JPH0727115B2 - 2 focal length optical system - Google Patents

Description

The present invention relates to a compact, bright and easy-to-operate two-focal-length optical system used in video cameras, cine cameras, and the like.

[Conventional technology]

Conventional ordinary still cameras have many zoom lenses and have automatic focus adjustment. In recent years, development and development of camera-integrated VTRs and electronic still cameras have been remarkable. In particular, the VTR with a built-in camera is currently being researched to reduce its size and weight.

However, as a conventional two-focal-length optical system, a front converter type used by attaching / detaching on the front surface of a photographic lens which has been known for a long time, or by adding a lens built in the camera on the rear side of the photographic lens is used. Alternatively, two photographing lenses are incorporated and used by switching them, that is, the photographing lens itself has a focal point and a focal point obtained by switching or adding another lens.

For example, as a zoom lens for a still camera, Japanese Patent Publication No. 61-
The first group, such as Japanese Patent No. 39649, is movable in the optical axis direction for focus adjustment, and includes a negative meniscus lens having a convex surface facing the object side, a biconvex lens, and a positive meniscus lens having a convex surface facing the object side in order. The second lens group has a refractive power, and the second lens group has a negative meniscus lens having a convex surface directed toward the object side and a negative lens having a negative lens and a positive lens cemented together. , The third lens unit is composed of a negative lens in which a negative lens and a positive lens are cemented together, and has a negative refractive power that moves at the same time as the second lens unit in order to compensate for the image surface movement. Is a zoom lens composed of a fourth lens group consisting of two positive lenses and an imaging lens group in order.

In the rear converter type, the first lens is a meniscus negative lens with a concave surface facing the front object side, the second lens is a biconvex lens, and the third lens is the third lens in order from the object side as in Japanese Patent Publication No. 58-32681.
The lens is a biconcave lens, the fourth lens is a biconvex lens, the fifth lens is a negative meniscus lens with the concave surface facing the object side, and the fourth lens and the fifth lens are cemented together to have a positive refracting power by combining. The sixth lens is an auxiliary lens system of five-group, six-lens structure consisting of a negative meniscus lens with a concave surface facing the object side.

The front converter type uses a first block consisting of a diffusive cemented lens facing the object space and having a convex surface facing the object, and a meniscus cemented lens having a convex surface facing the object, as in Japanese Patent Publication No. 41-71. And a third block consisting of a condensing meniscus single lens with a convex surface facing the image space.
A block and a block are arranged in front of the photographic objective lens with an air gap between them.

As a lens switching type camera, an exposure position is formed between the film winding chamber and the cartridge storage chamber as in JP-A-61-138930, and the exposure position is formed above the film winding chamber side or the cartridge storage chamber side. A camera body having an opening formed in a side portion, a movable lens barrel rotatably attached to the camera body so as to cover the opening, and a first telephoto lens having a very long focal length held in the movable lens barrel. A lens, a first mirror mounted in the movable lens barrel for reflecting light through the first telephoto lens toward the aperture, and a second mirror arranged on a reflection optical path of the first mirror. When the movable mirror barrel is aligned with the camera body, the second mirror is inserted into the reflection optical path of the first mirror, and the movable barrel is raised so as to be perpendicular to the camera body. Second mirror An interlocking mechanism for retracting from the reflection optical path of the first mirror, a second telephoto lens disposed in front of the second mirror and having a relatively long focal length, and the first mirror or the first mirror disposed above the exposure position. A third mirror that reflects the light reflected by the two mirrors to the front of the camera body, a fourth mirror that is arranged in front of the camera body and reflects the light from the third mirror downward, and is arranged in front of the exposure position. And a fifth mirror that reflects the light from the fourth mirror toward the exposure position, and a telescope lens built-in camera.

[Problems to be solved by the invention]

The conventional converter type is troublesome to handle. Further, in the zoom lens type, the lens becomes long and heavy, and the weight of the video camera is further increased. Especially in the case of video cameras, compared to photo cameras in general,
The size of the imaging surface is small, so the focal length of the lens used is considerably shorter than the lens for photographic cameras, and if the imaging unit uses a solid-state imaging device such as CCD, the lens and the element Since a relatively thick optical low-pass filter, cover glass, etc. are inserted between the two, it is difficult to insert a rear converter between the lens and the image pickup unit like a photographic camera. Further, the front converter method or the method of switching two lenses is structurally large in size and complicated, which is not preferable in terms of design.

