JPH0273321A - Soft focus method - Google Patents

Abstract

PURPOSE:To easily and continuously vary a soft focus effect by using a soft focus filter by providing the soft focus filter on an optical axis between an image forming lens and an image surface so that it can be displaced in the optical axis direction. CONSTITUTION:A soft focus filter 30 is provided between an image forming lens 10 and an image surface so that it can be displaced in the optical axis direction. In this case, the soft focus filter 30 is formed by distributing two- dimensionally and at random a small opening having a phase difference against other part than an opening. In such a way, by varying continuously a soft focus effect, a desired soft focus effect can be realized. Also, as for the soft focus filter 30, those of various constitutions can be used, and especially, since even plastic shaping can be executed, the mass production can be executed at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a soft focus method, and more particularly to a soft focus method in which the soft focus effect can be changed continuously. This method can be used for shooting with a camera, video camera, movie camera, etc.

U. Prior Art] Soft focus is an important technique in video shooting, and various methods for achieving the soft focus effect have been known.

Methods for achieving these soft focus effects can be roughly divided into a lens movement method in which the spherical aberration is changed by moving a lens group or a single lens in the imaging lens, and a method using a soft focus filter.

The former lens movement method requires highly accurate synchronization and tilting. Furthermore, if you change the F/No by aperture, such as when you want to take a slow shutter speed for a bright subject, you will not be able to obtain the desired soft focus effect.

Furthermore, it is difficult to produce the same soft focus effect at the center and periphery of the screen, and the soft focus effect tends to deteriorate at the periphery of the image.

[Problem to be solved by the invention] On the other hand, those who use a soft focus filter.

In the case of the method, it is not possible to change the soft focus effect using commercially available soft focus filters. As soft focus filters that can change the soft focus effect, optical phase filters using electro-optic crystal elements and liquid crystal cells are known (for example, Japanese Patent Application Laid-open No. 15125/1983, Japanese Patent Application Laid-open No. 61-15125, 110119), the structure as a filter is complicated, and a complicated circuit is required to change the soft focus effect.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a novel soft focus method that can easily and continuously change the soft focus effect using a soft focus filter.

[Means to solve the problem] The present invention will be explained below.

Two soft focus methods are proposed herein.

Both of the methods of claim 1 and 2 use a soft focus filter in which small apertures having a phase difference with respect to portions other than the apertures are randomly distributed two-dimensionally.

In the method of claim 1, the soft focus filter is disposed on the optical axis between the imaging lens and the image plane so as to be movable in the optical axis direction.

In the method according to claim 2, the soft focus effect is continuously changed by displacing the soft focus filter in the optical axis direction to obtain a desired soft focus effect. , a group of soft focus filters that are configured to be complementary to each other and combined in close proximity to each other are arranged on the optical axis near the imaging lens. - That is, the soft focus filter group may be arranged between the imaging lens and the image plane, or in front of the imaging lens.

The soft focus effect is continuously changed by displacing at least one soft focus filter in the group of soft focus filters in a plane perpendicular to the optical axis relative to the other soft focus filters. to achieve the desired soft focus effect.

In order to displace at least one of the soft focus filters relative to the other in a plane perpendicular to the optical axis, the soft focus filter to be displaced may be translated in a direction perpendicular to the optical axis. , may be rotated around the optical axis, or a combination of translational displacement and rotation 1
Also good. Note that the meaning of the plurality of soft focus filters being complementary to each other will be described later.

[Function] FIG. 5 shows a typical example of a conventionally known soft focus filter.

Reference numeral 1 indicates a glass substrate. On this glass substrate 1,
A phase section 2 is provided.

The phase portions 2 have a small circular shape and are two-dimensionally and randomly distributed on the substrate 1. These phase portions 2 are apertures with respect to other portions, and have a phase difference with respect to the portions other than the apertures.

In the example shown in this figure, the phase portion 2, that is, the opening is a transparent film formed by vapor deposition of SiO□, etc., and protrudes from the surface of the substrate 1 with a step.

The aperture is a portion that provides a phase difference to light passing through the aperture and light passing through a portion other than the aperture.

Therefore, to configure the aperture, it may be formed by unevenness in the area other than the aperture, or a soft focus filter may be configured by changing the internal distribution of refractive index between the area other than the aperture and the aperture. Alternatively, a soft focus filter can be constructed by combining the above-described unevenness and refractive index distribution.

