GB2281409A - Three group zoom lens system - Google Patents

Three group zoom lens system Download PDF

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Publication number
GB2281409A
GB2281409A GB9421233A GB9421233A GB2281409A GB 2281409 A GB2281409 A GB 2281409A GB 9421233 A GB9421233 A GB 9421233A GB 9421233 A GB9421233 A GB 9421233A GB 2281409 A GB2281409 A GB 2281409A
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United Kingdom
Prior art keywords
lens
magnification
telescopic
wide angle
overall
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GB9421233A
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GB2281409B (en
GB9421233D0 (en
Inventor
Takayuki Ito
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Pentax Corp
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Asahi Optical Industries Co Ltd
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Priority to JP23912592 priority
Application filed by Asahi Optical Industries Co Ltd filed Critical Asahi Optical Industries Co Ltd
Priority to GB9227033A priority patent/GB2262816B/en
Publication of GB9421233D0 publication Critical patent/GB9421233D0/en
Publication of GB2281409A publication Critical patent/GB2281409A/en
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Publication of GB2281409B publication Critical patent/GB2281409B/en
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Expired - Fee Related legal-status Critical Current

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Classifications

    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B15/00Optical objectives with means for varying the magnification
    • G02B15/14Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective
    • G02B15/143Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having three groups only
    • G02B15/1431Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having three groups only the first group being positive
    • G02B15/143105Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having three groups only the first group being positive arranged +-+

Abstract

A zoom lens system comprises in order from the object side, a first positive lens group r1 - r4, a second negative lens group r5 - r10 and a third positive lens group r11 - r20. The second lens group and the third lens group are moved along an optical axis for changing magnification and the second lens system group is moved for focusing. The system preferably satisfies the condition (h): (h) 0.0 < logz2/logz < 0.3 where z2 is the magnification ratio (z2=m2L/m2S) of the second lens group, m2L is a lateral magnification of the second lens group at the telescopic end, m2S is a lateral magnification of the second lens group at the wide angle end, z is the change ratio (z=ft/fw) of the magnification of the overall system, ft is the focal length of the overall system at the telescopic end, fw is the focal length of the overall system at the wide angle end. <IMAGE>

Description

ZOOM LENS SYSTEM The present invention relates to a zoom lens system used for a compact video camera, an electronic still camera, or the like.

Recently, there has been developed a compact video camera and are electronic still camera which have a 1/2 inch or a 1/3 inch screen and a CCD as a light receiving element.

A taking lens used for these kinds of camera is a compact zoom lens system which has a small F-number (it is bright). A retro-focus type 2 group zoom lens system has a negative first lens group and is known as a conventional compact zoom lens system. Ilowever if the retro-focus type 2 group zoom lens system has an F number oF about 1:2, the diameter of a lens of a back group becomes large. Moreover, high order spherical aberration occurs.

A 4 group zoom lens. system is also kllown for a small F number zoom lens system. The 4 gi-otip tye lens has a positive first lens group, a negative second lens group as a variable power lens, a negative third lens group as a compensator, and a positive fourth lens group as a master lens.

Ilowever, tie 4 group type zooln lens system has a long overall length, and the diameter oF a front side lens becomes especially large.

In a conventional three group lens system, a first lens group of a part of a third lens group (master lens group) is moved along an optical axis in order to adjust a focus.

However, when the first lens group is moved, if the minimum photography distance is to be shortened, the moving amount of the first lens and the diameter of the lens system becomes large. Moreover, when the third lens is moved, there is a large change of an aberration by focusing.

An object of the present invention is to provide a zoom lens system which is able to shorten the minimum photography distance without enlarging the diameter of the lens and to reduce the change of the aberration at the time of a focusing.

According to the present invention there is provided a zoom lens system comprising, in order from the object side, a first positive lens group, a second negative lens group and a third positive lens group, wherein said second lens group and said third lens group are moved along an optical axis for changing magnification, and wherein said second lens group is moved for focusing.

