JP2001042230A - Image pickup optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup optical system equipped with a thin infrared cut filter excellent in color reproducibility and preventing ghost by arranging an interference film and a light absorbing element having specified performance in an image-formation optical system. SOLUTION: This system is obtained by arranging one surface interference film and the light absorbing element in the image-formation optical system, and the interference film satisfies an expression: 620 (nm)<λ1<680 (nm). The light absorbing element absorbs reflected light in order to prevent the ghost caused by the reflected light between the interference film and an imaging device, and the synthetic characteristic of the interference film and the light absorbing element satisfies an expression 2<D3<10. Provided that λ1 expresses wavelength in which the transmissivity of the interference film becomes 50%, and the wavelength in which the transmissivity of the interference film becomes 50% within a range shown by an expression 620 (nm)<λ1<680 (nm), and D3 is a value given by an expression: D3=ln(1/τ3) when the transmissivity of the light absorbing element in the wavelength λ1 is defined as τ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device.

[0002]

2. Description of the Related Art In general, when a single color CCD is used,
An infrared cut filter is used to cut off near-infrared harmful light.

As the infrared cut filter, there are known an absorption filter that absorbs a specific wavelength range depending on the concentration of a dye and a reflection filter that uses an interference film to cancel only a specific wavelength range by using a phase difference. ing.

Among them, an absorption type infrared cut filter needs a certain thickness in order to obtain a specific spectral characteristic depending on a dye concentration. Therefore, it is not always optimal for an imaging device having a restriction in the length direction, particularly an endoscope or the like.
Further, since the cutoff characteristic draws a gentle curve, color reproduction is not preferable.

[0005] On the other hand, the reflection type filter has less restrictions in the length direction and has a sharp cut-off characteristic, so that it has relatively good color reproducibility. However, since the coating surface is a highly reflective surface, ghosts may occur.

[0006] A composite filter has been known in which such advantages and disadvantages of the filter are compensated. As an example,
The combination of an absorption filter and a reflection filter described in Japanese Utility Model Laid-Open No. 1-125417 (U.S. Pat. No. 5,177,505) shown in FIG. 19 improves color reproduction and reduces ghosts. is there.

In this conventional filter, the intensity of ghost light generated by multiple reflection between a reflection type filter and another high reflection surface is reduced by an absorption filter, and the cutoff characteristic of the absorption filter is reduced by a reflection type filter. Correction is made by the sharp cutoff of the filter.

However, as in this conventional example, in practice, simply combining different kinds of filters does not provide an effective function for satisfying the above requirements. In addition, the above publication does not disclose specific filters effective for satisfying the above-mentioned requirements or disclose characteristics of the filters.

Further, the above publications of the prior art describe problems caused by a single filter, such as color reproduction and ghost, but do not disclose any characteristics of the CCD used. The optimization of the infrared filter greatly depends on the characteristics of the CCD used, especially the color mosaic filter.

In general, a single-chip color CCD normally generates color difference signals with four vertical lines as shown in FIG. 18, and a mozaqui filter uses yellow Ye, cyan Cy, magenta Mg, and green G for each line as described below. It is composed of a combination. First line: Ye, Cy, Ye, Cy Second line: Mg, G, Mg, G Third line: Ye, Cy, Ye, Cy Fourth line: G, Mg, G, Mg

Here, the n-th color difference signal (RY, BY) of the A field is composed of Cy, Ye of the first line,
Made of G, Mg in the second line, RY = 2R-
G.

Further, the (n + 1) th color difference signal of the A field includes Cy and Ye of the third line and G and Y of the fourth line.
It is made of Mg, and BY = 2BG.

Note that R is a red signal, G is a green signal, B is a blue signal, and Y is a luminance signal.

Here, when strong light enters the CCD and becomes saturated, the signal levels of the color signals R, G, and B become 1: 1:
Becomes 1. However, since the spectral characteristics of the CCD itself have a peak in the infrared region, the output signal is not necessarily 1: 1: 1.
do not become. That is, only the signal from the nth line of the A field including the color signal R increases in level. As a result, it appears on the monitor as horizontal noise of red shading.

Normally, the level of the red signal is adjusted using an infrared cut filter so that the above-mentioned noise does not occur.

In particular, when observing the inside of a human body, such as a medical endoscope, the organ to be observed is mainly red. Therefore, the above-mentioned horizontal stripe noise is conspicuous. Furthermore, since the light source used in such an endoscope contains relatively more infrared spectrum components than natural light or fluorescent light, an infrared cut filter is essential.

[0017]

The imaging optical system used in the imaging apparatus is required to be compact and short in overall length, and the space for disposing filters and the like in the imaging optical system is insufficient. Therefore, the infrared cut filter arranged in the optical system is required to be compact. The interference filter is compact and space-saving,
Although color reproduction is good, there is a disadvantage that a reflection ghost occurs between the surface and a surface having a high reflectance.

