -r.sub.41)=0.088 
(4) .vertline.r.sub.42 /f.vertline.=0.451 
(5) D/f=0.897 
(6) N.sub.31 -N.sub.32 =0.123 
(7) N.sub.1 =1.547 
(8) N.sub.5 =1.581 
TABLE 2 
______________________________________ 
(Numerical Data of Embodiment 2) 
f = 28.9 
F.sub.NO = 2.87 
2.omega. = 73.0.degree. 
r d n .upsilon. 
______________________________________ 
1 12.475 1.50 1.57501 
41.6 
2 8.882 3.10 
3 12.551 4.40 1.84042 
43.3 
4 -1631.732 1.00 1.64831 
33.8 
5 12.856 4.00 
6 43.791 2.50 1.79668 
45.4 
7 -13.768 1.00 1.67270 
32.2 
8 77.172 1.10 
9 -25.300 2.70 1.79668 
45.4 
10 -10.647 1.00 
11 -8.993 1.50 1.58144 
40.8 
12 -17.685 20.51 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
(1) .vertline.t.sub.1 /f.sub.1 .vertline.=0.051 
(2) .vertline.t.sub.4 /f.sub.5 .vertline.=0.024 
(3) (r.sub.32 +r.sub.41)/(r.sub.32 -r.sub.41)=0.506 
(4) .vertline.r.sub.42 /f.vertline.=0.369 
(5) D/f=0.824 
(6) N.sub.31 -N.sub.32 =0.056 
(7) N.sub.1 =1.532 
(8) N.sub.5 =1.581 
TABLE 3 
______________________________________ 
(Numerical Data of Embodiment 3) 
f = 28.9 
F.sub.NO = 2.87 
2.omega. = 74.0.degree. 
r d n .upsilon. 
______________________________________ 
1 12.422 1.50 1.53172 
49.1 
2 8.919 3.37 
3 12.829 3.87 1.84042 
43.3 
4 -1726.972 1.00 1.64831 
33.8 
5 12.785 4.00 
6 51.931 2.50 1.81600 
46.8 
7 -17.040 1.00 1.61750 
30.8 
8 54.857 1.31 
9 -21.730 2.95 1.79668 
45.4 
10 -10.479 0.80 
11 -8.874 1.50 1.59507 
35.5 
12 -13.780 20.96 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
(1) .vertline.t.sub.1 /f.sub.1 .vertline.=0.048 
(2) .vertline.t.sub.4 /f.sub.5 .vertline.=0.017 
(3) (r.sub.32 +r.sub.41)/(r.sub.32 -r.sub.41)=0.433 
(4) .vertline.r.sub.42 /f.vertline.=0.363 
(5) D/f=0.824 
(6) N.sub.31 -N.sub.32 =0.199 
(7) N.sub.1 =1.532 
(8) N.sub.5 =1.595 
TABLE 4 
______________________________________ 
(Numerical Data of Embodiment 4) 
f = 28.9 
F.sub.NO = 2.87 
2.omega. = 73.4.degree. 
r d n .upsilon. 
______________________________________ 
1 18.080 1.50 1.56384 
60.9 
2 9.401 3.26 
3 13.713 4.18 1.80218 
44.7 
4 -28.737 1.10 1.61293 
37.0 
5 17.068 5.00 
6 48.775 3.14 1.80218 
44.7 
7 -11.832 1.00 1.68893 
31.1 
8 38.220 1.22 
9 -0.592 3.30 1.79668 
45.4 
10 -12.910 1.60 
11 -9.672 2.00 1.58144 
40.8 
12 -13.780 20.96 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
(1) .vertline.t.sub.1 /f.sub.1 .vertline.=0.088 
(2) .vertline.t.sub.4 /f.sub.5 .vertline.=0.028 
(3) (r.sub.32 +r.sub.41)/(r.sub.32 -r.sub.41)=-0.030 
(4) .vertline.r.sub.42 /f.vertline.=0.447 
(5) D/f=0.945 
(6) N.sub.31 -N.sub.32 =0.113 
(7) N.sub.1 =1.564 
(8) N.sub.5 =1.582 
TABLE 5 
______________________________________ 
(Numerical Data of Embodiment 5) 
f = 35.0 
F.sub.NO = 2.80 
2.omega. = 62.4.degree. 
r d n .upsilon. 
