Zoom lens device with five lens units

A zoom lens device including a total of five lens units which are in order of lens units from the lens unit closest to an object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, a fourth lens unit having a positive refractive power, and a fifth lens unit having a positive refractive power. During magnification changes, the first, second, and fourth lens units move along the optical axis, while the third and fifth lens units are stationary. The zoom lens device satisfies the following conditions: (1) 0.7<f.sub.2 /f.sub.T <1.2; (2) 2.2<.vertline.f.sub.3 .vertline./f.sub.W <3.5; (3) 0.6<.vertline.f.sub.3 .vertline./f.sub.4 <1.45; and (4) f.sub.T <f.sub.4 <f.sub.5, where fi represents the focal length of the ith lens unit, and f.sub.T and f.sub.W represent the focal lengths at the telephoto end and the wide angle end, respectively.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention broadly relates to a zoom lens device, and, more 
particularly, to a negative lead type zoom lens device having a wide angle 
of view and a long back focus, and which is substantially telecentric at 
an image plane side, and which is suitable for use in, for example, a 
video camera or a still video camera utilizing a solid-state imaging 
device. 
2. Description of the Related Art 
The so-called negative lead type zoom lens device in which a lens unit with 
a negative refractive power is placed at a leading position has the 
advantages that the angle of view can be made relatively wide easily and 
that the close shooting distance can be made short. However, this type of 
zoom lens device has the disadvantages that the stop diameter increases 
and that high magnification cannot be easily achieved. 
Japanese Examined Patent Publication No. 49-23912, and Japanese Unexamined 
Patent Publication Nos. 53-34539, 57-163213, and 58-4113 disclose zoom 
lens devices free from the above-described problems, in which the entire 
lens system is made smaller and has high magnification. 
The zoom lens devices disclosed in the above-described documents comprise 
four lens units whose refractive powers are, from the refractive power of 
the lens unit closest to the object side, negative, positive, negative, 
and positive. Among these lens units, a predetermined lens unit is 
properly moved in order to change magnification. 
The zoom lens device disclosed in Japanese Unexamined Patent Publication 
No. 4-264412 comprises five lens units whose refractive powers are from 
the refractive power of the lens unit closest to the object side, 
positive, negative, positive, and negative. Among these lens units, a 
predetermined lens unit is properly moved in order to change 
magnification. 
In recent years, there has been an increasing demand for video camera zoom 
lens devices which have high magnification and a wide angle of view. High 
magnifications of 10 times or more have been achieved as a result of 
progress made in design technology. 
However, it has been difficult to provide a wide angle of view because the 
lens diameter, in particular the outer diameter of the front lens, cannot 
be easily reduced. 
Similarly, in the still video camera field, there has also been an 
increasing demand for a zoom lens device providing a wide angle of view 
and having high resolution as a result of improvements made in imaging 
devices, such as charge coupled devices (CCDs) whose image pixels are 
closely compacted together. 
These video cameras and still video cameras utilize solid-state imaging 
devices (CCDs), thus making it necessary to provide a lowpass filter, such 
as a crystal plate, or an infrared absorption filter between the optical 
system and the image plane. Therefore, the zoom lens devices used in these 
cameras must have a long back focus. 
It is desirable that the zoom lens device be telecentric with respect to 
the CCD, since a color filter is provided in correspondence with the 
pixels of the CCD. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a 
substantially telecentric zoom lens device having a wide angle of view and 
high resolution, comprising a total of five lens units, wherein the 
refractive powers of predetermined lens units among the five lens units 
are properly set, so that sufficient back focus is provided to allow 
insertion of various filters, such as an optical lowpass filter or an 
infrared cut-off filter, and so that a principal ray incident to the 
imaging device, such as a CCD, is substantially perpendicular to the 
imaging device. 
