JPS5997124A - Zoom lens having single lens reflex finder - Google Patents

Abstract

PURPOSE:To reduce the size of a lens by providing a mirror for branching optical path behind a diaphragm and setting the area of a reflection surface and the max. stop quantity of the diaphragm. CONSTITUTION:A diaphragm 7 is so formed as to have the aperture to allow partial passage of incident light in a max. stop state. A mirror 8 for branching optical path is disposed behind the diaphragm 7 on the optical axis and is a mirror which reflects light substantially totally. The diameter of said mirror is so set as to be roughly equal to the aperture area of the diaphragm 7 in the max. stop state. A part of an incident luminous flux 17 is reflected by the reflection part 16 of the mirror 8 and is made incident as a branched luminous flux 18 to a single lens reflex finder to conduct the quantity of the light corresponding to the brightness of an object to the finder irrespectively of the stop state of the diaphragm 7. The distance from the top end of the lens to the diaphragm is thus reduced and the lens is made smaller in size.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a zoom lens having a single-lens reflex finder suitable for television cameras and the like.

[Prior art]

Conventionally, the finder of a zoom lens used in a video camera is generally a single-lens reflex type in which the optical path is split by a half mirror in the middle of the photographing optical system. The optical path branching mirror used in this eye reflex system is provided in front of the diaphragm on the subject side, and guides the viewfinder to a view according to the brightness of the subject, regardless of whether the diaphragm is opened or closed.

However, when placing an optical path branching mirror in front of the diaphragm, it is necessary to create a space between the diaphragm and the lens group in front of the diaphragm for the mirror to be placed, which inevitably leads to The distance increases.

For this reason, it is necessary to use a lens with a large outer diameter as the 1st lens group, which constitutes the front lens group, resulting in an increase in the size of the entire lens. Fl, 4 commonly used in video cameras
．． In the case of a 6x zoom lens, the distance from the diaphragm to the tip of the lens is approximately 50 m+ when no optical path splitting mirror is installed, but with the optical path splitting mirror installed, the distance is approximately 8 W.
Since it is necessary to widen the lens by approximately II+1, the outer diameter of the first lens group must be increased by approximately 20 inches. As described above, conventionally, in order to provide a single-lens reflex finder, it was inevitable to increase the size of the lens system.

On the other hand, in lenses combined with autofocus systems that automate focus adjustment, in order to eliminate visual discomfort caused by changes in the angle of view during operation, the first lens group has been moved, which was common in the past. Instead of the focus adjustment using the lens group V, a so-called rear focus method, in which focus adjustment is performed after the V-th lens group, is advantageous. When a single-lens reflex finder is provided using this focusing method, a lens group for adjusting the focus must be provided in front of the optical path branching mirror in order to detect blurring in the image with the finder.

In order to make the lens group movable, it is necessary to provide a space for it to move, but as a result, the size of the lens becomes unavoidable due to the same circumstances as the optical path branching mirror described above. becomes.

The distance required to move the lens is about half the distance required to insert the optical path branching mirror, but if both conditions are satisfied at the same time, the outer diameter of the lens will increase dramatically, making it impractical. It becomes difficult to submit the product to

[Purpose of the invention]

An object of the present invention is to eliminate the drawbacks of the above-mentioned prior art, to prevent the lens from increasing in size due to the provision of an optical path branching mirror, and in particular, to eliminate the drawbacks of the prior art, and in particular, to eliminate the drawbacks of the prior art.
A single-lens reflex camera that can be configured in 4'
The present invention provides a zoom lens having a finder.

[Summary of the invention]

In order to achieve this purpose, an optical path splitting mirror is provided behind the diaphragm, and the reflective surface area of the optical path splitting mirror is The maximum aperture amount of the aperture is set, and the distance from the leading edge of the lens to the aperture can be shortened, making it possible to downsize the lens.

[Summary of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a suppressed diagram showing an embodiment of a zoom lens having a single-lens reflex finder according to the present invention, and 1 is a suppressed view showing an example of a zoom lens having a single-lens reflex finder according to the present invention.
Lens groups, 2 is the V-th lens group, 3 is the V-th lens group, 4 is the 1st/2nd lens group, 5 is the V-th lens group, 6 is the image sensor, 7 is the diaphragm, 8 is the optical path branching mirror, 9 10 is an objective lens for the finder, 10 is an optical path changing mirror, 11 is a focusing plate, 12 is an objective lens system for the finder, 13 is an aperture opening/closing mechanism, 14
15 is an aperture control circuit, and 15 is a lens moving mechanism.