In the above-mentioned conventional example, an interference filter and an infrared absorption filter are combined, but the conditions necessary for ghost removal and color reproduction are not described. Absent.

The present invention relates to an image pickup optical system provided with a thin infrared cut filter having no ghost and excellent in color reproduction, specifically, a filter having a thickness of 1 mm or less, preferably 0.5 mm or less. An image pickup optical system is provided.

[0020]

According to the present invention, there is provided an imaging optical system comprising:
An imaging optical system that forms an object image and an imaging optical system
An image sensor for receiving the object image
In the imaging optical system, one interference film and a light absorbing element are arranged.
The interference film satisfies the following condition (1)
The light absorbing element is emitted by the reflected light between the interference film and the image sensor.
Absorb the reflected light to prevent ghosts
The characteristics of the synthesis of the interference film and the light absorbing element are as follows.
The condition (2) is satisfied. (1) 620 (nm) <λ₁<680 (nm) (2) 2 <D_Three<10 where λ₁Is the wavelength at which the transmittance of the interference film becomes 50%.
The transmittance of the interference film becomes 50% within the range shown in case (1).
Wavelength, D_ThreeIs the wavelength λ₁The transmittance of the light absorbing element at τ When
Is the value given by the following equation: D_Three= Ln (1 / τ^ThreeThe condition (1) is the lower limit wavelength 620n defined by this condition.
of wavelengths within the range of 680 nm from m
At least one wavelength at which the transmittance of the film is about 50%
Means to do.

If the lower limit of 620 mm of the condition (1) is exceeded, the infrared component is cut excessively, and the color reproduction is deteriorated. If it exceeds the upper limit of 680 mm, color reproduction and noise deteriorate due to insufficient cutting of infrared components. If the lower limit of 2 of the condition (2) is exceeded, the ghost removal effect is insufficient and the image quality deteriorates. If the upper limit of 10 is exceeded, the light-absorbing element becomes thick and it is difficult to make it compact.

Another imaging optical system of the present invention is an imaging optical system having an imaging optical system for forming an object image and an imaging device for receiving an object image formed by the imaging optical system. An interference optical film is provided on at least one surface of the imaging optical system;
In order to prevent a ghost caused by reflected light generated between the interference film and the image pickup device, a light absorbing element that absorbs the reflected light is disposed, and the following conditions (3), (4), and (5) are satisfied. It is characterized by doing. (3) 0.8 <A <2.7 (% / nm) (4) T (600)> 50% (5) T (700) <5% where A is the interference film and light absorption at λ ₁ Slope (ΔT / Δλ) of combined transmittance T of element, T (600), T (700)
Is the combined transmittance of the interference film and the light absorbing element at wavelengths of 600 nm and 700 nm, respectively.

If the lower limit of 0.8% / nm of the condition (3) is exceeded, the color reproduction will deteriorate. If the upper limit of 2.7% / nm is exceeded, the ghost removal effect of the light absorbing element is insufficient, and the image quality deteriorates. If the lower limit of 50% of the condition (4) is exceeded, the color reproduction will deteriorate. When the value exceeds the upper limit of 5% of the condition (5), the color reproduction deteriorates.

Another imaging optical system according to the present invention includes an imaging lens for forming an object image and an imaging device for receiving the object image formed by the imaging optical system. At least one interference film that satisfies, and a light absorbing element for preventing a ghost generated by reflected light between the interference film and the image sensor, wherein the light absorbing element is disposed between the interference film and the image sensor. Characterized by being arranged in

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an imaging optical system according to the present invention will be described.

The imaging optical system of the present invention includes the following composite filter, and the first embodiment of the present invention is characterized by the configuration of the composite filter.
As shown in FIG. 1, F1 is an absorption type infrared cut filter (light absorbing element), and F2 is a reflection type infrared cut coat (interference film) provided on the surface of the absorption type infrared cut filter F1. Thus, two types of filters are combined. FIG. 2 shows a total spectral transmittance characteristic of a combination of these filters. In FIG. 2, a, b, and c are filters F2 (interference film) and 0.4 m thick.
m: total spectral characteristic with filter F1 (light absorbing element), a ′, b ′, c ′: spectral characteristic of interference film only, e: spectral characteristic of general light absorbing element with thickness of 1.6 mm It is. D is an interference film having the characteristic of c ′ and a thickness of 0.3 m.
m is the total spectral characteristic of the light absorbing element. The spectral characteristics of only the 0.4 mm-thick filter F1 (light absorbing element) having the total spectral characteristics of a, b, and c respectively correspond to the total spectral characteristics a, b, and c of the filter F2 (interference film). By dividing each of the spectral characteristics a ′, b ′, and c ′. Similarly, 0.3 corresponding to the characteristic d
The spectral characteristic of only the filter F1 (light absorbing element) of mm can be obtained by dividing the total spectral characteristic d by the spectral characteristic c 'of the interference film for each wavelength.