To this end, according to the present invention, there is provided a zoom 
lens device comprising five lens units which are in order of lens units 
from the lens unit closest to an object side, a first lens unit having a 
negative refractive power, a second lens unit having a positive refractive 
power, a third lens unit having a negative refractive power, a fourth lens 
having a positive refractive power, and a fifth lens unit having a 
positive refractive power. In the zoom lens device, during magnification 
changes, the first, second, and fourth lens units move along the optical 
axis, while the third and fifth lens units are stationary. The zoom lens 
device satisfies the following conditions: 
EQU 0.7&lt;f.sub.2 /f.sub.T &lt;1.2 
EQU 2.2&lt;.vertline.f.sub.3 .vertline./f.sub.W &lt;3.5 
EQU 0.6&lt;.vertline.f.sub.3 .vertline./f.sub.4 &lt;1.45 
EQU f.sub.T &lt;f.sub.4 &lt;f.sub.5 
where f.sub.i is the focal length of the ith lens unit, and f.sub.T and 
f.sub.W are the focal lengths of the entire lens system (i.e., the zoom 
lens device) at the telephoto end and the wide angle end, respectively. 
In the zoom lens device, when the magnification changes from the telephoto 
end to the wide angle end, the second and fourth lens units move toward 
the image plane, with the second lens unit moving by a greater amount than 
the fourth lens unit. The fourth lens unit has at least one aspherical 
surface which is shaped so as to reduce the positive refractive power at a 
peripheral portion of the surface. The lens surface closest to the image 
plane side of the fourth lens unit is aspherically formed. The first lens 
unit has at least one aspherical surface which is shaped so as to reduce 
the positive refractive power at a peripheral portion of the surface. The 
lens surface closest to the object side of the first lens unit is 
aspherically formed. 
In view of the foregoing, in one aspect, the present invention relates to a 
zoom lens device comprising, in order of lens units from the lens unit 
closest to an object side of the zoom lens device a first lens unit having 
a negative refractive power, a second lens unit having a positive 
refractive power, a third lens unit having a negative refractive power, a 
fourth lens unit having a positive refractive power, and a fifth lens unit 
having a positive refractive power, wherein during magnification change, 
the first lens unit, the second lens unit, and the fourth lens unit move 
along an optical axis of the zoom lens device, while the third lens unit 
and the fifth lens unit are stationary, and wherein the following 
conditions are satisfied: 
EQU 0.7&lt;f.sub.2 /f.sub.T &lt;1.2, 
EQU 2.2&lt;.vertline.f.sub.3 .vertline./f.sub.W &lt;3.5, 
EQU 0.6&lt;.vertline.f.sub.3 .vertline./f.sub.4 &lt;1.45, and 
EQU f.sub.T &lt;f.sub.4 &lt;f.sub.5, 
where f.sub.2, f.sub.3, f.sub.4, and f.sub.5 represent the focal lengths of 
the second lens unit, the third lens unit, the fourth lens unit, and the 
fifth lens unit, respectively, and where f.sub.T and f.sub.W represent the 
focal lengths of the zoom lens device at a telephoto end and a wide-angle 
end, respectively. 
In another aspect, the present invention relates to a zoom lens device 
comprising, in order of lens units from the lens unit closest to an object 
side of the zoom lens device a first lens unit having a negative 
refractive power, a second lens unit having a positive refractive power, a 
third lens unit having a negative refractive power, a fourth lens unit 
having a positive refractive power, and a fifth lens unit having a 
positive refractive power, wherein during magnification change, the first 
lens unit, the second lens unit, and the fourth lens unit move along an 
optical axis of the zoom lens device, while the third lens unit and the 
fifth lens unit are stationary, wherein the following conditions are 
satisfied: 
EQU 0.7&lt;f.sub.2 /f.sub.T &lt;1.2, 
EQU 2.2&lt;.vertline.f.sub.3 .vertline./f.sub.W &lt;3.5, 
EQU 0.6&lt;51 f.sub.3 .vertline./f.sub.4 &lt;1.45, and 
EQU f.sub.T &lt;f.sub.4 &lt;f.sub.5, 
where f.sub.2, f.sub.3, f.sub.4, and f.sub.5 represent the focal lengths of 
the second lens unit, the third lens unit, the fourth lens unit, and the 
fifth lens unit, respectively, and where f.sub.T and f.sub.W represent the 
focal lengths of the zoom lens device at a telephoto end and a wide-angle 
end, respectively, and wherein the first lens unit moves toward the object 
side and second lens unit and the fourth lens unit move toward an image 
plane side during magnification change from the telephoto end to the 
wide-angle end, the second lens unit moving by an amount larger than that 
of the fourth lens unit, wherein the first lens unit comprises, in order 
from the object side, a negative meniscus lens whose convex surface faces 
the object side, a negative lens, and a positive meniscus lens whose 
convex surface faces the object side, wherein the second lens unit 
comprises (i) a positive lens subunit consisting of a negative lens 
cemented to a positive lens and (ii) a positive meniscus lens, wherein the 
third lens unit comprises a negative lens subunit consisting of a positive 
lens cemented to a negative lens, wherein the fourth lens unit comprises 
(i) a lens subunit consisting of a negative lens cemented to a positive 
lens and (ii) a positive lens, and wherein the fifth lens unit comprises 
one of (i) a lens subunit consisting of a negative lens cemented to a 
positive lens and (ii) in order from the object side, a negative lens, a 
positive meniscus lens with its convex surface facing the image plane 
side, and a positive meniscus lens with its convex surface facing the 
object side. 