Preferably, said zoom lens system satisfies the following condition (h) (h) 0.0 < logz2/logz < 0.3 where z2 is the magnification ratio (z2=m2L/m2S) of the second lens group, m2L is a lateral magnification of the second lens group at the telescopic end, m2S is a lateral magnification of the second lens group at the wide angle end, z is the change ratio (z = ft/fw) of the magnification of the overall system, ft is the focal length of the overall system at the telescopic end, fw is the focal length of the overall system at the wide angle end.

Conveniently, said first lens group is fixed at the time of focusing or zooming.

Reference is made to co-pending patent application GB-A-2-262 816, from which the present application has been divided, and which concerns a zoom lens system comprising, in order from the object side, a first positive lens group, a second negative lens group and a third positive lens group, wherein at least said second lens group and said third lens group are moved along an optical axis for changing magnification, said zoom lens system satisfying the following conditions (a) - (d):: (a) O < fw/fl < 0.25 (b) -0.9 < fw/f2 < -0.4 (c) 0.3 < fw/f3 < 0.8 (d) 0.7 < 1Ogz3/logz < 1.0 where fw is the focal length of the overall system at the wide angle end, fi is the focal length (i=l, 2, 3) of the i-th lens group, z is the change ratio (z=ft/fw) of the magnification of the overall system, ft is the focal length of the overall system at the telescopic end, z3 is the change ratio (z3=m3t/m3w) of the magnification of the third lens group, m3t is a lateral magnification of the third lens group at the wide angle end, m3w is a lateral magnification of the third lens group at the telescopic end.

Examples of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a section through a first example of a lens embodying the present invention.

Fig. 2 is a diagram of aberrations at the wide angle end of Example 1.

Fig. 3 is a diagram of aberrations at the intermediate focal length of Example 1.

Fig. 4 is a diagram of aberrations at the telescopic end of Example 1.

Fig. 5 is a section through a second example of a lens embodying the present invention.

-Fig. 6 is a diagram of aberrations at the wide angle end of Example 2.

Fig. 7 is a diagram of aberrations at the intermediate focal length of Example 2.

Fig. 8 is a diagram of aberrations at the telescopic end of Example 2.

Fig. 9 is a section through a third example of a lens embodying the present invention.

Fig. 10 is a diagram of aberrations at the wide angle end of Example 3.

Fig. 11 is a diagram of aberrations at the intermediate focal length of Example 3.

Fig. 12 is a diagram of aberrations at the telescopic end of Example 3.

Fig. 13 is a section through a fourth example of a lens embodying the present invention.

Fig. 14 is a diagram of aberrations at the wide angle end of Example 4.

Fig. 15 is a diagram of aberrations at the intermediate focal length of Example 4.

Fig. 1B Is a diagram of aberrations at the telescopic end of Example 4.

Fig. 17 is a section through a fifth example of a lens embodying the present invention.

Fig. 18 is a diagram of aberrations at the wide angle end of Example 5.

Fig. 19 is a diagram of aberrations at the intermediate focal length of Example 5.

Fig. 20 is a diagram of aberrations at the telescopic end of Example 5.

The present disclosure relates to subject matter contained in Japanese patent application Nos. H3-361412 (filed on December 25, 1991) and H4-239125 (filed on September 8, 1992) which are expressly incorporated herein by reference in their entireties.

A zoom lens system of the present invention uses a new zooming method and focusing method which Is like a combination of the conventional retro-focus type 2 group zoom lens system and a 4 group type zoom lens system.

The zooming methods of the present invention and the conventional 4 group type zoom system are compared below. The second and the third lens groups move in both systems. However, with the conventional system the function which mainly changes magnification is given to the second lens group, and the function which compensates focus error caused by changing of magnification is given to the third lens group.

On the other hand, in the system of the present invention, the third lens group is given the function of changing magnification and the function as a master lens, The second lens group has the auxiliary function of changing magnification, and has the function to compensate for focus error caused by changes of magnification.

