Soft focus filter, optical system, imaging device, and information processing device

Abstract

To provide a soft focus filter, an optical system, an imaging device, and an information processing device with which it is possible to obtain suitable soft focus filter effects without being affected by a luminous flux diameter.SOLUTION: Provided is a soft focus filter characterized by comprising a transparent substrate and a plurality of structures formed on the transparent substrate and having a light diffusion function. The plurality of structures have a plurality of target values within the range of 300 μm2 to 200000 μm2 in area, and the plurality of structures are arranged at an average pitch of 0.05 mm to 1 mm. The plurality of structures satisfy a condition that they have 50 nm or more of wavelength range of absorbance 0.3 or greater in 400 nm to 700 nm wavelength regions, and / or a condition that the average value of absorbance in 400 nm to 700 nm wavelength regions is 0.2 or greater.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a soft focus filter, an optical system, an imaging device, and an information processing device.

Background Art

[0002] Patent Document 1 describes a soft focus photographing lens system in which a circular region centered on the optical axis of a lens element located near the aperture is a smooth surface, and a peripheral portion excluding the circular region is a ring-shaped light diffusing portion that cuts high-frequency components of the spatial frequency.

[0003] Patent Document 2 describes a soft focus filter. In this soft focus filter, a group of reference figures of the same or different shapes, which are serially and continuously or discontinuously formed by line segments with a width of 10 to 200 μm, are arranged in a scattered manner on a transparent substrate so that the closest distance between adjacent reference figures is 300 μm or less to form a transmitted light shielding pattern. Further, the transmitted light shielding pattern is arranged randomly so that the light transmittance is locally non-uniform depending on the position, and is arranged with an equal dispersion rate over a wide area.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, according to the intensive research of the present inventor, Patent Documents 1 and 2 have room for improvement from the viewpoint of obtaining a suitable soft focus filter effect without being affected by the light beam diameter.

[0006] The present invention has been made in view of the above points, and an object thereof is to provide a soft focus filter, an optical system, an imaging device, and an information processing device that can obtain a suitable soft focus filter effect without being affected by the light beam diameter.

Means for Solving the Problems

[0007] The soft focus filter of the present embodiment has a transparent substrate and a plurality of structures having a light diffusing function formed on the transparent substrate, and the plurality of structures have an area of 300 μm 2 ~200000 μm 2 and have a plurality of target values within the range, the plurality of structures are arranged at an average pitch of 0.05 mm to 1 mm, and the plurality of structures satisfy at least one of having a wavelength range with an absorbance of 0.3 or more in the wavelength range of 400 nm to 700 nm of 50 nm or more and having an average value of absorbance in the wavelength range of 400 nm to 700 nm of 0.2 or more.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a soft focus filter, an optical system, an imaging device, and an information processing device that can obtain a suitable soft focus filter effect without being affected by the light beam diameter.

Brief Description of the Drawings

[0009]

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Mode for Carrying Out the Invention

[0010] <Prior Art and Its Technical Problems> In order to obtain a soft focus effect by adding a filter, there are methods of refracting, diffracting, and scattering a part of the light beam, such as making fine irregularities on a transparent substrate for refraction, forming a pattern for diffraction and interference, kneading powder for scattering, etc., which are already known.

[0011] However, such methods for imparting these shapes require a certain thickness of the transparent substrate. For fine pattern printing, the transparent substrate needs to be made of glass and still has the demerit of requiring a certain thickness.

[0012] Furthermore, even when considering (examining) the prior art including Patent Documents 1 and 2 described above, there is no method that combines the conditions of the structure (such as unevenness and patterns) on the transparent substrate with the transmission absorption characteristics of the structure, and there is room for improvement in that there is a lack of control factors for obtaining the desired soft focus effect. For example, Patent Document 1 does not specify the conditions for appropriately obtaining the soft focus effect without adverse effects (side effects) regarding the specific structure of the light diffusing portion. Also, Patent Document 2 requires a certain area for pattern formation, and there is concern about changes in the filter effect when narrowing down in a small optical system.

[0013] By the way, there is a certain number of requests from photography enthusiasts for a function that can easily turn the effect of the filter ON / OFF, and instead of manually attaching and detaching the filter in front of or behind the lens, a configuration that automatically inserts and removes the filter inside the camera is desired. Also, various expressions according to different shooting purposes are required for the soft focus effect.

[0014] Considering the placement of the soft focus filter inside the camera, in order to uniformly exhibit the filter effect across the entire screen, it is desirable to insert and remove the filter near the aperture within the lens system. However, there is a problem that the optical path length changes and the aberration deteriorates when inserting and removing the filter within the lens system, so it is necessary to thin the filter. Also, to thin the filter, it is desirable to impart the filter function with a thin structure on the surface of the thin transparent substrate, and appropriate settings for various conditions are required. To obtain various soft focus effects on a thin transparent substrate, appropriate condition settings are also required for the transmission absorption characteristics of the structure.

[0015] <Technical idea of the present invention> The present inventors have recognized the above problems as important technical issues and have found that it is possible to optimally set various conditions and transmission absorption characteristics of a plurality of structures having a light diffusion function formed on a transparent substrate. As a result, a suitable soft focus filter effect can be realized without being affected by the light beam diameter. For example, by thinning the soft focus filter and inserting it into or near the aperture stop, it is possible to prevent deterioration of aberration due to a change in the optical path length. Further, for example, even if the aperture diameter is changed from the wide open state to the minimum aperture, the change in the filter effect can be minimized, so it is suitable for a small optical system with a thin light beam even in the wide open state.

[0016] The soft focus filter of the present embodiment has, as a basic structure, a transparent substrate and a plurality of structures having a light diffusion function formed on the transparent substrate.

[0017] FIG. 1 is a conceptual diagram showing the basic structure of the soft focus filter of the present embodiment. As shown in FIG. 1, the soft focus filter has a transparent substrate 10 and a plurality of structures 20 having a light diffusion function formed on the transparent substrate 10. In FIG. 1, three structures 20X having a relatively large diameter, three structures 20Y having a relatively medium diameter, and three structures 20Z having a relatively small diameter are illustratively drawn. Although details will be described later, the structures 20X, 20Y, and 20Z are formed on the upper surface of the transparent substrate 10, for example, by inkjet printing using UV (Ultra Violet) ink. As an example, the area of the structure 20X may be a "first target value", the area of the structure 20Y may be a "second target value", and the area of the structure 20Z may be a "third target value". Of course, as the plurality of structures 20, a plurality of groups of structures having two or four or more levels of diameters (areas) may be formed.

