JPH10260352A - Ttl finder optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high finder power even if the focal length of a photography optical system as an objective is short and an image inversion system is present in the optical path of a finder ocular optical system between a real image formation plane and a pupil plane. SOLUTION: To make the actual length of the optical path of the finder ocular optical system G2 long, the finder ocular optical system G2 has a positive lens group FI and a negative lens group FII arranged in order from its image plane side to the pupil plane and its principal point is moved forward. The positive lens group FI is composed of two thick convex lenses L11 and L12 and then the interval between principal points is widened to make the overall lens length long without varying the focal length of the whole optical system. A concave lens is used as a lens L10 of the positive lens group FI of the finder ocular optical system G2 nearby the real image plane. The 1st surface of the said lens L10 is made plane and matched with the real image plane. The negative lens group FII is composed of two lenses which are a convex lens L13 and a concave lens L14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a finder optical system used for a camera such as a lens shutter camera, a video camera, and a digital camera. TTL (Through the Taking Le) observed with an optical system
ns) TTL system suitable for TTL finder system
It relates to a finder optical system.

[0002]

2. Description of the Related Art In recent years, a digital camera or the like is used, and a subject image is captured by a solid-state image sensor such as a CCD (Charge Coupled Device) image sensor, and a still image (still image) or a moving image (movie image) of the object is captured. 2. Description of the Related Art Cameras of the type that obtains image data of (1) and digitally records the data on an IC (integrated circuit) card or a video floppy disk are rapidly spreading. In this case, the IC card is a PCMCIA (Personal Computer Memory Card In).
PC cards, which are IC cards conforming to the ternational Association (PC Memory Card International Association) standard, are generally used.

[0003] This type of digital camera includes the components and components of a conventional camera using a silver halide film, ie, the body and optical system of a single-lens reflex camera (single-lens reflex camera) of a silver halide camera. There are a relatively large one incorporated therein and a relatively small one corresponding to a rangefinder-lens shutter type compact camera in a silver halide camera.

On the other hand, the performance of a conventional compact camera such as a so-called 35 mm lens shutter camera using a 35 mm silver halide film or a single-lens reflex camera is remarkably improved. For example, a compact camera is equipped with a variable focal length photographing lens such as a zoom lens, and further, its zoom ratio (zoom ratio) is enlarged.

In a finder system used for various cameras, a real image type finder system for forming a real image of a subject by an objective optical system and providing the real image to a user for observation through an eyepiece optical system is an objective optical system. It is suitable for configuring a TTL finder finder optical system using a photographing optical system as a system. This is because the photographing optical system is originally a lens system that forms a real image of a subject on a light receiving surface or a film surface of a solid-state imaging device using a CCD or the like. Such a TTL finder optical system is particularly suitable for a finder system of a digital camera or a video camera because a finder image equivalent to an actual photographed image can be observed and a diopter can be controlled relatively easily. It is.

A conventional example of a real image type finder system is disclosed in Japanese Patent Application Laid-Open No. 5-341187 filed by the present applicant. The real image type viewfinder disclosed in Japanese Patent Application Laid-Open No. 5-341187 has a description that "an objective lens and an eyepiece, both having a positive refractive power, have a positive refractive power in order from the object side. A first lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power.
Forming a real image between the group and the eyepiece, configured to observe the real image via the eyepiece, increasing the magnification by moving the second group from the object side to the eyepiece side, The diopter change accompanying the increase in magnification is corrected by moving the fourth lens unit. "

[0007] JP-A-5-341187 discloses that
It is shown that an image reversing system using a prism for reversing an observed image into an erect image and an eyepiece are arranged between a real image forming surface of a subject and a pupil surface by an objective lens of a real image type variable magnification finder. Have been. In this case, the image inversion system forms a lens system having a positive refractive power, and the eyepiece also has a positive refractive power.

[0008]

Generally, in a finder system, it is desirable to always obtain a high finder magnification, that is, a finder magnification sufficiently close to "1". However, when the TTL finder optical system is configured by using the optical system between the real image forming plane and the pupil plane of the real image type variable magnification finder described in Japanese Patent Laid-Open No. 5-341187 described above, When combined with an objective lens having a short distance, a sufficiently high finder magnification cannot be obtained. The TTL finder optical system includes a photographing optical system and a finder eyepiece optical system.

