will“ dl d2 d3 d5 d6 d7 d8 d9 dIO dll
350-454
SR
4/29/8151
CR
4.525.314
United States Patent [19]
Tateoka
-"
[54] PROJECTION LENS
[75] Inventor: Masamichi Tateoka, Yokohama,
Japan
[73] Assignee:
Canon Kabushiki Kaisha, Tokyo,
Japan
[21] Appl. No.: 603,767
[22] Filed:
[30]
Apr. 29, 1986
Attorney, Agent, or Firm-Fitzpatrick, Cella, Harper &
Scinto
_
[57]
ABSTRACT
This speci?cation discloses a projection lens for pro
jecting an original onto the surface of a sensor and for
use in a facsimile apparatus or a digital copying appara
tion magni?cations with the length of the optical path
Japan ................................ .. 58-75834
Int. Cl.‘ ....................... .. G02B 9/62; GOZB 13/04
US. Cl. ............................... .. 350/464; 350/426
Field of Search .............................. .. 350/464, 426
[56]
4,585,314
nal to be projected onto the sensor at different projec
Apr. 25, 1984
Apr. 28, 1983 [JP]
[451
Patent Number:
Date of Patent:
tus. The projection lens enables the image of the origi
Foreign Application Priority Data
[51]
[52]
[58]
[11]
between the surface of the original and the sensor kept
constant. The projection lens comprises, in succession
from the object side, a ?rst lens group comprising a
negative meniscus lens having its convex surface facing
the object side, and a positive meniscus lens having its
convex surface facing the object side, the ?rst lens
group as a whole having a negative refractive power,
References Cited
and a second lens group having three positive lenses and
U.Sv PATENT DOCUMENTS
a negative lens, the second lens group as a whole having
a positive refractive power. The ?rst lens group is sta
4,195,912
4/1980
Doi et al. .......................... .. 350/426
FOREIGN PATENT DOCUMENTS
tionary and the second lens group is movable, whereby
the image of the original is projectedonto the surface of
the sensor at different projection magni?cations with
-
0044554
4/1979
Japan ................................. .. 350/426
the object-image distance being kept constant.
Primary Examiner—John K. Corbin
2 Claims, 5 Drawing Figures
Assistant Examiner-Rebecca D. Gass
l'l r2 r3 r4 F5 r6 [7 re re HO l'll n2
l7
will“
dl d2 d3 d5 d6 d7 d8 d9 dIO dll
U.S. Patent Apr. 29,1986
,. Sheet20f2
4,585,314
F IG. 3A
SPHERICAL
ABERRATION
CURVATURE
[W042
O
OF FIELD
: (11/2: l80
DISTORTION
01/
5
O
(mm)
(mm)
IO
l we)
F l G. 3 B
SPHERICAL
CURVATURE
ABERRATION
OF ‘FIELD
FNO = 4.2
l
\
\
-0.4
o
0.4 (mm)
I
-
DISTORTION
1
4,585,314
-
2
robtain two different focal lengths with the object-image
distance being kept constant.
PROJECTION LENS
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a projection lens which is
used at a magni?cation in the vicinity of 1/10 times and
used at two kinds of focal length, i.e., at two kinds of
magni?cation with the object-image distance being kept
constant and in which the F-number is relatively bright
and various aberrations are well corrected and which is
inexpensive.
2. Description of the Prior Art
A number of ordinary zoom lenses for photography
in which a ?rst lens group has a negative refractive
power and a second lens group has a positive refractive
power are known. In the lenses of such a type, however,
the ?rst lens group comprises three or four lenses, and
this leads to a complicated construction as well as a high
cost. In the present invention, in view of the fluctuation
of the focal length between two points, the ?rst lens
group comprises two lenses, both of which are of a
meniscus shape and have a convex surface facing the
object side. Such construction of the ?rst lens group has
the effect of suitably correcting the spherical aberration
In recent years, a method has been used in which a
and curvature of image ?eld created by the second lens
solid state image pickup element is used as the reading
group.
