JP2015034995A - Optical system and image capturing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel optical system.SOLUTION: An optical system includes: first lenses LA1 through LA3 for condensing incident light; a first prism PA having a reflective surface for reflecting light transmitting through the first lenses; second lenses LB1 through LB3 for condensing incident light entering from a direction different from that of the light entering the first lenses; and a second prism PB having a reflective surface for reflecting light transmitting through the second lenses. The reflective surface of the first prism and the reflective surface of the second prism are positioned to face each other.

Description

  The present invention relates to an optical system and an imaging system.

  2. Description of the Related Art As an imaging system for “imaging” the omnidirectional sphere, one using two wide-angle lenses is known (Patent Documents 1 and 2).

  Such an omnidirectional imaging system can simultaneously acquire image information in all directions (solid angle of 4π radians), and can be effectively used for surveillance cameras for cameras, in-vehicle cameras, and the like.

  For example, when news gathering is performed, if a small omnidirectional imaging system is used in a “hand-held state”, extremely accurate and fair image information can be recorded.

  It is also possible to take an image of the weather condition of the celestial sphere and use it for analysis of weather information.

  Furthermore, the landscape information can be imaged and used in advertising and art fields.

  In such an imaging system, two wide-angle lenses (so-called “fish-eye lenses”) having an angle of view exceeding 180 degrees are used in combination.

  Images captured by the wide-angle lenses are converted into electrical signals by the same or individual imaging means, and an omnidirectional image can be captured by processing the electrical signals.

Neither Patent Documents 1 and 2 disclose a specific configuration of the wide-angle lens itself.
Further, in the imaging systems described in these documents, the image forming light beam by each imaging optical system is guided to the imaging means by individual light guiding means (path conversion device or reflection optical device).

As described above, since the light guiding means is used for each wide-angle lens, it is difficult to reduce the “maximum distance between the angles of view” between the two wide-angle lenses. The “maximum field angle distance” will be described later.
When two wide-angle lenses having an angle of view exceeding 180 degrees are combined, there is a space portion where the maximum angle-of-view beams incident on the wide-angle lenses do not overlap each other.

A subject existing in a “space portion where the maximum field angle light beams incident on the wide-angle lens do not overlap each other” cannot be imaged.
Such a “space portion” is hereinafter referred to as a “image-capable space portion”. Needless to say, the non-imagingable space is preferably as small as possible.

If the “maximum inter-view angle distance” is large, it is difficult to reduce the non-imaging space.
In order to reduce the non-imaging space in an imaging system having a large maximum field angle distance, it is necessary to increase the field angle of the two wide-angle lenses to be combined, and the lens design conditions become severe.

  In addition, even if the subject can be photographed, the parallax is different between the subject at the maximum angle of view and the subject at infinity, and the deviation on the image sensor increases. This point will also be described later.

  Patent Documents 1 and 2 do not mention a specific configuration of the wide-angle lens, and do not disclose any problems regarding such a non-imagingable space part or parallax problem.

  An object of the present invention is to provide a novel optical system.

  The optical system according to the present invention is different from the first lens that collects incident light, the first prism that includes the reflecting surface that reflects the light transmitted through the first lens, and the light incident on the first lens. A second lens that collects incident light incident from a direction, and a second prism that includes a reflective surface that reflects light transmitted through the second lens, the reflective surface of the first prism, and the second prism This is an optical system in which the reflecting surfaces of the prisms face each other.

  According to the present invention, a novel optical system having a first lens, a second lens, a first prism, and a second prism can be provided.

It is a figure which isolate | separates and shows two imaging systems which comprise an imaging system. It is a figure for demonstrating parallax and the imaging impossible space. It is a figure which shows the relationship between the distance between largest angles of view, and parallax. It is a figure of the spherical aberration of the specific example of a wide angle lens. It is a figure of the field curvature of the specific example of a wide angle lens. It is a figure of the spherical aberration of the specific example of a wide angle lens. It is a figure which shows the OFT characteristic of the specific example of a wide angle lens. It is a figure which shows the OFT characteristic of the specific example of a wide angle lens. It is a figure which shows one example of implementation of a reflective surface member. It is a figure for demonstrating the assembly to a reflective surface member and its lens-barrel part. It is a figure for demonstrating a lens-barrel part. It is a figure which shows the relationship between the right angle prism which comprises a reflective surface member, and an imaging light beam.

Hereinafter, embodiments will be described.
FIG. 1 shows an example of two imaging systems constituting the imaging system.
That is, the two imaging systems constituting the imaging system are the imaging system A and the imaging system B shown in the figure.
These imaging systems A and B have the same specifications.