That is, a photographing optical system that functions as an objective lens in the TTL finder optical system is an optical system from the real image forming surface to the pupil plane by the photographing optical system. It is called. TTL
In the finder optical system, in order to realize a high finder magnification in combination with an imaging optical system having a short focal length, it is necessary to shorten the focal length of the finder eyepiece optical system. On the other hand, in order to properly invert the image, the actual length of the finder eyepiece optical system must be increased, which is inconsistent with the aforementioned requirement of shortening the focal length. Ingenuity is required.

The present invention has been made in view of the above circumstances, and has a short focal length of a photographic optical system as an objective lens, and is provided in an optical path of a finder eyepiece optical system between a real image forming surface and a pupil surface. It is an object of the present invention to provide a TTL finder optical system capable of obtaining a high finder magnification even when an image inversion system exists. A second object of the present invention is to provide a TTL finder optical system capable of observing a subject image equivalent to that at the time of photographing at low cost.

A third object of the present invention is to provide a TTL finder optical system capable of appropriately correcting aberrations. An object of claim 4 of the present invention is to provide a TTL finder optical system capable of reducing the manufacturing cost. An object of claim 5 of the present invention is to provide a TTL finder optical system that can realize better aberration correction. An object of claim 6 of the present invention is to provide a photographing optical system in which an exit pupil position is sufficiently separated from an image plane, a sufficiently long back focus can be secured, and a high angle of view, a bright image, and a large zoom ratio are obtained. An object of the present invention is to provide a TTL finder optical system that can secure a high finder magnification even when an optical system is used.

[0012]

According to the first aspect of the present invention, there is provided a TTL finder optical system for directly observing a real image formed by a photographing optical system in order to achieve the above object. Wherein a finder eyepiece optical system disposed between a real image forming plane and a pupil plane by the photographing optical system includes a positive lens group and a negative lens group each including a plurality of lenses, and It is characterized in that, of the plurality of lenses constituting the lens group, the lens near the real image forming plane by the photographing optical system is constituted by a negative lens.

The TTL finder optical system according to the present invention according to the present invention is arranged closest to a real image forming plane of the photographing optical system among a plurality of lenses constituting a positive lens group of the finder eyepiece optical system. The negative lens is characterized in that the first surface of the negative lens is made flat and coincides with the real image plane. TT according to the invention as claimed in claim 3
The L finder optical system is characterized in that the negative lens group of the finder eyepiece optical system is composed of one positive lens and one negative lens.

In the TTL finder optical system according to the present invention, the positive lens group of the finder eyepiece optical system includes at least one convex lens, and the absolute value of the radius of curvature of the convex surface forming the convex lens is equal to or larger than the convex lens. It is characterized by being equal. The TTL finder optical system according to the present invention described in claim 5 is characterized in that the negative lens group of the finder eyepiece optical system includes a negative lens having at least one surface formed as an aspheric surface.

In a TTL finder optical system according to a sixth aspect of the present invention, the photographing optical system includes a first group optical system having a negative refractive power in order from the object side to the image side, and a positive refractive power. A second group optical system having a positive refractive power and a third group optical system having a positive refractive power, and a stop which moves integrally with the second group optical system during zooming is provided on the object side of the second group optical system. During zooming from the wide-angle end to the telephoto end, the first group optical system first moves on the optical axis to the image side, and reverses the moving direction to the object side on the way, thereby forming a convex arc convex on the image side. The second group optical system moves monotonously on the optical axis to the object side to perform magnification, and the third group optical system first moves the object on the optical axis. Move to the side,
By inverting the moving direction to the image side in the middle, the lens is moved in a convex arc shape convex to the object side to perform zooming, and the M-th group optical system (M =
When the focal length of 1 to 3) is f _M , the combined focal length of the entire system at the wide-angle end is f _W , and the distance between the final lens surface and the image plane of the third group optical system at the wide-angle end is bf _W , (1) 2.4 <| f ₁ | / f _W <2.6 (f ₁ <0) (2) f ₃ / f _W <6.8 (f ₃ > 0) (3) _{37 <f 2 / f 3 <} 0.41 (f 2> 0, f
₃ > 0), and (4) a zoom optical system that satisfies 1.75 <bf _W / f _W.

[0016]

That is, the TTL finder optical system according to the first aspect of the present invention is a TTL finder optical system for directly observing a real image formed by a photographic optical system. A finder eyepiece optical system disposed between the positive lens group and the negative lens group, each of which includes a plurality of lenses, and the photographing optical system of the plurality of lenses forming the positive lens group. The lens near the real image forming plane is constituted by a negative lens. With such a configuration, even if the focal length of the photographing optical system as the objective lens is short and the image inverting system exists in the optical path of the finder eyepiece optical system between the real image forming plane and the pupil plane, a high finder magnification is obtained. Can be obtained.