sensor in a facsimile apparatus or a digital copying appa
Further, in the projection lens according to the pres
ent invention, assuming that the negative meniscus lens
in the ?rst lens group is I-l lens, the positive meniscus
ratus, and is disposed as a scanning light-receiving ele
ment on the image plane to scan an original. Also, as the
functions of a facsimile apparatus, not only one-to-one
lens in the ?rst lens group is a I-2 lens and the second
magni?cation but also the enlarging and reducing func
lens group comprises, in succession from the object
tions have been required. Generally, in the case of re
side, two 11-1 and 11-2 lenses which are positive lenses,
duction, a method of thinning out picture elements read
a 11-3 lens which is a negative lens and a 11-4 lens which
by the solid state image pickup element is adopted. In
is a positive lens, the projection lens satis?es the follow
the case of enlargement, however, the method of softly 25 ing condition:
adding such picture elements aggravates the quality of
image, and therefore, if the magni?cation of the projec
tion lens during one-to-one magni?cation is [31 and the
enlargement ratio is 3;, projection is effected at a mag
ni?cation of [31x32 onto the surface of the solid state
image pickup element by a projection lens. If, then, an
attempt is made to use a ?xed focus lens to change the
0.4< Il'Q/fll (0.55
(n)
0.9 < Ir9/f2l < 1.4
(III)
where
f1: focal length of the ?rst lens group
magni?cation thereof, the ?xed focus lens must be
moved to vary the projection magni?cation and also the
object-image distance must be changed, and thus, the
f2: focal length of the second lens group
r3: radius of curvature of the surface of the I-2 lens
apparatus becomes complicated and the image perfor
which is adjacent to the object side
mance is deteriorated. Also, if two ?xed focus lenses are
r9: radius of curvature of the surface of the 11-3 lens
which is adjacent to the object side.
‘
The invention will hereinafter be described in detail
used with the object-image distance kept constant, the
change-over of these lenses becomes complex and the
use of the two lenses results in an increased cost.
with reference to the accompanying drawings.
SUMMARY OF THE INVENTION
BRIEF DESCRIPTION OF THE DRAWINGS
On the basis of such viewpoints, the present invention
FIG. 1 is a cross-sectional view showing an embodi
is intended to provide a projection lens in which the 45
ment of the projection lens according to the present
object-image distance is constant and two different
invention.
magni?cations are provided.
FIGS. 2A, 2B and 3A, 3B show the various aberra
It is a further object of the present invention to pro
tions in the projection lens according to the present
vide a projection lens having a bright F-number and a
invention.
high resolving power.
'50
It is still a further object of the present invention to
provide a projection lens which has a wide angle of
view and in which distortion is small.
It is yet a further object of the present invention to
provide a projection lens in which the off-axis aperture
ef?ciency is 100% and which has no irregularity of
illumination.
The projection lens according to the present inven
tion generally comprises, in succession from the object
side, a ?rst lens group comprising a negative meniscus
lens having its conyex surface facing the object side and
a positive meniscus lens having its convex surface fac
ing the object side, the ?rst lens group as a whole hav
ing a negative refractive power, and a second lens
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
If a ?rst lens group is a thin lens having a refractive
power of l/f; (<0) and a second lens group is a thin lens
having a refractive power of l/fz (>0), the object
image distance is L, the reference magni?cation is M,
the enlargement ratio is A, the magni?cation of the ?rst
lens group is B1 and the magni?cation of the second lens
group is 3;, then there are established the following
relations:
?1><1/B2=AM
(2)
group having three positive lenses and a negative lens, 65
the second lens group as a whole having a positive
refractive power, the ?rst lens group being stationary
and the second lens group being moved to thereby
When [5'] and B2 are found from equations (1) and (2)
and the relation between the object and the image is
inserted, there is obtained the following equation:
3
4,585,314
4
—continued
First Embodiment
fw = 33.0229, f7‘ = 41.2932, FNO = 4
I
2
.4 + AZM + l/AM
4
5
31.905
24.705
This equation shows the relation between the refractive
6
powers of the ?rst lens group and the second lens group
7
8
9
10
11
18.664
491.15
12
- 17.578
of the present invention.
The aforementioned condition (I) prescribes the ratio 10
of the refractive powers of the ?rst lens group and the
second lens group and, if |f1/f2| exceeds the upper limit
of this condition, that is, if the refractive power of the
second lens group becomes greater, correction of spher-_
ical aberration will become difficult. Also, if |f1/f2|
becomes smaller than the lower limit of this condition,
the Petzval sum of the entire system will become nega
tive and correction of the curvature of image ?eld will
become difficult and distortion will pose a problem.
The aforementioned condition (II) is a condition for
correcting the over-corrected spherical aberration and
curvature of image ?eld created by the negative menis
cus lens of the ?rst lens group, by the positive meniscus
lens of the same ?rst lens group, and if |r3/f1| exceeds
the lower limit of this condition, spherical aberration 25
_ 1900.55
?eld will become under-corrected.
The aforementioned condition (III) is a condition for
correcting the under-correction of the spherical aberra
tion created by two positive lenses disposed on the
object side of the second lens group, by the negative
lens of the same second lens group, and if |r9/f2| be
comes smaller than the lower limit of this condition,
spherical aberration will become over-corrected, while
if lrg/fgI exceeds the upper limit of this condition,
spherical aberration will become under-corrected. If
this is corrected by the radius of curvature no of the
image side surface of the II-3 lens, coma and curvature
of image ?eld will be aggravated.
