Zoom lens having focusing subunit in second lens unit and optical apparatus equipped with the same

A small-sized zoom lens in which the displacement of the focusing lens unit does not increase to an excessive degree during focusing, the zoom lens including a first lens unit of positive refractive power; a second lens unit of negative refractive power; and a subsequent lens unit of positive refractive power in that order from the object side, wherein focusing is effected by a subunit 2b of negative refractive power constituting a part of the second lens unit and wherein, assuming that the magnification of the subunit 2b at the wide-angle end is .beta.2bw, the following condition is satisfied: EQU 0<.beta.2bw<1.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a zoom lens and, in particular, to a 
high-variable-power-ratio zoom lens suitable for use in a single-lens 
reflex camera, a video camera, etc. 
2. Description of the Related Art 
Conventionally known zoom-lens focusing systems include a so-called front 
lens focusing system, in which the first lens unit is moved in the 
direction of the optical axis, and a so-called inner focusing system and a 
rear focusing system, in which a lens unit other than the first lens unit 
is moved in the direction of the optical axis. 
Generally speaking, compared with a zoom lens of the front lens focusing 
system, a zoom lens of the inner focusing system or the rear focusing 
system is advantageous in that the size of the entire lens system can be 
reduced since the effective aperture of the first lens unit is small. 
Further, since focusing is performed moving a relatively small and 
light-weight lens unit, quick focusing is possible in auto-focusing 
cameras, which are currently in vogue. 
As an example of such a zoom lens of the inner focusing system or the rear 
focusing system, the present applicant has disclosed in Japanese Patent 
Laid-Open Nos. 3-228008, 5-119260 and 6-230285 a so-called positive lead 
type zoom lens system which includes a first, positive lens unit, a 
second, negative lens unit, and subsequent lens units that are positive as 
a whole, arranged in that order from the object side, and which effects 
power variation by varying air gaps between the units, wherein focusing is 
effected by moving the second, negative lens unit. 
This system provides to a sufficient degree the above-mentioned advantage, 
particularly in a high-variable-power zoom lens including a standard 
range, and is endowed with an optical performance which is satisfactory 
over the entire object distance from an object at infinity to a near 
object. 
Here, the magnification of the second, negative lens unit when power 
variation is effected in a zoom lens of the positive lead type will be 
explained. 
Generally speaking, the second, negative lens unit of a positive lead type 
zoom lens has a negative reduction ratio at the wide-angle end, and the 
absolute value of the magnification increases as power variation is 
effected toward the telephoto end. Further, since the second lens unit is 
the principal power variation unit of the positive lead type zoom lens, 
the increase in magnification when power variation of the entire optical 
system from the wide-angle end to the telephoto end is effected is great 
(-1 is approached from the negative reduction ratio), which is 
particularly conspicuous in the case of a high-variable-power zoom lens. 
The magnification of a focusing lens unit and the focus sensitivity (the 
ratio of displacement of focus to displacement of a focus unit) can be 
expressed by the following formula: 
EQU ES=(1-.beta.f.sup.2).times..beta.r.sup.2 
where 
ES: focus sensitivity 
.beta.f: magnification of focus lens unit 
.beta.r: combined magnification of all the lens units arranged on the image 
side with respect to the focus lens unit. 
The above formula shows that the focus sensitivity is 0 when the absolute 
value of the magnification of the focus lens unit is 1, and that it 
increases as the absolute value departs from 1. 
However, as described above, the second, negative lens unit of a positive 
lead type zoom lens undergoes variation in power such that -1 is 
approached from a negative reduction ratio when variation In power is 
effected in the entire optical system from the wide-angle end to the 
telephoto end. Thus, when, for example, a near object is photographed with 
a high power variation zoom lens, the focus sensitivity of the second, 
negative lens unit decreases near the telephoto end, and the displacement 
of the focus lens unit increases to an excessive degree. Further, when the 
magnification of the second, negative lens unit becomes -1 during power 
variation, the focus sensitivity becomes 0, so that focusing becomes 
impossible. 
SUMMARY OF THE INVENTION 
The present invention has been made with a view toward solving the above 
problems. Accordingly, it is an object of the present invention to provide 
a small-sized zoom lens in which the displacement of the focus lens unit 
does not excessively increase during focusing even in the case of a 
high-power-variable zoom lens. 
To achieve the above object, there is provided, in accordance with the 
present invention, a zoom lens of the type which includes a first lens 
unit of positive refractive power, a second lens unit of negative 
refractive power, and a subsequent unit composed of a plurality of or a 
single lens unit that is positive as a whole, arranged in that order from 
the long conjugate side, and in which, when variation in power is effected 
from the wide-angle end to the telephoto end, the distance between the 
first lens unit and the second lens unit increases and the distance 
between the second lens unit and the subsequent lens unit decreases, 
wherein the second lens unit includes a subunit 2a of negative refractive 
power and a subunit 2b of negative refractive power which is closer to the 
short conjugate side than the subunit 2a, focusing being performed by the 
subunit 2b, and wherein, assuming that the magnification of the subunit 2b 
at the wide-angle end is .beta.2bw, the following condition is satisfied: 
EQU 0&lt;.beta.2bw&lt;1. 
In view of the foregoing, in one aspect, the present invention relates to a 
zoom lens comprising, in order from a long conjugate side, a first lens 
unit of positive refractive power; a second lens unit of negative 
refractive power, the second lens unit comprising a first lens subunit of 
negative refractive power and a second lens subunit of negative refractive 
power which is closer to a short conjugate side than the first lens 
subunit; and a subsequent unit composed of at least one lens unit, the 
subsequent lens unit being of positive refractive power as a whole, 
wherein, when variation in power is effected from a wide-angle end to a 
telephoto end, a distance between the first lens unit and the second lens 
unit increases and a distance between the second lens unit and the 
subsequent lens unit decreases, and wherein, assuming that the 
magnification of the subunit at the wide-angle end is .beta.2bw, the 
following condition is satisfied: 
EQU 0&lt;.beta.2bw&lt;1. 
In another aspect, the present invention relates to an optical apparatus 
comprising a zoom lens as discussed above, and a member for supporting the 
zoom lens. 
In yet another aspect, the present invention relates to a zoom lens 
comprising, in order from the object side to the image side: a first lens 
unit of positive refractive power; a second lens unit of negative 
refractive power, the second lens unit comprising, in order from the 
object side to the image side, a first lens subunit of negative refractive 
power and a second lens subunit of negative refractive power, focusing 
being performed by moving the second lens subunit in the optical axis 
direction while keeping the first lens subunit stationary; and one or more 
lens units having, as a whole, positive refractive power, wherein, when 
variation in power is effected from a wide-angle end to a telephoto end, a 
distance between the first lens unit and the second lens unit increases 
and a distance between the second lens unit and the one or more lens units 
decreases, and wherein, assuming that the magnification of the subunit at 
the wide-angle end is .beta.2bw, the following condition is satisfied: 
EQU 0&lt;.beta.2bw&lt;1. 
These and other aspects, objects, advantages, 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 
Embodiments of the zoom lens of the present invention will be described. 
As stated above, the focusing by the second, negative lens unit of a 
positive lead type zoom lens becomes impossible or the focusing 
displacement excessively increases when the magnification of the second 
lens unit is -1 or close to -1. 
In the zoom lens of the present invention, the second, negative lens unit 
is divided at least into a negative subunit 2a and a negative subunit 2b, 
and focusing is effected by moving the subunit 2b, which is arranged 
nearer to the image than the subunit 2a, in the direction of the optical 
axis. In this arrangement, the negative refractive power of the second 
lens unit is separated at least into two, so that, as compared to the case 
in which focusing is effected by the entire second lens unit, the negative 
refractive power of the focus lens unit is smaller, and it might seem that 
the focus sensitivity is still lower. However, in reality, the focus 
sensitivity increases. This principle will now be explained with reference 
to FIG. 13A and 13B. 
As shown in FIGS. 13A and 13B, the image point P1 of the first lens unit is 
also the object point of the subunit 2a (where reference numeral IIa 
indicates subunit 2a), an image being formed at P2a by the subunit 2a. 
Further, the point P2a is not only the image point of the subunit 2a, but 
also the object point of the subunit 2b (where reference numeral IIb 
indicates subunit 2b), an image being formed at P2b by the subunit 2b. The 
point P2b is not only the image point of the subunit 2b, but also the 
image point of the entire second lens unit. 
When, as in the case of FIG. 13A, the magnification of the subunit 2a is 
positive (when the object point P1 and the image point P2a of the subunit 
2a are on the same side of the subunit 2a), image formation of P2a is 
effected nearer to the image plane than P1 since the subunit 2a is a 
negative lens. The image point of the entire second lens unit and the 
image point of the subunit 2b are both P2b, that is, the same point, so 
that, when the entire second lens unit and the subunit 2b are compared 
with each other, the absolute value of the magnification of the subunit 
2b, of which the object point farther, is smaller. Since the magnification 
of the entire second lens unit is negative, the magnification of the 
subunit 2b is shifted toward the positive side from the magnification of 
the entire second lens unit. 