These and other aspects, objects, and features of the present invention 
will become apparent from the following detailed description of preferred 
embodiments thereof taken in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1A and 1B are sections of a zoom lens device of Embodiment 1 of the 
present invention at the telephoto end and at the wide angle end, 
respectively. 
Referring to FIGS. 1A and 1B, reference numeral 1 denotes a first lens unit 
with a negative refractive power, which comprises in the order of lenses 
starting from the lens closest to the object side, a negative meniscus 
lens whose convex surface faces the object side, a negative lens, and a 
positive meniscus lens whose convex face faces the object side. Reference 
numeral 2 denotes a second lens unit with a positive refractive power. The 
second lens unit comprises (a) a positive lens subunit, consisting of a 
positive lens subunit formed by a negative lens cemented to a positive 
lens, and (b) a positive meniscus lens. Reference numeral 3 denotes a 
third lens unit with a negative refractive power, which comprises a 
negative lens subunit consisting of a positive lens cemented to a negative 
lens. Reference numeral 4 denotes a fourth lens unit with a positive 
refractive power. The fourth lens unit comprises a lens subunit (formed by 
a negative lens cemented to a positive lens) and a positive lens. 
Reference numeral 5 denotes a fifth lens unit (with a positive refractive 
power), which comprises a lens subunit formed by a negative lens cemented 
to a positive lens. SP denotes a stop, LF denotes an optical block such as 
a crystal plate, or an infrared absorption filter, and reference character 
F denotes an image plane. The ith lens surface from the object side is 
represented by ri. 
Lens surface r1, closest to the object side, of the first lens unit and the 
lens surface r20, closest to the object side, of the fourth lens unit are 
aspherical. The aspherical surfaces are shown in FIGS. 2A and 2B, in which 
the solid line in each diagram represents a section of one side of the 
aspherically-shaped first surface (r1) and a section of one side of the 
aspherically-shaped 20th surface (r20), respectively, with respect to the 
optical axis, while the broken line in each diagram represents a paraxial 
spherical surface (R) with respect to the optical axis. 
According to the present embodiment, the lens units, which move when the 
magnification changes from the telephoto end to the wide angle end, move 
as indicated by the arrows in FIGS. 1A and 1B. More specifically, the 
first lens unit moves toward the object, the second lens unit moves toward 
the image plane, and the fourth lens unit moves toward the image plane. 
The third and fifth lens units are stationary. 
According to the present embodiment, there are five lens units whose 
refractive powers are from the refractive power of the lens unit closest 
to the object side, negative, positive, negative, positive, and positive. 
The refractive powers of the second, third, fourth, and fifth lens units 
are set so as to satisfy the following Conditions (1) to (4): 
EQU 0.7&lt;f.sub.2 /f.sub.T &lt;1.2 (1) 
EQU 2.2&lt;.vertline.f.sub.3 .vertline./f.sub.W &lt;3.5 (2) 
EQU 0.6&lt;.vertline.f.sub.3 .vertline.f.sub.4 &lt;1.45 (3) 
EQU f.sub.T &lt;f.sub.4 &lt;f.sub.5 (4) 
Therefore, it is possible to provide a zoom lens device with a long back 
focus, which is substantially telecentric with respect to the image plane, 
has a wide angle of view, and provides excellent optical performance. 
