JPH0695208A - Nd filter for light quantity diaphragm device - Google Patents

Abstract

PURPOSE:To enhance resolution and to solve the problem of ghosts by photographing an original plate by a camera using a film which has the specific value or below of the transmittance of a base and is provided with a halation preventive layer, subjecting this film to development processing and using the processed film as the ND filter. CONSTITUTION:The original plate which is formed with the density distribution corresponding to the density distribution of the determined ND filter (the density is reversed in order for reversal) and is enlarged to a certain magnification is produced. This original plate is photographed by the camera using the film satisfying specific conditions and is developed. The characteristics required for the ND filter are such that the quantity to shield light (transmittance) must be fixed in the same position within the filter. The film is required to meet the requirements that the grain size of the silver particles be <=0.5mum; the halation preventive layer be provided: the spectral transmission characteristic be + or -20% at 400 to 650nm (ratio to an average value) and the transmittance of the base of the film be >=80%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ND filter used in a light quantity diaphragming device suitable for use in a photographing system such as a video camera and a still video camera, and a method for manufacturing the ND filter.

[0002]

2. Description of the Related Art In a conventional diaphragm device, as shown in FIGS. 4 and 5, in order to correct a small diaphragm, an ND filter 14 covers an aperture diameter of about F8 to F11.
3 is attached or arranged by an adhesive 15 on the edge of the opening 13a. The conventional ND filter 14 uses a uniform density filter. Therefore, in recent years, as the sensitivity of the image sensor has increased, the density of the filter is increased to reduce the amount of light transmission, and the minimum aperture of the diaphragm is increased even if the brightness of the subject is the same. However, when the density of the ND filter is high, the difference in the amount of light between the light passing through the filter 14 and the light not passing through the filter 14 greatly differs in the state where the aperture amount is large as shown in FIG. 4, and the resolution deteriorates. Cause In order to solve this drawback, the applicant of the present application has proposed that the density of the ND filter has a structure in which the transmittance gradually increases toward the center of the optical axis.
It was already proposed as -77349.

In the drawing, reference numerals 1, 2, 3, and 5 are photographing optical systems, 5 is an optical low-pass filter, 6 is an image pickup element such as CCD, 7 is a base plate of a diaphragm device, 15 is an ND filter 14 and diaphragm blades 13. The adhesive part for attaching to is shown.

[0004]

Generally, as a method for producing an ND filter, a type in which a light-absorbing pigment is mixed in a film-shaped material (cellulose acetate, PET, etc.) and kneaded, There is a type of coating a material with a pigment that absorbs light. With these manufacturing methods, it is possible to manufacture a filter having a uniform concentration, but it is extremely difficult to manufacture a filter of which concentration varies.

To solve the above problems, it is an object of the present invention to provide a diaphragm device with improved uniformity of light quantity, and to provide a density change type ND filter used for the diaphragm device and a manufacturing method thereof. There is.

[0006]

In order to solve the above-mentioned problems, an original plate having a reflection density distribution having a predetermined relationship with a density distribution which gives a filtering effect to transmitted light when provided on a diaphragm blade of a light quantity diaphragm device is produced. However, this original plate is photographed by a camera using a film having a transmittance of 80% or more of a base and provided with an antihalation layer, developed, and used as an ND filter.

[0007]

[Embodiment] The embodiment of the present invention corresponds to the density distribution of a predetermined ND filter (the density is reversed to be inverted).
A density distribution is formed, and an original plate stretched to a certain enlargement ratio is produced, and this film is photographed with a camera and developed using a film satisfying a specific condition.

The photographed film is molded and used as it is as an ND filter.

The original plate has a uniform reflection density in the direction perpendicular to the direction in which the reflection density changes, and a pattern is formed so that a large number of predetermined filters can be obtained within one frame of the film (effective area 29 mm × 41 mm max). The reflection density distribution of the original plate is the density distribution shown in FIG.

As a characteristic of the ND filter, the amount of light shielding (transmittance) must be constant at the same position in the filter. As a variation in quality, it is necessary to put it within the average value ± 15% (8.5 to 11.5% when the transmittance is 10%) (± 0.05 in concentration). The relationship between the density D and the transmittance T is D = 0.78 × log ₁₀ 1 / T.

In the photographic method of this embodiment, a white paper having a high reflectance gives a high density portion, and a black paper having a low reflectance gives a low density. It is projected on the film from the original pattern that was reversed in black and white.

Since the density is determined by this chemical change, in order to obtain a uniform density in the film, it is necessary to set the conditions at the time of photographing and developing. For example, when shooting
It is necessary to pay attention to the lighting, and the shooting illuminance is ± 5
Must be within%.

Further, it is appropriate that the photographing scale factor is 1/5 to 1/15 depending on the relationship with the lens of the camera.