Conversely, when, as in the case of FIG. 13B, the magnification of the 
subunit 2a is negative (when the object point P1 and the image point P2a 
of the subunit 2a are on the opposite sides of the subunit 2a), the object 
point P2a and the image point P2b of the subunit 2b are on the object side 
of the subunit 2b, so that the magnification of the subunit 2b is 
positive. The magnification of the entire second lens unit is negative, so 
that, in this case also, the magnification of the subunit 2b Is shifted 
toward the positive side from the magnification of the entire second lens 
unit. 
Due to this effect, even when the magnification of the entire second lens 
unit is -1 or close to -1, as in the case, for example, of a 
high-variable-power zoom lens, the focus sensitivity of the entire subunit 
2b is high, so that focusing of a near object is possible. Within the 
range in which the effect is obtainable, the subunit 2a may be moved at a 
speed different from that of the subunit 2b during focusing, or an 
aberration correction unit, etc. may be arranged between the subunit 2a 
and the subunit 2b. Further, in the second lens unit, a subsequent lens 
unit may be provided nearer to the image than the subunit 2b. 
Another feature of the zoom lens of the present invention is that it 
preferably satisfies the following condition: 
EQU 0&lt;.beta.2bw&lt;1 (1) 
where .beta.2bw is the magnification of the subunit 2b at the wide-angle 
end. 
Formula (1) represents the condition determining the magnification of the 
subunit 2b. When the upper end of formula (1) is exceeded, the absolute 
value of the magnification of the entire second lens unit at the 
wide-angle end becomes too large, with the result that it is difficult to 
shorten the focal length of the entire optical system at the wide-angle 
end. On the other hand, beyond the lower end of formula (1), the 
refractive power of the entire second lens unit at the wide-angle end 
becomes too weak, so that it is difficult to adopt a retrofocus type lens 
construction. 
Further, the zoom lenses of the first to sixth embodiments satisfy the 
following condition: 
EQU -0.8&lt;.beta.2bt&lt;0.8 (2) 
where .beta.2bt is the magnification of the subunit 2b at the telephoto 
end. 
Formula (2) is the condition determining the magnification of the subunit 
2b at the telephoto end. When the condition of formula (2) is not 
satisfied and the value of .beta.2bt is in the following ranges: 
EQU 0.8.ltoreq..beta.2bt.ltoreq.1.2 
EQU -1.2.ltoreq..beta.2bt.ltoreq.-0.8 
the focus sensitivity of the subunit 2b at the telephoto end is too low, so 
that the focusing displacement becomes too large or focusing becomes 
impossible. When the value of .beta.2bt is further deviated from the 
condition and in the following ranges: 
EQU 1.2&lt;.beta.2bt 
EQU .beta.2bt&lt;-1.2 
the balance in the magnification sharing with the other optical systems in 
the second lens unit is deteriorated, with the result that it is difficult 
to correct field curvature, variation in spherical aberration as a result 
of focusing, etc. 
Preferably, the range of formula (1) should be as follows: 
EQU 0&lt;.beta.2bw&lt;0.5 (3) 
Further, in addition to formula (1) or formulas (1) and (2), the zoom 
lenses of the first through sixth embodiments satisfy the following 
conditions: 
EQU -2&lt;1/.beta.2at&lt;0.9 (4) 
EQU -0.5&lt;.beta.2bt&lt;0.8 (5) 
EQU .beta.2bt&lt;.beta.2bw (6) 
EQU 0.3&lt;logZ2/logZ&lt;0.9 (7) 
where 
Z2=.beta.2t/.beta.2w 
Z=ft/fw 
.beta.2at: magnification of the subunit 2a at the telephoto end 
.beta.2w: magnification of the second lens unit at the wide-angle end 
.beta.2t: magnification of the second lens unit at the telephoto end 
fw: focal length of the entire system at the wide-angle end 
ft: focal length of the entire system at the telephoto end 
In the present specification, "log" represents a common logarithm (the base 
of which is 10). 
Formula (4) is the condition determining the magnification of the subunit 
2a at the telephoto end. When the condition of formula (4) is departed 
from, it becomes difficult for the absolute value of the magnification of 
the subunit 2b at the telephoto end to be far from 1, and the focus 
sensitivity of the subunit 2b becomes too low. 
Formula (5) is the condition for determining the lower limit of formula (2) 
in a still more desirable range. 
Formula (6) is the condition determining the relationship between the 
magnifications at the wide-angle end and the telephoto end of the subunit 
2b. When the condition of formula (6) is satisfied, and the magnification 
of the subunit 2b at the telephoto end is positive, it becomes easier, 
from the above formula of focus sensitivity, to increase the focus 
sensitivity at the telephoto end. Further, even when the condition of 
formula (6) is satisfied, and the magnification of the subunit 2b at the 
telephoto end is negative, the above effect is not impaired much as long 
as the range of formula (5) is not departed from. 
Formula (7) is the condition for determining the sharing of power variation 
of the second lens unit in the entire optical system. When the upper limit 
of formula (7) is exceeded, the power variation sharing of the second lens 
unit becomes too large, so that it becomes difficult to correct variation 
in aberrations of the second lens unit during zooming. On the other hand, 
beyond the lower limit of formula (7), the power variation sharing of the 
lens units other than the second lens unit becomes too large, so that it 
becomes difficult to correct variation in aberrations of the lens units 
other than the second lens unit during zooming. 
Further, it is desirable that formulas (4) and (5) be in the following 
ranges: 
EQU -0.9&lt;1/.beta.2at&lt;0.5 (8) 
EQU -0.3&lt;.beta.2bt&lt;0.3 (9) 
Further, in addition to formula (1), or formulas (1) and (2), or formulas 
(1), (2) and (4) through (7), the zoom lenses of the first to sixth 
embodiments satisfy the following condition: 
EQU Dabw&lt;Dabt (10) 
where Dabw: air gap between the subunit 2a and the subunit 2b at the 
wide-angle end 
Dabt: air gap between the subunit 2a and the subunit 2b at the telephoto 
end 
Formula (10) is the condition for determining the relationship between the 
air gap between the subunit 2a and the subunit 2b at the wide-angle end 
and the air gap between the subunit 2a and the subunit 2b at the telephoto 
end. In accordance with the present invention, the focus sensitivity at 
the telephoto end of the zoom lens is made appropriate. However, depending 
upon restrictions in design in terms of, for example, the necessity to 
secure aberration correction and power variation, it can happen that the 
focus sensitivity at the telephoto end is lower than the focus sensitivity 
at the wide-angle end. When formula (10) is satisfied, it is possible to 
efficiently secure the replacement of the focus lens unit of the subunit 
2b at the wide-angle end and the telephoto end, so that it is possible, 
for example, to prevent an increase in the size of the front lens system 
at the wide-angle end. 
Next, zoom lenses according to first through sixth embodiments will be more 
specifically described. 
FIG. 1 is a sectional view of a zoom lens according to a first embodiment 
of the present invention. In the drawing, numeral I indicates a first, 
positive lens unit, numeral II indicates a second, negative lens unit, 
numeral IIa indicates a negative subunit 2a, numeral IIb indicates a 
negative subunit 2b, numeral III indicates a third, positive lens unit, 
numeral IV indicates a fourth, negative lens unit, numeral V indicates a 
fifth, positive lens unit, and symbol S indicates a diaphragm. 
When power variation is effected from the wide-angle end to the telephoto 
end, the first lens unit I moves toward the object, the subunit 2a, 
indicated by IIa, moves toward the object while increasing the distance 
between it and the first lens unit I, the subunit 2b, indicated by IIb, 
moves toward the object while increasing the distance between it and the 
subunit 2a, indicated by IIa, the third lens unit III moves toward the 
object while decreasing the distance between it and the second subunit 2b, 
indicated by IIb, the fourth lens unit IV moves toward the object while 
increasing the distance between it and the third lens unit III, and the 
fifth lens unit V moves toward the object integrally with the third lens 
unit III while increasing the distance between it and the fourth lens unit 
IV. The subunit 2b, indicated by IIb, is a focus lens unit, and moves from 
an infinite object toward the object in short-range focusing. 
FIGS. 2A, 2B and 2C are sectional views of a zoom lens according to a 
second embodiment of the present invention. In the drawing, numeral I 
indicates a first, positive lens unit, numeral II indicates a second, 
negative lens unit, numeral IIa indicates a negative subunit 2a, numeral 
IIb indicates a negative subunit 2b, numeral III indicates a third, 
positive lens unit, numeral IV indicates a fourth, positive lens unit, and 
symbol S indicates a diaphragm. 