Each of the two image pickup systems A and B is constituted by “a wide-angle lens having an angle of view wider than 180 degrees and an image pickup sensor for picking up an image by the wide-angle lens”.
The imaging sensor is a “two-dimensional solid-state imaging device”.

The wide-angle lens of the imaging system A has a front group, a reflecting surface, and a rear group.
The “front group” includes lenses LA1 to LA3, and the “rear group” includes lenses LA4 to LA7. The symbol PA indicates a “right angle prism”.

  An aperture stop SA is disposed on the object side of the lens LA4.

The wide-angle lens of the imaging system B has a front group, a reflecting surface, and a rear group.
The “front group” includes lenses LB1 to LB3, and the “rear group” includes lenses LB4 to LB7. The symbol PB indicates a “right angle prism”.

  An aperture stop SB is disposed on the object side of the lens LB4.

  The “front group” of these two wide-angle lenses has a negative refractive power, and the “rear group” has a positive refractive power.

The “front group” in one of these two wide-angle lenses corresponds to the “first lens” of the present invention, and the “front group” in the other of the wide-angle lenses corresponds to the “second lens” of the present invention.
Hereinafter, for the sake of concreteness of description, the front group of the wide-angle lens of the imaging system A will be described as a “first lens”, and the front group of the wide-angle lens of the imaging system B will be described as a “second lens”.

  In one of the wide-angle lenses, the rear group combined with the first lens corresponds to the “third lens” of the invention of claim 4, and the rear group combined with the second lens is “fourth of the invention of claim 4. Corresponds to “Lens”.

  As in the case of the front group, for the sake of concreteness of description, in the following description, the rear group of the wide-angle lens of the imaging system A is referred to as “third lens”, and the rear group of the wide-angle lens of the imaging system B is referred to as “fourth lens”. ".

  The prism combined with the first lens is referred to as a first prism, and the prism combined with the second lens is referred to as a second prism.

Then, in the example being described, the right-angle prism PA corresponds to a “first prism”, and the right-angle prism PB corresponds to a “second prism”.
The right-angle prisms PA and PB and the “reflection surface” will be described later.

The “lens constituting the front group (first lens)” of the wide-angle lens of the imaging system A includes the following three lenses in order from the object side.
That is, the negative meniscus lens LA1 made of glass material, the negative lens LA2 made of plastic material, and the negative meniscus lens LA3 made of glass material.

The “lens constituting the rear group (third lens)” includes the following four lenses in order from the aperture stop SA side.
That is, a biconvex lens LA4 made of glass material, a “laminated lens of biconvex lens LA5 and biconcave lens LA6” made of glass material, and a biconvex lens LA7 made of plastic material.

The “lens constituting the front group (second lens)” of the wide-angle lens of the imaging system B includes the following three lenses in order from the object side.
That is, in order from the side, a negative meniscus lens LB1 made of a glass material, a negative lens LB2 made of a plastic material, and a negative meniscus lens LB3 made of a glass material.

The “lens constituting the rear group (fourth lens)” includes the following four lenses in order from the aperture stop SB side.
That is, a biconvex lens LB4 made of glass material, a “laminated lens of biconvex lens LB5 and biconcave lens LB6” made of glass material, and a biconvex lens LB7 made of plastic material.

In these imaging systems A and B, the negative lenses LA2 and LB2 and the biconvex lenses LA7 and LB7 made of a plastic material are “aspheric on both surfaces”.
Each lens made of another glass material is a spherical lens.

  The position of the front principal point in each wide-angle lens is set between the lenses LA2 and LA3 and between the lenses LB2 and LB3.

  In the wide-angle lenses of the imaging systems A and B, the distance between the intersection of the front group optical axis and the reflecting surface and the front principal point is “d1, d2” in FIG.

  Since the imaging systems A and B have the same specifications, d1 = d2.

  The right-angle prisms PA and PB are preferably formed of “a material having a refractive index of d-line greater than 1.8”. The right-angle prisms PA and PB “internally reflect” light from the front group toward the rear group.

Therefore, the optical path of the imaging light flux of each wide-angle lens passes through the right-angle prisms PA and PB.
If the prism material has a high refractive index as described above, the “optical optical path length” in the right-angle prism becomes longer than the actual optical path length, and the distance for bending the light beam can be increased.

  Accordingly, the “optical path length between the front group and the rear group” in the front group, the right-angle prism, and the rear group can be made longer than the mechanical optical path length, and the wide-angle lens can be made compact.