The characteristics are as follows: Table Wavelength a'b'c '(d') 600 0.973 0.9801 0.986 610 0.987 0.9882 0.9823 620 0.7559 0 0.973 0.9927 630 0.4945 0.987 0.9801 640 0.2066 0.7559 0.9882 650 0.066 0.4945 0.973 660 0.0353 0.2066 0.987 670 0.0282 0 0.066 0.7559 680 0.016 0.0353 0.4945 690 0.068 0.0282 0.2066 700 0.0004 0.016 0.066 Wavelength abcd600 0.8228 0.7485 0.8338 0.8695 610 0.8006 0.7058 0.7968 0.83 96 620 0.5826 0.6401 0.7651 0.8165 630 0.3587 0.5889 0.7109 0.7703 640 0.1407 0.4075 0.6729 0.7408 650 0.0417 0.2365 0.6151 0.6898 660 0.0207 0.0873 0.5775 0.6603 670 0.0152 0.0245 0.4077 0.4758 680 0.0079 0.0114 0.2455 0.2925 690 0.0031 0.0079 0 0.0937 0.1142 700 0.0002 0.0039 0.0272 0.0340

As a result of the study, when only the reflection type (interference film) is used as the infrared cut filter, the color reproducibility is improved, but the level of horizontal stripe noise cannot be suppressed to a level that is not conspicuous. Further, a ghost peculiar to the reflection type filter occurred. The reflection type filter used here has a characteristic that the transmittance shows a half value at a wavelength of about 630 nm and becomes almost 0% at about 700 nm as shown by a curve a ′ in FIG. 2, for example. That is, noise is reduced by cutting the near-infrared region on the shorter wavelength side than the wavelength region of about 630 nm, and the
It has been found that color reproduction can be improved by providing a sharp cutoff characteristic that cuts the near infrared region near 00 nm as much as possible.

However, the reflection type filter is not desirable because the cutoff characteristic is steep, and if the cutoff region is shifted to a shorter wavelength side, light in the visible region is cut off.

In the above examination, a single-chip color CC having an organic complementary color mosaic filter as an image pickup device
D was used.

When only an absorption filter was used, it was found that horizontal stripe noise and ghost could be reduced, but the color reproducibility was inferior to that of a reflection filter. The absorption filter used at this time is a filter showing a half value near about 600 nm as shown by a curve e in FIG.

The composite filter according to the first embodiment of the present invention has a configuration in which the above-mentioned absorption filter F1 and reflection type filter F2 are combined as shown in FIG. 1, and the overall spectral characteristics are shown in FIG. The filters are as shown in a, b, and c, respectively.

The overall spectral characteristics in FIG.
Among the composite filters b and c, the filter b is particularly desirable in order to surely reduce ghosts and noises and to make color reproducibility the most desirable. However, it is necessary to consider the error in the manufacture of the filter and the spectral characteristics due to the angle dependence of the coating characteristics. Therefore, the wavelength 60
The transmittance at 0 nm is 50% or more, the transmittance at 700 nm is 5% or less, and the value of A is A = 1.
It is preferably 9 ± 0.3.

This is because characteristics at a wavelength of 600 to 700 nm particularly affect ghost and noise reduction and color reproducibility.

That is, in the product field, particularly in the endoscope field, the thickness of the filter may be reduced or increased depending on the use. However, within the range that satisfies the above-mentioned conditions, a composite filter of a practical level can be constructed without impairing color reproducibility.

The value of A of the filter according to the first embodiment of the present invention is as follows.

(Filter of characteristic a) A = | ΔT (a) / ΔW | = | (58.26−14.07) / 2
0 | ≒ 2.21 (Filter of characteristic b) A = | ΔT (b) / ΔW | = | (40.75−8.73) / 20
| ≒ 1.6 (filter with characteristic c) A = | ΔT (c) / ΔW | = | (40.77−9.37) / 20
｜ ≒ 1.81

The thickness th of the composite filter having the total spectral characteristics a, b, and c of this embodiment is 0.4 mm.

Further, D ₃ , D ₄ (= D ₃ × th), T (6
00) and T (700) are as follows. The interference film having the characteristic a 'is λ ₁ ≒ 630 nm. The interference film having the characteristic b' is λ ₁ ≒ 650 nm. The interference film having the characteristic c '(d') is λ ₁ ≒ 680 nm. The filter having the overall characteristic a D ₃ = 2.27 D ₄ = 0.91 T (600) = 82.28%, T (700) = 0.02
% Filter of overall characteristic b D ₃ = 3.46 D ₄ = 1.38 T (600) = 74.85%, T (700) = 0.39
% Filter with overall characteristic c D ₃ = 3.42 D ₄ = 1.37 T (600) = 83.38%, T (700) = 2.72
% Filter with overall characteristic d D ₃ = 6.28 D ₄ = 1.88 T (600) = 86.95%, T (700) = 3.40
% Where d is 0.3 mm in thickness.