The zoom lens system of the present invention is provided with, in order from the object side, a first positive lens group, a second negative lens group and a third positive lens group, wherein said second lens group and said third lens group are moved along an optical axis for changing magnification, and wherein said second lens group is moved for focusing.

It is desirable to give focusing function to the second lens group which has larger power than the first lens since if the focusing function is given to the first lens group, the light flux at the periphery of the field is insufficient.

In this case, it is desirable to satisfy the following condition (h).

(h) 0.0 < logz2/logz < 0.3 where z2 is the magnification.ratio (z2=m2L/m2S) of the second lens group, m2L is a lateral magnification of the second lens group at the telescopic end, and m2S is a lateral magnification of the second'lens group at the wide angle end.

Condition (h) specifies a magnification change function of the second lens group. By satisfying this condition, it is possible to reduce the dispersion of the lens moving amount for the focusing at each focal length.

For example, when the distance from an object to the image surface is 0.2m, the relationships between the focal length (f) and the lens moving amounts (X) of Examples 1 and 2 are shown in the following table.

f X (Example 1) X (Example 2) 6.15 1.14 1.01 12.0 1.51 1.22 17.5 1.57 1.21 Furthermore, in the Example 3, when the distance from an object to the image surface is O.lm, the range of the lens moving amount X is 2.95 3.06, and therefore, the dispersion of the amount X can be reduced to under O.lmm.

Another zoom lens system is provided with, in order from the object side, a first positive lens group, a second negative lens group and a third positive lens group. At least the second lens group and the third lens group are moved along an optical axis for changing magnification. This system further satisfies the following conditions: (a) O < fw/fl < 0.25 (b) -0.9 < fw/f2 < -0.4 (c) 0.3 < fw/f3 < 0.8 (d) 0.7 < logz3/logz < l.O.

where fw is the focal length of the overall system at the wide angle end, fi is the focal length (i=l, 2, 3) of the i-th lens group, z is the change ratio (z=ft/fw) of the magnification of the overall system, ft is the focal length of the overall system at the telescopic end, z3 is the change ratio (z3=m3t/m3w) of the magnification of the third lens group, m3t is a lateral magnification of the third lens group at the wide angle end, m3w is a lateral magnification of the third lens groups at the telescopic end.

Condition (a) is for determining the power of the first lens group.

If the lower limit of condition (a) is exceeded, since the power of the first lens group becomes negative, the diameter of a lens of a back group becomes large and a bright zoom lens system of which the F number is about 1:2 can not be obtained. On the other hand, if the upper limit is exceeded, the positive power of the first lens group becomes large, the magnification change function of the second lens group grows, and the change of the aberration at the time of changing the magnification becomes large.

Condition (b) specifies the power of the second lens group. If the lower limit of condition (b) is exceeded, the negative power becomes large and the aberration at the time of changing the magnification is changed.

On the other hand, the lens becomes large if the upper limit is exceeded.

Condition (c) specifies the power of the third lens group. If the lower limit of condition (c) is exceeded, since the power of the third lens group becomes small, the amount of movement of the third lens group for changing the magnification becomes large and the overall length of the lens becomes large. On the other hand, if the upper limit of condition (c) is exceeded, since the power becomes large, the change of the aberration at the time of changing the magnification becomes large.

Condition (d) specifies enlarging a magnification change function of the third lens group compared with the same of the second lens group. If the lower limit; of the condltioh (d) is exceeded, tile magnification change function of the secoiid lens group yrows, and correctlon of an aberration becomes hard. On the other hand, if the upper limit is exceeded, since only the tlilrd lens group comes to have a magnification change function, the ratio of magnification change cannot be made high.

When the zoom lens system satisfies these conditions at the same time, a compact zoom lens system of which the change ratio of magnification is about 3 times can be obtained.

In order to obtain a more compact zoom lens system, it is desirable to satisfy the following condltlons (e) mid (f).

(e) -1 > m2 > 0 (f) m3t < -1 < m3w where m2 is a lateral magnification of tlie second lens group from tlie wide angle side to a telescopic side.

