JP2009139483A - Illumination device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the focusing accuracy and range of automatic focus adjustment when auxiliary light is used by preventing illumination light from largely spreading with respect to a subject, even when a subject distance is made larger, in an illumination light projection device for assisting the automatic focus adjustment. <P>SOLUTION: An illumination device uses a light source which oscillates a laser beam and a computer synthetic hologram element which is designed so that a laser luminous flux from the laser light source may be diffracted to obtain a desired light distribution in a far field (Fraunhofer region) (to be a Fraunhofer hologram and a Fourier transform hologram). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an illuminating device for projecting illumination light for assisting focus adjustment used in an electronic imaging device such as a digital camera or a video camera.

  Conventionally, in digital still cameras and video cameras, when the brightness and contrast of a subject are low, a method has been proposed in which a predetermined light distribution illumination is projected onto the subject from an auxiliary light source and used for automatic focus adjustment.

  For example, the example disclosed in Patent Document 1 uses a light emitting diode (hereinafter referred to as LED) as a light source and illuminates with a plurality of mirrors whose tilt angles can be adjusted. In this example, patterns suitable for automatic focus adjustment such as vertical stripes and horizontal stripes can be projected according to the size of the subject by moving the mirror.

  In addition, the example disclosed in Patent Document 2 uses a diffraction plate in which rectangular microlenses having different curvatures in the vertical and horizontal directions are periodically arranged in the vertical and horizontal directions while changing the curvature and arrangement period, and a laser as a light source. A striped pattern is projected.

Further, the example disclosed in Non-Patent Document 1 uses an element called “laser hologram” and, like the previous example, irradiates the subject with laser light as auxiliary light and mounts it on the product as “holographic AF”. ing. In this example, a light distribution pattern having a discrete diagonal lattice pattern (shown in FIG. 3) is projected and has a focusable range of 4.5 m (catalog value).
JP 2004-165841 A JP 2004-012791 A Sony Corporation Cybershot DSC-F707, F828, V1, V3 product catalog homepage. (The main figure is reproduced in Figure 3)

  The conventional example has the following problems.

In the case of Patent Document 1,
(Problem 1) Since the movable mirror element has a drive portion, the mechanism is complicated, the element is expensive, and the configuration tends to be large.

(Problem 2) Since the diffused light emitted from the LED is simply used, the effective illumination distance is short, for example, the luminous flux greatly expands at an irradiation distance of about 2 m.
Have problems such as.

  Next, in the examples disclosed in Patent Document 2 and Non-Patent Document 1, a laser having a higher directivity than that of a general light source is used as a light source, so that the irradiation distance can be made longer than that of simple LED illumination.

  However, each has the following problems to be improved.

  In the case of the example disclosed in Patent Document 2, the microlens array acts as a so-called diffraction grating and uses simple diffracted light. By adjusting the period in the vertical and horizontal directions of the microlens, a fringe pattern advantageous for focus adjustment is irradiated at different diffraction angles.

  (Problem 1) Even a beam-type laser light source with high directivity expands by the diffraction angle. Based on the disclosed embodiment, the stripe spacing of 2 ° extends to 17 cm at a distance of 5 m. End up.

  (Problem 2) If the propagating light beam is simply separated by diffraction, the fringes projected on the subject are blurred.

  In the example disclosed in Non-Patent Document 1, a so-called hologram element called “laser hologram” is used. In this case, a high degree of freedom in designing the hologram element is used, for example, the projected light distribution pattern is a discrete oblique lattice pattern.

  (Problem 1) In the specification disclosed in Non-Patent Document 1, the effective focusing distance is 4.5 m, which is about twice that of the LED. In addition, this element is considered to belong to a so-called Fresnel hologram from the specifications such as the effective diameter, wavelength, and focusing distance.

  (Problem 2) Although numerical information is not disclosed, it is shown that the projected light distribution pattern has a relatively large spread equivalent to the angle of view. For this reason, the entire oblique grid pattern to be projected greatly expands with respect to the angle of view as the subject distance increases, and each line image rapidly expands with respect to the subject and the outline is blurred.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide an auxiliary light projection device for effective automatic focus adjustment even at a relatively far subject distance.

  The illumination light projection apparatus for assisting the automatic focus adjustment according to the present invention diffracts a light source that oscillates laser light and a laser beam from the laser light source into a desired light distribution in the far field (Fraunhofer region). And a computer-generated hologram element designed to be a Fraunhofer hologram or a Fourier transform hologram.