A TTL finder optical system according to a second aspect of the present invention is a lens disposed closest to a real image forming surface of a photographing optical system among a plurality of lenses constituting a positive lens group of a finder eyepiece optical system. Is made to be a flat surface and coincide with the real image surface. With such a configuration, it is possible to observe a subject image equivalent to that at the time of shooting at low cost. TT according to claim 3 of the present invention
In the L finder optical system, the negative lens group of the finder eyepiece optical system includes one positive lens and one negative lens. With such a configuration, it is particularly possible to appropriately perform aberration correction.

In a TTL finder optical system according to a fourth aspect of the present invention, the positive lens group of the finder eyepiece optical system includes one or more convex lenses, and the convex surfaces forming the convex lenses have the same radius of curvature. Such a configuration makes it possible to reduce the manufacturing cost. Claim 5 of the present invention
In the TTL finder optical system according to the above, the negative lens group of the finder eyepiece optical system includes a negative lens in which at least one surface is formed as an aspheric surface. With such a configuration, more favorable aberration correction can be realized.

In a TTL finder optical system according to a sixth aspect of the present invention, the photographing optical system includes, in order from the object side to the image side, a first group optical system having a negative refractive power, and a second optical system having a positive refractive power. A second-group optical system and a third-group optical system having a positive refractive power are provided, and a stop that moves integrally with the second-group optical system during zooming is provided on the object side of the second-group optical system. When zooming from the zoom lens to the telephoto end, the first group optical system first moves on the optical axis to the image side, and in the middle of the movement, reverses the moving direction to the object side, so that the first group optical system moves in a convex arc shape convex toward the image side and focuses. The second group optical system monotonically moves to the object side on the optical axis to perform the magnification change, and the third group optical system first moves to the object side on the optical axis, By reversing the moving direction to the image side with, moving in a convex arc shape convex to the object side to perform zooming, Optics (M = 1 to 3) The focal length f _M of the entire synthetic focal length f _W of the wide-angle end, bf the distance between the final lens surface and the image plane of the third group optical system at the wide-angle end _W Where: (1) 2.4 <| f ₁ | / f _W <2.6 (f ₁ <0) (2) f ₃ / f _W <6.8 (f ₃ > 0) _{(3) 0.37 <f 2 /} f 3 <0.41 (f 2> 0, f
₃ > 0) (4) Includes a zoom optical system that satisfies 1.75 <bf _W / f _W.

With such a configuration, as the photographing optical system, the position of the exit pupil can be sufficiently separated from the image plane, and a sufficiently long back focus can be ensured. Even if a system is used, a high finder magnification can be secured.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a TTL finder optical system according to the present invention will be described in detail based on embodiments with reference to the drawings. 1 and 2 show a configuration of a main part of a TTL finder optical system according to one embodiment of the present invention. FIG. 1 is an optical system layout diagram showing the configuration of the TTL finder optical system, and FIG. 2 is a perspective view schematically showing the configuration when the TTL finder optical system of FIG. 1 is incorporated in a camera.

The symbols ω, R,
D, Nd and νd are respectively: ω: half angle of view R: radius of curvature of the optical surface D: surface distance from the immediately preceding optical surface Nd: refractive index of the optical material of the lens νd: Abbe number of the optical material of the lens Shall be.

In this embodiment, in combination with a known photographing optical system having a short focal length, a finder eyepiece according to the present invention having a sufficient actual finder optical path and a sufficient optical path length for bending and guiding a light beam while securing a high finder magnification. An optical system is proposed. With this finder eyepiece optical system and the photographing optical system,
A TTL finder optical system according to this embodiment is configured.
The TTL finder optical system shown in FIG.
And a finder eyepiece optical system G2.

FIG. 1 shows a state in which the photographing optical system G1, which is a zoom lens, is set at the short focal length end, that is, at the wide angle end WIDE. The photographing optical system G1 includes a first lens group TI as a first group optical system, a second lens group TII as a second group optical system, and a third group optical system sequentially from the object, that is, the object side to the image side. Certain third lens group TIII
Is arranged. The first lens group TI has a negative refractive power, and the second lens group TII and the third lens group TIII
It has a positive refractive power. The stop S provided on the object side of the second lens group TII moves integrally with the second lens group TII during zooming for changing the focal length.