Conditions (e) and (f) specify the lateral magnification of the second lens group and Ilie third lens group. By satisfying these conditions, tlle direction of movement of the second lens group is charged at an intermediate focal length. Moreover, since the third lens group is moved to the side of an object corresponding to the increase in focal length, a more compact zoom lens system can be obtained.

Furthermore, in order to provide a bern splitter between the Image surface and the lens, it Is desirable to satisfy tlie following condition (g).

(g) 1.5 < fBw/fw where fBw is the back focus at the end of the wide angle.

The back focus is defined as the interval between a last surface of the lens system and the image surface.

Condition (g) specifies the back focus. By satisfying this condition, two or more beam splitters can be provided between the lens and the image side.

In addition, an aperture may be disposed in front of the third lens group, or inside the third lens group. When the aperture is disposed in front of the third lens group, the diameter of the lens at the front side can be made small. Moreover, when the aperture is disposed inside the third lens group, ghosting by the image surface or a surface of the master lens can be effectively prevented.

It is also desirable to satisfy the conditions (i) and (j) in order to obtain a long back focus.

(i) 1.0 < dS/ft < 2.0 (j) 2.1 < fBw/fw < 3.5 where dS is the distance between the second lens group and the third lens group.

The condition (i) specifies the distance between the second and the third lens groups. If the lower limit of the condition (i) is exceeded, the change of the aberration at the time of changing the magnification becomes large when obtaining long back focus.

If the upper limit of the condition (i) is exceeded, the overall length of the zoom lens system and the diameter of a lens of the front group becomes large.

The condition (j) specifies the back focus in a narrower range than the condition (g).

Next, some numerical examples of the invention will be described.

Example 1 Fig. 1 shows a first example illustrating the invention. Specific numerical values are shown in Tables 1 and 2.

In the tables, r is radius of curvature, d is inter-surface distance, N is refractive index, v is Abbe number, f is focal length, fB is back focus, FNo is f-number and 9 is half view angle. In the following embodiments, back focus fB is defined as the following equation.

fB = d20 + d21/n21 A plane parallel plate shown by surface numbers 21 and 22 indicates a beam splitter, which is shown in expanded form, mounted between the zoom lens system and the image surface.

Fig. 2, 3 and 4 show spherical aberration SA, sine condition SC, chromatic aberration shown by spherical aberrations in d-line (588nm), g-line (436nm) and C-line (656nm), chromatic aberration of magnification, astigmatism (S: sagittal, n: meridional) which are produced by this arrangement at the wide angle end, intermediate position and telescopic end respectively.

Table l Surface number r d n v 1 28.795 1.40 1.80518 25.4 2 20.910 0.45 3 31.730 2.60 1.69680 55.5 4 -135.229 variable 5 45.427 1.00 1.83481 42.7 6 6.656 2.72 7 -20.299 0.90 1.77250 49.6 8 44.075 1.11 9 17.912 2.40 1.84666 23.8 10 -357.973 variable 11 -311.568 2.02 1.80400 46.6 12 -23.121 0.10 13 15.462 2.63 1.77250 49.6 14 -77.216 0.49 15 -25.865 1.10 1.80518 25.4 16 127.915 3.67 17 33.345 1.00 1.84666 23.8 18 10.550 0.55 19 18.179 2.60 1.69680 55.5 20 -15.998 variable 21 # 16.20 1.49782 66.8 22 I'able 2 FNo. 2.1. 2.0 2.4 f 6.15 12.00 17.50 fB 0.00 0.00 0 0.00 # 26.5 13.8 9.6 d4 2.30 10.12 11.22 dlO 20.47 8.58 3.02 d20 2.01 6.09 10.54 Example 2 Fig. 5 shows a second example illustrating the inveiition Specific numerical values are shown in Tables 3 and 4 Fins. 6. 7 and 8 show the aberrations produced by this arrangement at the wide angle end, intermediate position and telescopic end respectively.