  Further, by arranging the right-angle prisms PA and PB near the aperture stops SA and SB for reducing the beam diameter, a small right-angle prism can be used, and the distance between the wide-angle lenses can be reduced.

Thus, the right-angle prisms PA and PB are arranged between the front group and the rear group.
The front group of the wide-angle lens has a “function to capture a light beam having a wide angle of view greater than 180 degrees”, and the rear group effectively functions to “correct the aberration of the formed image”.

An image sensor is arranged on the image side of the rear group of each wide-angle lens. In FIG. 1, symbols ISA and ISB indicate imaging surfaces of these imaging sensors.
What is indicated by a symbol F on the wide-angle lens side of the image surfaces ISA and ISB indicates various filters and cover glasses used in the image sensor.

  In FIG. 1, the right-angle prisms PA and PB are drawn separately, but this is to clearly show the configuration of the imaging systems A and B.

  In an actual imaging system, the right-angle prisms PA and PB forming a part of the wide-angle lenses of the imaging systems A and B are in contact with the inclined surfaces.

The “reflective surface” in each wide-angle lens is a reflective film shared by two wide-angle lenses, and is sandwiched between two optically equivalent transparent members (right-angle prisms PA and PB).
That is, the reflecting surface of the right-angle prism PA as the first prism and the reflecting surface of the right-angle prism PB as the second prism are “bonded”.

  That is, a reflection film is formed on the inclined surfaces of the right-angle prisms PA and PB, and the reflection film is sandwiched between the inclined surfaces of the right-angle prisms PA and PB.

  In this state, the reflecting film, the right-angle prism PA (first prism), and PB (second prism) are integrated to form a “reflecting surface member shared by two wide-angle lenses”.

  As will be described later, the reflecting surface member is held by “a common lens barrel portion for assembling each front group and each rear group” of the two wide-angle lenses.

  With such a configuration, the imaging systems A and B can have the smallest width in the incident optical axis direction.

The effect by such a structure is demonstrated.
FIG. 2 shows a simplified imaging system.
That is, in FIG. 2, reference signs A <b> 1 and B <b> 1 indicate “most object side lens surfaces (object side lens surfaces of the lenses LA <b> 1 and LB <b> 1 in FIG. 1)” of the front group of the two wide-angle lenses.

  Reference numerals A2 and B2 indicate the rear group of the two wide-angle lenses in a simplified manner, and reference numerals SNA and SNB indicate the imaging sensors of the imaging systems A and B.

Symbols PA and PB indicate right-angle prisms, and symbol RF indicates a “reflecting surface”.
Reference numeral LMA is a maximum field angle light beam that is incident on the wide-angle lens of the imaging system A at a maximum field angle, and reference numeral LMB is a maximum field angle light beam that is incident on the wide-angle lens of the imaging system B at a maximum field angle.

  The distance between the point P and the plane perpendicular to the incident optical axis through the intersection point Q with the optical axis AX of the maximum object side surface B1 of the front group and the maximum intersection angle LMA and LMB Let R be.

  Also, let L be the distance from the intersection point Q and the plane passing through the point P and parallel to the optical axis AX.

  Furthermore, the distance between the incident positions of the maximum field angle rays LMA and LMB on the front group is MGK.

  This distance: MGK is the “maximum distance between the angles of view” described above.

  As is apparent from the figure, the “space portion surrounded by the point P and the maximum field angle rays LMA and LMB” is the “imaging impossible space portion” described above.

  Light emitted from an object in the non-imaging space portion is not captured as image light by any of the two wide-angle lenses.

  The larger the non-imaging space part, the less information that can be imaged in an omnidirectional imaging system. Therefore, it is necessary to devise a method for reducing the non-imaging space.

What characterizes the size of the non-imaging space is the above-mentioned distances: R and L, and the maximum distance between the angles of view: MGK.
Even if any of these distances: R, L, and MGK is increased, the non-imagingable space portion is increased. Considering a method for reducing these distances, the following is obtained.

The first method is a method of reducing the distance L. If this method is to be executed alone, the angle of view of the wide-angle lens must be increased.
Increasing the angle of view of the wide-angle lens imposes stricter restrictions on lens design, but “parallax” increases as the angle of view increases.

  The second method is to reduce the distance: R.

Distance: Between R and L, the half angle of view of the wide-angle lens is Θ,
L = −R · tanΘ
There is a relationship.

  Accordingly, when R becomes smaller, the distance L where the images captured by the two wide-angle lenses overlap becomes shorter, and the non-imagingable space portion becomes smaller.