[0018] Here, a group of structures with a certain target value does not require that the areas of each structure exactly match. Rather, it may mean a group of structures that has some variation with respect to the target value (area) as a result of attempting to form a group of structures with a certain target value (area).

[0019] In the soft focus filter of this embodiment, the plurality of structures have a plurality of target values within the area range of 300 μm 2 to 200000 μm 2 Preferably, the plurality of structures have a plurality of target values within the area range of 700 μm 2 to 71000 μm 2 More preferably, the plurality of structures have a plurality of target values within the area range of 950 μm 2 to 30000 μm 2 and more preferably within the area range of

[0020] In the soft focus filter of this embodiment, the plurality of structures are arranged at an average pitch of 0.05 mm to 1 mm. Preferably, the plurality of structures are arranged at an average pitch of 0.1 mm to 0.7 mm, and more preferably at an average pitch of 0.1 mm to 0.5 mm.

[0021] The plurality of target values within the area range of 300 μm 2 to 200000 μm 2 that the plurality of structures have can be determined (measured) as follows. For example, the plurality of target values can be determined (measured) by setting various parameters such as the shape and size of the plurality of structures by inkjet printing using UV (Ultra Violet) ink described later.

[0022] The average pitch of the plurality of structures can be determined (measured) as follows. As an example, when the area of an arbitrary region on the soft focus filter is S (mm 2 ^2) and the number of structures (regardless of size) within the area is N, the average pitch P can be expressed by the following formula. P = (S / N) 1 / 2

[0023] The above formula calculates the length of one side when the area occupied by each structure on average is a square, and this is defined as the average pitch. When calculating the average pitch by actual measurement, it is desirable to calculate it for an area range of 20% or more of the optical effective range of the filter so as not to be biased towards local measurements within the filter.

[0024] A plurality of structures have a plurality of target values within an area range of 300μm 2 ~200000μm 2 and are arranged with an average pitch of 0.05 mm to 1 mm, thereby suppressing multiple images and color separation due to diffraction and interference and obtaining a natural soft focus effect.

[0025] If the area of the target value (e.g., defined by the lower limit value of the diameter) of the plurality of structures is less than 300μm 2 the contribution to the soft focus effect becomes too low. If the area of the target value (e.g., defined by the upper limit value of the diameter) of the plurality of structures exceeds 200000μm 2 the light-shielding region like the shadow caused by the structures generated in the optical path spreads too much, which has an adverse effect on the quality of the blurred image.

[0026] If the average pitch at which the plurality of structures are arranged is less than 0.05 mm, the density of the structures becomes too high, and depending on the variation in the arrangement, directional flare may occur, deteriorating the image quality, or the soft focus effect may become too high, also deteriorating the image quality. If the average pitch at which the plurality of structures are arranged exceeds 1 mm, it becomes difficult to obtain the soft focus effect, or it becomes necessary to increase the size of the structures, and the light-shielding region like the shadow caused by the structures generated in the optical path spreads too much, which has an adverse effect on the quality of the blurred image.

[0027] The plurality of structures are preferably arranged randomly such that locally (when viewed microscopically), the light transmittance is non-uniform depending on the position, and globally (when viewed macroscopically), the structures are arranged with a uniform dispersion rate. Also, the spatial frequency of the arrangement of the plurality of structures preferably has blue noise characteristics or green noise characteristics. The blue noise characteristics and green noise characteristics may be defined, for example, by the document "Digital halftoning" (written by Robert Ulichney).

[0028] Figure 2 is a first conceptual diagram when the distribution of structures in the soft focus filter is defined by spatial frequency using blue noise characteristics and green noise characteristics. Figure 2 conceptually shows the spatial frequency characteristics of the arrangement of each structure as a simple example of the arrangement of structures. As shown in Figure 2, the spatial frequency characteristics of blue noise and green noise have peaks in a frequency band avoiding approximately 0 - 8 Cycles / mm. Blue noise has higher peaks in higher frequency bands, and green noise has a peak around approximately 10 - 15 Cycles / mm.

[0029] Figure 3 is a second conceptual diagram when the distribution of structures in the soft focus filter is defined by spatial frequency using blue noise characteristics and green noise characteristics. Figure 3 is an explanatory diagram conceptually illustrating the spatial frequency characteristics of the threshold values set for each pixel of a blue noise dither matrix having blue noise characteristics as a simple example of the adjustment of the dither matrix. The spatial frequency characteristics of the blue noise matrix are such that the largest frequency component is in a high frequency region where the length of one cycle is near 2 pixels. Such spatial frequency characteristics are set in consideration of human visual characteristics. That is, it is a dither matrix in which the storage position of the threshold value is adjusted so that the largest frequency component occurs in the high frequency region, taking into account the human visual characteristic that the sensitivity is low in the high frequency region of the blue noise dither matrix.

[0030] Figure 3 further exemplifies the spatial frequency characteristics of the green noise matrix as a dashed curve. As shown, the spatial frequency characteristics of the green noise matrix have the largest frequency component in the intermediate frequency region where the length of one cycle is between 2 pixels and a dozen pixels. Since the threshold of the green noise matrix is set to have such spatial frequency characteristics, when determining whether to form dots for each pixel while referring to the dither matrix having green noise characteristics, dots are formed adjacent to each other in units of several dots, and as a whole, the dots are formed in a state where the clusters of dots are dispersed. In printers such as so-called laser printers where it is difficult to stably form fine dots of about 1 pixel, by referring to such a green noise matrix to determine whether to form dots, the generation of isolated dots can be suppressed. As a result, it becomes possible to quickly output an image with stable image quality. Conversely, the dither matrix referred to when determining whether to form dots in a laser printer or the like is set with a threshold adjusted to have green noise characteristics.

[0031] Thus, in the soft focus filter of this embodiment, a plurality of structures have a plurality of target values within the area range of 300 μm 2 ~200000 μm 2 and are arranged at an average pitch of 0.05 mm to 1 mm, and locally (when viewed microscopically), they are randomly arranged so that the light transmittance is non-uniform depending on the position, and widely (when viewed macroscopically), they are arranged so as to have a uniform dispersion rate. As a result, diffraction and interference phenomena occur respectively due to small structures, and the diffraction image gives a kind of blurring effect where light and shadow are blurred around the basic image. On the other hand, interference occurs due to the overlapping of diffraction images accompanying the diffraction phenomenon. However, since the structures have a plurality of target values, their sizes vary, and they are further randomly arranged, the regular components are weak even when interference occurs, and multiple images are less likely to occur, and as a whole, a soft focus effect like a beautiful "blur" can be obtained.