In zooming from the wide-angle end to the telephoto end shown in FIG. 1, the first lens unit TI first moves on the optical axis to the image side, and reverses the moving direction to the object side on the way.
Moves in a convex arc shape convex to the image side to correct the fluctuation of the focal position,
The second lens group TII monotonously moves on the optical axis to the object side to perform zooming, and the third lens group TIII moves first on the optical axis to the object side, and in the middle, moves the moving direction to the image side. By reversing, zooming is performed by moving in a convex arc shape convex toward the object side. Aperture S
Moves integrally with the second lens group TII during zooming, so that the stop S does not hinder the movement of the second lens group TII.

The focal length of the M-th lens unit (M = 1 to 3) is f _M , the combined focal length of the entire system at the wide-angle end is f _W , and the final lens surface and image plane of the third lens unit at the wide-angle end are The distance, that is, the back focus length at the wide angle end, is bf
_{When W} is set, these conditions are as follows: Condition (1) 2.4 <| f ₁ | / f _W <2.6 (f ₁ <
0), condition (2) f ₃ / f _W <6.8 (f ₃ > 0), condition (3) 0.37 <f ₂ / f ₃ <0.41 (f ₂ >)
0, f ₃ > 0) and condition (4) 1.75 <bf _W / f _W are satisfied.

Condition (1) is a condition for restricting the range of the focal length f ₁ of the first lens unit TI in order to reduce the size of the entire system and favorably correct aberrations. The negative refracting power of TI becomes too strong, which is advantageous for miniaturization of the whole lens system, but is not preferable because various aberrations such as spherical aberration deteriorate. When the value exceeds the upper limit of the condition (1), the aberration is improved, but it is difficult to reduce the size of the entire lens system. Condition (2) is a condition for restricting the positive refractive power of the third lens unit TIII.
The positive refractive power of III becomes insufficient, the exit pupil position approaches the image plane, and telecentricity is lost.

The condition (3) is a condition for regulating the distribution of the refractive power of the second lens group TII and the third lens group TIII, both of which have a positive refractive power. The second lens group TII and the third lens group TIII Are conditions for keeping the number of components small, facilitating miniaturization, and favorably correcting aberrations.
When the value is less than the lower limit of the condition (3), the refractive power of the third lens unit TIII becomes insufficient, and the effect of using the third lens unit TIII decreases. In order to supplement the refractive power of the third lens unit TIII,
The load of the refracting power of the second lens group TII becomes excessive, so that the spherical aberration deteriorates and the flatness of the image also deteriorates.

When the value exceeds the upper limit of the condition (3), the refractive load on the third lens unit TIII is increased, the refractive load on the second lens unit TII is reduced, the aberration is improved, and the flatness of the image is improved. However, the negative refractive power of the first lens unit TI and the positive refractive power of the second lens unit TII both tend to be weak, which makes it difficult to reduce the size of the entire optical system. Condition (4)
Is related to the back focus, and if the lower limit is exceeded, it becomes difficult to provide an optical element used for optical path division and optical path switching.

The first lens group TI includes three lenses L1,
The second lens group TII is composed of five lenses L4, L5, L6, L7 and L8, and the third lens group TIII is composed of one lens L9. In a camera for photographing with a solid-state imaging device such as a CCD imaging device, a cover glass and a filter (not shown) for protecting the solid-state imaging device are arranged behind the third lens group TIII, and a light-receiving surface of the solid-state imaging device is provided. Is imaged. The filter includes an infrared light shielding filter and a low-pass filter, and may further include a color filter for color separation.

In order to constitute a finder optical system, an optical element R such as a half mirror for splitting an optical path or switching an optical path is provided behind the third lens group TIII, that is, on the image side.
M (see FIG. 2) is provided to guide the light beam of the photographing optical system G1 to the finder eyepiece optical system G2. Since the optical element RM merely deflects and guides the optical path, it is irrelevant to the optical system arrangement and is not shown in the optical system arrangement diagram of FIG. The finder eyepiece optical system G2 has a positive lens group FI and a negative lens group FII. Positive lens group FI and negative lens group FII
Are arranged in the order of a positive lens unit FI and a negative lens unit FII from the image plane side to the pupil plane side, and the finder eyepiece optical system G2
Is composed.