______________________________________ 
1 13.804 1.40 1.61025 
57.6 
2 9.560 2.50 
3 11.800 4.20 1.79668 
43.3 
4 -1901.932 1.20 1.68893 
31.2 
5 12.250 5.75 
6 23.817 3.30 1.72000 
50.3 
7 -12.861 1.20 1.62588 
35.6 
8 23.478 1.25 
9 -92.286 3.20 1.79631 
40.9 
10 -13.150 1.00 
11 -10.885 1.40 1.67003 
47.1 
12 -26.314 22.10 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
(1) .vertline.t.sub.1 /f.sub.1 .vertline.=0.047 
(2) .vertline.t.sub.4 /f.sub.5 .vertline.=0.035 
(3) (r.sub.32 +r.sub.41)/(r.sub.32 -r.sub.41)=-0.595 
(4) .vertline.r.sub.42 /f.vertline.=0.376 
(5) D/f=0.747 
(6) N.sub.31 -N.sub.32 =0.094 
(7) N.sub.1 =1.670 
(8) N.sub.5 =1.670 
TABLE 6 
______________________________________ 
(Numerical Data of Embodiment 6) 
f = 35.0 
F.sub.NO = 2.80 
2.omega. = 62.4.degree. 
r d n .upsilon. 
______________________________________ 
1 15.140 1.40 1.51680 
64.1 
2 9.852 2.60 
3 13.541 4.20 1.79668 
45.4 
4 -1960.755 1.20 1.67270 
32.1 
5 16.374 5.75 
6 38.906 4.20 1.79668 
45.4 
7 -9.900 1.20 1.67270 
32.1 
8 39.474 1.40 
9 -56.315 3.00 1.74950 
35.2 
10 -15.623 2.30 
11 -10.487 1.40 1.53172 
49.1 
12 -22.411 20.87 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
(1) .vertline.t.sub.1 /f.sub.1 .vertline.=0.043 
(2) .vertline.t.sub.4 /f.sub.5 .vertline.=0.060 
(3) (r.sub.32 +r.sub.41)/(r.sub.32 -r.sub.41)=-0.176 
(4) .vertline.r.sub.42 /f.vertline.=0.446 
(5) D/f=0.819 
(6) N.sub.31 -N.sub.32 =0.124 
(7) N.sub.1 =1.517 
(8) N.sub.5 =1.532 
TABLE 7 
______________________________________ 
(Numerical Data of Embodiment 7) 
f = 35.0 
F.sub.NO = 2.80 
2.omega. = 62.6.degree. 
r d n .upsilon. 
______________________________________ 
1 11.026 1.50 1.57501 
41.6 
2 8.859 3.28 
3 14.478 4.60 1.84042 
43.3 
4 -226.717 1.00 1.64831 
33.8 
5 13.585 4.00 
6 78.289 2.50 1.80411 
46.4 
7 -13.768 1.00 1.67270 
32.2 
8 100.000 1.15 
9 -20.464 2.95 1.79668 
45.4 
10 -10.474 0.80 
11 -9.468 1.50 1.58267 
46.5 
12 -16.567 25.07 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
(1) .vertline.t.sub.1 /f.sub.1 .vertline.=0.031 
(2) .vertline.t.sub.4 /f.sub.5 .vertline.=0.019 
(3) (r.sub.32 +r.sub.41)/(r.sub.32 -r.sub.41)=0.660 
(4) .vertline.r.sub.42 /f.vertline.=0.299 
(5) D/f=0.694 
(6) N.sub.31 -N.sub.32 =0.131 
(7) N.sub.1 =1.575 
(8) N.sub.5 =1.583 
TABLE 8 
______________________________________ 
(Numerical Data of Embodiment 8) 
f = 28.9 
F.sub.NO = 2.88 
2.omega. = 73.8.degree. 
r d n .upsilon. 