When the composite filter of the present invention is used in an endoscope, it is desirable to reduce the size of the endoscope in addition to reducing ghost and noise and improving color reproducibility. As a result, it is conceivable to reduce the thickness of the absorption filter. However, as described above, when the absorption filter is extremely thin, the effect of reducing ghost and noise cannot be expected.

However, there are cases where the demand for miniaturization is very high depending on the application field, and it is necessary to give priority to miniaturization.

As a result of the examination, it was found that when the value of A was within a range satisfying the following conditions, ghost and noise were not conspicuous. 1.6 ≦ A ≦ 2.2

The second embodiment of the composite filter using the image pickup apparatus of the present invention has a structure as shown in FIG.
Is an absorption filter, and F2 and F3 are reflection filters. That is, the configuration is such that the reflection type filter F3 is further added to the filter of the first embodiment shown in FIG.

This second embodiment is a filter having a configuration suitable for use with a YAG laser in addition to a semiconductor laser.

The wavelength range of the YAG laser is about 1060 nm, and in the filter of the first embodiment, this YA
The wavelength range of the G laser cannot be cut sufficiently.
As shown in FIG. 4, the transmittance of the filter of this embodiment is almost zero in the wavelength range of about 1060 nm of the YAG laser in addition to the wavelength range of the semiconductor laser.
Here, in consideration of the production of the filter and the like, the cutoff wavelength of the YAG laser is desirably about 1060 ± 20 nm.

The third embodiment is an endoscope objective optical system to which a composite filter as shown in the first and second embodiments of the present invention is applied as shown in FIG.

This endoscope objective optical system includes, in order from the object side, a negative lens L1, a positive lens L2, a stop S, and a positive lens L.
3, a cover glass C and a CCD, and a negative lens L1.
A reflection type filter F5 is arranged between the positive lens L2 and a reflection filter F4, and an absorption type filter F4 is arranged between the stop S and the positive lens L3. That is, the filter of the second embodiment is used.

The endoscope objective optical system of this embodiment is a direct-view optical system having a viewing angle of 131 ° and a viewing direction of 0 °. Absorption type filter (infrared cut filter) F
The object side of No. 4 is provided with a YAG light cut coating F6. The reflection type infrared cut filter F5 also has a semiconductor laser light cut function.

When two or more different types of reflection filters are used as in the image pickup apparatus of this embodiment, it is necessary to consider the arrangement position of the reflection filters.

Generally, the spectral characteristics of a reflection type filter are affected by the angle of inclination of an incident light beam. Therefore, when the angle of inclination becomes large, it is necessary to consider the arrangement position.

The filters F4 and F6 used in the third embodiment have an incident angle θ (LD) of off-axis light incident on the absorption type infrared cut filter F6 also serving as a semiconductor laser light cut function, and a YAG light cutoff. The incident angle θ (Y) on the coating surface F6 has the following relationship. (6) θ (LD) <θ (Y)

An infrared cut filter having a cutoff near the visible wavelength range has a large effect on color reproducibility. Therefore, it is desirable that the infrared cut filter is disposed at a position where the incident angle is smaller than that of the YAG light cut coating. Therefore, it is desirable to satisfy the above conditions. In addition, it is considered that a ghost may occur due to multiple reflections between these coating surfaces, and therefore it is desirable that these incident angles have a certain angle. Note that θ (LD) and θ (Y) under the above conditions are shown as absolute values.

FIG. 6 is a view showing a fourth embodiment, and is another example in which the filter is applied to an endoscope objective optical system. This endoscope objective optical system includes, in order from the object side, a negative lens L1, a cover glass C1, a 45 ° prism P, a stop S, a positive lens L2, a positive lens L3, an absorption type infrared cut filter F7, a cover glass C, and a CCD. The optical system is composed of: The objective optical system of this embodiment has a viewing angle of 93.
° is an optical system with a front perspective.

The object side surface of the absorption type infrared cut filter F7 used in the optical system of this embodiment is provided with an infrared cut coating F8 having an improved color reproducibility and a semiconductor laser beam cut function. A YAG light cut coating F9 is applied to the object-side surface of the positive lens L2.

That is, the filter of the first embodiment (the reflection type filter F8 is provided on the surface of the absorption type filter F7).
And a YAG light cut coating is applied to the positive lens L2.

The fourth embodiment also satisfies the above condition (6).

It is desirable that θ (LD) and θ (Y) satisfy the following condition (7). (7) θ (LD) <θ (Y) ≦ 25 °

When the incident angles θ (LD) and θ (Y) become extremely large and exceed 25 °, color shading occurs and coloring occurs at the periphery of the image on the monitor. If the condition (7) is satisfied, an image having good color reproducibility without color shading can be obtained.