  In order to decrease the distance: R, it is preferable to decrease the maximum distance between the angles of view: MGK.

  In order to reduce the maximum inter-view angle distance: MGK, it is “most effective” to make the reflecting surfaces included in the two wide-angle lenses of the imaging systems A and B common as in the present invention.

  By sandwiching the reflecting film between the inclined surfaces of the right-angle prisms PA and PB and integrating them with the right-angle prisms PA and PB, the distance between the maximum angles of view: MGA can be reduced, and the distance: R can be reduced.

  Here, “parallax” will be described.

  In the imaging system being described, an image having a solid angle of 4π radians is obtained by combining two images by a wide-angle lens having an angle of view of 180 degrees or more by calibration.

  The “parallax” referred to in this specification means an “overlap amount” of two images that are pasted by calibration.

  In the case of such an omnidirectional imaging system, the “composite image” that is pasted is affected by the parallax, and the “parallax at the maximum angle of view” is shifted.

  When the parallax is converted into an angle and the angle is θ, the parallax: θ has a functional relationship with respect to the distance to the subject and the maximum inter-field angle distance: MGK.

  As an example, when calibration is performed at a distance to the subject of 20 cm, the parallax of an infinite image is 5 degrees when the distance between the maximum angles of view is 35 mm.

  That is, an image at infinity is shifted by 5 degrees.

  For example, when an image sensor having 5 million pixels is used, the pixels are arranged in 2592 × 1944 (pixels) in two orthogonal directions.

  Since an image by a wide-angle lens is formed on this rectangular area, the diameter of the image (circular) is 1994 pixels, that is, approximately 2000 pixels.

  If the angle of view of the wide-angle lens is 200 degrees, the number of pixels allocated per degree is 2000 (pixels) / 200 (degrees) = 10 (pixels) / degree.

  In this case, if there is “5 degree parallax” as described above, the image at infinity is shifted by 50 pixels.

  FIG. 3 shows a change in the shift amount θ of the seam between the two images to be joined when the imaging range is from the object distance of 20 cm to infinity in the above case.

The horizontal axis represents the maximum distance between the field angles (indicated as “the maximum distance between the light field positions in the drawing”).
The vertical axis represents the “angle: θ (ie,“ parallax ”) of the deviation. As shown in the figure, the angle of deviation: θ increases linearly in proportion to the increase in the maximum inter-field angle distance.

  When the parallax is large, the “overlapping region” between the two images to be joined increases.

  Therefore, the pixel density of the “portion from the peripheral portion to the optical axis portion” excluding the overlapping portion is lowered, and the resolution of the composite image is lowered.

  In the imaging system being described, as described above, the reflecting film is sandwiched between the oblique sides of the right-angle prisms PA and PB, and the reflecting film and one right-angle prism are integrated to form a reflecting surface member.

  Thereby, by setting the distance between the reflecting surfaces of the two wide-angle lenses to 0, the distance between the maximum angles of view is reduced and the parallax is reduced.

  Specific examples of wide-angle lenses will be given.

  The following data relates to the two imaging systems A and B shown in FIG. Since the imaging systems A and B have “same specifications”, the following data is common to each imaging system.

The distance: d1 is the “distance on the optical axis between the entrance pupil and the reflecting surface of the right-angle prism PA” of the wide-angle lens of the imaging system A.
The distance: d2 is the “distance on the optical axis between the entrance pupil and the reflecting surface of the prism PB” of the wide-angle lens of the imaging system B.

  In the following, f is the focal length of the entire system, No is the F number, and ω is the angle of view.

  “Surface numbers” are sequentially 1 to 23 from the object side, and these indicate a lens surface, a prism entrance / exit surface, a reflecting surface, a diaphragm surface, a filter surface of an image sensor, and an imaging surface.

  “R” is the radius of curvature of each surface, and “paraxial radius of curvature” for an aspherical surface.

  “D” is the surface separation, “Nd” is the refractive index of the d-line, and “νd” is the Abbe number. The object distance is infinite. The unit of the quantity having the dimension of length is “mm”.