______________________________________ 
1 14.953 1.50 1.59507 
35.5 
2 8.621 2.94 
3 10.597 3.76 1.80411 
46.4 
4 17.712 5.00 
5 24.439 2.50 1.79668 
45.4 
6 -12.240 1.00 1.67270 
32.2 
7 25.235 1.10 
8 -49.274 2.90 1.79631 
40.9 
9 -11.514 1.00 
10 -8.160 1.50 1.58144 
40.8 
11 -21.421 19.32 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
(1) .vertline.t.sub.1 /f.sub.1 .vertline.=0.078 
(2) .vertline.t.sub.4 /f.sub.5 .vertline.=0.042 
(3) (r.sub.32 +r.sub.41)/(r.sub.32 -r.sub.41)=-0.323 
(4) .vertline.r.sub.42 /f.vertline.=0.399 
(5) D/f=0.803 
(6) N.sub.31 -N.sub.32 =0.124 
(7) N.sub.1 =1.595 
(8) N.sub.5 =1.581 
By using popular aspherical lenses, it is of course possible to introduce 
an aspherical surface into the first lens component L1 or the fifth lens 
component L5 of the present invention to thereby correct astigmatism and 
curvature of image field better and achieve a wide-angle, and to introduce 
an aspherical surface into the second lens component L2, the third lens 
component L3 or the fourth lens component L4 to thereby further correct 
spherical aberration and achieve a great relative aperture. 
FIGS. 9A and 9B schematically show the refractive power arrangements of 
ninth to thirteenth embodiment of the present invention. FIG. 9A shows the 
refractive power arrangement when the object position is in the infinity 
state, and FIG. 9B shows the refractive power arrangement when the object 
position is in a short distance state. It is shown in FIGS. 9A and 9B that 
as the object position moves from the infinity to the short distance, the 
first lens unit G1 and the second lens unit G2 move toward the object 
side. 
Each of the ninth to twelfth embodiments, as shown in FIG. 10, is of a 
construction which comprises, in succession from the object side, a first 
lens component L1 which is a negative meniscus lens having its convex 
surface facing the object side, a second lens component L2 which is a 
cemented lens of positive refractive power comprising a biconvex lens and 
a biconcave lens cemented together and having its convex surface facing 
the object side as a whole, a third lens component L3 comprising a 
cemented lens component of positive refractive power comprising a biconvex 
lens having its convex surface of sharper curvature facing the image side 
and a biconcave lens cemented thereto and having its convex surface facing 
the object side as a whole, a fourth lens component L4 which is a positive 
lens component having its concave surface facing the object side, and a 
fifth lens component L5 which is a negative meniscus lens having its 
convex surface facing the image side, a stop S being disposed between the 
second lens component L2 and the third lens component L3. 
The numerical data of the ninth to twelfth embodiments of the present 
invention are given below. In the data Tables below, the numbers at the 
left end represents the order from the object side, r represents the 
radius of curvature of each lens surface, d represents the spacing between 
adjacent lens surface, and the refractive index n and Abbe number .nu. are 
values for d-line (.lambda.=587.6 nm). 
TABLE 9 
______________________________________ 
Numerical Data of the Ninth Embodiment 
f = 28.6 
FNO = 2.88 
2.omega. = 74.0.degree. 
r d n .upsilon. 
______________________________________ 
1 17.9178 1.500 1.58913 
61.2 
2 9.1148 3.000 
3 14.8517 4.000 1.79668 
45.4 
4 -22.6769 1.300 1.60342 
38.0 
5 19.6186 2.000 
6 .infin. (d6) (stop) 
7 85.5391 3.000 1.79668 
45.4 
8 -12.4521 1.300 1.67270 
32.2 
9 44.1538 1.300 
10 -49.9974 2.500 1.74810 
52.3 
11 -13.6254 2.700 
12 -9.5518 2.000 1.64831 
33.8 
13 -13.0360 (Bf) 
______________________________________ 
Variations in the spacing when the photographing distance is infinity 
(.infin.) and a short distance (300 mm) are shown below. 