FIGS. 3A and 3B are sections of a zoom lens device of Embodiment 2 of the 
present invention at the telephoto end and the wide angle end, 
respectively. 
The zoom lens device of the present embodiment is essentially the same as 
the zoom lens device of Embodiment 1, except for the construction of the 
fifth lens unit. The fifth lens unit comprises in the order of lenses from 
the lens closest to the object side, a negative lens, a positive meniscus 
lens with its convex surface facing the image plane, and a positive 
meniscus lens with its convex surface facing the object. 
In the present embodiment, the first lens surface r1 and the 20th lens 
surface r20 are aspherical. These aspherical surfaces are shown in the 
diagrams of FIGS. 4A and 4B, in which the solid line in each diagram 
represents a section of one side of the aspherically-shaped first surface 
(r1) and one side of the aspherically-shaped 20th surface (r20), 
respectively, with respect to the optical axis, and the broken line in 
each diagram represents a section of a paraxial spherical surface (R) with 
respect to the optical axis. 
According to the present embodiment, the lens units, which move when the 
magnification changes from the telephoto end to the wide angle end, move 
as indicated by the arrows in FIGS. 3A and 3B. More specifically, the 
first lens unit moves toward the object, and the second lens unit and the 
fourth lens unit move toward the image plane. The third and fifth lens 
units are stationary. 
According to the present embodiment, there are five lens units whose 
refractive powers are from the refractive power of the lens unit closest 
to the object side, negative, positive, negative, positive, and positive. 
The refractive powers of the second, third, fourth, and fifth lens units 
are set so as to satisfy Conditions (1) to (4), so that the zoom lens 
device is one having a long back focus, which is substantially telecentric 
with respect to the image plane, has a wide angle of view, and provides 
excellent optical performance. 
The technical meaning of each of the aforementioned conditions will be 
given. 
Condition (1) relates to the positive refractive power of the second lens 
unit. Satisfying this condition primarily results in a shorter overall 
length of the lens unit and proper correction of spherical aberration at 
the telephoto end. More specifically, when the f.sub.2 /f.sub.T value of 
the second lens unit, which plays the most part in changing the 
magnification in the zoom lens device construction, is less than the lower 
limit so that it has a high positive refractive power, the spherical 
aberration which is in particular large at the telephoto end cannot be 
corrected by the other lens units. On the other hand, when the f.sub.2 
/f.sub.T value of the second lens unit is greater than the upper limit of 
Condition (1), the lens unit must be moved by a larger amount in order to 
perform the predetermined magnification changes, resulting in a longer 
overall length of the zoom lens device, and a larger outside diameter of 
the first lens unit. 
Condition (2) relates to the negative refractive power of the third lens 
unit. Satisfying this condition primarily causes the zoom lens device as a 
whole to be a substantially telecentric optical system. Considering the 
characteristics of the zoom lens device of the present invention, it is 
desirable to use a telecentric lens system when, for example, an imaging 
device is used. With Conditions (1) and (3) set as described above, 
Condition (2) allows the proper back focus to be provided in order to make 
the zoom lens device into a substantially telecentric system. Without 
Condition (2) being satisfied, it becomes difficult to form the zoom lens 
device into a telecentric system. 
Condition (3) relates to the ratio of the refractive powers of the third 
and fourth lens units. When this condition is satisfied, a proper back 
focus can be ensured to form the zoom lens device into a nearly 
telecentric system, and astigmatism which occurs at the fourth lens unit 
can be properly controlled. 
Condition (4) relates to the ratio of the fourth and fifth lens units. 
Satisfying this condition primarily results in proper setting of the 
amount of movement of the fourth lens unit and proper correction of the 
various aberrations. When the fourth lens unit, which is moved to change 
the magnification, has a high positive refractive power, the fourth lens 
unit does not have to be moved by a large amount, thus reducing the size 
of the zoom lens device. However, variations in the various aberrations 
resulting from magnification changes are increased by an amount which 
cannot be corrected by the other lens units. 
According to the present embodiments of the present invention, the first 
lens unit has an aspherical surface which primarily corrects astigmatism 
and distortion which are difficult to correct at the wide angle side, so 
that changes in distortions are kept to a minimum over the entire zoom 
lens unit. 