"Concrete example"
f = 0.75, No = 2.14, ω = 190 degrees Face number R D Nd νd
1 17.1 1.2 1.834807 42.725324
2 7.4 2.27
3 * -1809 0.8 1.531131 55.753858
4 * 4.58 2
5 17.1 0.7 1.639999 60.078127
6 2.5 1.6
7 ∞ 0.3
8 ∞ 5 1.834000 37.160487
9 ∞ 1.92
10 ∞ (aperture stop) 0.15
11 93.2 1.06 1.922860 18.896912
12-6.56 1.0
13 3.37 1.86 1.754998 52.321434
14-3 0.7 1.922860 18.896912
15 3 0.3
16 * 2.7 1.97 1.531131 55.753858
17 * -2.19 0.8
18 ∞ 0.4 1.516330 64.142202
19 ∞ 0
20 ∞ 0.3 1.516330 64.142202
21 ∞ 0.3
22 Imaging surface.

"Aspherical surface"
The surfaces marked with “*” in the above data (both surfaces of the second lens in the front group and both surfaces of the final lens in the rear group) are aspherical surfaces.

  The aspherical shape is represented by the following well-known expression.

^{X = CH 2 / [1 +} √ {1- (1 + K) C 2 H 2}]
+ A4 · H ⁴ + A6 · H ⁶ + A8 · H ⁸ + A10 · H ¹⁰ + A12 · H ¹² + A14 · H ¹⁴
In this equation, C is the reciprocal of the paraxial radius of curvature (paraxial curvature), H is the height from the optical axis, K is the conic constant, A1 etc. is the aspheric coefficient of each order, and X is the aspherical surface in the optical axis direction. Amount.
The shape is specified by giving the paraxial radius of curvature: R, the conic constant: K, and the aspherical coefficients: A1 to A14.

  The aspherical data of the above example is given below.

Third side
4th: 0.001612
6th: -5.66534e-6
8th: -1.99066e-7
10th: 3.69959e-10
12th: 6.47915e-12
4th page
4th: -0.00211
6th: 1.66793e-4
8th: 9.34249e-6
10th: -4.44101e-7
12th: -2.96463e-10
16th page
4th: -0.006934
6th: -1.10559e-3
8th: 5.33603e-4
10th: -1.09372e-4
12th: 1.80753-5
14th: -1.52252e-7
17th page
4th: 0.041954
6th: -2.99841e-3
8th: -4.227219e-4
10th: 3.426519e-4
12th: -7.19338e-6
14th: -1.69417e-7.

In the above aspherical notation, for example, “-1.69417e-7” means “-1.69417 × 10-7”.
“4th to 14th” is “A4 to A14”, respectively.

In the wide-angle lens of the example, “d1 = d2 = d = 6 mm”.
The distance from the lens surface closest to the object side to the reflecting surface of the right-angle prism: DA is
DA = 8.87 mm.

  Therefore, when the reflecting surface is shared by two wide-angle lenses, the distance on the optical axis of the surface closest to the object side of the front group of the two wide-angle lenses is 8.87 × 2 = 17.74 mm.

  From this, the maximum distance between the angles of view is 17 mm.

  The parallax: θ when the maximum distance between the angles of view is 17 mm is “2.4 degrees” as shown in FIG. 3, and the “deviation amount” of the image at infinity is reduced to 24 pixels.

  Further, since the reflecting surfaces are made common, the distance between the principal points of the two wide-angle lenses becomes as small as d1 + d2 = 2d1, which also contributes to the reduction of parallax.

  A spherical aberration diagram of a specific example of the wide-angle lens is shown in FIG. Further, FIG. 5 shows a field curvature diagram. FIG. 6 shows a coma aberration diagram.

  7 and 8 are diagrams showing the OTF characteristics, and the horizontal axis represents “spatial frequency” in FIG. 7 and the half angle of view in “degrees” in FIG. 8.

  As is clear from these figures, the wide-angle lens of the specific example has extremely high performance.

  In this way, the reflecting surfaces of the two wide-angle lenses included in the imaging system are made common, sandwiched between the two transparent members (right angle prisms PA and PB), and integrated as a reflecting surface member.

  Thereby, as explained above, the parallax can be effectively reduced.

  However, due to the common reflecting surface, it is necessary to pay attention to the following points.

  That is, if each wide-angle lens has a separate reflecting surface, each reflecting surface is required to guarantee the positional accuracy with respect to the front group and the rear group within one wide-angle lens.

  However, when the reflecting surfaces are shared by the two wide-angle lenses, the shared reflecting surfaces must be guaranteed to have a positional relationship with the front group and the rear group for each of the two wide-angle lenses.

  That is, if there is an error in the tilt or position of the reflecting surface, it affects the two wide-angle lenses.

  The reflecting film forming the reflecting surface is integrated with the right-angle prisms PA and PB to form one reflecting surface member, and the performance depends on one optical element in assembling.

  This problem is solved as follows.