TABLE 10 
______________________________________ 
Photographing Distance 
Infinity 
300 mm 
______________________________________ 
d6 3.000 2.651 
Bf 21.891 25.382 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
EQU .DELTA..multidot.(.phi..sub.a -.phi..sub.b)/.phi.=0.071 (1) 
EQU .vertline..phi.1/.phi..vertline.=0.051 (2) 
TABLE 11 
______________________________________ 
Numerical Data of the Tenth Embodiment 
f = 28.9 
FNO = 2.88 
2.omega. = 73.8.degree. 
r d n .upsilon. 
______________________________________ 
1 17.8000 1.500 1.58913 
61.2 
2 9.3309 3.100 
3 13.9124 3.900 1.79668 
45.4 
4 -29.7570 1.100 1.60342 
38.1 
5 17.4563 (d5) 
6 .infin. 2.400 (stop) 
7 49.4089 3.600 1.79668 
45.4 
8 -10.5646 1.000 1.67270 
32.2 
9 35.7839 1.400 
10 -47.3829 3.300 1.79668 
45.4 
11 -13.1267 1.600 
12 -9.9212 2.000 1.60432 
38.1 
13 -15.6720 (Bf) 
______________________________________ 
Variations in the spacing when the photographing distance is infinity 
(.infin.) and a short distance (300 mm) are shown below. 
TABLE 12 
______________________________________ 
Photographing Distance 
Infinity 
300 mm 
______________________________________ 
d5 12.600 2.369 
Bf 21.940 24.832 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
EQU .DELTA..multidot..phi./(.phi..sub.a -.phi..sub.b)=0.061 (1) 
EQU .vertline..phi.1/.phi..vertline.=0.811 (2) 
TABLE 13 
______________________________________ 
Numerical Data of the Eleventh Embodiment 
f = 28.9 
FNO = 2.88 
2.omega. = 73.8.degree. 
r d n .upsilon. 
______________________________________ 
1 12.5065 1.500 1.53172 
49.1 
2 8.7834 3.450 
3 12.5521 3.950 1.84042 
43.3 
4 -1626.4800 
1.000 1.64831 
33.8 
5 12.6942 (d5) 
6 .infin. 2.350 (stop) 
7 45.2763 2.500 1.80411 
46.3 
8 -13.7592 1.000 1.67270 
32.2 
9 56.7133 1.150 
10 -25.5838 2.950 1.79668 
45.4 
11 -10.3313 0.800 
12 -8.8304 1.500 1.58144 
40.8 
13 -16.1578 (Bf) 
______________________________________ 
Variations in the spacing when the photographing distance is infinity 
(.infin.) and a short distance (300 mm) are shown below. 
TABLE 14 
______________________________________ 
Photographing Distance 
Infinity 
300 mm 
______________________________________ 
d5 1.650 1.545 
Bf 20.514 24.033 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
EQU .DELTA..multidot..phi./(.phi..sub.a -.phi..sub.b)=0.022 (1) 
EQU .vertline..phi.1/.phi..vertline.=0.447 (2) 
TABLE 15 
______________________________________ 
Numerical Data of the Twelfth Embodiment 
f = 28.9 
F.sub.NO = 2.88 
2.omega. = 73.8.degree. 
r d n .upsilon. 
______________________________________ 
1 17.1000 1.500 1.54739 
53.6 
2 9.2824 2.700 
3 12.9097 3.900 1.84042 
43.3 
4 -60.1829 1.100 1.62588 
35.6 
5 14.6504 (d5) 
6 .infin. 2.400 (stop) 
7 50.3000 3.300 1.79668 
45.4 
8 -10.6591 1.000 1.67270 
32.2 
9 43.9560 1.400 
10 -36.8415 3.000 1.79668 
45.4 
11 -13.0249 1.500 
12 -9.8051 1.500 1.58144 
40.8 
13 -14.8205 (Bf) 
______________________________________ 
Variations in the spacing when the photographing distance is infinity 
(.infin.) and a short distance (300 mm) are shown below. 