FIG. 7 is a view showing a fifth embodiment of the present invention. In order from the object side, a negative lens L1 and a cover glass C1 are sequentially arranged.
And a positive lens L2, an aperture S, a reflection type infrared cut filter F11, an absorption type infrared cut filter F12, a positive lens L3, a cover glass C2, a cover glass C, and a CCD. It is a mirror objective optical system. That is, this is an endoscope objective optical system using the filter of the second embodiment, which is a composite filter composed of the reflection filter F11 and the absorption filter F12.

The reflection type cut filter used in this optical system is provided with an infrared cut coating having a semiconductor laser beam cutting function on the object side surface.
The side surface is provided with a YAG light cut coating.

This embodiment is an example in which the rear optical system behind the stop S is made as simple as possible, thereby improving the assemblability and simplifying the frame structure to reduce the cost. It is an example.

As can be seen from FIG. 7, in this embodiment, the incident angle of the light beam on each filter is an angle sufficiently smaller than the condition (7). If the incident angle is sufficiently small as described above, the condition (6) does not always need to be satisfied because the influence of the inclination angle of the incident light beam is small.

Further, an infrared cut coating having a semiconductor laser light cut function and a YAG light cut coating, in which the incident angles of light beams on the respective coatings are substantially equal, may be provided on either surface of the reflection type infrared cut filter. .

FIG. 8 shows a sixth embodiment.
In order from the object side, a negative lens L1, an aperture S, and a positive lens L2
And a positive lens L3, an absorption cut filter F13, a cover glass C, and a CCD.
An infrared cut coating F14 having a semiconductor laser light cutting function is applied to the surface on the side, and a YAG light cut coating F15 is applied to the object side surface of the absorption type infrared cut filter F13. That is, this is an example in which a YAG light cut coat F15 is further provided on the filter of the second embodiment of the composite filter including the absorption filter F13 and the reflection filter F14.

The optical system of this embodiment is also an example in which the angles θ (LD) and θ (Y) are made sufficiently small, as in the fifth embodiment. The fifth embodiment is characterized in that the lens configuration is simplified and the size is further reduced as compared with the fifth embodiment. In other words, the aperture S is disposed closer to the object side, and the positive lenses L2 and L3 on the image side than the aperture S are provided with strong power, so that the size and diameter are reduced.

In this embodiment, the mask M for limiting the field of view and preventing harmful light is formed by depositing chromium on the CCD-side surface of the infrared absorption type filter F13. By adopting such a configuration, the configuration is further simplified as described above, and the assemblability is improved.

This optical system is a direct-view type endoscope objective optical system having a viewing angle of 114 °.

FIG. 9 is a diagram showing an optical system according to the seventh embodiment. In order from the object side, a negative lens L1, a stop S, a positive lens L2, a positive lens (infrared cut lens) L3, and a CC
D cover glass C and CCD.

In this embodiment, the absorption type infrared cut filter 16 is obtained by giving the positive lens L3 an infrared cut function. That is, the function as a positive lens is provided by giving a curvature to the absorption type infrared cut filter. As a result, a space for disposing the filter is omitted to make the optical system more compact, and the distal end portion of the endoscope can be made smaller. Further, a YAG light laser cut coating F18 is applied to the object side surface of the positive lens L2, and an infrared cut lens F which is a surface having a relatively small incident angle of light rays.
On the object side of the positive lens 16 (positive lens L3), a reflective infrared cut coating F17 is applied. The reflection type infrared cut coating F16 can also have a semiconductor laser beam cut function.

That is, the seventh embodiment is different from the seventh embodiment in that the filter of the first embodiment is provided on the positive lens L2 (the positive lens L2 has the filter function of the first embodiment). It is characterized by using a composite filter in which the positive lens L2 is an absorption type infrared cut filter and its object side surface is a reflection type infrared cut filter.

The absorption type infrared cut filter F16 of this embodiment may be manufactured by a sol-gel method. Thereby, the water resistance and abrasion resistance of the filter are improved, and the workability is also improved. That is, when the absorption type infrared cut filter is processed into a spherical surface or the like to form a lens as in this embodiment, the workability is good and effective.

FIG. 10 is a view showing an eighth embodiment of the present invention. In order from the object side, a negative lens L1, a stop S, a positive lens L2, a positive lens L3, an absorption type YAG light cut filter are shown. F21 and absorption type infrared cut filter F1
9 and a CCD. The reflection type infrared cut coating F20 is provided on the surface of the positive lens L3 on the CCD side. That is, the optical system includes a composite filter including the absorption-type infrared cut filter F19 and the reflection-type infrared cut filter F20 provided on the positive lens L3, like the filter of the second embodiment.

In this embodiment, an absorption type infrared cut filter F19 and an absorption type YAG light cut filter F21 are used.
This is an example in which a ghost is reduced by providing a ghost.