The positive lens group FI includes three lenses L10,
L11 and L12, and these three lenses L10, L11 and L12 are sequentially arranged in the order of L10, L11 and L12 from the image plane side to the pupil plane side. The lens L10 is a concave (negative) lens having the first surface as a plane, and the lenses L11 and L12 are both thick convex (positive) lenses. The lens L1 immediately after the optical element RM
0 is arranged such that the first plane, which is a plane, coincides with the image plane. The thick convex lenses L11 and L12 are respectively
A convex lens in which the absolute values of the radii of curvature of both surfaces are matched to form a symmetrical convex surface on both surfaces, and for reversing the image direction to form an erect erect image and bending the optical path to secure the optical path length. It is configured as a prism.

That is, the thick convex lenses L11 and L11
Reference numeral 12 designates a convex lens, with the entrance surface and the exit surface of the prism being convex surfaces having the same absolute value of the radius of curvature. The negative lens unit FII includes two lenses L13 and L1.
4 and these lenses L13 and L14 are
L13 and L14 are sequentially arranged in order from the image plane side to the pupil plane side. The lens L13 is a convex (positive) lens, and the lens L14 is a concave (negative) lens.

That is, the finder eyepiece optical system G2 is
In order to lengthen the actual length of the optical path, the positive lens group FI is arranged in the order of the negative lens group FII from the image plane side to the pupil plane, and the principal point position is pushed further forward. further,
The positive lens group FI is configured by using two convex lenses L11 and L12, and by increasing the thickness of both lenses L11 and L12, the distance between the principal points is widened and the lens is not changed without changing the focal length of the entire optical system. The total length is longer.

However, since the negative lens unit FII is arranged on the pupil plane side, an appropriate eye point cannot be secured unless the light beam height of the positive lens unit FI is increased. On the other hand, the exit light beam of the photographing optical system G1 has its exit pupil position sufficiently separated from the image plane to enhance telecentricity, and
The effect of shading, vignetting, color misregistration, and the like in the D imaging device and the like is reduced. Therefore, the lens L10 near the real image plane in the positive lens group FI of the finder eyepiece optical system G2 is configured as a concave lens so as to guide a light beam to a desired eye point.

Further, the first surface of the lens L10 near the real image plane by the photographing optical system G1 was made to be the same as the real image plane as a plane. By providing a target mark or the like for displaying information on this plane, it is not necessary to separately provide an information display or the like for displaying information in the finder. For aberration correction, the negative lens unit FII is composed of two lenses, a convex lens L13 and a concave lens L14, and achieves good aberration correction.

[0037]

Next, two embodiments of the TTL finder optical system having such a configuration will be described. First, Tables 1 to 5 show lens data in the first example. Table 1
Table 2 shows the data of the finder eyepiece optical system G2. Table 3 shows the variable range of the variable portion, and Table 4 shows the data of the aspherical surface. The numerals 1 to 30 in FIG. 1 indicate the surface numbers of the respective surfaces of the lenses L1 to L3, the aperture S, and the lenses L4 to L14.

[0038]

[Table 1] Imaging optical system

[0039]

[Table 2] Viewfinder eyepiece optical system

In Tables 1 and 2, the radius of curvature R is set to "0.
“00000” means that the radius of curvature R is infinity (∞), and indicates that the surface is flat. Therefore, the aperture S and the finder eyepiece optical system G
The twentieth surface closest to the real image plane of the concave lens L10 closest to the real image plane in the second positive lens group FI is arranged as a plane and coincident with the real image plane. Also, the convex lens L1 of the positive lens group FI
Both surfaces of the convex lens L12 have opposite radii and equal curvature radii R, and both surfaces of the convex lens L12 have opposite radii.

In Table 1, the surface spacing between the sixth, seventeenth, and nineteenth surfaces where the surface spacing D was "variable" and the surface immediately after these surfaces was, as shown in Table 3, the wide-angle end. It can be changed in the range of Table 3 between WIDE, intermediate focal length MEAN, and telephoto end TELE. As shown in Table 4, the focal length of the photographing optical system G1 is 5.20 mm at the wide-angle end WIDE, and the intermediate focal length.
MEAN is 8.80mm and telephoto end TELE is 14.99mm.

[0042]

[Table 3] Variable range of surface spacing

[0043]

Table 4 Variable range of focal length of photographing optical system

Regarding the fifth surface and the eighth surface in Table 1, the symbol "* (asterisk)" is added to the surface number to indicate that the surface is aspherical. It has an aspherical shape defined by giving the parameters shown in Table 5 to the aspherical expression. That is, no aspherical surface is used in the finder eyepiece optical system G2 according to the first embodiment.