TABLE 16 
______________________________________ 
Photographing Distance 
Infinity 
300 mm 
______________________________________ 
d5 2.600 2.427 
Bf 20.830 5.727 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
EQU .DELTA..multidot.(.phi..sub.a -.phi..sub.b)/.phi.=0.046 (1) 
EQU .vertline..phi.1/.phi..vertline.=0.726 (2) 
The thirteenth embodiment, as shown in FIG. 11, is of a construction which 
comprises, in succession from the object side, a first lens component L1 
which is a negative meniscus lens having its convex surface facing the 
object side, a second lens component L2 which is a positive meniscus lens 
having its convex surface of sharp curvature facing the object side, a 
third lens component L3 which is a positive lens component comprising a 
biconcave lens having its concave surface of sharper curvature facing the 
image side and a biconvex lens having its convex surface of sharper 
curvature facing the object side, said biconcave lens and said biconvex 
lens being cemented together, a fourth lens component L4 of positive 
refractive power comprising a biconcave lens and a biconvex lens cemented 
together and having its convex surface facing the image side as a whole, 
and a fifth lens component L5 which is a negative meniscus lens having its 
convex surface facing the image side, a stop S being disposed between the 
third lens component L3 and the fourth lens component L4. 
The numerical data of the thirteenth embodiment of the present invention 
are given below. In the data Table below, the numbers at the left end 
represents the order from the object side, r represents the radius of 
curvature of each lens surface, d represents the spacing between adjacent 
lens surfaces, and the refractive index n and Abbe number .nu. are values 
for d-line (.lambda.=587.6 nm). 
TABLE 17 
______________________________________ 
Numerical Data of the Thirteenth Embodiment 
f = 28.9 
F.sub.NO = 2.88 
2.omega. = 73.8.degree. 
r d n .upsilon. 
______________________________________ 
1 11.8420 1.500 1.59507 
36.6 
2 8.4410 2.998 
3 10.9528 3.300 1.79668 
27.8 
4 15.7309 1.354 
5 -449.9259 1.000 1.67270 
40.5 
6 13.7678 2.500 1.80411 
46.3 
7 -117.2633 (d7) 
8 .infin. 2.650 (stop) 
9 -24.4051 1.000 1.64831 
38.4 
10 5.0605 2.973 1.84042 
29.2 
11 -12.1107 1.674 
12 -8.8483 1.500 1.59507 
36.6 
13 -18.9952 (Bf) 
______________________________________ 
Variations in the spacing when the photographing distance is infinity 
(.infin.) and a short distance (300 mm) are shown below. 
TABLE 18 
______________________________________ 
Photographing Distance 
Infinity 
300 mm 
______________________________________ 
d7 1.350 1.492 
Bf 18.460 21.287 
______________________________________ 
The condition-corresponding values of the above data are shown below. 
EQU .DELTA..multidot.(.phi..sub.a -.phi..sub.b)/.phi.=0.012 (1) 
EQU .vertline..phi.1/.phi..vertline.=0.489 (2) 
By using popular aspherical lenses in the ninth to thirteenth embodiments 
of the present invention, introducing an aspherical surface into the first 
lens component L1 or the fifth lens component L5, it is possible to 
correct astigmatism and curvature of image field better and achieve a 
wider angle. By introducing an aspherical surface also into the second 
lens component L2, the third lens component L3, or the fourth lens 
component L4, it is of course possible to correct spherical aberration 
further and achieve a greater aperture. 
According to the present invention, there can be achieved a wide-angle lens 
which is compact and high in performance and as small as the order of F 
2.8. The present invention can be used not only in 35 mm format cameras, 
but also in large format cameras. Further, when focusing is effected by 
general axial movement, the fluctuations of aberrations are very small and 
a good performance can be obtained.