When power variation is effected from the wide-angle end to the telephoto 
end, the first lens unit I moves toward the object, the subunit 2a, 
indicated by IIa, moves toward the object while increasing the distance 
between it and the first lens unit I, the subunit 2b, indicated by IIb, 
moves toward the object while increasing the distance between it and the 
subunit 2a, indicated by IIa, the third lens unit III moves toward the 
object while decreasing the distance between it and the second subunit 2b, 
indicated by IIb, and the fourth lens unit IV moves toward the object 
while decreasing the distance between it and the third lens unit III. The 
subunit 2b, indicated by IIb, is a focus lens unit, and moves from an 
infinite object toward the object in short-range focusing. 
FIGS. 3A, 3B and 3C and 4A, 4B and 4C are sectional views of zoom lenses 
according to third and fourth embodiments of the present invention, 
respectively. In the drawings, numeral I indicates a first, positive lens 
unit, numeral II indicates a second, negative lens unit, numeral IIa 
indicates a negative subunit 2a, numeral IIb indicates a negative subunit 
2b, numeral III indicates a third, positive lens unit, numeral IV 
indicates a fourth, negative lens unit, numeral V indicates a fifth, 
positive lens unit, and symbol S indicates a diaphragm. 
When power variation is effected from the wide-angle end to the telephoto 
end, the first lens unit I moves toward the object, the subunit 2a, 
indicated by IIa, moves toward the object while increasing the distance 
between it and the first lens unit I, the subunit 2b, indicated by IIb, 
moves over in a locus convex toward the object while increasing the 
distance between it and the subunit 2a, indicated by IIa, the third lens 
unit III moves toward the object while decreasing the distance between it 
and the second subunit 2b, indicated by IIb, the fourth lens unit IV moves 
toward the object while increasing the distance between it and the third 
lens unit III, and the fifth lens unit V moves toward the object 
integrally with the third lens unit III while decreasing the distance 
between it and the fourth lens unit IV. The subunit 2b, indicated by IIb, 
Is a focus lens unit, and moves from an infinite object toward the object 
in short-range focusing. 
FIGS. 5A, 5B and 5C and 6A, 6B and 6C are sectional views of zoom lenses 
according to fifth and sixth embodiments of the present invention, 
respectively. In the drawings, numeral I indicates a first, positive lens 
unit, numeral II indicates a second, negative lens unit, numeral IIa 
indicates a negative subunit 2a, numeral IIb indicates a negative subunit 
2b, numeral III indicates a third, positive lens unit, numeral IV 
indicates a fourth, negative lens unit, numeral V indicates a fifth, 
positive lens unit, numeral VI indicates a sixth, negative lens unit, 
symbol S indicates a diaphragm, symbol MS indicates a movable diaphragm, 
and symbol FS indicates a flare cutter. 
When power variation is effected from the wide-angle end to the telephoto 
end, the first lens unit I moves toward the object, the subunit 2a, 
indicated by IIa, moves toward the object while increasing the distance 
between it and the first lens unit I, the subunit 2b, indicated by IIb, 
moves toward the object while increasing the distance between it and the 
subunit 2a, indicated by IIa, the movable diaphragm MS moves toward the 
object while decreasing the distance between it and the subunit 2b, 
indicated by IIb, and enlarging the aperture diameter, the third lens unit 
III moves toward the object while decreasing the distance between it and 
the subunit 2b, indicated by IIb, the fourth lens unit IV moves toward the 
object while increasing the distance between it and the third lens unit 
III, the fifth lens unit V moves toward the object while decreasing the 
distance between it and the fourth lens unit IV, and the sixth lens unit 
VI moves toward the object while increasing the distance between it and 
the fifth lens unit V. The subunit 2b, indicated by IIb, is a focus lens 
unit, and moves from an infinite object toward the object in short-range 
focusing. The flare cutter FS is stationary with respect to the image 
plane. 
In FIGS. 1A through 6C, W, M and T respectively correspond to the 
wide-angle end, an intermediate focal length, and the telephoto end. 
Numerical examples of the embodiments are given below. Numerical examples 1 
through 6 correspond to the zoom lenses of the first through sixth 
embodiments, respectively. 
In the numerical examples, symbol Ri indicates (in mm) the radius of 
curvature of the i-th lens surface as counted from the object side, symbol 
Di indicates (in mm) the thickness or the air gap of the i-th lens as 
counted from the object side, and Ni and .nu.i respectively indicate the 
refractive index and the Abbe number of the i-th lens as counted from the 
object side. Symbols A, B, C, D and E indicate aspherical coefficients. 
The notation e+i stands for .times.10.sup.ii and e-i for .times.10.sup.-i. 
Assuming that the intersection of the lens surface and the optical axis is 
the origin and that the direction in which light travels is positive, the 
aspherical configuration is expressed as follows: 
##EQU1## 
where X is the position in the optical axis direction, and Y is the 
position perpendicular to the optical axis. 
FIGS. 7A(1)-7B(12) through 12A(1)-12B(12) are aberration diagrams 
corresponding to the zoom lenses of numerical examples 1 through 6, 
respectively. In the drawings, W represents an aberration diagram at the 
wide-angle end, M represents an aberration diagram at intermediate focal 
length, and T represents an aberration diagram at the telephoto end. Part 
A shows a case in which the object is at infinity, and part B shows a case 
in which the object is near. 
In the aberration diagrams of FIGS. 7A(1) through 12B(12) showing spherical 
aberrations, the solid line indicates the d-line wavelength, the two-dot 
chain line indicates g-line wavelength, and the broken line indicates the 
sine condition. In the aberration diagrams showing astigmatism, the solid 
line indicates the sagittal image surface, and the dashed line indicates 
the meridional image surface. 
NUMERICAL EXAMPLE 1 
______________________________________ 
f = 28.90-101.58 F.sub.no = 3.57-4.67 2.omega. = 73.6-24.1 
R1 = 102.026 
D1 = 2.00 N1 = 1.846659 
.nu.1 = 23.8 
R2 = 51.893 
D2 = 6.04 N2 = 1.696797 
.nu.2 = 55.5 
R3 = 424.300 
D3 = 0.12 
R4 = 44.599 
D4 = 4.78 N3 = 1.696797 