Now, in the soft focus filter as described above, S is the average diameter of each phase section 2 which is the aperture, t is the thickness of the phase section 2, and S is the part of the sum of the areas of the phase section 2 other than the aperture. Assuming that the area ratio to area, λ is the wavelength, δ is the phase difference given by the phase section, and n is the refractive index of the phase section 2, then M when the soft focus filter is placed on the pupil plane of the imaging lens.
The influence on TF is as shown in FIG. 2 (I).

Fc and Me in the figure are Fc=s/bλ (1)
Mc= l 1-3+5exp(-ikδ)+2
It is given by (2). However, in equation (1), b represents the distance between the soft focus filter and the image plane, and (2
) in the formula is δ=(n-1)t (3)
It is.

The method of claim 1 is made by focusing on the above equation (1).

That is, looking at equation (1), Fc is determined by S, b, and E. Among these, S is a value specific to the soft focus filter, and is a constant determined by the soft focus filter. However, since b is the distance between the soft focus filter and the image plane as described above, by changing this distance and changing b, Fc can be changed. That is, the minimum value Fc of the spatial frequency at which the MTF becomes a constant value can be changed by changing the position of the soft focus filter.

Therefore, in the method of claim 1, the soft focus filter is disposed on the optical axis between the imaging lens and the image plane, and the soft focus filter is displaceable in the optical axis direction. Fc
By changing , the soft focus effect is continuously changed and a desired soft focus effect is achieved.

The soft focus filter can be displaced in the optical axis direction manually, or automatically by a motor or the like. As this displacement means, a lens moving mechanism or the like conventionally known in connection with zoom lenses or the like can be used as appropriate.

Next, regarding the method of claim 2, in the invention of claim 2, which is characterized by its operation, the soft focus filter group is used as described above. This soft focus filter group is configured to be complementary to each other.

Here, it will be explained that the soft focus filters of the soft focus filter group are complementary to each other.

First, the plurality of soft focus filters constituting the soft focus filter group have mutually congruent aperture distribution patterns. Therefore, these plural soft focus filters can be stacked on top of each other so that their aperture distribution patterns exactly overlap each other. At this time, the meaning that each soft filter is complementary means that when a light beam is transmitted through a group of soft focus filters with multiple soft focus filters superimposed as described above, the aperture, that is, the phase part. , which means that there is no phase difference between the transmitted light and the portion other than the aperture. In other words, when light passes through each soft focus filter, a phase difference occurs between the aperture and the other parts, but when the light is superimposed as described above, the phase difference generation effect of each filter is are canceling each other out.

The state in which the soft focus filters are superimposed so that no phase difference occurs is called the inphase state of the soft focus filter group. In this case, by substituting equation (3) into equation (2) and setting δ=0, as is clear, c: 1.0, and the soft focus effect is reduced as shown in Figure 2 (II). Not at all.

However, if at least one soft focus filter in a group of soft focus filters is displaced in a plane perpendicular to the optical axis relative to the other filters, the aperture distribution pattern of the displaced soft focus filter and other As the aperture distribution pattern of the filter shifts and the amount of shift increases, the above-mentioned area ratio S gradually increases when the soft focus filter group is regarded as one soft focus filter. The influence of soft focus filter group on MTF is also mentioned in (1) above.
It is regulated by equations (2) and (3).

Therefore, as is clear from equation (2), as the area ratio S increases, the MTF decreases and the soft focus effect increases.

The area ratio S is minimum at O during the in-phase, and maximum when the aperture distribution patterns of the displaced soft focus filter and the other filters are completely shifted. This state is called out of phase.
e). In this way, the soft focus effect can be continuously changed according to the amount of displacement of the soft focus filter.

The soft focus filter can be displaced manually in a plane perpendicular to the optical axis, or automatically by a motor or the like.

[Example code] Hereinafter, description will be given based on specific examples.

1 (I) and (II) are diagrams for explaining an embodiment of the method of claim 1, and FIG. 1 (III) is a diagram for explaining an embodiment of the method of claim 2. .

The lens 10 shown in FIG. 1(I) is a master lens with four elements in three groups and is used for wide-angle photography. At this time, the converter lens 20 and soft focus filter 30 are retracted from the optical axis.