[0045]

X = CY ² / ｛1+ [1- (1 + k) C ² Y
² ] ^1/2 ｝ + A4Y ⁴ + A6Y ⁶ + A8Y ⁸ + A10Y
¹⁰ However, C = 1 / R

[0046]

[Table 5] Aspherical surface

FIGS. 3 to 5 show aberration diagrams in the first embodiment described above. 3 to 5, broken lines indicate sine conditions, and solid lines C, d, and F indicate wavelengths of 656.28 nm, respectively.
C, the d-line at a wavelength of 587.56 nm, and the F-line at a wavelength of 486.13 nm. FIG. 3 shows the spherical aberration when the imaging optical system is at the wide-angle end WIDE and the half angle of view ω is 27.3 °,
FIG. 4 is an aberration diagram showing astigmatism and distortion.
Has an intermediate focal length MEAN and a half angle of view ω of 16.5 °
FIG. 5 is an aberration diagram showing spherical aberration, astigmatism, and distortion when the zoom lens is in a state of.
FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, and distortion when LE has a half angle of view ω of 9.8 °. It can be seen that the aberration is well corrected in any of FIGS.

Next, Tables 6 to 9 show lens data in the second embodiment. Table 5 shows data of the photographing optical system G1, which is exactly the same as Table 1 in the first embodiment. Table 6 shows the data of the finder eyepiece optical system G2 in the second embodiment, which is slightly different from Table 2 in the first embodiment. Table 7 shows the variable range of the variable portion and Table 8 shows the data of the aspherical surface.

[0049]

[Table 6] Imaging optical system

[0050]

[Table 7] Viewfinder eyepiece optical system

In Tables 6 and 7, similarly to Tables 1 and 2, the radius of curvature R = 0.
= ∞, indicating that the surface is flat.
Accordingly, the stop S and the twentieth surface closest to the real image surface of the concave lens L10 closest to the real image surface of the positive lens group FI of the finder eyepiece optical system G2 are arranged so as to coincide with the real image surface. Also, both surfaces of the convex lens L11 of the positive lens group FI have opposite signs and have the same radius of curvature R, and both surfaces of the convex lens L12 also have opposite signs and have the same radius of curvature R.

In Table 6, the distance between the surfaces immediately before the sixth surface, the seventeenth surface, and the nineteenth surface when the inter-surface angle D is “variable” is from the wide-angle end WIDE to the intermediate focal length MEAN to the telephoto end TELE. Can be changed within the range of Table 8 similar to Table 3. As shown in Table 9, the focal length of the photographing optical system G1 is
The wide-angle end WIDE is 5.20 mm, the intermediate focal length MEAN is 8.80 mm, and the telephoto end TELE is 14.99 mm.

[0053]

[Table 8] Variable range of surface spacing

[0054]

Table 9: Variable range of focal length of photographing optical system

In Table 6, the fifth surface, the eighth surface and the twenty-eighth surface, which indicate that the surface is an aspherical surface by adding "*" to the surface number, are respectively given by the aspherical expression of Formula 1. Table 1
It has an aspherical shape defined by giving a parameter shown as 0. In the case of the second embodiment, the photographing optical system is exactly the same as that of the first embodiment. In Table 10, the fifth and eighth surfaces are the same as those in Table 4. In this case, the 28th surface, which is the object-side surface of the concave lens L14 closest to the pupil surface of the negative lens unit FII of the finder eyepiece optical system G2, is made aspheric, so that aberrations can be corrected more favorably.

[0056]

[Table 10] Aspherical surface

FIGS. 6 to 8 show aberration diagrams in the second embodiment described above. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion when the photographing optical system is at the wide-angle end WIDE and the half angle of view ω is 27.3 °. FIG. Aberration diagrams showing spherical aberration, astigmatism, and distortion aberrations when the half angle of view ω is 16.5 ° at the distance MEAN,
FIG. 8 shows that the photographing optical system is at the telephoto end TELE and the half angle of view ω is 9.
FIG. 9 is an aberration diagram showing spherical aberration, astigmatism, and distortion when the angle is 8 °. 6 to 8, it can be seen that the aberration is more sufficiently corrected than in the case of FIGS. 3 to 5 of the first embodiment. Viewfinder eyepiece optical system G in the first and second embodiments described above
The full length of 2 and the shooting optical system at each are wide-angle end WIDE,
Table 11 shows the finder magnification (image magnification) of the intermediate focal length MEAN and the telephoto end TELE.