.nu.3 = 55.5 
R5 = 129.757 
D5 = variable 
R6 = 66.293 
D6 = 1.20 N4 = 1.712995 
.nu.4 = 53.8 
R7 = 15.769 
D7 = variable 
R8 = -66.529 
D8 = 1.10 N5 = 1.882997 
.nu.5 = 40.8 
R9 = 24.176 
D9 = 1.13 
R10 = 24.357 
D10 = 3.26 N6 = 1.846658 
.nu.6 = 23.9 
R11 = -53.985 
D11 = 0.35 
R12 = -38.850 
D12 = 1.10 N7 = 1.834000 
.nu.7 = 37.2 
R13 = 112.860 
D13 = variable 
R14 = diaphragm 
D14 = 0.00 
R15 = 24.496 
D15 = 1.20 N8 = 1.846659 
.nu.8 = 23.8 
R16 = 13.997 
D16 = 5.42 N9 = 1.603112 
.nu.9 = 60.7 
R17 = -66.163 
D17 = 0.12 
R18 = 28.916 
D18 = 1.86 N10 = 1.772499 
.nu.10 = 49.6 
R19 = 61.152 
D19 = variable 
R20 = -39.670 
D20 = 2.92 N11 = 1.755199 
.nu.11 = 27.5 
R21 = -12.463 
D21 = 1.10 N12 = 1.804000 
.nu.12 = 46.6 
R22 = -564.896 
D22 = variable 
R23 = 206.930 
D23 = 5.62 N13 = 1.487490 
.nu.13 = 70.2 
R24 = 918.031 
D24 = 0.12 
R25 = 86.970 
D25 = 2.65 N14 = 1.696797 
.nu.14 = 55.5 
R26 = -67.777 
D26 = 2.81 
R27 = -18.100 
D27 = 1.40 N15 = 1.846659 
.nu.15 = 23.8 
R28 = -49.826 
variable-distance.backslash.focal-length 
28.90 50.00 101.58 
D5 0.50 11.27 24.99 
D7 6.87 7.74 10.17 
D13 14.94 8.77 2.29 
D19 2.58 6.69 10.13 
D22 7.70 3.59 0.15 
______________________________________ 
NUMERICAL EXAMPLE 2 
______________________________________ 
f = 29.00-100.53 F.sub.no = 3.45-4.65 2.omega. = 73.5-24.3 
R1 = 70.805 
D1 = 1.70 N1 = 1.846659 
.nu.1 = 23.8 
R2 = 42.561 
D2 = 7.99 N2 = 1.696797 
.nu.2 = 55.5 
R3 = 170.878 
D3 = 0.10 
R4 = 56.638 
D4 = 4.92 N3 = 1.696797 
.nu.3 = 55.5 
R5 = 179.665 
D5 = variable 
*R6 = 68.405 
D6 = 1.50 N4 = 1.804000 
.nu.4 = 46.6 
R7 = 16.581 
D7 = 4.65 
R8 = 1611.036 
D8 = 1.55 N5 = 1.805181 
.nu.5 = 25.4 
R9 = -120.905 
D9 = variable 
R10 = -51.179 
D10 = 1.00 N6 = 1.804000 
.nu.6 = 26.6 
R11 = 25.714 
D11 = 0.45 
R12 = 23.010 
D12 = 2.93 N7 = 1.805181 
.nu.7 = 25.4 
R13 = -127.838 
D13 = 0.73 
R14 = -35.068 
D14 = 0.80 N8 = 1.772499 
.nu.8 = 49.6 
R15 = 174.407 
D15 = variable 
R16 = diaphragm 
D16 = 0.30 
R17 = 211.934 
D17 = 1.55 N9 = 1.603112 
.nu.9 = 60.7 
R18 = -96.893 
D18 = 0.22 
R19 = 22.077 
D19 = 4.88 N10 = 1.696797 
.nu.10 = 55.5 
R20 = -37.091 
D20 = 0.37 
R21 = -26.587 
D21 = 3.94 N11 = 1.800999 
.nu.11 = 35.0 
R22 = 132.289 
D22 = variable 
R23 = 67.196 
D23 = 5.90 N12 = 1.583126 
.nu.12 = 59.4 
*R24 = -19.777 
D24 = 3.56 
R25 = -13.582 
D25 = 1.29 N13 = 1.805181 
.nu.13 = 25.4 
R26 = -20.431 
variable-distance.backslash.focal-length 
29.00 49.99 100.53 
D5 0.50 11.41 26.87 
D9 2.06 3.46 5.33 
D15 14.02 7.50 1.65 
D22 10.23 8.37 7.18 
______________________________________ 
Aspherical Coefficient 
surface 6: A=0.00000e+00 B=1.40664e-06 C=-2.16669e-09 D=6.23480e-12 
E=0.00000e+00 
surface 24: A=0.00000e+00 B=3.84723e-06 C=-3.92884e-08 D=3.96369e-10 
E=-4.61841e-12 
NUMERICAL EXAMPLE 3 
______________________________________ 
f = 28.90-101.53 F.sub.no = 3.63-4.67 2.omega. = 73.6-24.1 
R1 = 97.387 
D1 = 2.00 N1 = 1.846659 
.nu.1 = 23.8 
R2 = 53.704 
D2 = 6.45 N2 = 1.696797 
.nu.2 = 55.5 
R3 = 285.841 
D3 = 0.12 
R4 = 45.288 
D4 = 5.50 N3 = 1.696797 
.nu.3 = 55.5 
R5 = 133.190 
D5 = variable 
R6 = 67.158 
D6 = 1.20 N4 = 1.804000 
.nu.4 = 46.6 
R7 = 17.316 
D7 = 4.75 
R8 = -214.243 
D8 = 1.50 N5 = 1.698947 
.nu.5 = 30.1 
R9 = -142.144 
D9 = variable 
R10 = -65.466 
D10 = 1.10 N6 = 1.882997 
.nu.6 = 40.8 
R11 = 22.588 
D11 = 1.72 
R12 = 25.191 
D12 = 2.99 N7 = 1.846658 
.nu.7 = 23.9 
R13 = -81.927 
D13 = 0.36 
R14 = -50.106 
D14 = 1.10 N8 = 1.806098 
.nu.8 = 41.0 
R15 = 155.874 
D15 = variable 
R16 = diaphragm 
D16 = 0.00 
R17 = 25.211 
D17 = 1.20 N9 = 1.846659 
.nu.9 = 23.8 
R18 = 13.902 
D18 = 5.41 N10 = 1.603112 
.nu.10 = 60.7 
R19 = -71.675 
D19 = 0.12 
R20 = 28.195 
D20 = 1.75 N11 = 1.772499 
.nu.11 = 49.6 
R21 = 54.525 
D21 = variable 
R22 = -53.616 
D22 = 3.21 N12 = 1.755199 
.nu.12 = 27.5 
R23 = -12.463 
D23 = 1.10 N13 = 1.804000 
.nu.13 = 46.6 
R24 = -632.315 
D24 = variable 
R25 = 304.344 
D25 = 5.06 N14 = 1.487490 
.nu.14 = 70.2 
R26 = -18.198 
D26 = 0.12 
R27 = 72.084 
D27 = 2.66 N15 = 1.696797 
.nu.15 = 55.5 
R28 = -69.699 
D28 = 2.75 
R29 = -18.477 
D29 = 1.40 N16 = 1.846659 
.nu.16 = 23.8 
R30 = -74.753 
variable-distance.backslash.focal-length 
28.90 50.00 101.53 
D5 0.50 11.26 26.01 
D9 2.21 2.91 5.87 
D15 15.52 8.99 2.26 
D21 2.31 7.14 10.18 
D24 8.12 3.29 0.25 
______________________________________ 
NUMERICAL EXAMPLE 4 
______________________________________ 
f = 28.90-129.62 F.sub.no = 3.63-5.05 2.omega. = 73.6-18.9 
R1 = 99.438 
D1 = 2.00 N1 = 1.846659 
.nu.1 = 23.8 
R2 = 53.376 
D2 = 8.81 N2 = 1.696797 
.nu.2 = 55.5 
R3 = 416.468 
D3 = 0.12 
R4 = 42.711 
D4 = 6.58 N3 = 1.696797 
.nu.3 = 55.5 
R5 = 104.659 
D5 = variable 
R6 = 61.437 
D6 = 1.20 N4 = 1.804000 
.nu.4 = 46.6 
R7 = 18.345 
D7 = 5.45 
R8 = -164.382 
D8 = 1.50 N5 = 1.698947 
.nu.5 = 30.1 
R9 = -63.504 
D9 = variable 
R10 = -52.701 
D10 = 1.10 N6 = 1.882997 
.nu.6 = 40.8 
R11 = 19.537 
D11 = 1.31 
R12 = 21.028 
D12 = 3.35 N7 = 1.846658 
.nu.7 = 23.9 
R13 = -126.059 
D13 = 0.61 
R14 = -45.272 
D14 = 1.10 N8 = 1.806098 
.nu.8 = 41.0 
R15 = 113.769 
D15 = variable 
R16 = diaphragm 
D16 = 0.00 
R17 = 25.691 
D17 = 1.20 N9 = 1.846659 
.nu.9 = 23.8 
R18 = 13.450 
D18 = 4.76 N10 = 1.603112 
.nu.10 = 60.7 
R19 = -70.911 
D19 = 0.12 
R20 = 26.195 
D20 = 1.77 N11 = 1.772499 
.nu.11 = 49.6 
R21 = 63.034 
D21 = variable 
R22 = -52.944 
D22 = 3.08 N12 = 1.755199 
.nu.12 = 27.5 
R23 = -12.463 
D23 = 1.10 N13 = 1.804000 
.nu.13 = 46.6 
R24 = 579.525 
D24 = variable 
R25 = 132.613 
D25 = 4.95 N14 = 1.487490 
.nu.14 = 70.2 
R26 = -18.301 
D26 = 0.12 
R27 = 79.081 
D27 = 2.45 N15 = 1.696797 
.nu.15 = 55.5 
R28 = -73.176 
D28 = 3.70 
R29 = -17.191 
D29 = 1.40 N16 = 1.846659 
.nu.16 = 23.8 
R30 = -62.994 
variable-distance.backslash.focal-length 
28.90 58.86 129.62 
D5 0.50 14.24 28.14 
D9 1.28 2.46 6.60 
D15 16.62 9.04 1.77 
D21 1.97 7.12 9.48 
D24 7.74 2.59 0.23 
______________________________________ 
NUMERICAL EXAMPLE 5 
______________________________________ 
f = 28.94-193.10 F.sub.no = 3.40-5.85 2.omega. = 73.6-12.8 
R1 = 148.679 
D1 = 2.90 N1 = 1.846658 
.nu.1 = 23.9 
R2 = 83.648 
D2 = 0.91 
R3 = 89.856 
D3 = 7.86 N2 = 1.592400 
.nu.2 = 68.3 
R4 = -435.833 
D4 = 0.15 
R5 = 69.249 
D5 = 4.99 N3 = 1.729157 
.nu.3 = 54.7 
R6 = 199.367 
D6 = variable 
R7 = 102.576 
D7 = 1.50 N4 = 1.804000 
.nu.4 = 46.6 
R8 = 20.203 
D8 = variable 
R9 = -40.571 
D9 = 1.10 N5 = 1.882997 
.nu.5 = 40.8 
R10 = 82.046 
D10 = 0.25 
R11 = 47.203 
D11 = 4.14 N6 = 1.846660 
.nu.6 = 23.8 
R12 = -35.566 
D12 = 0.18 
R13 = -33.768 
D13 = 1.10 N7 = 1.882997 