  That is, the reflection film shared by the two wide-angle lenses is sandwiched between two optically equivalent transparent members.

  The “size of the surface in contact with the reflection film” in the two transparent members sandwiching the reflection film is made different, and the “outside of the light flux reflection region” with the larger contact surface is defined as the free surface portion.

  This free surface portion is “the same surface as the reflecting surface” if the minute thickness of the reflecting film is ignored.

  Therefore, a contact surface that contacts the free surface portion is formed in the lens barrel portion that holds the reflecting surface member, and the free surface portion is contacted to the contact surface to perform alignment with the lens barrel portion. .

In this way, the reflecting surface can be “directly aligned” with respect to the lens barrel portion.
On the other hand, the front and rear groups of the two wide-angle lenses are assembled to the lens barrel portion with high accuracy.

  Therefore, the reflection surface of the reflection surface member assembled to the lens barrel portion as described above is accurately aligned with each of the two wide-angle lenses.

  When this is applied to the embodiment being described, the following results.

  FIG. 9 is a diagram for explaining the reflecting surface member. For simplicity of explanation, two right angle prisms are denoted by reference numerals 200 and 300.

  The right-angle prisms 200 and 300 are used in the specific examples of the above-described wide-angle lenses, and are formed of the same material having a refractive index of 1.834 and an Abbe number of 37.160487.

  A reflective film is formed on the inclined surfaces of the right-angle prisms 200 and 300 by an aluminum coating. For the sake of simplicity, the “reflection film” is not shown.

  The slopes of the right-angle prisms 200 and 300 are bonded and fixed with an adhesive at an interval of 5 μm or less via a reflective film.

  The two prism surfaces forming the prism angle of the right-angle prisms 200 and 300 are “incident surfaces / reflecting surfaces”, and these surfaces are subjected to antireflection treatment.

  Among the right-angle prisms 200 and 300, the right-angle prism 200 has “the length of the prism surfaces perpendicular to each other in the tangential direction” larger than that of the right-angle prism 300.

For this reason, a part of the slope of the right-angle prism 200 (both end portions in the ridge line direction) protrudes from the slope of the right-angle prism 300.
In FIG. 9, the portions denoted by reference numerals 201 </ b> A and 201 </ b> B are “protruded portions” and are “free surface portions”. The free surface portions 201A and 201B are “the same surface as the reflecting surface”.

  FIG. 10A is a diagram illustrating the reflecting surface member so that the “ridge line direction” is the vertical direction. The reflecting surface member is assembled to the lens barrel portion in this state.

  In FIG. 10A, the end portions of the joining surfaces of the right-angle prisms 200 and 300 of the reflecting surface member are “chamfered”.

  FIG. 10B shows a state where the reflecting surface member is attached to the lens barrel portion 100 as an explanatory diagram. The lens barrel portion 100 includes a rear group optical axis and is cut along a virtual plane parallel to the front group optical axis.

  In FIG. 11, the part which attaches the reflective surface member in the lens-barrel part 100 is shown.

  11A is a perspective view, and FIG. 11B is a front view.

  The vertical direction of the front view of FIG. 11B is the “optical axis direction of the rear group” of the two wide-angle lenses, and each front group is assembled to the hole portion of the lens barrel portion 100 in the direction orthogonal to the drawing. It is done.

  In the lens barrel portion 100, a step is formed in a portion that receives the reflection surface of the reflection surface member, and the surfaces of the step are used as contact surfaces 101A and 101B.

  The contact surfaces 101A and 101B are accurately formed as “reflection surface positions” in accordance with the positions of the front and rear groups of the two wide-angle lenses assembled to the lens barrel portion 100.

  The free surface portion 201A and the free surface portion 201B of the reflecting surface member constituted by the right-angle prisms 200 and 300 are brought into contact with the contact surface 101A and the contact surface 101B, respectively.

  By doing in this way, the reflective surface of a reflective surface member can be set to the state which should be with respect to the front group and rear group of each wide angle lens.

  By doing as described above, the state of the reflecting surface is determined, but the reflecting surface member in this state has a degree of freedom of “movement in a direction along the reflecting surface”.

In order to determine the position of the reflecting surface member within the lens barrel portion 100 while maintaining the state of the reflecting surface properly, it is necessary to fix at least one point other than the free surface portions 201A and 201B.
In the embodiment being described, the exit surface 202A of the right-angle prism 200 is brought into contact with the second contact surfaces 102A and 102B formed as protrusions on the lens barrel portion, and bonded with an adhesive.