More specifically, the lens surface closest to the object, that is the 
first surface r1, where the point of passage of the nonaxial light beam 
changes the most between the telephoto side and the wide angle side, is 
made aspherical. The aspherical surface is shaped so as to increase the 
positive refractive power at a peripheral portion thereof. 
In addition, according to the present embodiments of the present invention, 
the fourth lens unit has an aspherical surface shaped as described above 
to properly correct astigmatism which occurs over the entire zoom lens 
device. More specifically, the lens surface of the fourth lens unit which 
is closest to the image, that is the 20th surface r20, where the point of 
passage of the nonaxial light beam changes the most between the telephoto 
side and the wide angle side, is made aspherical. The aspherical surface 
is shaped so as to reduce the positive refractive power at a peripheral 
portion thereof. 
It was believed to be difficult to correct astigmatism and distortion which 
occur, in particular, at the peripheral portions of the screen and to 
provide high optical performance in a zoom lens device having a wide angle 
of view and a long back focus. The present invention makes it possible to 
satisfactorily correct spherical aberration, coma, and astigmatism 
occurring over the entire zoom lens device, as well as distortion 
occurring particularly at the wide angle side by forming a surface of the 
fourth lens unit into an aspherical surface to reduce positive refractive 
power at the surface peripheral portions. 
When a surface of the first lens unit is formed into an aspherical shape, 
it is possible to correct astigmatism, which is corrected more than is 
necessary over the entire zoom lens device when an attempt is made to 
properly correct spherical aberration and coma, and to correct distortion, 
as it is corrected by the aspherical surface of the fourth lens unit, 
which is insufficiently corrected at the wide angle side. 
According to the present embodiments, the second and fourth lens units move 
toward the image plane when the magnification changes from the telephoto 
end to the wide angle end, with the second lens unit moving by a larger 
amount than the fourth lens unit, as a result of which changes in the 
various aberrations occurring due to magnification changes are canceled. 
A description will now be given of the numerical examples of the present 
invention. In the numerical examples, ri represents the radius of 
curvature of an ith lens surface from the object side; di represents the 
distance from the ith lens surface to the i+1th lens surface from the 
object side; and ni and vi represent the index of refraction and the Abbe 
constant, respectively, of the material of the ith lens from the object 
side. The stop is considered as one planar surface in the numerical 
examples. 
The aspherical shape of the surface is defined by the following formula: 
##EQU1## 
where the x-axis extends along the optical axis, the H-axis (with only 
positive values) extends along a direction perpendicular to the optical 
axis, the direction of travel of light is defined as positive, ri 
represents the paraxial radius of curvature (paraxial R), and A, B, C, D, 
and E, and A', B', C', D', and E' each represent aspherical coefficients. 
In addition, e-X represents 10.sup.-x. 
NUMERICAL EXAMPLE 1 
The zoom lens device of Numerical Example 1 has a magnification change-over 
ratio of 2.38. 
______________________________________ 
f = 14.68.about.6.19 FNo = 1:2.8.about.2.0 2.omega. = 34.8.degree..about 
.73.4.degree. 