[0032] In the soft focus filter of the present embodiment, the plurality of structures satisfy at least one of the following conditions in a predetermined area on the filter: having a wavelength range of 50 nm or more with an absorbance of 0.3 or more in the wavelength range of 400 nm to 700 nm; and having an average value of absorbance in the wavelength range of 400 nm to 700 nm of 0.2 or more.

[0033] Preferably, in a predetermined area on the filter, the plurality of structures have a wavelength range of 70 nm or more with an absorbance of 0.3 or more in the wavelength range of 400 nm to 700 nm.

[0034] Preferably, the average value of absorbance of the plurality of structures in the wavelength range of 400 nm to 700 nm is 0.25 or more.

[0035] By satisfying one, preferably both, of the two requirements: "having a wavelength range of 50 nm or more with an absorbance of 0.3 or more in the wavelength range of 400 nm to 700 nm" and "having an average value of absorbance in the wavelength range of 400 nm to 700 nm of 0.2 or more", the amount of transmitted light of the structure is controlled, and the factor for controlling the intensity of diffused light in the filter section for obtaining the soft focus effect increases, making it easier to obtain the desired soft focus effect.

[0036] Here, "absorbance of 0.3 or more" is equivalent to a state where the amount of transmitted light is 50% or less when the incident light on the object is 100%. By giving this characteristic to the structure, the transmitted light of the structure becomes EV1 or more under for the proper exposure part, and by having a total wavelength range of 50 nm or more in this wavelength range, it is possible to suppress excessive flare generation on the entire screen.

[0037] Here, "absorbance of 0.2 or more" is equivalent to a state where the amount of transmitted light is 63% or less when the incident light on the object is 100%. By giving this characteristic to the structure, the transmitted light of the structure becomes on average about EV1 / 3 or more under for the proper exposure part, and it is possible to suppress excessive flare generation on the entire screen.

[0038] As described above, diffraction and interference phenomena occur in components shielded by small structures, while components passing through the structures are refracted to produce an optical path that scatters with respect to the normal optical path. By controlling the amount of transmitted light of the structure in the wavelength direction and the transmittance direction, the strength and appearance of the soft focus effect can be changed. For example, when the structure is formed of a black body with a transmittance of exactly zero, the components that pass through the structure and become scattered light disappear, and the soft focus effect across the entire screen becomes relatively weak, enabling an expression in which the soft focus effect appears strongly only for high-brightness subjects with respect to proper exposure. Conversely, when the structure is formed of a transparent body with a transmittance of exactly 100%, the components that pass through the structure and become scattered light are not excluded, and the soft focus effect across the entire screen becomes relatively strong, making it easier for the soft focus effect to appear even for properly exposed subjects.

[0039] Here, when the intensity of incident light on the object (sample) is defined as I0, the intensity of transmitted light from the object (sample) is defined as I, the optical path length in the object (sample) is defined as L [cm], the molar extinction coefficient is defined as ε [L / (mol·cm)], and the molar concentration [mol / L] is defined as c, the absorbance (Abs) = -log(I / I0) = εcL can be calculated.

[0040] In the soft focus filter of the present embodiment, the plurality of structures have at least three target values within a range of an area of 2500 μm 2 ~800000 μm 2 and it is preferable that the value obtained by dividing the maximum value among at least three target values by the minimum value is 2.25 or more. By satisfying this condition, the effect of suppressing multiple images can be fully exerted. If this condition is not satisfied, that is, when there are no at least three target values within a range of an area of 300 μm 2 ~200000 μm 2 or when there are at least three target values but the value obtained by dividing the maximum value by the minimum value is less than 2.25, the effect of suppressing multiple images may be insufficient.

[0041] In the soft focus filter of the present embodiment, it is preferable that the plurality of structures are formed by UV (Ultra Violet) ink. Thereby, the following structure characteristic of the soft focus filter of the present embodiment can be realized. (X) The plurality of structures have a plurality of target values within a range of an area of 300 μm 2 to 200000 μm 2 . (Y) The plurality of structures are arranged at an average pitch of 0.05 mm to 1 mm. (Z) The plurality of structures satisfy at least one of having a wavelength range of 50 nm or more with an absorbance of 0.3 or more in the wavelength range of 400 nm to 700 nm and having an average value of absorbance in the wavelength range of 400 nm to 700 nm of 0.2 or more.

[0042] Since inkjet printing directly ejects ink droplets discharged from an inkjet head onto a medium, it is not necessary to consider the thickness of the medium. In addition, since the position of the ink droplets can be controlled in units of several tens of μm, it is suitable for easily manufacturing a structure on a thin transparent substrate that exhibits a filter effect. Inkjet printing has high suitability for mass production. In addition, since it is a printing method without a master plate, it is easy to change the printing conditions according to the manufacturing model and individual, and is also suitable for small-lot, multi-variety production. In addition, as a characteristic of inkjet printing, there is a point that the color and density of the ink used can be adjusted as appropriate. For example, not only K ink, but also various colors such as C, M, Y ink, or R, G, B ink, O (orange), G (green), and W (white), and it is also possible to design complex colors by mixing these pigments. Furthermore, if the dilution rate of the ink is adjusted, it is also possible to control the transmittance.

[0043] As a plurality of structures, by manufacturing using inkjet printing such as UV ink, it becomes possible to form minute structures while minimizing the thickness of the transparent substrate. Also, according to inkjet printing, it becomes possible to create various expressions using a soft focus filter, and further, it becomes possible to house them singly or in plural within a camera housing. It is also easy to change the design values (diameter, diameter ratio, arrangement, etc.) of the structures for each individual. Further, by appropriately adjusting the color and concentration of the ink or controlling the dilution rate, it becomes possible to adjust the diffused light from the structures, and the degree of freedom of the soft focus expression can be improved.

[0044] Furthermore, the following can be cited as technical features when forming structures by inkjet printing (especially UV inkjet printing). By adjusting the concentration of the ink, an appropriate amount of light shielding can be obtained for the filter. Also, by controlling the irradiation timing of the UV lamp, an appropriate shape of the structure can be obtained for the filter. By adjusting the ejection waveform, the size of the structure can be changed stepwise.

[0045] Note that the method of forming a plurality of structures on a transparent substrate (the method of manufacturing a soft focus filter) is not limited to the form of ejecting and fixing structures that perform light diffusion by an inkjet printer as described above, and various modes can be adopted. For example, it is also possible to form a plurality of structures (manufacture a soft focus filter) on a transparent substrate by using various printing techniques.