  In this way, the right-angle prism 200 is fixed to the lens barrel portion 100, and the position of the reflecting surface member with respect to the lens barrel portion 100 is determined.

  In the embodiment in the description, the lens barrel portion 100 is provided with the two protruding portions as the second contact surfaces 102A and 102B. However, only one of the second contact surfaces 102A and 102B may be provided.

  In the embodiment being described, the exit surface 202A of the right-angle prism 200 is bonded to the second contact surfaces 102A and 102B. This has the following implications.

  FIG. 12 shows an optical path diagram of an imaging system (imaging system A shown in FIG. 1) constituting the imaging system. The light beam incident from the front group enters the right-angle prism 200 with the diameter of the light beam being reduced.

Then, the light beam is further narrowed in the right-angle prism 200 and exits from the exit surface. Therefore, the beam diameter of the imaging light beam (light beam effective diameter) is large on the entrance surface and small on the exit surface.
Therefore, the portion of the exit surface 202A having a small effective beam diameter of the right angle prism 200 of the two right angle prisms sandwiching the reflection film is brought into contact with the second contact surface.

  By doing so, there is no possibility that the outer peripheral portion of the imaging light beam is shielded from light by the protruding portions forming the second contact surfaces 102A and 102B.

  Specifically, the light beam diameters in FIG. 12 are L1 = 3.8 mm, L2 = 2.3 mm, and the length of one side of the entrance / exit surface of the right-angle prism 200 is 5 mm.

  Thus, the part which fixes a reflective surface member with respect to a lens-barrel part is made into the reflective surface.

  Therefore, the size of the right-angle prism is changed, and a free surface portion is provided on the reflection surface of the larger right-angle prism and applied to the contact surface of the lens barrel portion.

  By doing so, it is possible to reduce the cause of performance deterioration due to the shift and tilt of the reflection surface without being affected by the external accuracy of the reflection surface member.

  Although the case where two right angle prisms are combined as the reflecting surface member has been described above, the two optically equivalent transparent members sandwiching the common reflecting film are not limited to the right angle prisms.

  For example, a transparent parallel plate may be used as two equivalent transparent members, and the reflective film may be sandwiched between them.

  Also in this case, one transparent parallel plate may be enlarged, a free surface portion may be formed on the extended portion of the reflecting surface, and the position may be determined by applying the free surface portion to the contact surface. .

  In principle, when the reflective film is sandwiched between the two transparent parallel flat plates, there is a method of obtaining the positional accuracy of the reflective surface without forming a free surface portion in the extended portion of the reflective surface.

  That is, it is conceivable to obtain positional accuracy by pressing the surface of the transparent parallel plate that is not in contact with the reflection surface against the contact surface formed on the side of the lens barrel portion.

  In this case, if the thickness of the transparent parallel flat plate is t, the contact surface position of the lens barrel portion may be formed by translating in the vertical direction by “t” from the ideal position of the reflection surface.

  However, in the case of this method, since the alignment is not performed by the reflecting surface itself, the position accuracy of the reflecting surface is affected by the parallelism of the transparent parallel plate and the thickness error.

  As described above, according to the present invention, the following optical system and imaging system can be realized.

[1]
A first lens (LA1 to LA3) that condenses incident light, a first prism PA that includes a reflective surface that reflects light transmitted through the first lens, and a direction different from the direction of light incident on the first lens A second lens (LB1 to LB3) that condenses incident light incident from the second lens PLB, and a second prism PB that includes a reflecting surface that reflects the light transmitted through the second lens, and is reflected by the first prism. An optical system in which the surface and the reflecting surface of the second prism face each other.

[2]
[1] The optical system according to [1], wherein the reflecting surface of the first prism and the reflecting surface of the second prism are close to each other.

[3]
The optical system according to [1], wherein the reflection surface RF of the first prism PA and the reflection surface RF of the second prism PB are bonded together.

[4]
In the optical system according to any one of [1] to [3], a third lens (LA4 to LA7) that guides light emitted from the first prism PA and a fourth that guides light emitted from the second prism PB. An optical system further comprising a lens (LB4 to LB7).

[5]
[4] An imaging system, further comprising the optical system according to [4] and imaging sensors SNA and SNB that photoelectrically convert light guided by the optical system.

[6]
[5] The imaging system according to claim 5, further comprising a lens barrel 100 for assembling the first lens and the second lens, wherein a reflection surface of the first prism 200 is larger than a reflection surface of the second prism 300, An imaging system characterized in that portions 201A and 201B of the reflecting surface of the first prism that are not bonded to the second prism are held by the lens barrel.