The known examples are all methods in which a zooming effect is obtained by inserting / removing a part of the optical system on the optical axis, which is different from the zoom lens type.

Recently, there are many examples of using a low-magnification zoom lens to reduce the size of the camera.However, in the case of a zoom lens, an optical system and mechanism are added to correct image plane fluctuations during zooming, and The number of lenses in the optical system is large, for example, it is necessary to improve the performance over the entire area, and the total length of the optical system is inevitably long and tends to be large.

In addition, zoom lenses naturally require zooming and helicoid focus adjustment on the subject independently, so in many cases manual operations are cumbersome, so there is often no choice but to automate autofocus. Therefore, it has a drawback that it is inevitably multi-functional, large-sized, and expensive.

It is an object of the present invention to provide a two-focal length optical system used for a video camera, a cine camera or the like which is small in size, low in cost, lightweight and easy to operate, which cannot be achieved by a conventional variable power optical system. It is a thing.

[Means for solving problems]

It is an object of the present invention to provide an optical system including a plurality of lens groups each including a first lens group positive, a second lens group negative, and a third lens group positive from the object side. The third lens unit is fixed, and the second lens unit is moved in the optical axis direction so that the wide-angle system and the telephoto system can be photographed at both ends and in the vicinity thereof. A two-focal-length optical system for performing focus adjustment, wherein the focal length of the first group is f ₁ , the focal length of the second group is f ₂ , and the image point distance of the third group is b ₃ . When the combined focal length at the wide-angle end is fw, it is configured to satisfy the condition of 0.1 <fw / f ₁ <0.5 0.3 <| fw / f ₂ | <1.2 0.3 <fw / b ₃ <1.2 2 Achieved by the focal length optical system, the rear converter system and the front converter on the optical axis as the conventional two focal length optical system. Without using a switching or detachable to scheme by scheme, it can be said to be one that employs an intermediate method between this and the zoom lens system.

[Action]

The operation of the optical system of the present invention will be described with reference to FIGS. 1, 2 and 3 of the accompanying drawings.

The two-focal-length optical system of the present invention has a three-group configuration including positive, negative, and positive lens groups from the object side, as shown in FIG. The focal lengths of the lens groups are f ₁ , f ₂ , and f ₃ , and the principal point distance between the first and second groups is l ₁ , and the principal point distance between the second and third groups is
when the l _2, indicating that possible object point to an image point is A is B.

Next, FIG. 2 shows that the focal position (image point position) when the first and third groups are fixed and the second group is moved and the magnification is changed. Therefore, in this zooming method, when the object point A is at a constant distance from the first lens group, the focus is out of focus except at the wide-angle end, the telephoto end and its vicinity, and it is not appropriate to use as a zoom lens. However, if it is used as a two-focal length optical system that uses the vicinity of both ends, the structure will be simple and the performance can be used without problems.

Further, in FIG. 2, the object point A is located at a constant distance a ₁ from the first lens group during zooming, but this time, conversely, when the image point B is zoomed to a constant distance from the third lens group. FIG. 3 shows how the position a ₁ of the object point A changes.

Depending on how the object point distance a ₁ at the wide-angle end and the telephoto end is taken, as the second lens group is moved from the wide-angle end and the magnification is changed, the object point distance a ₁ gradually increases until it reaches infinity. It reaches a distance and diverges. If you continue to change the magnification,
The object point A passes through infinity again and becomes gradually smaller, and becomes equal to the object point distance at the wide-angle end at the telephoto end.

Therefore At a Figure 3, the range of the range to the point P ₁ becomes far object point distance a ₁ is infinite from the wide angle end, and the telephoto end than the object distance a ₁ is P ₂ point becomes infinity again Inside, it is possible to perform both zooming and focus adjustment operations by moving the second group, and since it was possible to combine zooming operations and focus adjustment operations that were previously impossible into the same operation It can be said that it is a meaningful invention.

Next, in order to downsize the optical system and obtain high performance, the focal lengths of the lens groups must be balanced, and it is necessary to satisfy some conditional expressions. To do.

The condition (1) is a conditional expression for determining the focal length f ₁ of the first lens unit, and the magnitude of f ₁ is related to the size of the optical system, and particularly to the performance on the telephoto side. The combined focal length at the wide-angle end of the optical system
With fw, if f ₁ becomes small and the value of fw / f ₁ exceeds the upper limit, spherical aberration, astigmatism, etc. on the telephoto side become large and correction becomes difficult. When the value goes below the lower limit, aberration correction is advantageous, but the optical system becomes large.