[0046] The soft focus filter of this embodiment is preferably held so as to be insertable into and removable from the optical path of the optical system and satisfy the following conditional expression (1). (1)(d*(Nd - 1)) / D < 0.040 However, D: The air interval in the optical path of the optical system into which the soft focus filter is inserted and removed (the distance between the lens surface immediately before and the lens surface immediately after the soft focus filter), d: The thickness of the transparent substrate, n_d: Refractive index of the transparent substrate.

[0047] Conditional expression (1) is a conditional expression that stipulates thinning the transparent substrate and thus the soft focus filter by optimally setting various conditions of a plurality of structures having a light diffusion function and the transmission absorption characteristics. By satisfying conditional expression (1), when the soft focus filter is inserted and removed in the optical path of the optical system, the change in the optical path length and thus the change in aberration can be suppressed, and excellent imaging performance and thus image quality can be realized.

[0048] To impart a uniform soft focus effect to the entire screen, it is desirable to place the filter near the aperture stop through which the light beam at each picture angle passes through the closest position. Inserting and removing the filter in the optical path may cause a change in the optical path length at the inserted and removed air gap, resulting in changes in field curvature and spherical aberration, etc., which may lead to deterioration of the image quality. However, if the filter is thin, it becomes possible to suppress this aberration variation. By satisfying conditional expression (1), it is possible to thin the soft focus filter and suppress the aberration variation within an allowable range. If conditional expression (1) is not satisfied, the thinning of the soft focus filter will be insufficient, and there is a risk that the aberration variation will exceed the allowable range.

[0049] The soft focus filter of the present embodiment is held at a position adjacent to the aperture stop within the optical path of the optical system (in Numerical Example 1 described later, the soft focus filter is inserted immediately before the aperture stop, and in Numerical Example 2 described later, the soft focus filter is inserted immediately after the aperture stop). As a result, the light beams at all picture angles pass through approximately the same region of the filter, making it possible to impart a uniform filter effect to the entire imaging screen. In particular, by holding the soft focus filter of the present embodiment at a position adjacent to the aperture stop within the optical path of the optical system and satisfying the above-described conditional expression (1), a more suitable soft focus filter effect can be realized.

[0050] Thus, the soft focus filter of this embodiment has a transparent substrate and a plurality of structures having a light diffusion function formed on the transparent substrate, and the plurality of structures have a plurality of target values within a range of an area of 300 μm 2 ~200,000 μm 2 and are arranged at an average pitch of 0.05 mm to 1 mm, and the plurality of structures satisfy at least one of having a wavelength range of 50 nm or more with an absorbance of 0.3 or more in a wavelength range of 400 nm to 700 nm and having an average value of absorbance in a wavelength range of 400 nm to 700 nm of 0.2 or more.

[0051] More specifically, based on the absorbance of the structure that performs light diffusion to obtain a soft focus effect and the distribution of the structures in the soft focus filter, the physical characteristics of the soft focus filter are defined to specify the constituent elements of the soft focus filter. The distribution of the structures in the soft focus filter can be defined by spatial frequency using, for example, blue noise characteristics and green noise characteristics. Further, the soft focus filter is not an external filter, but is mounted by an insertion / extraction mechanism that is inserted into the optical system during soft focus shooting and withdrawn from the inside of the optical system during normal shooting.

[0052] Specific numerical examples 1 and 2 are shown. The meanings of the respective symbols in Numerical Examples 1 and 2 are as follows. The glass types (glass materials) in the examples are the optical glass type names of HOYA Corporation (HOYA) and Ohara Corporation (OHARA). The unit of length is [mm]. Here, the aspherical surface is defined by the following formula when the reciprocal of the paraxial curvature radius (paraxial curvature) is C and the height from the optical axis is H. x = CH / [1 + [1 - (1 + K)C 2 [[ID=ID=18]]H 2 2 + A4H 1 / 2 + A6H 4 + A8H 6 + A 8 H 10 + A 10 H 12 + A​12 +A 14 H 14 f: Overall focal length F: F-number w: Half field angle Ya: Maximum image height R: Radius of curvature D: Spacing between surfaces Nd: Refractive index for d-line νd: Abbe number for d-line BF: Back focus K: Conic constant of aspheric surface A4: Fourth-order aspheric coefficient A6: Sixth-order aspheric coefficient A8: Eighth-order aspheric coefficient A10: Tenth-order aspheric coefficient A12: Twelfth-order aspheric coefficient A14: Fourteenth-order aspheric coefficient

[0053] [Numerical Example 1] FIG. 4A, FIG. 4B, and Table 1-3 show the optical system of Numerical Example 1. FIG. 4A is a lens configuration diagram with the soft focus filter SFF inserted into the optical system, and FIG. 4B is a lens configuration diagram with the soft focus filter SFF retracted from the optical system. Table 1 is surface data (lens data), Table 2 is aspheric surface data, and Table 3 is focal length data.

[0054] The optical system of Numerical Example 1 is composed of, in order from the object side, a first lens group G1 with negative refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with positive refractive power. Filters F1 and F2 are arranged between the fourth lens group G4 and the image plane (image plane in design) I. Filters F1 and F2 are composed of, for example, flat plate members such as a low-pass filter, an infrared cut filter, and a cover glass of an image sensor. In the following surface data, filters F1 and F2 are described as optical glass.

[0055] An aperture stop SP for adjusting the amount of light is provided between the second lens group G2 and the third lens group G3. Further, a soft focus filter SFF is provided between the second lens group G2 and the third lens group G3 and immediately before (in the vicinity of) the aperture stop SP so that it can be inserted (ON) / retracted (OFF). FIG. 4A shows the inserted (ON) state of the soft focus filter SFF, and FIG. 4B shows the retracted (OFF) state of the soft focus filter SFF.

[0056] The first lens group G1 is composed of a negative meniscus lens 11 that is convex on the object side.

[0057] The second lens group G2 is composed of, in order from the object side, a negative meniscus lens 21 that is convex on the image side, a biconvex positive lens 22, and a biconcave negative lens 23. The negative meniscus lens 21 has an aspherical surface on the object-side surface. The biconvex positive lens 22 and the biconcave negative lens 23 are joined together.

[0058] The third lens group G3 is composed of, in order from the object side, a biconvex positive lens 31, a positive meniscus lens 32 that is convex on the image side, and a biconcave negative lens 33. The positive meniscus lens 32 and the biconcave negative lens 33 are joined together.