An embodiment of the projection lens of the present
55.5
0.5
22.59
—97l.434
-25.557
3.49
3.73
1.15
2.24
1.97
1.69979
55.5
1.81265
25.4
1.76651
40.1
1
B
fW
10.51
—O. 1 12
fr
2.94
I -0. 1474
FIG. 2A shows the aberrations when fW=33.0229,
and FIG. 2B shows the aberrations when f7~=4l.2932.
Second Embodiment
fw = 28.6195, f7-= 36.5594, FNO = 4
and curvature of image ?eld will become over-cor
rected, while if |r3/f1] exceeds the upper limit of this
condition, spherical aberration and curvature of image
1 (variable)
3.26
1.69979
Surface
r
d
n
v
1.76651
40.1
1.76168
27.5
1 (variable)
3.16
1.69979
55.5
1
2
3
89.339
15.329
19.517
1.74
5.85
2.08
4
5
28.74
21.938
6
— 105.87
0.47
7
8
9
10
11
17.205
50.988
—31.108
14.83
404.91
12
— 17.427
2.64
3.24
1.0
1.75
2.16
1.69979
55.5
1.81265
25.4
1.76651
40.1
1
B
fw
8.66
--0.1 12
f;-
1.45
—0.1471
invention will now be described. In that embodiment,
frand f W represent the two focal lengths of the projec
tion lens, and the case where the value of his shown is 45
a case where both lens groups are close to each other asv
compared with the case of f W. FNO represents the F
number of the lens, r,- represents the radius of curvature
FIG. 3A shows the aberrations when fW=28.6195,
and FIG. 3B shows the aberrations when fT== 36.5594.
As described above, if the projection lens according
of the ith surface from the object side, direpresents the
to the present invention is applied to a reading appara
on-axis air space or the on-axis thickness between the ith
surface and the i+ 1th surface, 11 represents the refrac
tive indices of the lenses v represents the dispersion
tus such as a facsimile apparatus or a digital copying
apparatus, a ?uorescent lamp of low illuminance is us
able because the F-number of the lens is bright, and the
spacing between an original and the surface of a sensor
may be short to make the apparatus compact, because
values of the lenses, B represents the imaging magni?ca
tion, and 1 represents the variable value of d4.
Also, FIG. 1 shows a cross-sectional view of the lens 55 the angle of view of the lens is great. Further, since the
lens of the present invention has a high resolving
according to a ?rst embodiment, FIGS. 2A and 2B
show the various aberrations in the ?rst embodiment,
power, suf?cient resolution can be achieved even if
each of the solid state image sensing elements is
1511-1311., and the vignetting factor off the axis of the
of image ?eld indicates the meridional image surface
lens is 100%, whereby there is no irregularity of the
and S indicates the sagittal image surface.
quantity of light on the solid state image sensing ele
ments. Furthermore, in the projection lens of the pres:
ent invention, distortion is small, and therefore, the
First Embodiment
surface of the original is uniformly projected onto the
fw = 33.0229, f7- = 41.2932, FNO = 4
solid
state image sensing elements, and the number of
65
Surface
r
d
n
v
lens components constituting the lens is small and thus,
1
94.093
2.0
1.76651
40.1
the lens can be provided inexpensively.
2
16.997
5.96
What is claimed is:
3
21.422
2.39
1.76168
27.5
and FIGS. 3A and 3B show the various aberrations in a I
second embodiment. In FIGS. 2 and 3, M in curvature
5
4,585,314
1. A projection lens having different focal lengths
w
with the object-image distance kept constant, said pro-
6
moved during magni?cation change with the ob
ject-image distance kept constant.
jection lens comprising, in succession from the object
_
2. A projection lens according to claim 1, satisfying
the following conditions:
side:
a ?rst lens group comprising a negative meniscus lens 5
‘
having its convex surface facing the object side and
1'2< ‘Wm <17
a positive meniscus lens having its convex surface
“GU/{1K0 55
facing the object side, said ?rst lens group as a
'
whole having a negative refractive power, said ?rst
'
0,9< lr9/fz | (1.4,
lens group being stationary during magni?cation 10
change; and
asecond lens group disposed on the image side of said
?rst lens group and comprising a 11-1 positive lens,
a 11-2 positivc lens, a 11-3 negative lcnS and 11-4
where f] is the focal length of said ?rst lens group, f; is
the focal length of said second lens group, 1-; is the
radius of curvature of the surface of the positive menis
cus lens of said ?rst lens group which is adjacent to the
positive lens disposed in the named order in succes- l5 object side, and r9 is the radius of curvature of the sur
sion from the object side to the image side, said
face of said II-3 negative lens which is adjacent to the
second lens group as a whole having a positive
object side.
i
U
i
i
i
refractive power, said second lens group being
20
25
30
35
50
55
65
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