When switching to telephoto mode, as shown in FIG. 1 (II), the master lens is extended toward the object side on the optical axis, and the converter lens 20 is placed on the optical axis.

A case will be described in which the method of claim 1 is carried out in a telephoto state suitable for portrait photography. A soft focus filter 30 is disposed between the imaging lens and the image plane, and is movable in the optical axis direction.

In the state shown in Fig. 1 (II), the radius of curvature of the first surface from the object side (including the aperture surface) is <Ri, the distance between the surfaces is Di1, the fifth lens from the object side, soft focus The refractive index and Atsube number of the filter material are Nj1νj
Then, these values are as follows.

i Ri Di j Nj
νJ1 11.543 3.71 1 1.
7995 42.32 31.8 0.86 3 -65.802 1.46 2 1.755
2 27.54 10.849 1.23 5 26.687 3.42 3 1.804
5 39.66-11゜451 0.83 4
1.5814440.97 -99.277 1.3 8 (aperture) O) 1.85 9 -352.816 :136 5 1.5
814440.910-11.36 0.69 11 -11.068 1.04 6 1.80
42046.512 38.369 0.13 13 22.86 3.45 7 1.531
7248.814 -10.849 1.38 8
1.6968055.515-82.501 0
．． 5 16 0) 1.0 9 1
．． 5163364.217 (X) The F/No is 2.88 at wide angle and 5.44 at telephoto, and the focal length f is 36 at wide angle and 68 at telephoto.

When an aperture is formed on the object side of the soft focus filter 30, the optical length from that surface to the image plane is 2 x b= It is 37.1 mm.

At this position, 15 lines/mm as a soft focus effect
Soft focus filter 30 so that it is 25%
designed. According to this design condition, from equation (1) above, Fc=15=s/(37,1x58.76-10-')
Therefore, the average value of the opening diameter S is 0.327 mm.

If the area ratio S=1, then from equation (2), Mc=cos2(kδ/2)=25 Therefore, cos(kδ/2)=0.5 Therefore, kδ/2:±(π/3)±2nπ Become. If we choose δ/2=π/3, then δ=λ/3, so
Substituting this into equation (3), we get t=37 as the thickness of the opening.
Obtain 9 nm.

That is, if a glass plate with a refractive index of 1.51633 is used as the soft focus filter 30 and an aperture is formed with unevenness on the side surface of the object, the step of the aperture will be 379 nm and the average diameter of the aperture will be 0.327 mrn.

The soft focus effect is maximum when such a soft focus filter is placed at the position indicated by the solid line in FIG. 1 (I).

FIG. 3 shows the soft focus filter 30 in the first
An MTF characteristic diagram when placed at the position indicated by the solid line in Figure (II) is shown. Graph line 3-1 shows the MTF characteristic of the imaging lens, line 3-2 shows the MTF characteristic of the soft focus filter 30, and line 3-3 shows the combined MTF characteristic of the imaging lens and soft focus filter 30.

At this time, the soft focus effect by the soft focus filter 30 is maximum.

Figure 4 shows one soft focus filter 30 in Figure 1 (
In II), the MTF characteristics are shown at the position of the broken line, that is, in the state where the image plane has recently appeared. 4-1 is the one using the soft focus filter 30, and 4-2 is the one using the imaging lens, which is the same as 3-2 in FIG. 4-3 is the combined MTF characteristic of the imaging lens and soft focus filter.

In this state, the soft focus effect is minimal, but if we consider the case where Fc is 100 lines/mm in this state, from equation (1), 1) = s/(FC・λ)・0.327 /(10(10,
5876·1O−3)=5.6mm. Therefore, in this case, the soft focus filter 30 may be arranged so that the object side surface is at an optical distance of 5.6+nm from the image plane.

As shown in FIG. 4, in this state, the combined MTF characteristic is approximately at the same level as the MTF characteristic of a normal imaging lens, so a sharp image can be captured.

For simplicity, the MTF characteristic of the soft focus filter 30 is represented by the d-line, but Fc is large for short wavelength light, and Fc is small for long wavelength light, so even when considering the sum weighted by wavelength, There is no major difference from those shown in Figs. 3 and 4 above. In addition, in Figure 3.4, M of the imaging lens
TF is for white light.

Next, an embodiment of the method of claim 2 will be described with reference to FIG. 1 (III).