[0059] The fourth lens group G4 is composed of a positive meniscus lens 41 that is convex on the image side. The positive meniscus lens 41 has aspherical surfaces on both sides.

[0060] (Table 1) f = 13.9, F = 3.61, w = 46.3, Ya = 14.127, BF = 0.7 Surface number R D Nd νd Glass type (glass material) 1 23.625 0.700 1.49700 81.54 S-FPM2 (OHARA) 2 6.574 3.490 3* -26.619 0.700 1.68948 31.02 L-TIM28 (OHARA) 4 -125.862 0.200 5 11.555 2.820 1.90525 35.04 S-LAH98(OHARA) 6 -10.821 0.600 1.68430 26.81 S-NPH7(OHARA) 7 21.915 1.500 8 aperture 1.235 9 13.407 1.870 1.85400 40.38 S-LAH98(OHARA) 10 -37.040 0.350 11 -19.883 1.850 1.88300 40.76 S-LAH59(OHARA) 12 -7.868 0.600 1.75211 25.05 FF8(HOYA) 13 110.687 1.330 14* -8.648 1.390 1.85400 40.38 L-LAH94(OHARA) 15* -8.454 9.350 16 ∞ 0.770 1.56200 61.80 Optical glass 17∞1.300 18 ∞ 0.700 1.50000 64.00 Optical glass 19∞BF * denotes a rotationally symmetric aspheric surface. (Table 2) Surface number K A4 A6 A8 A10 3 -0.6704 -9.76999E-05 -3.73079E-07 -1.91918E-08 0.00000E+00 14 -0.9583 -3.70200E-05 2.86718E-05 9.49331E-07 -5.04121E-08 15 -0.9660 2.79491E-04 1.65754E-05 1.18765E-06 -3.49979E-08 (Table 3) focal length First lens group: -18.58 Second lens group: 20.01 Third lens group: 18.64 Fourth lens group 102.62

[0061] FIG. 5 is a diagram showing the structure of the soft focus filter SFF of Numerical Example 1. More specifically, FIG. 5 shows an aspect of the structure on the transparent substrate that constitutes the soft focus filter SFF of Numerical Example 1. The base material is a polycarbonate sheet with a thickness of 0.05 mm and a refractive index of 1.58. The sizes of the structures are formed aiming at three types with a small diameter = 70 μm, a medium diameter = 90 μm, and a large diameter = 150 μm respectively in terms of diameter. In terms of area conversion, the small diameter ≒ 3848 μm 2 , the medium diameter ≒ 6362 μm 2 , the large diameter ≒ 17671 μm 2 . The average pitch is about 0.22 mm. The soft focus filter SFF of Numerical Example 1 is arranged in a form adjacent to the object side of the aperture stop SP, and the on-axis light beam on the soft focus filter SFF is φ4.58 mm. The diameter of the structure on the soft focus filter SFF is about 1.5% to 3.3% with respect to the on-axis light beam. If the structure in the light beam becomes too large, when the image is blurred, the shadow of the structure appears significantly and degrades the quality of the blurred image. Therefore, it is desirable that the size of the structure on the soft focus filter SFF is less than 10% of the diameter of the on-axis light beam. Further, the structure on the transparent substrate is formed with UV (Ultra Violet) ink, and black ink with an average absorbance value of 0.83 in the wavelength range of 400 nm to 700 nm is used. By forming the structure with a material having a relatively large absorbance, it is possible to suppress the soft filter effect and suppress the occurrence of excessive flare for a bright subject.

[0062] Table 4 shows the conditional correspondence numerical values (calculation results) of the soft focus filter SFF of Numerical Example 1 and the optical system equipped with the same. (Table 4) Area of structure: small diameter ≒ 3848 μm 2 , medium diameter ≒ 6362 μm 2 , large diameter ≒ 17671 μm 2 Average pitch: 0.22 mm Wavelength range with an absorbance of 0.3 or more in the wavelength range of 400 nm to 700 nm: 300 nm (that is, the entire range of 400 nm to 700 nm) Average value of absorbance in the wavelength range of 400 nm to 700 nm: 0.83 Target number of the area of the structure: 3 Ratio of the minimum value to the maximum value of the target area: 4.59 (= 17671 μm 2 / 3848 μm 2 ) (d * (Nd - 1)) / D = (0.05 * (1.58 - 1)) / 2.735 ≒ 0.011

[0063] [Numerical Example 2] FIGS. 6A, 6B, and Table 5-7 show the optical system of Numerical Example 2. FIG. 6A is a lens configuration diagram with the soft focus filter SFF' inserted into the optical system, and FIG. 6B is a lens configuration diagram with the soft focus filter SFF' retracted from the optical system. Table 5 is surface data (lens data), Table 6 is aspherical data, and Table 7 is focal length data.

[0064] The optical system of Numerical Example 2 is composed of a first lens group G1' with positive refractive power, a second lens group G2' with positive refractive power, and a third lens group G3' with negative refractive power, in order from the object side. Filters F1' and F2' are arranged between the third lens group G3' and the image plane (designed image plane) I'. The filters F1' and F2' are composed of flat plate members such as a low-pass filter, an infrared cut filter, and a cover glass of an image sensor, for example. In the following surface data, the filter F1' is described as an optical filter, and F2' is described as an optical glass.

[0065] An aperture stop SP' for adjusting the light amount is provided between the first lens group G1' and the second lens group G2'. Further, a soft focus filter SFF' is provided between the first lens group G1' and the second lens group G2' and immediately after (in the vicinity of) the aperture stop SP' so that it can be inserted (ON) / retracted (OFF). FIG. 6A shows the inserted (ON) state of the soft focus filter SFF', and FIG. 6B shows the retracted (OFF) state of the soft focus filter SFF'.

[0066] The first lens group G1’ is composed of, in order from the object side, a negative meniscus lens 11’ convex on the object side, a biconcave negative lens 12’, and a biconvex positive lens 13’. The negative meniscus lens 11’ has an aspherical surface on the image side. The biconcave negative lens 12’ and the biconvex positive lens 13’ are joined together.

[0067] The second lens group G2’ is composed of, in order from the object side, a biconvex positive lens 21’, a biconcave negative lens 22’, and a positive meniscus lens 23’ convex on the image side. The positive meniscus lens 23’ has aspherical surfaces on both sides. The biconvex positive lens 21’ and the biconcave negative lens 22’ are joined together.

[0068] The third lens group G3’ is composed of a negative meniscus lens 31’ convex on the image side. The negative meniscus lens 31’ has aspherical surfaces on both sides.