The ghost can be sufficiently reduced by making the YAG light cut coating having a high reflectivity into an absorption filter. In this case, HO is used as the absorption type YAG light cut filter F21.
The infrared cut filter HA-15 made of YA is used, and infrared light in a wavelength range of 1000 nm to 1200 nm can be cut. Also, if there is room in the size (length) of the endoscope distal end portion, HOYA having a smaller infrared light absorption coefficient than this is used.
May be used.

That is, it is desirable to select an absorption type infrared cut filter having an appropriate infrared light absorption coefficient depending on the size of the end portion of the endoscope.

FIG. 11 shows a ninth embodiment. The ninth embodiment is an example in which a reflective infrared cut filter is used for a television adapter for an endoscope.
As shown in FIG. 11, a cover glass C3, an imaging lens system IL including a positive lens, a negative lens, and a positive lens, a cover glass C4, a cover glass C5, and a filter group FG are arranged in this order from the object side. , CCD cover glass C
And a CCD. Here, the infrared cut coating F2 on the most object side of the filter group FG
The filter F22 provided with 3 reflects the light beam incident from the object side on a surface having a high reflectance, such as the CCD cover glass C, after passing through the infrared cut coating F23, and then re-enters on the infrared cut coat surface. Reflect, CCD
The light enters the imaging surface as a ghost.

FIG. 12 is a diagram showing a spectral curve of a reflection type infrared cut filter. Here, assuming that the transmittance of the coated surface is τ and the reflectance of the coated surface is (1−τ), the transmittance of the ghost light is approximately τ × (1−τ), as shown in a portion C of FIG. It becomes an intensity distribution.

FIG. 13 is a diagram showing a tenth embodiment. In the tenth embodiment, in order from the object side, a negative lens L1, a positive lens L2, a stop S, and positive lenses L3, L
4, a reflection filter F4 is disposed between the negative lens L1 and the positive lens L2, and an absorption filter F5 is disposed between the positive lens L3 and the positive lens L4. is there.

A flare stop FS1 is provided between the negative lens L1 and the positive lens L2, and a positive lens L3 and a filter L5 are provided.
A flare stop FS2 is also disposed between them, and a CCD cover glass C and a CCD are disposed on the image side of the plane of the positive lens L4.

The imaging lens shown in FIG.
All of the lenses 1 to L4 have a flat surface, and each of these lenses has a shape that is easy to process, and has a configuration that is less susceptible to image deterioration due to assembly errors.

By coating the plane portions of these lenses with an interference film, the substrate of the interference filter can be omitted.

As described above, the lens system according to the ninth embodiment has a large number of flat surfaces and many surfaces on which an interference film or the like can be provided. Also, the wavelength that needs to be cut can be cut into a plurality of surfaces without being cut on one surface.

FIG. 14 is a diagram showing the eleventh embodiment. The imaging lens of this embodiment is, in order from the object side,
Negative lens L1, aperture S, positive lens L2, negative lens L3
And a cemented lens in which the positive lens L4 is cemented. An absorption filter F5 is arranged between the cemented lens and the CCD cover glass C. A YAG cut coat is provided on the object side surface of the absorption filter F5, and an infrared cut coat is provided on the CCD side surface of the lens L4. These coats are the CCD of lens L4
A YAG cut coat may be provided on the object side, or an infrared cut coat may be provided on the object side of the absorption filter. The absorption filter is for reducing the YAG laser and red ghost.

FIG. 15 shows an imaging lens of the present invention, for example,
FIG. 15 is a diagram illustrating an electronic camera including the imaging lens of the eleventh embodiment illustrated in FIG. 14. 15, (A) is a perspective view seen from the front, (B) is a perspective view seen from the rear,
(C) is a diagram showing the arrangement of the optical system inside the camera.

In FIG. 15, reference numeral 11 denotes an imaging lens, 21 denotes a finder optical system, 31 denotes a shutter, 32 denotes a flash, and 33 denotes a liquid crystal monitor.

The imaging lens 11 of the camera shown in FIG.
As described above, the lens system according to the eleventh embodiment shown in FIG. 14 includes a cemented lens in which a negative lens L1, a positive lens L2, and a negative lens L3 and a positive lens L4 are cemented. 1
2 is an optical path for photography. Also, the finder optical system 21
Are the objective optical system 22, the image inverting optical system 23, and the eyepiece 2.
4 is a type of optical system that can directly see the field of view.
Reference numeral 25 denotes a finder window cover.

FIG. 16 is a diagram showing an overall system of a video camera as an example of an electronic image apparatus. In the figure, an imaging optical system LS is an imaging optical system according to the eleventh embodiment of the present invention shown in FIG. 14, in which a solid-state imaging device CCD as imaging means is arranged on an image forming surface so as to be capable of focusing. The image signal converted by the element CCD is processed by the processing unit 3.
6, and is displayed on the liquid crystal display element 37.
On the other hand, it is converted into a signal that can be recorded on a magnetic tape as the recording medium 38 and recorded.