.nu.7 = 40.8 
R14 = 150.049 
D14 = variable 
R15 = adjustable 
D15 = variable 
diaphragm 
R16 = diaphragm 
D16 = 0.00 
R17 = 66.231 
D17 = 3.29 N8 = 1.603112 
.nu.8 = 60.7 
*R18 = 67.824 
D18 = 0.15 
R19 = 42.000 
D19 = 5.85 N9 = 1.696797 
.nu.9 = 55.5 
R20 = -22.270 
D20 = 1.15 N10 = 2.022040 
.nu.10 = 29.1 
R21 = -91.685 
D21 = variable 
R22 = -106.676 
D22 = 4.05 N11 = 1.846660 
.nu.11 = 23.8 
R23 = -19.073 
D23 = 1.10 N12 = 1.834807 
.nu.12 = 42.7 
R24 = 82.915 
D24 = variable 
R25 = 62.805 
D25 = 1.50 N13 = 1.728250 
.nu.13 = 28.5 
R26 = 25.086 
D26 = 6.79 N14 = 1.603112 
.nu.14 = 60.7 
R27 = -59.528 
D27 = 0.15 
R28 = 325.424 
D28 = 4.27 N15 = 1.516330 
.nu.15 = 64.2 
*R29 = -39.058 
D29 = 0.15 
R30 = 40.900 
D30 = 6.90 N16 = 1.516330 
.nu.16 = 64.2 
R31 = -34.710 
D31 = 1.20 N17 = 1.901355 
.nu.17 = 31.6 
R32 = 1136.527 
D32 = variable 
R33 = -76.329 
D33 = 1.30 N18 = 1.772499 
.nu.18 = 49.6 
R34 = 30.046 
D34 = 2.42 
R35 = 33.653 
D35 = 3.18 N19 = 1.846658 
.nu.19 = 23.9 
R36 = 70.208 
D36 = variable 
R37 = flare cutter 
variable-distance.backslash.focal-length 
28.94 60.30 193.10 
D6 1.00 21.02 43.71 
D8 9.49 14.14 13.77 
D14 9.48 3.97 0.83 
D15 15.32 10.40 1.19 
D21 1.30 6.31 11.32 
D24 18.00 9.32 0.50 
D32 2.11 3.02 10.52 
D36 1.76 15.98 28.04 
______________________________________ 
NUMERICAL EXAMPLE 6 
______________________________________ 
f = 29.01-293.80 F.sub.no = 3.71-5.85 2.omega. = 73.4-8.4 
R1 = 183.319 
D1 = 2.90 N1 = 1.846658 
.nu.1 = 23.9 
R2 = 88.512 
D2 = 0.83 
R3 = 93.306 
D3 = 9.51 N2 = 1.592400 
.nu.2 = 68.3 
R4 = -239.268 
D4 = 0.15 
R5 = 55.594 
D5 = 5.49 N3 = 1.729157 
.nu.3 = 54.7 
R6 = 117.057 
D6 = variable 
R7 = 115.092 
D7 = 1.50 N4 = 1.804000 
.nu.4 = 46.6 
R8 = 20.275 
D8 = variable 
R9 = -39.253 
D9 = 1.76 N5 = 1.805181 
.nu.5 = 25.4 
R10 = -31.927 
D10 = 1.00 N6 = 1.882997 
.nu.6 = 40.8 
R11 = 86.386 
D11 = 0.15 
R12 = 49.417 
D12 = 4.45 N7 = 1.846660 
.nu.7 = 23.8 
R13 = -35.125 
D13 = 0.08 
R14 = -35.387 
D14 = 1.10 N8 = 1.882997 
.nu.8 = 40.8 
R15 = 111.411 
D15 = variable 
R16 = adjustable 
D16 = variable 
diaphragm 
R17 = diaphragm 
D17 = 0.00 
R18 = 51.158 
D18 = 4.34 N9 = 1.603112 
.nu.9 = 60.7 
*R19 = -58.489 
D19 = 0.15 
R20 = 41.917 
D20 = 6.96 N10 = 1.696797 
.nu.10 = 55.5 
R21 = -21.065 
D21 = 1.15 N11 = 2.022040 
.nu.11 = 29.1 
R22 = -115.329 
D22 = variable 
R23 = -83.130 
D23 = 4.38 N12 = 1.846660 
.nu.12 = 23.8 
R24 = -17.289 
D24 = 1.10 N13 = 1.834807 
.nu.13 = 42.7 
R25 = 61.631 
D25 = variable 
R26 = 47.886 
D26 = 1.50 N14 = 1.728250 
.nu.14 = 28.5 
R27 = 26.482 
D27 = 7.17 N15 = 1.603112 
.nu.15 = 60.7 
R28 = -85.988 
D28 = 0.15 
R29 = 188.993 
D29 = 4.65 N16 = 1.516330 
.nu.16 = 64.2 
*R30 = -344.991 
D30 = 0.15 
R31 = 48.830 
D31 = 7.40 N17 = 1.516330 
.nu.17 = 64.2 
R32 = -30.259 
D32 = 1.20 N18 = 1.901355 
.nu.18 = 31.6 
R33 = -463.789 
D33 = variable 
R34 = -230.987 
D34 = 1.30 N19 = 1.772499 
.nu.19 = 49.6 
R35 = 28.265 
D35 = 3.03 
R36 = 36.311 
D36 = 3.28 N20 = 1.846658 
.nu.20 = 23.9 
R37 = 80.886 
D37 = variable 
R38 = flare cutter 
variable-distance.backslash.focal-length 
29.01 68.17 293.80 
D6 1.00 24.53 49.47 
D8 8.15 11.88 14.20 
D15 11.01 6.03 1.04 
D16 15.03 10.57 1.18 
D22 1.30 6.00 10.71 
D25 19.33 9.86 0.48 
D33 1.95 2.52 7.63 
D37 3.51 18.51 33.79 
______________________________________ 
Aspherical Coefficient 
surface 19: A=-0.00000e+00 B=-4.25847e-06 C=-1.01614e-08 D=-4.72845e-11 
E=-0.00000e+00 
surface 30: A=0.00000e+00 B=1.54192e-06 C=-9.35298e-10 D=-2.63002e-12 
E=0.00000e+00 
Table 1 shows values of the parameters in the conditional expressions in 
the numerical examples. 
TABLE 1 
______________________________________ 
Numer- 
Numer- 
Numer- 
ical ical ical 
Numerical Numerical 
Numerical 
Exam- Exam- Exam- 
Example 1 Example 2 
Example 3 
ple 4 ple 5 ple 6 
______________________________________ 
.beta.2bw 
0.372 0.267 0.342 0.137 0.422 0.404 
.beta.2bt 
0.223 0.125 0.182 -0.161 
0.269 0.107 
1/.beta.2at 
-0.338 -0.218 -0.270 0.185 -0.438 
-0.109 
logZ2/ 
0.585 0.572 0.605 0.672 0.505 0.609 
logZ 
Dabw 6.870 2.060 2.210 1.280 9.490 8.150 
Dabt 10.170 5.330 5.870 6.600 13.770 
14.200 
______________________________________ 
As described above, in zoom lenses according to the above-described 
embodiments of the present invention, there is no concern that the 
displacement of the focusing lens unit will increase to an excessive 
degree during focusing. 
Next, zoom lenses of forms (seventh through tenth embodiments) different 
from those of the first through sixth embodiments will be described. 
Like the zoom lenses of the first through sixth embodiments, the zoom 
lenses of the seventh through tenth embodiments are positive lead type 
zoom lenses, in which a second lens unit of negative refractive power is 
divided into first and second lens subunits 2a and 2b, focusing being 
effected with the subunit 2b. 
In the zoom lenses of the seventh through tenth embodiments, a negative 
lens is arranged on the most object side of the subunit 2a, and at least 
one aspheric surface is provided, whereby a reduction in the size of the 
optical system and a satisfactory optical performance are achieved. 
Due to the aspheric surface in the subunit 2a, the correction of distortion 
aberration is facilitated. The aspheric surface is formed such that the 
positive refractive power increases toward the periphery, and is provided 
on the object-side surface of the lens on the most object side of the 
subunit 2a, whereby the negative distortion aberration on the wide-angle 
side, in particular, can be corrected in a satisfactory manner. Further, a 
negative refractive power is arranged on the most object side of the 
second lens unit, and the entrance pupil of the optical system as a whole 
is shifted toward the object side, whereby the reduction in the size of 
the front lens is facilitated as in the above-described first through 
sixth embodiments. 
Further, in the zoom lenses of the seventh through tenth embodiments, the 
following conditions are satisfied in addition to formula (1): 
EQU 0.20&lt;f1/ft&lt;0.75 (11) 
EQU -0.40&lt;f2a/ft&lt;-0.05 (12) 
EQU -0.35&lt;f2b/ft&lt;-0.05 (13) 
EQU -0.50&lt;.beta.2bt&lt;0.50 (14) 
EQU -1.50&lt;.beta.2t&lt;-0.65 (15) 
where 
f1: focal length of the first lens unit 
f2a: focal length of the subunit 2a 
f2b: focal length of the subunit 2b 
ft: focal length of the zoom lens as a whole at the telephoto end 
.beta.2bt: magnification of the subunit 2b at the telephoto end 
.beta.2t: magnification of the second lens unit at the telephoto end. 