Table 3 Sur face number r d n p 1 48.453 1.40 1.80518 25.4 2 32.536 0.00 3 32.536 2.59 1.89680 55.5 4 -520.921 variable 5 17.833 1.00 1.77250 49.6 6 5.742 2.89 7 -15.626 0.90 1.77250 49.6 8 24.610 0.54 9 14.675 2.30 1.84666 23.8 10 -238.854 variable 11 -187.185 1.84 1.69680 55.5 12 -20.008 0.10 13 13.745 3.10 1.77250 49.6 14 -145.272 0.36 15 -26.752 1.00 1.84666 23.8 16 28.172 2.20 17 19.509 3.50 1.80518 25.4 18 9.719 0.37 19 14.255 2.20 1.77250 49.6 20 -17.484 variable 21 # 16.20 1.49782 66.8 22 Table 4 ENo. 2.0 2.4 2.8 f 6.15 12.00 17.50 fB 0.00 0.00 0.00 # 26.7 -14.0 9.7 d4 2.30 9.00 8.78 d10 18.09 G.77 1.80 (120 1.93 6.55 11.74 Example 3 Fig. 9 shows a third example illustrating the invention. Specific numerical values are shown In Tables 5 and 6. Flogs. 10, 11 and 12 show the aberrations produced by this arrangement at the wide angle end, intermediate position and telescopic end respectively.

Table 5 Surface number r d n 1 53.595 1.40 1.80518 25.4 2 36.114 0.00 3 36.114 2.85 1.69680 55.5 4 -346.993 variable 5 18.487 1.00 1.77250 49.6 6 5.744 3.46 7 -14.666 1.00 1.77250 49.6 8 31.999 0.10 9 14.503 2.30 1.84666 23.8 10 -319.236 variable 11 -309.023 1.92 1.69680 55.5 12 -19.418 0.10 13 14.518 3.10 1.77250 49.6 14 -106.483 0.36 15 -26.562 1.00 1.84666 23.8 16 26.562 2.16 17 17.284 3.50 1.80518 25.4 18 10.313 0.46 19 18.044 2.40 1.77250 49.6 20 -18.044 variable 21 oo 17.00 1.49782 66.8 22 Table 6 FNo. 2.0 2.4 2.8 f 6.15 12.00 17.50 fB 0.00 0.00 0.00 26.6 13.9 9.7 d4 3.60 10.34 9.99 d10 19.58 8.05 3.00 d20 1.50 6.29 11.71 Example 4 Fig. 13 shows a fourth example illustratinq the invention.Specific numerical values are shown in Tables 7 and 8. rigs. 14. 15 and 16 show the intermediate produced by this arrangement at the wide angle end, intermediate position and telescopic end respectively.

Table 7 Surface number r (3 n v 1 30.068 1.40 1.80518 25.4 2 19.874 0.59 3 25.140 3.78 1.58267 46.4 4 -107.221 variable 5 60.319 1.00 1.83481 42.7 6 6.573 2.71 7 -16.257 1.00 1.80400 46.6 8 45.243 0.10 9 16.256 2.90 1.84666 23.8 10 -41.887 variable 11 -388.257 3.90 1.74950 35.3 12 -25.427 0.10 13 16.085 2.54 1.77250 49.6 14 -74.583 0.32 15 -28.012 1.10 1.84666 23.8 16 28.012 3.31 17 25.756 1.20 1.80518 25.4 18 13.011 0.34 19 19.623 2.63 1.77250 49.6 20 -19.623 variable 21 m 23.00 1.49782 66.8 22 Table 8 FNo. 2.0 2.4 2.8 r 6.20 12.00 18.00 rB 0.00 0.00 0.00 # 26.4 -13.9 9.4 d4 3.20 12.39 14.45 d10 23.88 10.72 4.06 d20 1.00 4.97 9.57 Example 5 Fig. 17 shows a fifth example illustrating the invention Specific numerical values are shown in Tables 9 alld 10. Ftgs. 18, 19 and 20 show the aberrations produced by this arrangement at the wide angle end, intermediate position and telescopic end respectively.