______________________________________ 
r1 = 30.093 
d1 = 1.10 n1 = 1.74320 
v1 = 49.3 
r2 = 15.866 
d2 = 6.05 
r5 = 123.092 
d3 = 1.00 n2 = 1.77250 
v2 = 49.6 
r4 = 18.627 
d4 = 2.13 
r5 = 21.219 
d5 = 2.80 n3 = 1.84666 
v3 = 23.8 
r6 = 36.029 
d6 = varies 
r7 = 21.472 
d7 = 0.70 n4 = 1.84666 
v4 = 23.8 
r8 = 12.223 
d8 = 2.00 n5 = 1.77250 
v5 = 49.6 
r9 = 560.166 
d9 = 0.10 
r10 = 17.272 
d10 = 1.30 n6 = 1.80400 
v6 = 46.6 
r11 = 75.829 
d11 = varies 
r12 = (stop) 
d12 = 1.30 
r13 = -44.705 
d13 = 1.50 n7 = 1.80518 
v7 = 25.4 
r14 = -6.706 
d14 = 0.60 n8 = 1.72342 
v8 = 38.0 
r15 = 16.210 
d15 = varies 
r16 = -5.952 
d16 = 0.60 n9 = 1.80518 
v9 = 25.4 
r17 = 33.624 
d17 = 3.50 n10 = 1.77250 
v10 = 49.6 
r18 = -8.583 
d18 = 0.10 
r19 = 16.058 
d19 = 2.80 n11 = 1.74320 
v11 = 49.3 
r20 = -38.957 
d20 = varies 
r21 = -40.677 
d21 = 0.80 n12 = 1.62004 
v12 = 36.3 
r22 = 24.335 
d22 = 2.90 n13 = 1.77250 
v13 = 49.6 
r23 = -25.006 
d23 = 3.00 
r24 = 0.000 
d24 = 4.10 n14 = 1.51633 
v14 = 64.2 
r25 = 0.000 
back focus 9.93 
(Retrofocus ratio with respect to focal length at wide angle end 
1.605) 
Variation Interval Data 
Focal length 
14.68 10.17 6.19 
d6 0.32 11.35 35.21 
d11 6.91 4.39 2.31 
d15 2.10 4.19 5.90 
d20 5.20 3.12 1.40 
Amount of Lens Unit Movement 
Focal length 
14.68 10.17 6.19 
1st Lens Unit 
0.0 -8.51 -30.29 
2nd Lens Unit 
0.0 2.52 4.60 
4th Lens Unit 
0.0 2.09 3.80 
Distance from Image Plane to Exit Pupil 
Focal length 
14.68 10.17 6.19 
Pupil Distance 
185.8 124.0 55.3 
______________________________________ 
______________________________________ 
Aspherical Coefficients in Numerical Example 1 
1st surface 20th surface 
______________________________________ 
A = 0 A = 0 
B = 2.38906e-5 B = 1.30197e-4 
C = 1.24735e-7 C = -2.2072e-7 
D = -3.7749e-10 D = -3.82378e-8 
E = 9.79614e-13 E = 2.87962e-10 
A' =0 A' = 0 
B' = -2.67954e-6 B' = -7.61226e-6 
C' = 6.50446e-9 C' = 4.00208e-7 
D' = -1.56913e-11 D' = -2.04102e-9 
E' = 0 E' = 0 
______________________________________ 
______________________________________ 
Shape of 1st surface 
Shape of 20th surface 
H x xr(paraxial R) 
H x xr(paraxial R) 
______________________________________ 
0.0 0.00000 0.00000 0.0 0.00000 0.00000 
1.0 0.01664 0.01662 1.0 -0.01271 
-0.01284 
2.0 0.06684 0.06653 2.0 -0.04951 
-0.05137 
3.0 0.15130 0.14991 3.0 -0.10655 
-0.11568 
4.0 0.27099 0.26703 4.0 -0.17745 
-0.20590 
5.0 0.42713 0.41829 5.0 -0.25291 
-0.32220 
6.0 0.62125 0.60421 6.0 -0.32093 
-0.46482 
7.0 0.85529 0.82546 7.0 -0.36723 
-0.63406 
8.0 1.13186 1.08285 
9.0 1.45436 1.37735 
10.0 1.82719 1.71011 
11.0 2.25595 2.08249 
12.0 2.74755 2.49610 
13.0 3.31122 2.95283 
14.0 3.95847 3.45489 
15.0 4.70595 4.00491 
______________________________________ 
FIGS. 1A to 1B are sections of Numerical Example 1. FIGS. 5a to 7D are each 
diagrams showing the different aberrations at the telephoto end zoom 
position, the intermediate zoom position, and the wide angle end zoom 
position, respectively. 
In the diagrams (FIGS. 5A through 10D), d stands for the spectral d-line, g 
for the spectral g-line, M for the meridional image focus, and S for the 
sagittal image focus. 
The back focus in Numerical Example 1 is 8.53 (as measured from the 23rd 
surface to the image plane in terms of air), which is 1.378 times the 
focal length at the wide angle end and thus which is large enough to 
provide space for a crystal plate or an infrared absorption filter. 
The distances from the image plane to the exit pupil are as given in the 
table, which are large enough to make the optical system into a 
substantially telecentric system. 
At any zoom position in Numerical Example 1, spherical aberration and 
astigmatism are small, distortion is at most 1.5%, and chromatic 
aberration of magnification is less than 0.006, so that the zoom lens 
device provides excellent optical performance. 