Formula (11) is a condition determining the focal length of the first lens 
unit; when the upper limit is exceeded, it is impossible to obtain a 
sufficient telephoto type at the telephoto end, and it is difficult to 
secure the requisite F number; when the lower limit is exceeded, the front 
lens tends to be large, which is undesirable. 
Formula (12) is a condition determining the focal length of the subunit 2a; 
when the upper limit is exceeded, the correction of the negative 
distortion aberration on the wide-angle side, in particular, is difficult; 
when the lower limit is exceeded, it is difficult to secure a sufficient 
variable power ratio. Further, since the focus sensitivity of the subunit 
2b is reduced, the focus displacement of the subunit 2b increases. 
Formula (13) is a condition determining the focal length of the subunit 2b; 
when the upper limit is exceeded, the negative spherical aberration and 
coma-aberration generated in the subunit 2b increase, so that the 
fluctuations in aberration as a result of focusing increase; when the 
lower limit is exceeded, the focus displacement increases, which is not 
desirable. 
Formula (15) is a condition determining the magnification of the second 
lens unit at the telephoto end; when the upper limit is exceeded, the 
magnification of the second lens unit (the absolute value thereof) becomes 
too low, so that, to satisfy the specifications, the relay magnification 
of the subsequent unit becomes too high, with the result that the 
aberration correction of the optical system as a whole becomes difficult; 
when the lower limit is exceeded, the magnification of the second lens 
group (the absolute value thereof) becomes too high, so that, the residual 
aberration of the first lens unit is enlarged by the second lens unit, 
with the result that the aberration cannot be cancelled with the 
subsequent unit, making it difficult to effect aberration correction on 
the optical system as a whole. Further, an attempt to make the residual 
aberration of the first lens unit infinitely close to zero will lead to an 
increase in the number of lenses of the first lens unit, resulting in an 
increase in size, which is not desirable. 
More preferably, formulas (11) through (15) are set in the following 
ranges: 
EQU 0.25&lt;f1/ft&lt;0.65 (16) 
EQU -0.35&lt;f2a/ft&lt;-0.05 (17) 
EQU -0.30&lt;f2b/ft&lt;-0.12 (18) 
EQU -0.10&lt;.beta.2bt&lt;0.45 (19) 
EQU -1.20&lt;.beta.2t&lt;-0.70 (20) 
Further, in addition to formulas (11) through (15), the zoom lenses of the 
seventh through tenth embodiments satisfy the following conditions: 
EQU -1.0&lt;1/.beta.2at&lt;0.5 (21) 
EQU .beta.2bt&lt;.beta.2bw (22) 
EQU 0.3&lt;logZ2/logZ&lt;0.9 (23) 
Formula (21) is a condition determining the magnification of the subunit 2a 
at the telephoto end, specifying the upper and lower limit values of 
formula (4) to the seventh through tenth embodiments to set them in more 
desirable ranges. 
Formulas (22) and (23) are completely the same as formulas (6) and (7), 
respectively, their effects also being the same. 
More preferably, formulas (21) and (23) are set to the following ranges: 
EQU -0.5&lt;1/.beta.2at&lt;0.1 (24) 
EQU 0.45&lt;logZ2/logZ&lt;0.8 (25) 
Further, the zoom lenses of the seventh through tenth embodiments satisfy 
the following condition: 
EQU Dabw&lt;Dabt (26) 
where 
Dabw: air gap between the subunit 2a and the subunit 2b at the wide-angle 
end 
Dabt: air gap between the subunit 2a and the subunit 2b at the telephoto 
end. 
Formula (26) is completely the same as formula (10), the effects thereof 
also being the same. 
The effects of the above conditional formulas can be obtained by 
individually satisfying each of them. However, it is naturally more 
desirable to satisfy all the conditional formulas simultaneously. 
The construction of the zoom lenses of the seventh through tenth 
embodiments will be specifically described. 
FIGS. 15A, 15B, and 15C are sectional views of the seventh embodiment. 
Numeral I indicates a first, positive lens unit, numeral II indicates a 
second, negative lens unit, numeral IIa indicates a negative subunit 2a, 
numeral IIb indicates a negative subunit 2b, numeral III indicates a 
third, positive lens unit, numeral IV indicates a fourth, positive lens 
unit, numeral V indicates a fifth, negative lens unit, numeral VI 
indicates a sixth, negative lens unit, symbol FS indicates a movable flare 
cutter, and symbol S indicates a diaphragm. 
When power variation is effected from the wide-angle end to the telephoto 
end, the first lens unit I moves toward the object, the subunit 2a, 
indicated by IIa, moves toward the object while increasing the distance 
between it and the first lens unit I, the subunit 2b, indicated by IIb, 
moves toward the object while increasing the distance between it and the 
subunit 2a, indicated by IIa, the third lens unit III moves toward the 
object while decreasing the distance between it and the second subunit 2b, 
indicated by IIb, the fourth lens unit IV moves toward the object while 
increasing the distance between it and the third lens unit III, the fifth 
lens unit V moves toward the object while increasing the distance between 
it and the fourth lens unit IV, and the sixth lens unit VI moves toward 
the object integrally with the third lens unit III while decreasing the 
distance between it and the fifth lens unit V, the flare cutter moves 
toward the object while decreasing the distance between it and the subunit 
2b, and the diaphragm S moves toward the object integrally with the third 
lens group III. The subunit 2b, indicated by IIb, is a focus lens unit, 
and moves toward the object in focusing from an infinite object toward the 
object in short-range focusing. 
FIGS. 16A, 16B, and 16C are sectional views of the eighth embodiment. 
Numeral I indicates a first, positive lens unit, numeral II indicates a 
second, negative lens unit, numeral IIa indicates a negative subunit 2a, 
numeral IIb indicates a negative subunit 2b, numeral III indicates a 
third, positive lens unit, numeral IV indicates a fourth, positive lens 
unit, numeral V indicates a fifth, negative lens unit, numeral VI 
indicates a sixth, positive lens group, symbol FS indicates a movable 
flare cutter, and symbol S indicates a diaphragm. 
When power variation is effected from the wide-angle end to the telephoto 
end, the first lens unit I moves toward the object, the subunit 2a, 
indicated by IIa, moves toward the object while increasing the distance 
between it and the first lens unit I, the subunit 2b, indicated by IIb, 
moves toward the object while increasing the distance between it and the 
subunit 2a, indicated by IIa, the third lens unit III moves toward the 
object while decreasing the distance between it and the second subunit 2b, 
indicated by IIb, and the fourth lens unit IV moves toward the object 
while increasing the distance between it and the third lens unit III until 
the intermediate focus and decreasing the distance between it and the 
third lens unit III from the intermediate focus to the telephoto end, the 
fifth lens unit moves toward the object while increasing the distance 
between it and the fourth lens unit IV, the sixth lens unit VI moves 
toward the object while decreasing the distance between it and the fifth 
lens unit V, the flare cutter FS moves toward the object while decreasing 
the distance between it and the subunit 2b, and the diaphragm S moves 
toward the object integrally with the third lens unit III. The subunit 2b, 
indicated by IIb, is a focus lens unit, and moves toward the object in 
focusing from an infinite object toward the object in short-range 
focusing. 
FIGS. 17A, 17B, and 17C are sectional views of the ninth embodiment. 
Numeral I indicates a first, positive lens unit, numeral II indicates a 
second, negative lens unit, numeral IIa indicates a negative subunit 2a, 
numeral IIb indicates a negative subunit 2b, numeral III indicates a 
third, positive lens unit, numeral IV indicates a fourth, negative lens 
unit, numeral V indicates a fifth, positive lens unit, numeral VI 
indicates a sixth, negative lens unit, symbol S indicates a diaphragm, 
symbol FS indicates a movable flare cutter, and numeral ST indicates a 
stationary flare cutter. 
When power variation is effected from the wide-angle end to the telephoto 
end, the first lens unit I moves toward the object, the subunit 2a, 
indicated by IIa, moves toward the object while increasing the distance 
between it and the first lens unit I, the subunit 2b, indicated by IIb, 
moves over in a locus convex toward the object while increasing the 
distance between it and the subunit 2a, indicated by IIa, the third lens 
unit III moves toward the object while decreasing the distance between it 
and the second subunit 2b, indicated by IIb, the fourth lens unit IV moves 
toward the object while Increasing the distance between it and the third 
lens unit III, the fifth lens unit V moves toward the object while 
decreasing the distance between it and the fourth lens unit IV, the sixth 
lens unit VI moves toward the object while decreasing the distance between 
it and the fifth lens unit V until the intermediate focus and increasing 
the distance between it and the fifth lens unit V from the intermediate 
focus to the telephoto end, the flare cutter FS moves toward the object 
while decreasing the distance between it and the subunit 2b and enlarging 
the aperture diameter, the diaphragm S moves toward the object integrally 
with the third lens unit III, and the stationary flare cutter ST is 
stationary with respect to the image plane. The subunit 2b, indicated by 
IIb, is a focus lens unit, and moves toward the object in focusing from an 
infinite object toward the object in short-range focusing. 