[0069] (Table 5) f = 18.35, F = 2.87, w = 37.9, Ya = 14.13, BF = 0.7 Surface number R D Nd νd Glass type (glass material) 1 13.163 0.70 1.58313 59.38 L - BAL42 (OHARA) 2* 10.800 2.21 3 - 37.730 0.60 1.64769 33.79 S - TIM22 (OHARA) 4 6.645 2.94 1.88300 40.76 S - LAH58 (OHARA) 5 - 40.496 1.10 6 Aperture stop 1.21 7 16.251 2.23 1.88300 40.76 S - LAH58 (OHARA) 8 - 10.978 0.50 1.68893 31.07 S - TIM28 (OHARA) 9 13.041 1.43 10* - 20.013 1.33 1.85135 40.10 MTAFD305 (HOYA) 11* -15.533 5.271 12* -20.015 0.85 1.58313 59.38 L-BAL42(OHARA) 13* -60.000 3.398 14 ∞ 0.77 1.56200 61.80 Optical filter 15 ∞ 1.30 16 ∞ 0.70 1.50000 64.00 Optical glass 17 ∞ BF * is a rotationally symmetric aspherical surface. (Table 6) Surface number K A4 A6 A8 A10 A12 A14 2 0 2.6842E-04 1.9135E-06 2.0622E-07 -3.4685E-09 1.3440E-10 2.1535E-13 10 0 1.7845E-04 -7.6428E-06 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 11 1.60673 4.5363E-04 -1.8081E-06 5.4014E-08 2.7568E-10 0.0000E+00 0.0000E+00 12 3.72112 1.0709E-05 -4.9579E-06 7.9678E-08 0.0000E+00 0.0000E+00 0.0000E+00 13 24.10589 -1.1114E-04 -3.3387E-06 4.6772E-08 -5.7777E-11 -1.6059E-12 1.2206E-14 (Table 7) Focal length First lens group 31.65 Second lens group 29.44 Third lens group -51.91

[0070] FIG. 7 is a diagram showing the structure of the soft focus filter SFF' of Numerical Example 2. More specifically, FIG. 7 shows an aspect of the structure on the transparent substrate that constitutes the soft focus filter SFF' of Numerical Example 2. The base material is a sheet made of cycloolefin polymer with a thickness of 0.013 mm and a refractive index of 1.55. The sizes of the structures are formed aiming at three types with diameters of small diameter = 50 μm, medium diameter = 80 μm, and large diameter = 120 μm, respectively. In terms of area conversion, the small diameter is approximately 1963 μm 2 , the medium diameter is approximately 5027 μm 2 , and the large diameter is approximately 11310 μm 2 . The average pitch is about 0.40 mm. The soft focus filter SFF' of Numerical Example 2 is arranged adjacent to the image side of the aperture stop SP', and the on-axis light beam on the soft focus filter SFF' is φ6.32 mm. The diameter of the structure on the soft focus filter SFF' is about 0.8% - 1.9% with respect to the on-axis light beam. The structure on the transparent substrate is formed with UV (Ultra Violet) ink, and black ink with an average absorbance value of 0.83 in the wavelength range of 400 nm to 700 nm is used. By forming the structure with a material having a relatively large absorbance, it becomes possible to suppress the soft filter effect and suppress the occurrence of excessive flare for a bright subject. Note that the absorbance of the material of the structure on the transparent substrate can be variously selected according to the desired soft filter effect. For example, when using yellow with an average absorbance of 0.27, which is relatively low, in the wavelength range of 400 nm to 700 nm, it is possible to produce a flare feeling even under relatively dark exposure conditions. When using cyan with an average absorbance of 0.49 in the wavelength range of 400 nm to 700 nm, an intermediate effect between yellow and black can be obtained.

[0071] Table 8 shows the conditional correspondence numerical values (calculation results) of the soft focus filter SFF' of Numerical Example 2 and the optical system equipped with the same. (Table 8) Area of the structure: small diameter ≈ 1963 μm 2 , medium diameter ≈ 5027 μm 2 , large diameter ≈ 11310 μm 2 Average pitch: 0.40 mm Wavelength range with absorbance of 0.3 or more in the wavelength range of 400 nm to 700 nm: In the case of black, 300 nm (that is, the entire range of 400 nm to 700 nm) In the case of yellow, 80 nm (400 nm to 480 nm) In the case of cyan, 146 nm (554 nm to 700 nm) Average value of absorbance in the wavelength range of 400 nm to 700 nm: In the case of black, 0.83 In the case of yellow, 0.27 In the case of cyan, 0.49 Target number of areas of the structure: 3 Ratio of the minimum value to the maximum value of the target area: 5.76 (= 11310 μm 2 / 1963 μm 2 ) (d * (Nd - 1)) / D = (0.013 * (1.55 - 1)) / 2.31 ≒ 0.003

[0072] <Soft focus filter insertion (ON) / retraction (OFF) switching mechanism> For example, the soft focus filters SFF and SFF' in the above-described numerical examples 1 and 2 are built in a shutter unit disposed near the aperture stops SP and SP'. By adopting a configuration that enables "arrangement on the optical axis" and "retraction from the optical axis" by a drive system provided in this shutter unit, it is possible to share the mechanism and power source for inserting and retracting the soft focus filter with respect to the optical axis position with the shutter within the shutter unit, and it becomes possible to configure the imaging optical device compactly. Further, in response to an operation from the camera body, during normal shooting, the soft focus filter is retracted from the optical axis, and when turning on the filter effect, the soft focus filter can be inserted on the optical axis so as to cover the entire aperture stop.

[0073] Figures 8A and 8B are the first conceptual diagrams illustrating the insertion / removal mechanism of the soft focus filter SFF”. Here, an insertion / removal mechanism equipped with a retracting mechanism that realizes thinning when the lens barrel is stored by moving the soft focus filter SFF” away from the optical axis when the lens barrel is stored will be described. However, there is freedom in the specific form of the insertion / removal mechanism, and various design changes are possible.