  In the present invention, the illumination light for assisting automatic focus adjustment (hereinafter referred to as auxiliary light) can be designed so that it does not spread greatly with respect to the subject when the subject distance increases. In addition, the light distribution pattern of the auxiliary light projected on the subject does not always blur even if the distance varies greatly in the Fraunhofer region where the subject distance is a certain distance or more. Therefore, it is possible to improve the focusing accuracy and range of automatic focus adjustment when auxiliary light is used.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

<Configuration of digital still camera>
FIG. 2 shows a configuration of a digital still camera 3 including an auxiliary light projection device for automatic focus adjustment according to the first embodiment of the present invention. The automatic focus adjustment means is suitable for a general contrast detection method in the apparatus, but the automatic focus adjustment method is well known and will not be described. Further, since the method of using the illumination light for assisting the automatic focus adjustment is well known, the description is omitted.

<Configuration of auxiliary light projector>
FIG. 1 shows a configuration of an illumination light projector for assisting automatic focus adjustment according to the first embodiment of the present invention.

  In the figure, 1 is a semiconductor laser diode which is an auxiliary light source, 2 is a hologram element, 3 is a digital still camera body, 4 is a light distribution pattern of auxiliary light in a short distance of the camera, and 5 is a camera. 2 is a light distribution pattern of auxiliary light projected onto a subject that is a predetermined distance away from the object.

  The diffused light beam emitted from the semiconductor laser 1 is diffracted by the hologram element 2 and propagates toward the subject. The hologram element 2 is a so-called computer-generated hologram, which is a known element, but will be described briefly. The hologram element is a phase conversion element that modulates the amplitude and phase of a light beam that illuminates the hologram element by a diffraction action. In particular, a computer-generated hologram is an element in which a phase conversion distribution function necessary for obtaining desired light is obtained by calculation, and a diffraction grating structure that performs this function is manufactured as a diffraction element. Therefore, any phase conversion that can be calculated is possible, and the degree of freedom in design is high. There are several types of holograms, but the present invention is characterized in that the reproduced image is set in the Fraunhofer region set at infinity. That is, the distribution of auxiliary light to be projected onto the subject is made to be an infinite diffraction image, that is, a Fraunhofer diffraction pattern.

  For example, in the case of an interference fringe type hologram, the interference fringe pattern using the diffused spherical wave of the semiconductor laser as the reference light is calculated using the Fourier spectrum of the amplitude distribution of the desired auxiliary light distribution as the distribution function of the object light. It ’s fine. At this time, it is necessary to calculate the reference wavefront including the astigmatism component of the semiconductor laser in advance. As a result, the influence of the astigmatism component inherent to the semiconductor laser can be substantially eliminated.

  Further, it is preferable that the hologram configuration is Gabor type (inline type) and all are arranged coaxially.

  Assuming that the effective diameter of the hologram is D = 1 mm, the semiconductor laser wavelength, and λ = 650 nm, the distance to the diffraction image is Z ≧ D ^ 2 / λ≈1.5 m as a condition of the Fraunhofer diffraction region. .

  The illumination light distribution in the Fraunhofer region may be, for example, vertical stripes that are easy to perform automatic focus adjustment, as long as there is a boundary line that changes contrast in the direction in which contrast detection is performed by automatic focus adjustment. .

  When the subject is closer than the Fraunhofer region, the diffraction image projected on the subject becomes a blurred image as a geometric optical projection region and a Fresnel diffraction region. However, in this case, focus adjustment depending on the contrast inherent to the object surface can be performed as so-called illumination equivalent to that by a conventional LED or the like.

  The auxiliary illumination by the Fraunhofer diffraction image preferably projects auxiliary light near the center of the screen in the Fraunhofer region.

  The size of the auxiliary illumination is preferably designed to be within a range on the screen where automatic focus adjustment is performed.

  The semiconductor laser preferably has a low output of class 1 or less.

  If the wavelength of the semiconductor laser is on the longest wavelength side that can be detected by the image sensor, the area on the short distance side of the Fraunhofer area approaches the camera, so that the effective range becomes wide.

  Using a high-brightness LED instead of the semiconductor laser can also reduce the sharpness of the light distribution of the diffracted light to be projected because the spatial coherence is reduced.

(Industrial applicability)
INDUSTRIAL APPLICABILITY The present invention is effective in the field of an auxiliary illumination device that uses the operation of an automatic focus adjustment device in a dark place of an imaging device equipped with an automatic focus adjustment device such as a digital still camera or a video camera.

The side view of the auxiliary | assistant illumination device of the automatic focus adjustment apparatus by this invention. The figure which shows the state equipped on the digital camera of the auxiliary | assistant illumination device of the automatic focus adjustment apparatus by this invention. The figure which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Computer-generated hologram element 3 Digital camera 4 Light distribution of illumination light in Fresnel area 5 Light distribution of illumination light in Fraunhofer area

Claims (1)

  A high-brightness LED or semiconductor laser is used as a light source, and the light source light beam is phase-modulated by a transmission type phase modulation element or a reflection type phase modulation element (diffractive optical element, hologram), and the diffracted light has a desired light distribution. A lighting device using a phase modulation element designed so that a region to be formed is a far field (Fraunhofer diffraction region).

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