[0058]

[Table 11]

According to Table 11, even when an image pickup optical system having a short focal length is used, the entire length of the finder eyepiece optical system G2 is set to a sufficient length for image inversion, and the photographing optical system is used at the wide-angle end.
It can be seen that a high finder magnification is obtained in any of the WIDE, intermediate focal length MEAN and telephoto end TELE situations. As described above, in the TTL finder optical system, the finder eyepiece optical system combined with the photographing optical system having a short focal length is devised so that a high finder magnification can be secured and the actual length for image inversion can be increased. Can be Further, since a lens having a plane that matches the real image plane is included, display information at the time of shooting can be provided at low cost by using the plane.

The finder eyepiece optical system G2 is composed of a positive lens group FI and a negative lens group FII, and each of the positive lens group FI and the negative lens group FII is composed of a combination of a positive lens and a negative lens. Thus, a TTL finder optical system in which aberration is appropriately corrected can be obtained.
In addition, the thick convex lens L of the finder eyepiece optical system G2
By making the convex lenses 11 and L12 symmetrical in shape, the manufacturing cost of the TTL finder optical system can be reduced.

Further, by using an aspherical lens for the negative lens unit FII, a TTL finder optical system with better aberration correction can be obtained. In addition, a high finder can be obtained even if the exit pupil position is sufficiently separated from the image plane, and a sufficiently long back focus is secured. The magnification can be secured.

[0062]

As described above, according to the present invention, there is provided a TTL finder optical system for directly observing a real image formed by a photographing optical system, wherein a real image forming plane and a pupil plane are formed by the photographing optical system. The finder eyepiece optical system disposed between the positive lens group and the negative lens group, each of which includes a plurality of lenses, and a real image formed by the photographing optical system among the plurality of lenses forming the positive lens group By forming the lens in the vicinity of the imaging plane with a negative lens, the focal length of the photographing optical system as the objective lens is short, and the image inverting system is located in the optical path of the finder eyepiece optical system between the real image imaging plane and the pupil plane. TTL that can obtain high finder magnification even when
A finder optical system can be provided.

According to the TTL finder optical system of the second aspect of the present invention, of the plurality of lenses constituting the positive lens group of the finder eyepiece optical system, the lens is arranged closest to the real image forming plane of the photographing optical system. By making the first surface of the lens a flat surface and matching the real image surface, it is possible to observe display information at the time of photographing at low cost, particularly by using the flat surface.

According to the TTL finder optical system of the third aspect of the present invention, the negative lens group of the finder eyepiece optical system is
By using a combination of one positive lens and one negative lens, it is particularly possible to appropriately correct aberrations. According to the TTL finder optical system of claim 4 of the present invention, the positive lens group of the finder eyepiece optical system includes one or more convex lenses, and has a configuration in which the absolute values of the radii of curvature of the convex surfaces forming the convex lenses are equal. In particular, the manufacturing cost can be reduced. According to the TTL finder optical system of the present invention, the negative lens group of the finder eyepiece optical system includes a negative lens in which at least one surface is formed as an aspherical surface, thereby achieving better aberration correction. Can be.

Further, according to the TTL finder optical system of the sixth aspect of the present invention, the photographing optical system includes, in order from the object side to the image side, a first group optical system having a negative refractive power; A second group optical system having a power and a third group optical system having a positive refractive power are provided, and a stop which moves integrally with the second group optical system during zooming is provided on the object side of the second group optical system. Along with zooming from the wide-angle end to the telephoto end,
The first group optical system first moves on the optical axis to the image side, and in the middle, reverses the moving direction to the object side, thereby moving in a convex arc shape convex on the image side, and correcting the change of the focal position. The two-group optical system monotonously moves on the optical axis to the object side to perform zooming, and
The group optical system first moves to the object side on the optical axis, and in the middle, reverses the moving direction to the image side to move in a convex arc shape convex to the object side to perform zooming. The focal length of (M = 1 to 3) is f _M , the combined focal length of the entire system at the wide-angle end is f _W , and the distance between the final lens surface and the image plane of the third group optical system at the wide-angle end is bf _W. When these conditions are satisfied: (1) 2.4 <| f ₁ | / f _W <2.6 (f ₁ <0) (2) f ₃ / f _W <6.8 (f ₃ > 0) (3) _{) 0.37 <f 2 / f 3} <0.41 (f 2> 0, f
₃ > 0) (4) The zoom lens system includes a zoom optical system satisfying 1.75 <bf _W / f _W.