When it becomes smaller than 1/15 (for example, 1
/ 24) Density unevenness becomes large and does not fall within the above 15%. On the other hand, if it is larger than ⅕, the original size becomes small and the resolution (change in density) is lowered.

The liquid temperature during development is controlled to ± 0.3 ° C. The liquid temperature and the film density have a relationship as shown in FIG.

Next, the characteristics of the filter are 400 nm to
It is necessary that the transmittance be constant in the wavelength range of 650 nm. When the reflectance is 10% or more, it causes ghost and cannot be used. Furthermore, the higher resolution is preferable. It is necessary that the density of the brightest part is also low (the range of density change can be wide).

From the above, the film has a silver edge grain size of 0.5 μm or less. An antihalation layer is provided (see FIG. 9). Spectral transmission characteristic is ± 20% at 400nm-650nm
(Ratio to average value). The transmittance of the base of the film is 80% or more. It is necessary to have one.

What is particularly important for the ND filter is the transmittance of the base and the presence or absence of an antihalation layer.

As the camera, a flat-bed type copying camera as shown in FIG. 6 was used. This was chosen in terms of resolution.

An automatic developing machine for copying was selected as the developing machine.

Next, a state after the original plate has been photographed by a camera using a film which meets the above conditions will be described.

FIG. 1 shows the film developed after photography.

FIG. 1A shows a first example, in which a region having a constant density and a variable region having a gradually decreasing density are connected to each other and cut along the cutting line shown in FIG. 2A. By doing so, a large number of ND films (enlarged view is shown in FIG. 3) can be obtained. As is clear from the figure, the film is provided with a density distribution that allows the ND filters having a substantially triangular shape to be alternately cut into two rows. Of particular importance is the method of forming the concentration distribution for cutting the ND filters in a staggered manner in order to take a large number of them.
Regions where the concentration was gradually reduced were formed above and below (in the figure) the region of constant concentration in the center. As a result, the ND filter cut as shown in the enlarged view of FIG. 3 has a density variable region not only in the lower position (in the drawing) but also in the upper position (in the drawing). 1
Since the adhesive portion 15 to 3 is used, no problem occurs. In the ND filter shown in FIG. 3, a white line is formed in the area of the adhesive portion 15 as an index for making the attachment position to the diaphragm blade 13 accurate (obviously, it is formed on the original plate). By adhering this white line to a specific position of the diaphragm blade and adhering it, an extremely accurate mounting position can be obtained.

FIG. 1 (b) shows a second example, in which all the densities are variable, and by cutting as shown in FIG. 2 (b), a multi-cavity ND filter can be obtained. it can. As shown in FIG. 2B, in the case of the second example, the density distribution on the film is set so that the ND filters can take two rows alternately. Also, a white line as an index for making the mounting position accurate is formed similarly to the first example.

The effect of using the ND filter formed in the first example shown in FIGS. 1A and 2A will be described.

Although there is no problem in the conventional ND filter having only uniform density, when the density changes in the same ND filter, the substantial aperture value at the time of a small aperture varies from camera to camera. It is possible that it will end up. In the case of a video lens, when the field of view exceeds a certain level of brightness, it will be fixed at the minimum aperture and will not stop further. This is because the resolution is lowered when the aperture is less than a certain aperture, and the aperture is fixed. Therefore, in the case of shooting outdoors that requires the ND filter most, the probability of controlling the aperture to the minimum aperture increases. In the case of the ND filter shown in the first example, which has a region of constant density, only the region of constant density is located inside the aperture opening when the minimum aperture is opened. The target aperture value does not vary.

Next, FIG. 1 (a), (b), FIG. 2 (a),
The characteristics of the ND filter shown in (b) will be described.

FIG. 10 shows the difference in the transmittance of the three types of filters. A shows the ND filter of the first example in this embodiment, and B is a general ND filter different from this embodiment (for example, 35 mm).
The ND filter shown in the first example is made of a film for use with the ND filter, and C is an ND filter having a constant density as in the conventional case. The ND filter A has a constant density transmittance of about 5%, but the transmittance gradually changes and the maximum transmittance exceeds 80%. This is because the transmittance of the film base itself exceeds 80%. On the other hand, the ND filter B has the same constant transmittance of about 5%, but the maximum transmittance is slightly lower than 40%.
This is because the film base itself has a low transmittance.
The ND filters C all have a constant density (about 5%).

FIG. 11 shows the resolutions of the above three types of ND filters. As is clear from the figure, FNO 4.0.
Between -8.0, there is a difference in resolution due to the difference in transmittance. That is, it is understood that only the ND filter A in this embodiment can obtain high resolution. In FIG. 11, the ND filters A to C are experimentally made to have film-based silver salt particles of 0.2 to 0.5 μm. The ND filter D shown in FIG. 11 has the transmittance of the ND filter B and has a film-based silver salt particle of 1 μm to 5 μm.
The resolution is lower than that of the filter B.