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above, and the invention described in the claims unless otherwise specified in the above description. Various modifications and changes are possible within the scope of the above.
The effects described in the embodiments of the present invention are merely a list of suitable effects resulting from the invention, and the effects of the present invention are not limited to those described in the embodiments.

A Imaging system
B Imaging system
200 right angle prism
300 right angle prism
201A free surface
201B Free surface part
100 Lens barrel part
101A Contact surface
101B Contact surface
102A Second contact surface
102B second contact surface

JP 2010-271675 A Japanese Patent No. 3290993

The optical system of the present invention includes two wide-angle lenses having an angle of view wider than 180 degrees having the same structure in which a front group and a rear group are arranged from the object side to the image side, a reflecting surface that reflects incident light, Arranged between the front group and the rear group, the optical axes of the light incident from the respective front group of each wide-angle lens is matched or brought close to each other and incident on one surface and the other surface of the reflection surface, A transparent member that emits light reflected toward the rear group of each wide-angle lens in a direction opposite to each other on each surface of the reflecting surface, and the front group has a negative refractive power and has a beam diameter. Is an optical system for picking up an omnidirectional image, which is characterized by being narrowed down and made incident on the transparent member.

The wide-angle lens of the imaging system B has a front group, a reflecting surface, and a rear group.
The “front group” includes lenses LB1 to LB3, and the “rear group” includes lenses LB4 to LB7. The symbol PB indicates a “right angle prism”.
The right-angle prisms PA and PB are examples of “transparent members”.

[1]
Two wide-angle lenses having an angle of view wider than 180 degrees with the same structure in which the front group and the rear group are arranged from the object side to the image side, a reflecting surface that reflects incident light, and the front group and the rear group The optical axes of the light incident from the respective front groups of the wide-angle lenses are aligned or brought close to each other and are incident on one surface and the other surface of the reflecting surface, and are mutually connected on each surface of the reflecting surface. A transparent member that emits light reflected toward the rear group of each wide-angle lens in the opposite direction, and the front group has a negative refractive power and narrows the beam diameter to the transparent member. An optical system for picking up an omnidirectional image characterized by being incident.

[2]
In the optical system according to [1], the transparent member is the first and second prisms (200, 300), and the reflective surface of the first prism and the reflective surface of the second prism are close to each other. An optical system.

[3]
In the optical system according to [1], the transparent member is the first and second prisms (200, 300), and the reflective surface of the first prism and the reflective surface of the second prism are bonded together. An optical system characterized by

[4]
In the optical system according to [2] or [3] , the rear group in one wide-angle lens is a third lens that guides light emitted from the first prism, and the rear group in the other wide-angle lens is from the second prism. An optical system comprising a fourth lens for guiding emitted light .

[6]
[5] The imaging system according to [5], further including a lens barrel 100 for assembling the first lens and the second lens, wherein the reflecting surface of the first prism and the reflecting surface of the second prism are bonded to each other. The reflecting surface of the prism is larger than the reflecting surface of the second prism, and is held by the lens barrel at portions 201A and 201B of the reflecting surface of the first prism that are not bonded to the second prism. An imaging system.
[7]
In the imaging system according to any one of [1] to [6], a light beam diameter of a light beam incident on the transparent member 200, reflected by the reflecting surface, and emitted from the transparent member is within the transparent member 200. An imaging system characterized by decreasing toward the exit side.

Claims (6)

A first lens for condensing incident light;
A first prism having a reflecting surface for reflecting light transmitted through the first lens;
A second lens that condenses incident light incident from a direction different from the light incident on the first lens;
A second prism having a reflecting surface that reflects light transmitted through the second lens,
An optical system in which the reflecting surface of the first prism is opposed to the reflecting surface of the second prism. The optical system according to claim 1.
An optical system, wherein the reflecting surface of the first prism and the reflecting surface of the second prism are close to each other. The optical system according to claim 1.
An optical system, wherein a reflection surface of a first prism and a reflection surface of the second prism are bonded together. The optical system according to any one of claims 1 to 3,
A third lens for guiding light emitted from the first prism;
And a fourth lens for guiding light emitted from the second prism.   An imaging system, further comprising: the optical system according to claim 4; and an imaging sensor that photoelectrically converts light guided by the optical system. The imaging system according to claim 5, wherein
A lens barrel for assembling the first lens and the second lens;
The reflecting surface of the first prism is larger than the reflecting surface of the second prism, and is held by the lens barrel at a portion of the reflecting surface of the first prism that is not bonded to the second prism. An imaging system.

Images