NUMERICAL EXAMPLE 2 
The zoom lens device of Numerical Example 2 has a magnification change-over 
ratio of 2.37. 
______________________________________ 
f = 14.00.about.5.90 FNo = 1:2.8.about.2.0 2.omega. = 34.8.degree..about 
.73.6.degree. 
______________________________________ 
r1 = 22.492 
d1 = 0.80 n1 = 1.74320 
v1 = 49.3 
r2 = 11.236 
d2 = 3.40 
r5 = 469.614 
d3 = 0.80 n2 = 1.74320 
v2 = 49.3 
r4 = 12.570 
d4 = 1.25 
r5 = 14.433 
d5 = 1.89 n3 = 1.80518 
v3 = 25.4 
r6 = 28.160 
d6 = varies 
r7 = 22.279 
d7 = 0.80 n4 = 1.84666 
v4 = 23.8 
r8 = 10.752 
d8 = 1.90 n5 = 1.77250 
v5 = 49.6 
r9 = -35.126 
d9 = 0.10 
r10 = 11.879 
d10 = 1.20 n6 = 1.77250 
v6 = 49.6 
r11 = 37.124 
d11 = varies 
r12 = (stop) 
d12 = 1.00 
r13 = -16.164 
d13 = 1.20 n7 = 1.84666 
v7 = 23.8 
r14 = -7.722 
d14 = 0.70 n8 = 1.56757 
v8 = 58.4 
r15 = 10.696 
d15 = varies 
r16 = -10.106 
d16 = 0.70 n9 = 1.84666 
v9 = 25.8 
r17 = 16.408 
d17 = 1.60 n10 = 1.77250 
v10 = 49.6 
r18 = -17.585 
d18 = 0.10 
r19 = 30.283 
d19 = 1.80 n11 = 1.74320 
v11 = 49.3 
r20 = -13.325 
d20 = varies 
r21 = -24.418 
d21 = 0.80 n12 = 1.80518 
v12 = 25.4 
r22 = -52.777 
d22 = 1.40 
r23 = -9.666 
d23 = 1.50 n13 = 1.69680 
v13 = 55.5 
r24 = -8.474 
d24 = 0.10 
r25 = 11.918 
d25 = 2.20 n14 = 1.69680 
v14 = 55.5 
r26 = 40.575 
d26 = 2.20 
r27 = 0.000 
d27 = 5.00 n15 = 1.51633 
v15 = 64.2 
r28 = 0.000 
Back focus 9.33 
(Retrofocus ratio with respect to focal length at wide angle end 
1.583) 
Variation Interval Data 
Focal length 
14.00 9.54 5.90 
d6 0.80 6.54 18.17 
d11 4.74 2.44 0.54 
d15 1.42 3.64 5.47 
d20 4.72 2.50 0.68 
Amount of Lens Unit Movement 
Focal length 
14.00 9.54 5.90 
1st Lens Unit 
0.0 -3.44 -13.17 
2nd Lens Unit 
0.0 2.30 4.20 
4th Lens Unit 
0.0 2.22 4.05 
Distance from Image Plane to Exit Pupil 
Focal length 
14.00 9.54 5.90 
Pupil Distance 
210.8 161.8 61.7 
______________________________________ 
______________________________________ 
Aspherical Coefficients in Numerical Example 2 
1st surface 20th surface 
______________________________________ 
A = 0 A = 0 
B = 3.8344e-5 B = 1.94349e-4 
C = 1.99462e-8 C = -3.07401e-6 
D = 9.0222e-10 D = -2.67122e-8 
E = 0 E = 0 
A' = 0 A' = 0 
B' = 0 B' = 0 
C' = 0 C' = 0 
D' = 0 D' = 0 
E' = 0 E' = 0 
______________________________________ 
______________________________________ 
Shape of 1st surface 
Shape of 20th surface 
H x xr(paraxial R) 
H x xr(paraxial R) 
______________________________________ 
0.0 0.00000 0.00000 0.0 0.00000 0.00000 
1.0 0.02228 0.02224 1.0 -0.03738 
-0.03758 
2.0 0.08971 0.08910 2.0 -0.14765 
-0.15095 
3.0 0.20410 0.20097 3.0 -0.32429 
-0.34210 
4.0 0.36850 0.35854 4.0 -0.55395 
-0.61455 
5.0 0.58742 0.56279 5.0 -0.81459 
-0.97366 
6.0 0.86719 0.81505 6.0 -1.07685 
-1.42728 
7.0 1.21662 1.11701 7.0 -1.31247 
-1.98676 
8.0 1.64824 1.47082 
9.0 2.18015 1.87914 
10.0 2.83889 2.34529 
11.0 3.66351 2.87338 
12.0 4.71119 3.46859 
13.0 6.06482 4.13743 
14.0 7.84300 4.88834 
15.0 10.21288 5.73222 
16.0 13.40665 6.68409 
17.0 17.74246 7.76481 
18.0 23.65138 9.00534 
19.0 31.71330 10.45497 
20.0 42.71014 12.20171 
______________________________________ 
FIGS. 3A and 3B are sections of Numerical Example 2. FIGS. 8A to 10D are 
diagrams showing the different aberrations at the telephoto end zoom 
position, intermediate zoom position, and wide angle end zoom position in 
Numerical Example 2, respectively. 