FIGS. 18A, 18B, and 18C are sectional views of the tenth embodiment. 
Numeral I indicates a first, positive lens unit, numeral II indicates a 
second, negative lens unit, numeral IIa indicates a negative subunit 2a, 
numeral IIb indicates a negative subunit 2b, numeral III indicates a 
third, positive lens unit, numeral IV indicates a fourth, positive lens 
unit, numeral V indicates a fifth, negative lens unit, numeral VI 
indicates a sixth, positive lens unit, symbol FS indicates a movable flare 
cutter, and symbol S indicates a diaphragm. 
When power variation is effected from the wide-angle end to the telephoto 
end, the first lens unit I moves toward the object, the subunit 2a, 
indicated by IIa, moves over in a locus convex toward the object while 
increasing the distance between it and the first lens unit I, the subunit 
2b, indicated by IIb, moves over in a locus convex toward the object while 
increasing the distance between it and the subunit 2a, indicated by IIa, 
the third lens unit III moves toward the object while decreasing the 
distance between it and the second subunit 2b, indicated by IIb, the 
fourth lens unit IV moves toward the object while increasing the distance 
between it and the third lens unit III, the fifth lens unit V moves over 
in a locus convex toward the object while decreasing the distance between 
it and the fourth lens unit IV, the sixth lens unit VI moves toward the 
object integrally with the third lens unit III while decreasing the 
distance between it and the fifth lens unit V, the flare cutter FS moves 
toward the object while decreasing the distance between it and the subunit 
2b, indicated by IIb, and the diaphragm S moves toward the object 
integrally with the third lens unit III. The subunit 2b, indicated by IIb, 
is a focus lens unit, and moves toward the object in focusing from an 
infinite object toward the object in short-range focusing. 
Numerical examples of the seventh through tenth embodiments are shown 
below. Numerical Examples 7 through 10 respectively correspond to the 
seventh through tenth embodiments. 
FIGS. 19A(1)-19B(12) through 22A(1)-22B(12) are aberration diagrams, which, 
like FIGS. 15 through 18, correspond to the seventh through tenth 
embodiments. 
NUMERICAL EXAMPLE 7 
______________________________________ 
f = 28.90-193.24 F.sub.no = 3.60-5.75 2.omega. = 73.6-12.8 
R1 = 110.462 
D1 = 1.50 N1 = 1.846658 
.nu.1 = 23.9 
R2 = 65.858 
D2 = 9.62 N2 = 1.569070 
.nu.2 = 71.3 
R3 = 3801.583 
D3 = 0.20 
R4 = 57.450 
D4 = 6.76 N3 = 1.712995 
.nu.3 = 53.9 
R5 = 153.053 
D5 = variable 
*R6 = 98.252 
D6 = 1.70 N4 = 1.696797 
.nu.4 = 55.5 
R7 = 20.065 
D7 = variable 
R8 = -53.136 
D8 = 1.10 N5 = 1.882997 
.nu.5 = 40.8 
R9 = 23.560 
D9 = 0.52 
R10 = 24.222 
D10 = 4.12 N6 = 1.846660 
.nu.6 = 23.8 
R11 = -48.645 
D11 = 0.40 
R12 = -35.185 
D12 = 1.00 N7 = 1.882997 
.nu.7 = 40.8 
R13 = 278.283 
D13 = variable 
R14 = movable 
D14 = variable 
flare cutter 
R15 = diaphragm 
D15 = 0.39 
R16 = 29.436 
D16 = 1.00 N8 = 1.846660 
.nu.8 = 23.8 
R17 = 16.511 
D17 = 5.42 N9 = 1.696797 
.nu.9 = 55.5 
R18 = -45.131 
D18 = variable 
R19 = 27.883 
D19 = 4.52 N10 = 1.487490 
.nu.10 = 70.2 
R20 = -25.709 
D20 = 1.00 N11 = 1.882997 
.nu.11 = 40.8 
R21 = 368.478 
D21 = variable 
R22 = -33.741 
D22 = 2.25 N12 = 1.846660 
.nu.12 = 23.8 
R23 = -14.714 
D23 = 1.00 N13 = 1.712995 
.nu.13 = 53.9 
R24 = 97.111 
D24 = variable 
R25 = 62.233 
D25 = 6.63 N14 = 1.563839 
.nu.14 = 60.7 
R26 = -25.157 
D26 = 0.20 
R27 = -1590.680 
D27 = 2.76 N15 = 1.487490 
.nu.15 = 70.2 
*R28 = -44.310 
D28 = 3.13 
R29 = -21.158 
D29 = 1.40 N16 = 1.846658 
.nu.16 = 23.9 
R30 = -50.050 
variable-distance.backslash.focal-length 
28.90 67.79 193.24 
D5 1.00 18.64 42.21 
D7 7.97 10.57 15.25 
D13 11.39 10.27 1.13 
D14 11.24 1.38 1.49 
D18 0.80 2.27 2.42 
D21 1.80 6.06 9.55 
D24 11.46 5.73 2.09 
______________________________________ 
Aspherical Coefficient 
surface 6: A=0.00000e+00 B=2.78935e-06 C=-4.14745e-09 D=8.35869e-12 
E=3.40595e-15 
surface 28: A=0.00000e+00 B=7.15437e-06 C=-1.89273e-11 D=8.90354e-11 
E=-2.70570e-13 
NUMERICAL EXAMPLE 8 
______________________________________ 
f = 28.90-193.17 F.sub.no = 3.58-5.75 2.omega. = 73.6-12.8 
R1 = 117.085 
D1 = 2.00 N1 = 1.846659 
.nu.1 = 23.8 
R2 = 69.555 
D2 = 10.59 N2 = 1.592400 
.nu.2 = 68.3 
R3 = -400.829 
D3 = 0.15 
R4 = 58.695 
D4 = 5.12 N3 = 1.712995 
.nu.3 = 53.8 
R5 = 110.569 
D5 = variable 
*R6 = 116.203 
D6 = 1.20 N4 = 1.772499 
.nu.4 = 49.6 
R7 = 24.948 
D7 = variable 
R8 = -51.434 
D8 = 1.10 N5 = 1.834807 
.nu.5 = 42.7 
R9 = 25.950 
D9 = 0.67 
R10 = 25.829 
D10 = 4.42 N6 = 1.846659 
.nu.6 = 23.8 
R11 = -52.258 
D11 = 0.28 
R12 = -42.033 
D12 = 1.10 N7 = 1.834807 
.nu.7 = 42.7 
R13 = 78.563 
D13 = variable 
R14 = movable 
D14 = variable 
flare cutter 
R15 = diaphragm 
D15 = 0.30 
R16 = 31.898 
D16 = 1.00 N8 = 1.846659 
.nu.8 = 23.8 
R17 = 17.393 
D17 = 5.26 N9 = 1.639300 
.nu.9 = 44.9 
R18 = -57.523 
D18 = variable 
R19 = 24.876 
D19 = 5.04 N10 = 1.487490 
.nu.10 = 70.2 
R20 = -35.107 
D20 = 1.00 N11 = 1.846659 
.nu.11 = 23.8 
R21 = -439.995 
D21 = variable 
R22 = -63.863 
D22 = 3.51 N12 = 1.846660 
.nu.12 = 23.8 
R23 = -17.080 
D23 = 1.00 N13 = 1.772499 
.nu.13 = 49.6 
R24 = 62.417 
D24 = variable 
R25 = 101.234 
D25 = 4.89 N14 = 1.583126 
.nu.14 = 59.4 
*R26 = -32.722 
D26 = 0.15 
R27 = -215.499 
D27 = 2.82 N15 = 1.516330 
.nu.15 = 64.2 
R28 = -37.755 
D28 = 5.20 
R29 = -17.384 
D29 = 1.80 N16 = 1.846659 
.nu.16 = 23.8 
R30 = -30.941 
variable-distance.backslash.focal-length 
28.90 74.72 193.17 
D5 1.00 21.70 42.28 
D7 8.27 10.85 15.61 
D13 11.61 4.80 1.56 
D14 14.49 8.77 1.46 
D18 0.80 3.19 0.99 
D21 1.80 5.85 6.89 
D24 12.34 6.41 2.09 
______________________________________ 
Aspherical Coefficient 
surface 6: A=0.00000e+00 B=1.21212e-06 C=-2.25771e-09 D=8.60639e-12 
E=-1.05530e-14 
surface 26: A=0.00000e+00 B=-2.22453e-06 C=-2.75194e-08 D=1.02088e-10 
E=-5.33539e-13 
NUMERICAL EXAMPLE 9 