In the figure, an optical path branching mirror 8 is placed behind the aperture to form a rear focus type zoom lens, and a fixed gI lens group 1 is arranged along the optical axis from the lens subject side.
, a V-th lens group 2 that moves on the optical axis according to zooming.
, which also moves back and forth on the optical axis according to zooming.
Lens group 3, Vth lens group 4 that moves according to focus adjustment
, an aperture 7 whose aperture is adjusted according to the amount of light on the image plane of the image sensor 6, an optical path branching mirror 8, a fixed V-th lens group 5 that shares the imaging function, and a formed image.

An image sensor 6 that converts the signal into an optical signal is disposed, and on the optical path branched by the optical path branching mirror 8, there are a finder objective lens 9, an optical path changing mirror 10, a focusing plate 11, an erector lens, and an eyepiece lens. A finder eyepiece system 12 is arranged to form a single-lens viewfinder, and a lens moving mechanism 15 for moving the V-th lens group 4 is further provided to realize a rear focus system. .

The output of the image sensor 6 is applied to the aperture control circuit 14, and the output signal of this aperture control circuit 14 is supplied to the aperture opening/closing mechanism 13, which operates to adjust the illuminance of the image plane of the image sensor 6. teeth! The opening and closing of the diaphragm 7 is feedback-controlled so that it remains constant. The diaphragm 7 exhibits an aperture state so that a part of the incident light passes through even in the maximum aperture state, and has a maximum aperture diameter in the fully open state and a minimum aperture diameter in the maximum aperture state depending on the incident light. The aperture diameter changes between.

The optical path branching mirror 8 is placed behind the on-axis aperture 7, and is a mirror that almost completely reflects the light. The area projected onto is 1/20 of the maximum aperture area when the aperture 7 is fully open.
~115, which is set to be approximately equal to the aperture area of the aperture 7 in its maximum aperture state, and approximately 1/4 to 1/3 of the maximum aperture diameter when the aperture 7 is fully open. a) *(b) is an explanatory diagram showing the relationship between the aperture state of the aperture 7 and the reflection state of the incident light on the optical path branching mirror 8 in FIG. , 18 is a branched light beam, and 19 is a passing light beam.

Figure 2 (,) shows the aperture 7 fully open, and a part of the incident light beam 17 is reflected by the reflection part 16 of the optical path branching mirror 8, and as a branched light beam 18, the single-lens reflex finder (first
Figure). Incident light flux 1 that is not reflected by the reflection section 16
The remainder of the lens 7 is the passing light beam 19, and the V-th lens group 5 (the first
) and enters the image sensor 6 (FIG. 1).

As the sight of the incident light beam 17 increases, the amount of light of the passing light beam 19 also increases, and the image pickup device 6, aperture control circuit 14, and aperture control circuit 14 shown in FIG.
A feedback control system consisting of an aperture opening/closing mechanism operates the aperture 7 so that the image plane illuminance of the image sensor 6 is constant, and the aperture diameter of the aperture 7 is reduced.

FIG. 2(b) shows a state in which the diaphragm 7 is in the maximum aperture state corresponding to the fully closed state in a conventional aperture. At this time, the projected area of the incident light beam 17 of the reflection section 16 onto a plane perpendicular to the optical axis becomes approximately equal to the aperture area of the aperture 7, and the incident light beam 17 passing through the aperture 7
7 is reflected by the entire surface of the reflecting section 16.

In this way, regardless of the aperture state of the diaphragm 7, the incident light beam 17 is always reflected on the entire surface of the reflecting section 16, and the branched light beam 18 is not cut off in the middle of the optical path.

Therefore, the light amount of the branched light beam that enters the single-lens reflex finder is always proportional to the light amount of the incident light beam 17.In the prior art, a half mirror is provided in front of the diaphragm, and the branched light beam enters the single-lens reflex finder. Similar to the one that allows light to enter the viewfinder, the amount of light can be guided to the viewfinder according to the brightness of the subject, regardless of whether the aperture is opened or closed.
It would be possible to realize a viewfinder without shadows.

Therefore, by making the amount of light incident on the finder proportional to the amount of light incident on the subject, an optical path branching mirror can be installed behind the diaphragm without impairing the function of conventional finders, and the tip of the lens Since the distance from the zoom lens to the aperture diaphragm is reduced, the lens can be made more compact, and the overall configuration of the zoom lens can be made more compact.