[0074] In FIGS. 8A and 8B, the left side indicates the front (object side) in the optical axis direction, and the right side indicates the rear (image side) in the optical axis direction. The insertion / removal mechanism includes a filter holding unit 1000 that holds the soft focus filter SFF”, a front lens holding unit 2000 that holds the front lens GF, and a rear lens holding unit 3000 that holds the rear lens GR. The front lens GF corresponds to, for example, the second lens group G2 in Numerical Example 1 or the first lens group G1’ in Numerical Example 2, and the rear lens GR corresponds to, for example, the third lens group G3 in Numerical Example 1 or the second lens group G2’ in Numerical Example 2. A guide piece 1100 having a guide hole is formed in the filter holding unit 1000, a guide piece 2100 having a guide hole is formed in the front lens holding unit 2000, and a guide piece 3100 having a guide hole is formed in the rear lens holding unit 3000. The insertion / removal mechanism has a guide axis GS that extends parallel to the optical axis of the optical system. The guide holes of the guide piece 1100 of the filter holding unit 1000, the guide holes of the guide piece 2100 of the front lens holding unit 2000, and the guide holes of the guide piece 3100 of the rear lens holding unit 3000 are inserted through the guide axis GS. The guide axis GS is rotationally driven to switch between the extended state and the stored state of the lens barrel. As the guide axis GS rotates, the front lens holding unit 2000 and the rear lens holding unit 3000 can move in the optical axis direction along the guide axis GS. Further, as the guide axis GS rotates, the filter holding unit 1000 moves in the optical axis direction along the guide axis GS and can be inserted / removed on the optical path of the optical system by rotating around the guide axis GS.

[0075] As shown in Fig. 8A, when the lens barrel is extended, the filter holding unit 1000 (soft focus filter SFF”), the front lens holding unit 2000 (front lens GF), and the rear lens holding unit 3000 (rear lens GR) are extended to predetermined positions along the guide axis GS parallel to the optical axis of the optical system. Even in this extended state, when soft focus shooting is not performed, the filter holding unit 1000 (soft focus filter SFF”) is retracted from the optical path of the optical system. On the other hand, when performing soft focus shooting, the filter holding unit 1000 (soft focus filter SFF”) is inserted onto the optical path of the optical system, that is, between the front lens holding unit 2000 (front lens GF) and the rear lens holding unit 3000 (rear lens GR) by the rotational drive of the guide axis GS. That is, the filter holding unit 1000 (soft focus filter SFF”) is inserted onto the optical path of the optical system only when performing soft focus shooting. Fig. 8A depicts a state where the filter holding unit 1000 (soft focus filter SFF”) is inserted onto the optical path of the optical system.

[0076] As shown in Fig. 8B, when the lens barrel is retracted, the filter holding unit 1000 (soft focus filter SFF”) is retracted from the optical path of the optical system by the rotational drive of the guide axis GS. Further, in accordance with the lens barrel being retracted and the optical system being housed, the filter holding unit 1000 (soft focus filter SFF”), the front lens holding unit 2000 (front lens GF), and the rear lens holding unit 3000 (rear lens GR) are housed to predetermined positions along the guide axis GS. Comparing the extended state of Fig. 8A and the housed state of Fig. 8B, it can be seen that the former has a larger distance between the front lens holding unit 2000 (front lens GF) and the rear lens holding unit 3000 (rear lens GR), and the latter has a smaller distance between the front lens holding unit 2000 (front lens GF) and the rear lens holding unit 3000 (rear lens GR).

[0077] In this way, a guide axis GS parallel to the optical axis of the optical system is provided, and a soft focus filter SFF” is installed on the guide axis GS. In accordance with the extension / retraction of the lens barrel, the soft focus filter SFF” also performs extension / retraction. By rotating the guide axis GS, insertion onto the optical axis / retreat from the optical axis of the soft focus filter SFF” can be realized.

[0078] Note that the position where the soft focus filter is inserted and removed in the lens barrel is a position inside the camera body even when the lens barrel is extended, that is, when the soft focus filter is retracted from the optical axis, a hole for inserting the soft focus filter is required in the lens barrel. Since the barrel portion with the hole is inside the camera body even when the lens barrel is extended, it cannot be recognized from the outside. In FIG. 8A, the line defining the inside and outside of the camera body is drawn as a dashed line, and the line defining the inside and outside of the lens barrel is drawn as a two-dot chain line. The left side of the dashed line is the outside of the camera body, and the right side of the dashed line is the inside of the camera body. The upper side of the two-dot chain line is the outside of the lens barrel, and the lower side of the two-dot chain line is the inside of the lens barrel. In the extended state of the lens barrel, even when the filter holding unit 1000 (soft focus filter SFF”) retreats from the optical path of the optical system, since the filter holding unit 1000 (soft focus filter SFF”) is located inside the camera body, it cannot be visually recognized from the outside.

[0079] FIGS. 9A and 9B are a second conceptual diagram illustrating the insertion / removal mechanism of the soft focus filter. As shown in FIGS. 9A and 9B, a shutter unit 30 is provided between the front lens GF and the rear lens GR (the boundary), and the round hole formed in the central portion of the shutter unit 30 serves as the aperture stop SP” of the optical system. At the peripheral edge of the round hole forming the aperture stop SP”, aperture blades, shutter blades, and a soft focus filter are housed, and these aperture blades, shutter blades, and soft focus filter move back and forth between the peripheral edge of the round hole forming the aperture stop SP” and the inside of the round hole forming the aperture stop SP” as shown by the arrows in FIG. 9A as required.

[0080] <Insertion position of soft focus filter> In the above embodiment, the case where the insertion position of the soft focus filter is the aperture stop or the vicinity thereof has been illustrated and described (in Numerical Example 1, the soft focus filter SFF is inserted immediately before the aperture stop SP, and in Numerical Example 2, the soft focus filter SFF' is inserted immediately after the aperture stop SP'). On the other hand, even when the soft focus filter is inserted at a position away from the aperture stop, it is possible to obtain a certain soft focus effect. However, when considering the light beam, inserting the soft focus filter at the aperture stop or its vicinity is most preferable from the viewpoint of miniaturizing (reducing the diameter) the soft focus filter and suitably inserting and removing the soft focus filter on the optical axis of the optical system.

[0081] <Application examples to digital cameras, interchangeable lenses, etc.> Referring to FIGS. 10 and 11, a digital camera (imaging device) 100 equipped with the soft focus filter or the optical system of the present embodiment will be described.

[0082] The digital camera 100 includes a camera body (housing) 101, a photographing lens 102, a viewfinder 103, a flash 104, a shutter button 105, a power button 106, a liquid crystal monitor 107, operation buttons 108, and a memory card slot 109.