The audio signal simultaneously obtained from the microphone 39 is also electrically processed by the processing means 31.
The signal is converted into a signal that can be recorded on the recording medium 33 and recorded.

Note that the liquid crystal display element is an example of a display means, and any display means may be used as long as the display means can be monitored such as a cathode ray tube.

FIG. 17 is a conceptual diagram when the imaging lens of the present invention is used as an objective lens of an observation system of an electronic endoscope. In FIG. 17, (A) is a diagram showing the entire configuration of the electronic endoscope, in which 41 is an electronic endoscope, 42 is a light source for supplying illumination light, and 43 is a signal corresponding to the electronic endoscope. A video processor 44 for displaying an image based on the video signal output from the video processor 43, and VTR decks 45, 46 and 47 connected to the video processor 43 for recording the video signal and the like therefrom. , Video discs and video printers.

FIG. 17B is a cross-sectional view showing the arrangement of the optical system at the tip of the electronic endoscope 41. As shown in FIG. In the figure, reference numeral 51 denotes an objective lens, which uses the imaging lens of the tenth embodiment of the present invention shown in FIG. Reference numeral 52 denotes an illumination objective optical system, and reference numeral 53 denotes a light guide fiber bundle.

According to this electronic endoscope system, the illumination light from the light source device 42 is transmitted by the light guide fiber bundle 53 and is illuminated by the illumination objective optical system 52.
The illuminated observation object is imaged by the imaging lens 51, and its image is displayed and observed on the monitor 44. Further, it is recorded on a VTR deck 45 or a video disk 46 and printed out by a video printer 47.

The present invention can achieve the object of the invention not only in the claims, but also in the following items.

(1) an imaging optical system for forming an object image;
An imaging device that receives an object image formed by an imaging optical system
Having the imaging optical system and at least one interference film
A light absorbing element, and the interference film satisfies the following condition (1).
In addition, the light-absorbing element is provided between the interference film and the imaging element.
Also to prevent ghosting caused by reflected light between
The characteristic of the combination of the interference film and the light absorbing element is
An imaging optical system that satisfies the following condition (2-1): (1) 620 (nm) <λ₁<680 (nm) 1 <D_Four<2 (2-1) D_Four= Ln (1 / τ^Three) × d where λ₁Is a wave at which the transmittance of the interference film becomes 50%.
Long, τ Is the wavelength λ₁The transmittance of the light absorbing element at d
Is the thickness of the light absorbing element.

(2) In the optical system according to claim 1, 2, or 3 or (1), the thickness d of the light absorbing element satisfies the following condition (8). Characteristic imaging optical system. (8) 0.2 mm <d <1 mm

(3) The optical system according to claim 1, 2 or 3, or (1) or (2), wherein the optical system includes a stop and the interference film is bright. An imaging optical system, which is located on the object side of the stop.

(4) Claim 3 of the Claims
Optical system that satisfies the following condition (1):
Imaging optical system. (1) 620 (nm) <λ₁<680 (nm) (2) 2 <D_Three<10 where D_ThreeIs the wavelength λ₁Transmittance of the light absorbing element at
To τ Is a value given by the following equation. D_Three= Ln (1 / τ^Three)

(5) Claim 1 or 3 of the Claims
Alternatively, the optical system described in the above item (1), wherein the following conditions (3), (4) and (5) are satisfied. (3) 0.8 <A <2.7 (% / nm) (4) T (600)> 50% (5) T (700)> 5%

(6) The optical system according to claim 1, 2 or 3 or the optical system according to the above (1), (2), (3), (4) or (5), wherein An imaging optical system, wherein the absorption element comprises an infrared cut filter.

(7) Claims 1, 2 or 3 of the claims or the above (1), (2), (3), (4),
The optical system according to (5) or (6), wherein the interference film comprises an interference filter formed by coating a flat plate having no power.

(8) The optical system according to the above (6) or (7), wherein at least one positive lens is provided between the infrared absorption filter and the interference filter. Imaging optics.

(9) Claims 1, 2 or 3 of the claims or the above (1), (2), (3), (4),
The optical system according to (5) or (6), wherein the imaging optical system has at least a lens having a flat surface on the object side with respect to the light absorbing element, and the lens has a flat surface. An imaging optical system having an interference film formed thereon.

(10) Claims 1 and 2 of the claims
Or 3 or the above (1), (2), (3),
(4), (5), (6), (7), (8) or (9), wherein the imaging optical system includes a negative first lens group and a negative first lens group in order from the object side. An imaging optical system comprising a positive second lens group and a positive third lens group.

(11) The optical system according to the above (10), wherein the negative first lens group comprises a plano-concave lens having a flat object side.