Next, the effect of providing the antihalation layer, which is a condition of the film of this example, will be described.

When the ND filter is used for the video lens as shown in FIG. 4, the subject light which has passed through the photographing optical systems 1 to 4 is incident on the image pickup device 6, but a part of the surface of the image pickup device 6 is used. Is reflected by. When this reflected light is re-reflected on the back surface side of the ND filter, it becomes a ghost and re-enters the image sensor 6. By using the film base provided with the antihalation layer as in the present embodiment, false reflection is extremely reduced and ghost can be prevented from occurring.

[0032]

INDUSTRIAL APPLICABILITY The present invention uses an ND filter used in a light quantity diaphragming device, in which a base has a transmittance of 80% or more and an antihalation layer is provided, and a reflection density distribution different depending on the region is formed. ND with different transmittance depending on the area by shooting the original plate with a camera, developing it and using it as an ND filter.
The filter can be easily manufactured, the resolution can be increased, and the ghost problem can be solved.

[Brief description of drawings]

FIG. 1 is a view showing a film after development which is used as an ND filter as an example of the invention.

FIG. 2 is a diagram showing a method of cutting the film of FIG.

FIG. 3 is an enlarged view of a cut ND filter.

FIG. 4 is a cross-sectional view showing an arrangement inside a lens of a general light amount diaphragm device.

5 is a perspective view showing diaphragm blades of the light quantity diaphragm device of FIG. 4. FIG.

FIG. 6 is an explanatory diagram showing a shooting method according to an embodiment.

FIG. 7 is a graph showing a relationship between shooting illuminances at the time of shooting.

FIG. 8 is a cross-sectional view showing an antihalation layer of the film.

FIG. 9 is a graph showing the relationship between liquid temperature and film density.

FIG. 10 is a graph showing changes in transmittance of three types of ND filters.

FIG. 11 is a graph showing the resolution of four ND filters.

[Explanation of symbols]

 13 Aperture blade 14 ND filter

Claims (11)

[Claims] 1. A method of manufacturing an ND filter, which is located in an opening formed by diaphragm blades of a light quantity diaphragm device and is provided so as to have a different transmittance depending on a region, wherein the transmittance of a base is 80% or more. A film having an antihalation layer is provided and an original plate having a reflection density distribution having a predetermined relationship with the different transmittance is prepared, and the original plate is photographed by a camera using the film and developed. A method for manufacturing an ND filter for a light amount diaphragm device, which is used as an ND filter. 2. The method for producing an ND filter for a light amount diaphragm device according to claim 1, wherein the film has silver salt particles of 0.5 μm or less. 3. The light amount according to claim 1 or 2, wherein the film has a transmission spectral characteristic in which the variation of the transmittance is within 20% in the maximum and the minimum in the wavelength range of 400 nm to 650 nm. Manufacturing method of ND filter for diaphragm device. 4. The ND filter for a light amount diaphragm device according to claim 1, wherein a plurality of ND filters are photographed on the film at the same time, and a plurality of ND filters are taken by cutting after development processing. Manufacturing method. 5. The reflection density of the original plate is such that a region having a constant density and a continuously variable region in which the density is gradually lowered from the constant density are connected in one direction. 2. A method for manufacturing an ND filter for a light amount diaphragm device according to 2, 3, or 4. 6. The film is provided with a mark on the ND filter, the mark indicating a position where the film is attached to the diaphragm blade when the film is cut into the ND filter. 4. A method for manufacturing an ND filter for a light amount diaphragm device according to 4, or 5. 7. Located within the aperture formed by the diaphragm blades,
ND provided to have different transmittance depending on the area
In a light quantity diaphragm device using a filter, a master plate having a reflection density distribution having a predetermined relationship with the different transmittance is used by using a film having a base transmittance of 80% or more and an antihalation layer. A light amount diaphragm device using an ND filter, which is formed by taking a photograph using a camera with the film and developing it. 8. The light amount diaphragm device using an ND filter according to claim 7, wherein the film has silver salt particles of 0.5 μm or less. 9. The ND according to claim 7, wherein the film has a transmission spectral characteristic in which the variation in the transmittance is within 20% in the maximum and the minimum in the wavelength range of 400 nm to 650 nm. Light amount diaphragm device using a filter. 10. The ND filter according to claim 7, 8 or 9, wherein a constant transmittance region and a continuously variable region where the transmittance is gradually increased are connected in one direction. Light amount diaphragm device using the ND filter. 11. A light amount diaphragm device using an ND filter according to claim 7, 8, 9 or 10, wherein a mark indicating a mounting position on said diaphragm blade is formed on said ND filter.