______________________________________ 
f = 29.01-293.62 F.sub.no = 3.37-5.85 2.omega. = 73.4-8.4 
R1 = 105.399 
D1 = 2.90 N1 = 1.846658 
.nu.1 = 23.9 
R2 = 65.146 
D2 = 0.69 
R3 = 66.481 
D3 = 9.60 N2 = 1.592400 
.nu.2 = 68.3 
R4 = 2247.452 
D4 = 0.15 
R5 = 77.227 
D5 = 5.78 N3 = 1.729157 
.nu.3 = 54.7 
R6 = 296.702 
D6 = variable 
*R7 = -211.721 
D7 = 1.50 N4 = 1.772499 
.nu.4 = 49.6 
R8 = 22.555 
D8 = variable 
R9 = -1356.061 
D9 = 2.93 N5 = 1.805181 
.nu.5 = 25.4 
R10 = -42.608 
D10 = 1.00 N6 = 1.882997 
.nu.6 = 40.8 
R11 = 55.575 
D11 = 0.15 
R12 = 44.532 
D12 = 3.20 N7 = 1.846660 
.nu.7 = 23.8 
R13 = -691.545 
D13 = 1.54 
R14 = -46.696 
D14 = 1.10 N8 = 1.882997 
.nu.8 = 40.8 
R15 = -3613.461 
D15 = variable 
R16 = movable 
D16 = variable 
flare cutter 
R17 = diaphragm 
D17 = 0.00 
R18 = 44.529 
D18 = 5.15 N9 = 1.603112 
.nu.9 = 60.7 
*R19 = -62.539 
D19 = 0.15 
R20 = 48.533 
D20 = 7.54 N10 = 1.696797 
.nu.10 = 55.5 
R21 = -24.694 
D21 = 1.15 N11 = 2.022040 
.nu.11 = 29.1 
R22 = -121.827 
D22 = variable 
R23 = -89.876 
D23 = 4.80 N12 = 1.846660 
.nu.12 = 23.8 
R24 = -18.504 
D24 = 1.10 N13 = 1.834807 
.nu.13 = 42.7 
R25 = 65.409 
D25 = variable 
R26 = 50.719 
D26 = 1.50 N14 = 1.846660 
.nu.14 = 23.8 
R27 = 28.316 
D27 = 8.11 N15 = 1.603112 
.nu.15 = 60.7 
R28 = -50.456 
D28 = 0.15 
R29 = 401.413 
D29 = 4.91 N16 = 1.516330 
.nu.16 = 64.2 
*R30 = -41.026 
D30 = 0.15 
R31 = 146.253 
D31 = 8.05 N17 = 1.639799 
.nu.17 = 34.5 
R32 = -22.289 
D32 = 1.20 N18 = 1.901355 
.nu.18 = 31.6 
R33 = -307.942 
D33 = variable 
R34 = -98.739 
D34 = 1.30 N19 = 1.882997 
.nu.19 = 40.8 
R35 = 41.939 
D35 = 1.12 
R36 = 34.991 
D36 = 2.85 N20 = 1.846658 
.nu.20 = 23.9 
R37 = 58.689 
D37 = variable 
R38 = stationary 
flare cutter 
variable-distance.backslash.focal-length 
29.01 66.33 293.62 
D6 1.00 24.47 49.93 
D8 7.60 12.96 17.88 
D15 13.30 7.65 0.47 
D16 17.85 12.17 1.16 
D22 1.30 6.37 11.00 
D25 22.28 12.98 0.46 
D33 2.04 0.47 7.56 
D37 2.13 20.18 38.55 
______________________________________ 
Aspherical Coefficient 
surface 7: A=0.00000e+00 B=4.85872e-06 C=-2.45613e-09 D=2.05320e-11 
E=-9.53801e-14 F=1.22963e-16 
surface 19: A=-0.00000e+00 B=3.36075e-07 C=-5.40669e-09 D=-1.19043e-11 
E=-0.00000e+00 
surface 30: A=0.00000e+00 B=3.98970e-06 C=5.13108e-09 D=-2.36767e-11 
E=0.00000e+00 
NUMERICAL EXAMPLE 10 
______________________________________ 
f = 28.90-130.81 F.sub.no = 3.60-5.75 2.omega. = 73.6-18.8 
R1 = 125.660 
D1 = 1.50 N1 = 1.846660 
.nu.1 = 23.8 
R2 = 63.983 
D2 = 8.18 N2 = 1.622992 
.nu.2 = 58.2 
R3 = -2908.494 
D3 = 0.20 
R4 = 45.133 
D4 = 6.40 N3 = 1.712995 
.nu.3 = 53.9 
R5 = 111.631 
D5 = variable 
*R6 = 158.004 
D6 = 1.70 N4 = 1.772499 
.nu.4 = 49.6 
R7 = 24.066 
D7 = variable 
R8 = -121.300 
D8 = 1.10 N5 = 1.882997 
.nu.5 = 40.8 
R9 = 20.782 
D9 = 2.83 
R10 = 24.864 
D10 = 3.76 N6 = 1.846660 
.nu.6 = 23.8 
R11 = -67.923 
D11 = 0.08 
R12 = -63.426 
D12 = 1.00 N7 = 1.882997 
.nu.7 = 40.8 
R13 = 57.613 
D13 = variable 
R14 = movable 
D14 = variable 
flare cutter 
R15 = diaphragm 
D15 = 0.39 
R16 = 28.480 
D16 = 1.00 N8 = 1.846660 
.nu.8 = 23.8 
R17 = 14.559 
D17 = 5.20 N9 = 1.696797 
.nu.9 = 55.5 
R18 = -43.893 
D18 = variable 
R19 = 28.417 
D19 = 4.04 N10 = 1.516330 
.nu.10 = 64.1 
R20 = -26.283 
D20 = 1.00 N11 = 1.882997 
.nu.11 = 40.8 
R21 = 181.303 
D21 = variable 
R22 = -59.195 
D22 = 2.61 N12 = 1.846660 
.nu.12 = 23.8 
R23 = -14.290 
D23 = 1.00 N13 = 1.772499 
.nu.13 = 49.6 
R24 = 57.734 
D24 = variable 
R25 = 61.833 
D25 = 6.37 N14 = 1.583126 
.nu.14 = 59.4 
*R26 = -29.255 
D26 = 0.20 
R27 = 92.873 
D27 = 5.11 N15 = 1.570989 
.nu.15 = 50.8 
R28 = -31.972 
D28 = 2.07 
R29 = -23.212 
D29 = 1.40 N16 = 1.846660 
.nu.16 = 23.8 
R30 = 4315.550 
variable-distance.backslash.focal-length 
28.90 61.48 130.81 
D5 1.00 12.71 29.68 
D7 6.63 9.38 12.01 
D13 10.87 8.85 1.68 
D14 10.32 2.50 1.53 
D18 0.80 2.95 3.90 
D21 1.80 5.43 9.19 
D24 12.58 6.81 2.10 
______________________________________ 
Aspherical Coefficient 
surface 6: A=0.00000e+00 B=1.99338e-06 C=1.68526e-10 D=0.00000e+00 
E=0.00000e+00 
surface 26: A=0.00000e+00 B=5.05093e-06 C=-2.17169e-10 D=3.36024e-11 
E=-1.92890e-13 
Table 2 shows values of the parameters in the conditional expressions in 
Numerical Examples 7 through 10. 
TABLE 2 
______________________________________ 
Numerical 
Numerical Numerical 
Numerical 
Example 1 
Example 2 Example 3 
Example 4 
______________________________________ 
f1/ft 0.4642 0.4760 0.3205 0.5827 
f2a/ft -0.1889 -0.2140 -0.0896 
-0.2825 
f2b/ft -0.1729 -0.1723 -0.2041 
-0.2519 
.beta.2bt 
0.0391 -0.0027 0.3329 0.0297 
.beta.2t -0.8239 -0.8024 -0.8899 
-0.8190 
1/.beta.2at 
-0.0475 0.0034 -0.3741 
-0.0363 
logZ2/ 0.5946 0.5807 0.5214 0.7443 
logZ 
______________________________________ 
By constructing the zoom lens as described above, it is easy to achieve a 
reduction in the size of the entire optical system, to simplify the 
structure of the lens barrel for focusing, to achieve a reduction in cost, 
etc. Further, even in focusing in tight close-up photographing, there is 
no concern that the displacement of the focus lens unit will increase to 
an excessive degree. 
FIG. 14 shows an example of a single-lens reflex camera equipped with a 
zoom lens according to the present invention. In the drawing, numeral 10 
indicates a zoom lens according to the present invention, and numeral 20 
indicates a camera body (which supports the zoom lens). In this way, the 
zoom lens of the present invention is suitable for use in optical 
apparatus, such as single-lens reflex cameras and video cameras, for 
example. 
Except as otherwise disclosed herein, the various components shown in 
outline in block form in the figures are individually well-known and their 
internal construction and operation are not critical either to the making 
or using of this invention or to a description of the best mode of the 
invention. 
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.