The condition (2) is a condition for determining the focal length f ₂ of the second lens group, and is an important formula for the size performance of the optical system and the like, like the condition (1). When f ₂ becomes smaller and the value of | fw / f ₂ | exceeds the upper limit, spherical aberration, astigmatism, distortion, etc. on the wide angle side increase, and when it exceeds the lower limit, the optical system becomes large. Finish.

The condition (3) is related to the conditions (1) and (2) and the image point distance b ₃
It is a formula for determining the focal length on the wide-angle side in a variable-magnification optical system such as a video camera or cine camera, which is shorter than that of a lens for a photo camera, and between the imaging surface and the lens. Since a relatively thick filter etc. can be inserted, it is important to secure b ₃ at an appropriate value while keeping the overall size of the optical system compact. b ₃
Decreases, fw / b ₃ is sufficient back Fuo dregs can not be secured I Ryo exceeds the upper limit, also, more than the lower limit b ₃
Even if the value is increased, the size of the optical system becomes large and the balance with other lens groups is lost, which is not preferable.

〔Example〕

Next, an embodiment of the optical system 0 of the present invention will be explained in detail. In FIG. 4, a positive first lens unit L ₁ , a negative second lens unit L _{2 and a} positive third lens unit L ₁ are formed from the object side in FIG. In an optical system composed of a plurality of lens groups of the group L ₃ , the first group L ₁ and the third group L ₃
Are fixed, and only the second lens unit L ₂ is attached to the first lens unit L ₁ in the optical axis direction.
When it is obtained by a movable between third group L _3, and its movement both ends wide at its top near an optical system having two focal length focus of telescopic fit. L ₄ is an optical low pass filter, a cover glass, or the like.

Then, the focal length of the first lens unit L ₁ is f ₁ , the focal length of the second lens unit L ₂ is f ₂ , the focal length of the third lens unit L ₃ is f _3, and a ₁ is the object distance, l ₁ Is the principal point spacing between the first group L ₁ and the second group L ₂ , l ₂ is the principal point spacing between the second group and the third group, W ₁ is the wide-angle end, and the state is focused on a _1. , P ₁ is a point where a ₁ is infinity, P ₂ is that a ₁ is returned to infinity, the state T ₁ is the a ₁ at the telephoto end and focused, b ₃ is the image point length of the third group (Distance from the principal point of the third group to the image point), S is the object-image distance, and fw is the combined focal length at the wide-angle end. Example 1 (fourth illustrated) f ₁ = 41.00 f ₂ = -15.5 _{f 3 = 12.08 b 3 = 15.83} fw = 9.19 fw / f 1 = 0.224 | fw / f 2 | = 0.593 fw / b 3 = 0.592 The lens data of the optical system is F _NO = 1.6 f =, where each lens group is Li, the radius of curvature is r, the surface spacing is d, the refractive index is nd, the Abbe number is ν, and the focal length of the entire system is f. 9.19 ~ 17.7 However, L ₄ is an optical low pass filter, a cover glass or the like. The aberrations of this embodiment are as shown in FIG.

Example 2 (6 _{shown) f 1 = 41.00 f 2 =} -15.5 f 3 = 11.15 b 3 = 14.62 fw = 9.19 fw / f 1 = 0.224 | fw / f 2 | = 0.593 fw / b 3 = 0.627 The lens data of the optical system is such that when each lens group is Li, the radius of curvature is r, the surface spacing is d, the refractive index is nd, the Abbe number is ν, and the focal length of the entire system is f _NO = 1.6 f = 9.19 ~ 17.7 However, L ₄ is an optical low pass filter, a cover glass or the like. The aberrations of this embodiment are shown in FIG.

Next, a mechanical embodiment of the present invention will be described.

In FIG. 8, the optical system 0 has a positive lens first group (L ₁ ) and a positive lens third group (L ₃ ) fixed to fixed lens barrels 1 and 1 ′ connected by screws 2.

In addition, a straight groove 3 parallel to the optical axis provided on the fixed lens barrel 1,
3 '(1 straight groove is enough, but 2 is drawn to show the moving position of the second lens unit L ₂ and is shown with a dash added to the code)
And 'axis 6,6 fitted in the' cam grooves 5, 5 provided on the cam ring 4 by rotation of the cam ring 4 through 6 ", the lens group 2 only (L ₂₎ is in the optical axis direction It is designed to move.

