JP4061637B2 - Flash device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flash device applied to a camera, and more particularly to a flash device capable of changing an irradiation angle (light distribution angle).
[0002]
[Prior art]
According to the variable illumination angle strobe device disclosed in Japanese Patent Application Laid-Open No. 6-242496, the Fresnel lens is used when the reflector mounted with the flash tube (flash tube) moves to a position away from the Fresnel lens. In order to solve the problem that a useless light flux that is not captured by the light is generated and the emission efficiency is reduced, a structure in which a convex lens is inserted immediately before the reflecting mirror in the tele mode is provided.
[0003]
An electronic flash device disclosed in Japanese Patent Laid-Open No. 6-160947 includes a first condensing Fresnel lens (positive lens) in front of a reflector equipped with a flash tube. A second condensing Fresnel lens (positive lens) is disposed on the outer portion of the optical axis so that an outer light beam emitted from the tube can enter the first condensing Fresnel lens.
[0004]
[Problems to be solved by the invention]
However, the conventional apparatus disclosed in each of the above publications has an extra lens member such as a convex lens or a second condensing Fresnel lens in addition to a normal condensing lens (first condensing Fresnel lens). This has the disadvantage of increasing the equipment space.
[0005]
The present invention has been made in view of such circumstances, and provides a flash device capable of preventing a reduction in emission efficiency at the time of telephoto and achieving miniaturization and space saving without adding an extra lens member. To do.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a flash device according to the present invention includes a flash tube that emits flash light, a substantially semi-cylindrical reflection that holds the flash tube and reflects light generated from the flash tube forward. And a Fresnel lens that is disposed in front of the reflector on the opening side and functions as a concave lens. The irradiation angle is changed by changing the distance between the flash tube and the light-emitting portion including the reflector and the Fresnel lens. It is characterized by being configured to change.
[0007]
According to the present invention, since a Fresnel lens (hereinafter referred to as a concave Fresnel lens) that functions as a concave lens (negative lens) is disposed in front of the reflector on the opening side, when the light emitting unit is brought closer to the concave Fresnel lens, The irradiation angle becomes narrower, and the irradiation angle becomes wider as the light emitting portion is moved away.
[0008]
When shooting with the photographic lens set to telephoto, the concave Fresnel lens and the light-emitting part are brought close to each other to achieve a narrow light distribution, and when shooting at wide, the concave Fresnel lens And a light distribution with a large irradiation angle is realized by increasing the distance between the light emitting portions.
[0009]
If the distance between the concave Fresnel lens and the light emitting part is increased when wide, the light from the light emitting part diffuses and some light beams do not enter the concave Fresnel lens. Since the F number is smaller than that at tele time, even if the guide number is lowered due to the above phenomenon, there is substantially no problem.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the flash device according to the present invention will be described in detail with reference to the accompanying drawings.
[0011]
FIG. 1 is a front view of a flash device according to an embodiment of the present invention, and FIG. 2 is a schematic sectional view taken along line 2-2 of FIG. 2A shows a state where the irradiation angle is the smallest (telephoto), and FIG. 2B shows a state where the irradiation angle is the largest (wide).
[0012]
For example, the flash device 10 is built in a compact camera in which a zoom lens is mounted on a photographing optical system, and an irradiation angle is varied according to a focal length of the photographing optical system. On the wide side, the field of view is wide, so the light distribution range is widened. On the tele side, the irradiation angle is narrowed to increase the guide number.
[0013]
As shown in FIGS. 1 and 2, in the flash device 10 according to the present embodiment, a flash tube (for example, a xenon tube) 14 is disposed in the reflector 12 having a substantially semi-cylindrical shape. The concave Fresnel lens 16 is provided in front of the flash tube 14 (in front of the opening of the reflector 12). The “substantially semi-cylindrical shape” includes those whose cross-sectional shape forms part of a parabola or an ellipse.
[0014]
The light emitting unit 18 including the flash tube 14 and the reflector 12 can be moved back and forth along the optical axis direction of the concave Fresnel lens 16, and the irradiation angle is variable by changing the distance between the concave Fresnel lens 16 and the light emitting unit 18. Is done. When the light emitting part 18 is brought closer to the concave Fresnel lens 16, the irradiation angle of the light emitted from the concave Fresnel lens 16 becomes smaller. When the light emitting part 18 is moved away from the concave Fresnel lens 16, the light is emitted from the concave Fresnel lens 16. The irradiation angle of the emitted light increases.
[0015]
Although means for moving the light emitting unit 18 is not shown, for example, there is a mode in which a motor (zoom motor) for driving the photographing lens barrel is also used and the reflector 12 is driven by the power of the motor. Moreover, the aspect which displaces the light emission part 18 is also possible by transmitting the movement (displacement by operation) of the tele / wide switching operation member to the reflector 12 by mechanical means such as a cam.