(12) The optical system according to the above (10) or (11), wherein the positive second lens group is a plano-convex lens having one plane. .

(13) In the optical system described in the above item (10), (11) or (12), the third positive lens unit is composed of a cemented lens of a negative lens and a positive lens. Imaging optical system.

(14) The optical system according to the above (10), (11) or (12), wherein the third positive lens group comprises a single positive lens. .

(15) Claims 1 and 2 of the claims
Or 3 or the above (1), (2), (3),
(4), (5), (6), (7), (8), (9),
(10), (11), (12), (13) or (14)
A camera device comprising the imaging optical system described in the above section and a finder optical system.

(16) In the camera according to the item (15), a recording medium for recording an image of the image pickup optical system received by the image pickup device, and a display for displaying the image so that the image can be observed. Electronic camera provided with an element.

(17) Claims 1 and 2 of the claims
Or 3 or the above (1), (2), (3),
(4), (5), (6), (7), (8), (9),
(10), (11), (12), (13) or (14)
And an illumination optical system for illuminating an object imaged by the imaging optical system.

[0111]

The imaging optical system of the present invention achieves good color reproducibility, low ghosting, and reduced electrical noise by using a composite filter having the above-described overall spectral characteristics. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a composite filter used in a first embodiment of the present invention.

FIG. 2 is a diagram showing spectral characteristics of the composite filter shown in FIG.

FIG. 3 is a diagram showing a configuration of a composite filter used in a second embodiment of the present invention.

FIG. 4 is a diagram showing spectral characteristics of the composite filter shown in FIG. 3;

FIG. 5 is a diagram showing a configuration of a third exemplary embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a fourth embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a fifth embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a sixth embodiment of the present invention.

FIG. 9 is a diagram showing a configuration of a seventh embodiment of the present invention.

FIG. 10 is a diagram showing a configuration of an eighth embodiment of the present invention.

FIG. 11 is a diagram showing a configuration of a ninth embodiment of the present invention.

FIG. 12 is a diagram illustrating spectral characteristics of ghost light.

FIG. 13 is a diagram showing a configuration of a tenth embodiment of the present invention.

FIG. 14 is a diagram showing a configuration of an eleventh embodiment of the present invention.

FIG. 15 is a diagram showing a configuration of an electronic camera using the imaging lens of the present invention.

FIG. 16 is a diagram showing a configuration of a video camera using the imaging lens of the present invention.

FIG. 17 is a diagram showing a configuration of an endoscope system using the imaging lens of the present invention.

FIG. 18 is a diagram showing an arrangement of color separation filters.

FIG. 19 is a diagram illustrating a configuration and spectral characteristics of a filter used in a conventional imaging apparatus.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 5/335 H04N 5/335 V 9/07 9/07 A

Claims (3)

[Claims] 1. An imaging optical system for forming an object image, and said imaging system
An image sensor that receives an object image formed by the optical system;
Wherein the imaging optical system has at least one interference film and light.
An interference element, wherein the interference film satisfies the following condition (1):
And the light absorbing element is located between the interference film and the imaging element.
To prevent ghosting caused by reflected light
The characteristic of the combination of the interference film and the light absorbing element is
An imaging optical system that satisfies the following condition (2). (1) 620 (nm) <λ₁<680 (nm) (2) 2 <D_Three<10 where λ₁Is the wavelength at which the transmittance of the interference film becomes 50%, and D_Three
Is the wavelength λ₁The transmittance of the light absorbing element at τ And when
It is a value given by the following equation. D_Three= Ln (1 / τ^Three) 2. An image forming optical system for forming an object image, and an image pickup device for receiving an object image formed by the image forming optical system, wherein the image forming optical system has at least one interference film, A light absorbing element that absorbs the reflected light in order to prevent a ghost caused by the reflected light generated between the interference film and the image pickup element, and satisfies the following conditions (3), (4), and (5). Satisfactory imaging optics. (3) 0.8 <A <2.7 (% / nm) (4) T (600)> 50% (5) T (700) <5% where A is within a wavelength range of 620 nm to 680 nm. The slope of the combined transmittance of the interference film and the light absorbing element at the wavelength λ ₁ where the transmittance of the interference film is 50%, T (600), T (7
00) is the combined transmittance of the interference film and the light absorbing element at wavelengths of 600 nm and 700 nm, respectively. 3. An imaging optical system for forming an object image, and an imaging device for receiving an object image formed by the imaging optical system, wherein the imaging optical system includes at least one interference film. A light absorbing element, wherein the interference film satisfies the following condition (1), and the light absorbing element arranges an absorption filter between the interference film and the imaging element to prevent ghost. An imaging optical system characterized by the above-mentioned. (1) 600 (nm) <λ ₁ <680 (nm) where λ ₁ is a wavelength at which the transmittance of the interference film becomes 50%.