The above was a case where the incident light flux was parallel to the lens optical axis, but
For example, if a light source is present at a close distance position offset from the lens optical axis, the light beam 21 passes through the aperture of the diaphragm 7 at an angle to the lens optical axis, as shown in FIG. , Furthermore, since the reflecting section 16 is inclined with respect to the diaphragm 7, the light passes between the diaphragm 7 and the reflecting section 16, and the second lens group 5
(FIG. 1) The light passes through the Z direction and is irradiated onto the image plane of the image sensor 6 (FIG. 1). This light beam 21 is incident on the periphery of the scanning surface of the image sensor 6, and due to the relationship between the reflection section 16 and the aperture of the diaphragm 7, the light amount of this light beam 21 is much larger than the sight of the light beam 20 parallel to the lens optical axis. If it becomes large, the brightness at the periphery of the imaging screen will increase abnormally. By the way, the video camera is equipped with a shading correction means, which performs shading correction. However, if there is a large difference in the brightness of the image due to the light beam 21, the shading correction will be performed excessively, and the central part of the screen will be distorted. This results in shadowing compared to the surrounding area.

4(a) and 4(b) are explanatory diagrams showing specific examples of the reflecting portion 16 of the optical path branching reflecting mirror 8 of FIG. 1 to solve these problems, respectively, and 22 is the outer periphery of the aperture aperture, 2
3 is a completely reflective part, 24 is a semi-transparent part @Figure 4 (a)
In this case, the shape of the reflecting part 16 is replaced with a simple circular one and is made into an elliptical shape that spreads from the center of the optical axis in the direction of the finder branch optical path. ) to reduce the amount of light.

In addition, in FIG. 4(b), part of the reflection part 16 is made into a complete reflection part 23, and the other part is made into a semi-transmission part 24, so that the reflection part 1
6, the reflectance is changed depending on the location, and a part of the light beam 20 parallel to the optical axis of the lens (Fig. 3) is allowed to pass therethrough.

In the case of the specific example shown in FIG. 4(a), the imaging of the light beam 21 obliquely incident on the optical axis of the lens is reduced, and the amount of light incident on the image plane of the lens 6 is reduced, and the specific example shown in FIG. 4(b) is In the case of the example, the amount of light incident on the image plane of the image sensor 6 of the light beam 20 that is incident parallel to the optical axis of the lens is increased, and in either case, the amount of light on the entire image surface of the image sensor 6 is increased. The same effect can be achieved by shading correction.

FIG. 5 is a perspective view showing the zoom lens having the single-lens reflex finder shown in FIG. , and parts corresponding to those in Figure 1 are given the same numbers.

In FIG. 5, a helicoid ( (not shown), the lens group 4 can be moved in the lens optical axis direction by the drive gear 25 and the drive mechanism 15, which are connected to the moving gear 26 provided on the support extension 27, in accordance with focus adjustment. has been done. In the focus lens constructed in this manner, the arrangement of the aperture 7 and the optical path branching mirror 8 is set as described above, so that the lens does not become particularly large, and is rather It would be possible to create a zoom lens that is more compact and more compact than other zoom lenses.

Note that the adjustment means for the aperture 7 may be configured mechanically and the aperture may be adjusted manually.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to make the view of the branched light branched into the finder always proportional to the amount of incident light without being affected by the aperture condition of the aperture, etc. It is now possible to position the optical path branching mirror behind the diaphragm on the optical axis of the lens, shortening the distance from the lens tip to the diaphragm.
The overall configuration can be downsized without impairing the quality of the finder, and it is possible to provide a zoom lens having a single-lens reflex finder with excellent functionality, except for the drawbacks of the prior art described above.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of a zoom lens having a single-lens reflex finder according to the present invention, Fig. 2 (&),
(b) shows the relationship between the aperture state of the diaphragm and the reflection state of the incident light on the optical path branching mirror in Fig. 1, and Fig. 3 shows an example of the incident state of the incident light in Fig. 1. 4(a) and 4(b) are explanatory diagrams showing other specific examples of the shape of the reflecting part of the optical path branching mirror in FIG. 1, respectively, and FIG. This is a perspective view showing a zoom lens with a finder. 1... 1st L/7 lens group, 2... 1st lens group,
3... No. 1 lens group, 7... Aperture, 8... Optical path branching mirror, 16... Reflective section, 23... Completely reflective section, 24... Semi-transmissive section. Agent Patent Attorney Take Tsujibe (and 1 other person) 1111 Figure 4 1I2 Figure 3B! 1 @Figure 4 (G) (b) Figure 15 4

Claims (1)

[Claims] In a zoom lens having a single-lens reflex funder, the first lens group, which is the front lens group, is fixed and is movable in the optical axis direction by a speed change operation, and the second lens group and an aperture. An optical path branching mirror is provided on the image plane side of the diaphragm to branch a part of the incident light to the finder, and the diaphragm has a minimum aperture diameter that allows part of the incident light to pass through in the maximum aperture state, and the optical path branching mirror The mirror has an aperture that reflects incident light in an area corresponding to the minimum aperture diameter of the aperture, and is configured such that the amount of light branched to the finder is proportional to the amount of the incident light. A single-lens reflex zoom lens that lacks a viewfinder.