In FIG. 1 (III), reference numerals 31 and 32 indicate soft focus filters. These soft focus filters 31 and 32 constitute a soft focus filter group and are provided near the imaging lens.

The soft focus filter 31 is fixed, and the soft focus filter 32 is movable within a plane perpendicular to the optical axis.

These soft focus filters 31 and 32 are made of unevenness on one side of a transparent plate such as glass, so that two of the apertures, which are phase parts, are
Although the soft focus filter 31 is configured by forming a dimensional distribution, the aperture is formed as a convex portion, whereas the soft focus filter 3
In No. 2, the openings are formed as recesses, and the distribution patterns of the openings are congruent with each other. Further, both soft focus filters 31 and 32 are made of the same material, and the height difference between the convex portion and the recess portion are equal to each other. Therefore, when the soft focus filters 31 and 32 are placed in the in-phase state as shown, the light ray passing through any part of the soft focus filter group has a constant optical path length, and no soft focus effect occurs.

As mentioned above, this soft focus filter group can be placed near the imaging lens, but here it is placed at the pupil plane, which is the ideal position, and an MTF of 15 lines/mm is used as a guide for the soft focus effect. I got it under control.

550nm as representative wavelength, b=f;lo as medium telephoto
omm, these values are substituted into the above-mentioned equation (1) to obtain 0.8 mrn as the average diameter S of the circular opening.

When the soft focus filter group is placed in an out-of-phase state, the area ratio S is 0.5.
The area ratio of the openings in each soft focus filter 31 and 32 is assumed to be 0.25.

When formula (2) is modified and the above conditions are used, Mc=cos
2 (kδ/2), and when δ=λ/2, Mc”0 is achieved, and the MTF can be reduced the most.

The refractive index of the soft focus filters 31 and 32 is set to 1.
5, the above formula (3) becomes t;λ=550 nm, and from this, the value of the step size t of the unevenness of the opening in each soft focus filter 31, 32 can be found.

In this way, by displacing the soft focus filter 32 of the soft focus filter group from an in-phase state to an out-of-phase state in a plane perpendicular to the optical axis, the soft focus effect can be continuously changed.

It should be noted that here as well, for the sake of simplicity, the explanation has been given in terms of representative wavelengths. In actual use, it is the sum of wavelengths from 400 to 700 nm that are appropriately weighted, and does not equal 0. However, since the MTF can be made extremely small, the soft focus effect can be arbitrarily selected in practice.

[Effects of the Invention] As described above, according to the present invention, a novel soft focus method can be provided.

Since the method of claim 1.2 is configured as described above,
The soft focus effect can be changed continuously and the desired soft focus effect can be selected.

The soft focus filter can be used in various configurations, and in particular, it can be formed into plastic, so it can be mass-produced at low cost.

Furthermore, the soft focus filter or soft focus filter group does not lose any amount of light when used.

Furthermore, since particularly high precision is not required for the displacement of the soft focus filter, the displacement mechanism can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the present invention based on an example,
FIG. 2 is a diagram for explaining the present invention in detail, FIGS. 3 and 4 are diagrams for explaining the effect of the embodiment of claim 1, and FIG. 5 is a diagram for explaining the soft focus filter. This is a diagram for 10. Master lens of imaging lens, 20. ,
, converter lens of imaging lens, 30. ,,soft focus filter,31,32. ,, Soft focus filters that make up the soft focus filter group? Matata (TI) Ichi Rimata M-chome F

Claims (1)

[Claims] 1. A small aperture that has a phase difference with respect to a portion other than the aperture; 2.
A soft focus filter that is randomly distributed dimensionally is arranged on the optical axis between the imaging lens and the image plane so that it can be displaced in the optical axis direction, and by the displacement of the soft focus filter in the optical axis direction, , a soft focus method characterized by continuously changing the soft focus effect to achieve a desired soft focus effect. 2. A small aperture with a phase difference with respect to the part other than the aperture is 2.
A plurality of soft focus filters, which are dimensionally randomly distributed, are configured to be complementary to each other, and a group of soft focus filters, which are combined in close proximity to each other, is arranged on the optical axis near the imaging lens, and the above-mentioned software By displacing at least one soft focus filter in the group of focus filters in a plane perpendicular to the optical axis relative to other soft focus filters, the soft focus effect can be continuously changed to achieve the desired effect. A soft focus method characterized by realizing a soft focus effect.