[0016]
The concave Fresnel lens 16 of this example has a Fresnel groove 16A formed on the surface (incident surface side) on the side of the flash tube 14, but a Fresnel groove is formed on the surface opposite to the flash tube 14 (exit surface side). A configuration is also possible.
[0017]
According to the flash device 10 configured as described above, when the photographing optical system of the camera is set to the tele side, the light emitting unit 18 is brought close to the concave Fresnel lens 16 as shown in FIG. . At the telephoto end, the light emitting portion 18 is closest to the concave Fresnel lens 16.
[0018]
Flash light generated from the flash tube 14 is reflected by the inner surface of the reflector 12 and is not diffused to the outside, and enters the concave Fresnel lens 16 without waste. Thereby, the light collection efficiency is improved, and a good light distribution characteristic with a relatively narrow irradiation angle suitable for telephotographing can be obtained.
[0019]
On the other hand, when the photographing optical system of the camera is set to the wide side, the light emitting unit 18 is moved to a position away from the concave Fresnel lens 16 as shown in FIG. At the wide end, the light emitting unit 18 moves to a position farthest from the concave Fresnel lens 16. For the intermediate position from the wide end to the tele end, the stop position of the light emitting unit 18 is set according to the focal length.
[0020]
When the distance between the concave Fresnel lens 16 and the light emitting unit 18 is increased, the irradiation angle is increased by the action of the concave Fresnel lens 16, and light distribution characteristics suitable for wide-angle imaging can be obtained.
[0021]
When the light emitting unit 18 is moved away from the concave Fresnel lens 16 at the wide time, a part of the light from the light emitting unit 18 is diffused outward, and a useless light beam that does not enter the concave Fresnel lens 16 may be generated. However, since the F number is smaller at the time of wide-angle than at the time of telephoto, even if the amount of light emitted from the flash device 10 slightly decreases due to this phenomenon, there is almost no influence on actual use.
[0022]
As shown in FIG. 3, there is also an aspect in which the auxiliary reflecting mirror 20 is provided outside the reflector 12 so as to cover the periphery of the optical path. According to FIG. 3, the auxiliary reflecting mirror 20 is arranged parallel to the optical axis of the concave Fresnel lens 16. Flash light generated from the flash tube 14 is reflected by the inner surfaces of the reflector 12 and the auxiliary reflecting mirror 20, and is guided to the concave Fresnel lens 16 while being prevented from diffusing outward. Thereby, the light collection efficiency is increased, and the above-described problem of a decrease in the amount of light can be solved. In addition, the light reflected by the auxiliary reflecting mirror 20 enters the concave Fresnel lens 16 at a large incident angle and increases the irradiation angle, but advantageously contributes to the light distribution characteristics in the wide range.
[0023]
In the above-described embodiment, the example in which the light emitting unit 18 is moved in the direction toward or away from the concave Fresnel lens 16 fixed in place has been described. However, the scope of application of the present invention is not limited to this, and A mode in which the Fresnel lens 16 side is moved is also possible. That is, the present invention can be applied to a flash device having a structure in which the concave Fresnel lens 16 and the light emitting unit 18 are relatively movable and the irradiation angle is variable by changing the relative position of the two.
[0024]
【The invention's effect】
As described above, according to the present invention, the concave Fresnel lens is arranged in front of the light emitting unit, and the irradiation angle is changed by changing the distance between the concave Fresnel lens and the light emitting unit. The light emitting part can be brought close to each other to realize a light distribution with a narrow irradiation angle, and when it is wide, the concave Fresnel lens and the light emitting part can be moved away to realize a light distribution with a large irradiation angle.
[0025]
When the distance between the light emitting part and the concave Fresnel lens is increased, useless light flux that does not enter the concave Fresnel lens may be generated. However, since the F number is smaller at the wide time than at the tele time, the guide number is substantially reduced. It doesn't matter. As a result, lens members such as a convex lens and a second condensing Fresnel lens, which have been conventionally required, become unnecessary, and a reduction in size and space can be achieved.
[Brief description of the drawings]
FIG. 1 is a front sectional view of a flash device according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view taken along line 2-2 in FIG. 2 (b) is a diagram showing a state in which the irradiation angle is the largest (when wide). FIG. 3 is a schematic cross-sectional view showing another embodiment of the present invention.
DESCRIPTION OF SYMBOLS 10 ... Flash apparatus, 12 ... Reflector, 14 ... Flash tube, 16 ... Concave Fresnel lens, 18 ... Light emission part, 20 ... Auxiliary reflector

Claims (1)

A flash tube emitting light,
A substantially semi-cylindrical reflector that holds the flash tube and reflects light generated from the flash tube forward;
A Fresnel lens that is disposed in front of the reflector on the opening side and functions as a concave lens,
A flashing device configured to change an irradiation angle by changing a distance between a light emitting unit including the flash tube and the reflector and the Fresnel lens.

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