By adopting such a structure, the exit pupil position can be sufficiently separated from the image plane and a sufficiently long back focus can be ensured as a photographing optical system. Even if an optical system having a specific ratio is used, a high finder magnification can be secured.

[Brief description of the drawings]

FIG. 1 is an optical system layout diagram schematically showing a configuration of a TTL finder optical system according to one embodiment of the present invention.

FIG. 2 is a perspective view schematically showing a configuration of a main part in a state where the TTL finder optical system of FIG. 1 is actually incorporated in a camera.

FIG. 3 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion at a wide-angle end according to the first example of the TTL finder optical system of FIG. 1;

FIG. 4 is an aberration diagram showing spherical aberration, astigmatism, and distortion at an intermediate focal length according to the first example of the TTL finder optical system of FIG. 1;

FIG. 5 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end according to the first example of the TTL finder optical system of FIG. 1;

FIG. 6 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion at a wide-angle end according to a second example of the TTL finder optical system of FIG. 1;

FIG. 7 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion at an intermediate focal length according to the second example of the TTL finder optical system in FIG. 1;

8 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion at a telephoto end according to a second example of the TTL finder optical system of FIG. 1;

[Explanation of symbols]

 G1 Photographing optical system G2 Viewfinder eyepiece optical system TI First lens group TII Second lens group TIII Third lens group FI Positive lens group FII Negative lens group L1 to L14 Lens RM Optical path switching optical element 1 to 30 Surface number 20 Real image Plane 30 pupil plane S aperture

Claims (6)

[Claims] 1. A TTL finder optical system for directly observing a real image formed by a photographing optical system, wherein a finder eyepiece optical system disposed between a real image forming surface of the photographing optical system and a pupil surface is provided. A positive lens group and a negative lens group each including a plurality of lenses, and a lens in the vicinity of a real image forming plane by the photographing optical system among a plurality of lenses configuring the positive lens group was configured as a negative lens. TTL finder optical system characterized by the above-mentioned. 2. A plurality of lenses constituting a positive lens group of a finder eyepiece optical system, wherein a first surface of a negative lens arranged closest to a real image forming surface of the photographing optical system is
2. The TTL finder optical system according to claim 1, wherein the TTL finder optical system is configured to be flat and coincide with a real image plane. 3. A negative lens group of a finder eyepiece optical system,
3. The TTL finder optical system according to claim 1, wherein the TTL finder optical system comprises one positive lens and one negative lens. 4. The positive lens group of the finder eyepiece optical system includes:
The TTL finder optical system according to any one of claims 1 to 3, wherein the TTL finder optical system includes one or more convex lenses, and the convex surfaces forming the convex lenses have the same radius of curvature. 5. The negative lens group of the finder eyepiece optical system comprises:
The TTL finder optical system according to any one of claims 1 to 4, further comprising a negative lens having at least one surface formed as an aspheric surface. 6. The photographing optical system has, in order from the object side to the image side, a first group optical system having a negative refractive power, a second group optical system having a positive refractive power, and a positive refractive power. A third-group optical system is provided, and a stop that moves integrally with the second-group optical system during zooming is provided on the object side of the second-group optical system, and when zooming from a wide-angle end to a telephoto end, the first group is set. The group optical system first moves on the optical axis to the image side, and in the middle of the movement, reverses the moving direction to the object side, thereby moving in a convex arc shape convex on the image side to correct the fluctuation of the focal position, and The group optical system monotonously moves on the optical axis to the object side to perform zooming, and the third group optical system first moves on the optical axis to the object side, and reverses the moving direction to the image side on the way. Then, the lens is moved in a convex arc shape convex toward the object side to perform zooming, and the focal length of the M-th optical system (M = 1 to 3) _M, when the distance bf _W of the composite focal length of the entire system at the wide-angle end f _W, the final lens surface and the image plane of the third group optical system at the wide angle end, they conditions: (1) 2.4 <| F ₁ | / f _W <2.6 (f ₁ <0) (2) f ₃ / f _W <6.8 (f ₃ > 0) (3) 0.37 <f ₂ / f ₃ <0 .41 (f ₂ > 0, f ₃
> 0) (4) The TTL finder optical system according to any one of claims 1 to 5, including a zoom optical system that satisfies 1.75 <bf _W / f _W.