[0083] The camera body 101 houses each component of the digital camera 100. The photographing lens 102 is, for example, a unit in which the optical system of the present embodiment is incorporated into a lens barrel and / or an interchangeable lens. The viewfinder 103 is a peephole for determining a subject and composition. The flash 104 emits a flash during night photography or low-light photography. The shutter button 105 is a physical switch for executing photography by the digital camera 100. The power button 106 is a physical switch for switching the power of the digital camera 100 on and off. The liquid crystal monitor 107 displays a photographed image or the like by the digital camera 100. The operation button 108 is a physical switch for setting the photographing mode or the like of the digital camera 100. The memory card slot 109 is a slot for inserting a memory card for storing a photographed image or the like by the digital camera 100.

[0084] As internal functional components of the camera body 101, the digital camera 100 includes a central processing unit 111, an image processing unit 112, a light receiving element 113, a signal processing unit 114, a semiconductor memory 115, and a communication card 116.

[0085] The central processing unit 111 performs various arithmetic processes inside the digital camera 100. The image processing unit 112 performs various image processes on the photographed image by the digital camera 100. The light receiving element 113 takes in and receives external light used for photometry processing. The signal processing unit 114 performs various signal processes such as a photographing instruction signal and an image processing signal. The semiconductor memory 115 constitutes a temporary storage area for the photographed image by the digital camera 100. The communication card 116 enables wireless communication with an external device such as a PC. The digital camera 100 functions as an information processing device that performs various processes on the captured image information.

[0086] FIG. 12 is an external perspective view showing an example of the interchangeable lens (lens barrel) 102 of the present embodiment. As shown in FIG. 12, the interchangeable lens 102 has a lens holding cylinder 102X and an optical system held by the lens holding cylinder 102X. In FIG. 12, among the optical systems, the lens 11 or 11' disposed on the most object side of the first lens group G1 or G1' is depicted.

[0087] The configuration of the digital camera 100 described herein is merely an example, and various design changes are possible (there is freedom in the specific form of the digital camera 100). Further, it is also applicable to an information processing apparatus equipped with a photographing function.

[0088] The optical system of the present embodiment can be applied to, for example, an interchangeable lens, a portable information terminal device, a video camera, a silver halide camera, an optical sensor, a projection optical system (projector), etc., other than the digital camera 100 described above.

[0089] Hereinafter, the invention described in the claims of the present application at the time of filing is appended. [Appendix 1] A transparent substrate, a plurality of structures having a light diffusion function formed on the transparent substrate, and having, <000049�>the plurality of structures have a plurality of target values within a range of an area of 300 μm 2 to 200,000 μm 2 and are arranged at an average pitch of 0.05 mm to 1 mm, the plurality of structures satisfy at least one of having a wavelength range of 50 nm or more with an absorbance of 0.3 or more in the wavelength range of 400 nm to 700 nm and having an average value of absorbance in the wavelength range of 400 nm to 700 nm of 0.2 or more, A soft focus filter characterized by the above. [Appendix 2] The plurality of structures are locally arranged randomly so that the light transmittance becomes non-uniform depending on the position, and are arranged so as to have a uniform dispersion rate over a wide area. 2. The soft focus filter according to claim 1, [Appendix 3] The plurality of structures are 300 μm 2 ~200,000μm 2 It has at least three target values within the area of a value obtained by dividing the maximum value of the at least three target values by the minimum value thereof is 2.25 or more; 3. The soft focus filter according to claim 1 or 2, [Appendix 4] the plurality of structures are formed by UV (Ultra Violet) ink; 4. The soft focus filter according to claim 1, wherein the soft focus filter is a polyimide film. [Appendix 5] the soft focus filter is held in an optical path of the optical system so as to be insertable and detachable; The following condition (1) is satisfied: 5. The soft focus filter according to claim 1, wherein the soft focus filter is a polyimide film. (1)(d*(Nd-1)) / D<0.040 however, D: Air gap in the optical path of the optical system where the soft focus filter is inserted or removed, d: the thickness of the transparent substrate, Nd: the refractive index of the transparent substrate. [Appendix 6] The soft focus filter is held in a position adjacent to the aperture stop in the optical path of the optical system. 6. The soft focus filter according to claim 1, wherein the soft focus filter is a [Appendix 7] 7. An optical system comprising the soft focus filter according to any one of claims 1 to 6. [Appendix 8] An imaging device comprising the soft focus filter according to any one of Supplementary Note 1 to Supplementary Note 6. [Appendix 9] 7. An information processing device comprising the soft focus filter according to any one of Supplementary Note 1 to Supplementary Note 6.

Description of Symbols

[0090] 10 transparent substrate 20 20X 20Y 20Z structure 30 shutter unit G1 G1’ first lens group G2 G2’ second lens group G3 G3’ third lens group G4 fourth lens group SP SP’ SP” aperture stop SFF SFF’ SFF” soft focus filter

Claims

1. A transparent substrate, A plurality of structures having a light diffusion function formed on the transparent substrate, And having, The plurality of structures have a plurality of target values within a range of an area of 300 μm ２ to 200,000 μm ２ and The plurality of structures are arranged at an average pitch of 0.05 mm to 1 mm, The plurality of structures satisfy at least one of having a wavelength range of 50 nm or more with an absorbance of 0.3 or more in the wavelength range of 400 nm to 700 nm and having an average value of absorbance in the wavelength range of 400 nm to 700 nm of 0.2 or more, A soft focus filter characterized by the above.

2. The plurality of structures are locally arranged randomly so that the light transmission amount is non-uniform depending on the position, and are arranged so as to have a uniform dispersion rate over a wide area, The soft focus filter according to claim 1, characterized by the above.

3. The plurality of structures have at least three target values within a range of an area of 300 μm ２ to 200,000 μm ２ and The value obtained by dividing the maximum value among the at least three target values by the minimum value is 2.25 or more, The soft focus filter according to claim 1 or claim 2, characterized by the above.

4. The plurality of structures are formed by UV (Ultra Violet) ink, The soft focus filter according to claim 1 or claim 2, characterized by the above.

5. The soft focus filter is held so as to be insertable into and removable from the optical path of an optical system, Satisfies the following conditional expression (1), The soft focus filter according to claim 1 or claim 2, characterized by the above. (1) (d * (Nd - 1)) / D < 0.040 However, D: The air gap in the optical path of the optical system into which the soft focus filter is inserted and removed, d: The thickness of the transparent substrate, Nd: The refractive index of the transparent substrate.

6. The soft focus filter is held at a position adjacent to the aperture stop in the optical path of the optical system, The soft focus filter according to claim 1 or claim 2, characterized by the above.

7. An optical system having the soft focus filter according to claim 1 or claim 2.

8. An imaging device having the soft focus filter according to claim 1 or claim 2.

9. An information processing device having the soft focus filter according to claim 1 or claim 2.

Images