The cam ring 4 is provided with a lever 7 having a pin 8 at the tip, and the cam ring 4 is rotated by turning the lever 7 so that the second lens group (L ₂ ) has a cam groove 5 and a rectilinear groove 3. When the shaft 6 is engaged, the shaft 6 is moved rearward so that the shaft 6 is located at the rear end (A) of the rectilinear groove 3 (8th position).
(Solid line in the figure), it becomes possible to shoot as a telephoto system, the second lens unit L ₂ moves straight forward, and the shaft 6 ′ moves forward in the forward groove 3 ′.
When it is located at the front end (B), it is possible to shoot as a wide-angle system.

Also, the focus adjustment for shooting is a zone focus method,
In the wide angle system, the shaft 6'is at the position of the front end (B) of the straight groove 3 ',
It is a fixed focus set to the hyperfocal length.

In the telephoto system, when the axis 6 is located at the rear end (A) of the straight-ahead groove 3, it is used for near-field photography, and when it is set to a predetermined position (C) that provides a hyperfocal distance like the position of the intermediate axis 6 ″. The zone focus is used for shooting a distant view, and the points (A), (B) and (C) are click-stopped by the click ball 9, the spring 10 and the click groove 11. As shown in FIGS. Shows one embodiment of a method of switching between a telephoto system and a wide-angle system and adjusting the zone focus when the optical system 0 is attached to a VTR image pickup device, and is provided on the cam ring 4 in FIG. The pin 8 at the tip of the lever 7 is slidably fitted in the long groove 12 ′ of the fork 12.

Since the finger hook 13 projects from the outer end of the fork 12, by manually moving the finger hook 13 up and down, the cam ring 4 rotates and the second lens group (L ₂ ) moves in the optical axis direction. .

In Fig. 10, when the finger rest 13 is at the lower end, the telescopic view is taken in the near view (position A in Fig. 8), the telescopic view is taken at a position slightly moved upward (position in Fig. 8 C), and the upper end is taken. It becomes a wide angle system at the moved position, and click stop is made at each position.

Of course, depending on the degree of depth of focus due to the focal length of the lens,
You can increase or decrease the number of focus zones set.

[Advantages of the Invention] The two-focal-length optical system can change the screen more than that of a single-focus lens, and it is lightweight, compact, and low-priced without increasing the size of a converter or zoom type, which is extremely suitable for VTR imaging. A wide focal length optics that can be used as a compact camera that is easy to operate and easy for anyone to use, because it has a simple optical system and can be switched between a one-touch telephoto system, a wide-angle system, and a zone focus freely. It is a system.

Furthermore, zoom lenses naturally require zooming and autofocusing because the focus adjustment operation on the subject by the helicoid is performed independently, so manual operations are often troublesome. Therefore, all the drawbacks that are inevitably multi-functional, large-sized, and expensive are solved.

[Brief description of drawings]

The drawings show an embodiment of a focal length optical system of the present invention. FIG. 1 shows the paraxial relation of the present optical system, and FIG. 2 shows the focus movement (image point movement) associated with zooming. 3A and 3B are views showing a range in which focus adjustment is possible at the time of zooming by utilizing the focus movement, FIG. 4 is a sectional view of the first embodiment, FIG. 6 is a sectional view of Example 2, FIG. 7 is the same aberration diagram, FIG. 8 is a cutaway sectional view of a lens barrel, and FIG. 9 is a front view of a lens incorporated in a video camera. Figure 10 is a side view of the same. L ₁ ... lens first group, L ₂ ... lens second group, L ₃ ... lens third group, A ... object point, B ... image point

Claims (1)

[Claims] 1. A first group is positive, a second group is negative, and a third group is from the object side.
An optical system in which a group is composed of a plurality of lens groups each including a positive lens group, wherein the first group and the third group are fixed,
Two focal lengths that move the second lens group in the direction of the optical axis so that wide-angle and telephoto systems can be photographed at both ends and in the vicinity thereof, and that the focus of the subject is adjusted by the focus movement that accompanies the movement of the second lens group. In the optical system, the focal length of the first group is f ₁ , and the focal length of the second group is
When f ₂ and the image point distance of the third lens unit are b _3, and the combined focal length at the wide-angle end is fw, 0.1 <fw / f ₁ <0.5 0.3 <| fw / f ₂ | <1.2 0.3 A two-focal length optical system characterized by satisfying the conditions of <fw / b ₃ <1.2.