Table 9 Surface number r d n u 1 35.284 1.39 1.80518 25.4 2 23.039 0.37 3 27.427 3.34 1.62374 47.1 4 -248.837 variable 5 39.943 0.99 1.83481 42.7 6 7.067 2.58 7 -18.771 0.99 1.77250 49.6 8 49.642 0.12 9 16.139 2.77 1.84666 23.8 10 -73.666 variable 11 -315.129 1.85 1.69680 55.5 12 -26.062 1.71 13 15.927 2.49 1.80610 40.9 14 -79.506 0.32 15 -28.702 1.09 1.84666 23.8 16 28.702 3.47 17 25.490 1.19 1.80518 25.4 18 12.854 0.33 19 19.777 2.57 1.77250 49.6 20 -19.777 variable 21 # 23.00 1.49782 66.8 22 Table 10 FNo. 2.0 2.4 2.8 r 7.20 14.00 21.00 fB 0.00 0.00 0.00 # 23.1 12.0 8.1 d4 3.57 | 13.77 16.15 d10 24.43 10.12 3.08 d20 0.88 4.98 9.65 The following Table 11 shows the relationship between the conditions and respective examples described hereinbefore.

Table 11 Condition Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 fw/fl (1.104 0.090 0.086 0.094 0.096 fw/f2 -0.62 -0.63 -0.65 -0.59 -0.58 fw/f3 0.43 0.47 0.45 0.40 0.45 logz3/logz 0.79 0.88 0.88 0.76 0.765 m2 -0.22~ -0.18~ -0.17~ -0.21~ -0.22~ -0.28 -0.21 -0.20 -0.27 -0.29 m3w -0.47 -0.49 -0.50 -0.45 -0.43 m3t -1.07 -1.24 -1.25 -1.00 -0.98 fBw 12.83 12.75 12.85 16.36 16.23 fBw/fw 2.09 2.07 2.09 2.64 2.25 logz2/logz 0.21 0.12 0.12 0.24 0.235 dS/ft 1.17 0.97 1.12 1.33 1.16

Claims (3)

  1. CLAIMS: 1. A zoom lens system comprising, in order from the object side, a first positive lens group, a second negative lens group and a third positive lens group, wherein said second lens group and said third lens group are moved along an optical axis for changing magnification, and wherein said second lens group is moved for focusing.
  2. 2. A zoom lens system according to claim 1 wherein said zoom lens system satisfies the following condition (h): (h) 0.0 < logz2/logz < 0.3 where z2 is the magnification ratio (z2=m2L/m2S) of the second lens group, m2L is a lateral magnification of the second lens group at the telescopic end, m2s is a lateral magnification of the second lens group at the wide angle end, z is the change ratio (z = ft/fw) of the magnification of the overall system, ft is the focal length of the overall system at the telescopic end, fw is the focal length of the overall system at the wide angle end.
  3. 3. A zoom lens system according to claim 1 or 2 wherein said first lens group is fixed at the time of focusing or zooming.
GB9421233A 1991-12-25 1992-12-29 Three group zoom lens system Expired - Fee Related GB2281409B (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
JP36141291 1991-12-25
JP23912592 1992-09-08
GB9227033A GB2262816B (en) 1991-12-25 1992-12-29 Three group zoom lens system

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GB9421233D0 GB9421233D0 (en) 1994-12-07
GB2281409A true GB2281409A (en) 1995-03-01
GB2281409B GB2281409B (en) 1995-10-11

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4230397A (en) * 1978-09-21 1980-10-28 Bell & Howell Company Large aperture extended range zoom lens
US4452513A (en) * 1981-06-19 1984-06-05 Nippon Kogaku K.K. Zoom lens capable of close range photography and method of focusing the same to a short distance

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4230397A (en) * 1978-09-21 1980-10-28 Bell & Howell Company Large aperture extended range zoom lens
US4452513A (en) * 1981-06-19 1984-06-05 Nippon Kogaku K.K. Zoom lens capable of close range photography and method of focusing the same to a short distance

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GB2281409B (en) 1995-10-11

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