The back focus in Numerical Example 2 is 7.63 (as measured from the 26th 
surface to the image plane in terms of air), which is 1.293 times the 
focal length at the wide angle end, and which is thus large enough to 
provide space for a crystal plate or an infrared absorption filter. 
The distances from the image plane to the exit pupil are as given in the 
table, which are large enough to make the optical system into a 
substantially telecentric system. 
At any zoom position in Numerical Example 2, the spherical aberration is 
small, astigmatism is less than 0.075, distortion is 2% at most, and 
chromatic aberration of magnification is less than 0.0075, so that the 
zoom lens device provides excellent optical performance. 
Numerical values for the aforementioned conditions for each of the 
numerical examples are given below. 
______________________________________ 
Numerical 
Numerical 
Example 1 
Example 2 
______________________________________ 
Condition (1) 
0.7 &lt; f.sub.2 /f.sub.T &lt; 1.2 
1.014 0.748 
Condition (2) 
2.2 &lt; .vertline.f.sub.3 .vertline./f.sub.W &lt; 3.5 
3.168 2.413 
Condition (3) 
0.6 &lt; .vertline.f.sub.3 .vertline./f.sub.4 &lt; 1.45 
1.307 0.722 
Condition (4) 
f.sub.T &lt; f.sub.4 &lt; f.sub.5 
14.8 &lt; 15 14 &lt; 19.7 
&lt;44.16 &lt;21.06 
______________________________________ 
The focal lengths at the wide angle end and telephoto end, and the focal 
lengths of the lens units are given in the following table. 
______________________________________ 
Numerical Example 1 
Numerical Example 2 
______________________________________ 
f.sub.W 6.187 5.9 
f.sub.T 14.80 14.0 
f.sub.1 -24.499 -15.797 
f.sub.2 15.0 10.472 
f.sub.3 -19.6 -14.238 
f.sub.4 15.0 19.727 
f.sub.5 44.159 21.056 
______________________________________ 
Though in the numerical examples, the surface closest to the object in the 
first lens unit and the surface closest to the image in the fourth lens 
unit are formed aspherically, any other surface in the first lens unit and 
any other surface in the fourth lens unit may be formed aspherically, in 
order to substantially achieve the object of the present invention. 
By virtue of the above-described construction in which predetermined lens 
units among the five lens units have their refractive powers properly set 
with respect to each other, it is possible to provide a telecentric zoom 
lens device with a wide angle of view and high resolution, which has 
sufficient back focus allowing insertion of various filters such as 
optical lowpass filters or infrared cut-off filters, and which allows a 
principal light beam incident to an imaging device, such as a CCD, to be 
directed substantially perpendicular to the imaging device. 
While the present invention has been described with respect to what is 
presently considered to be the preferred embodiments, it is to be 
understood that the invention is not limited to the disclosed embodiments. 
To the contrary, the invention is intended to cover various modifications 
and equivalent arrangements included within the spirit and scope of the 
appended claims. The scope of the following claims is to be accorded the 
broadest interpretation so as to encompass all such modifications and 
equivalent structures and functions.