JP2533466B2 - Strobe flash - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stroboscopic flash device used for a camera or the like, and more particularly to a stroboscopic flash device which is downsized.

[0002]

2. Description of the Related Art A conventional stroboscopic flash device using an elliptical mirror has an elliptical cross section x = as shown in FIG.
Semi-elliptical cylindrical reflector 1 represented by a {1- [1- (y ² / b ² )] ^1/2 }
And a cylindrical strobe flash tube 2 arranged at the focal position of the reflector 1. “A” represents the major axis length of the ellipse, and “b” represents the minor axis length of the ellipse. In such a strobe flash device, at the front opening 1a of the strobe reflector 1, the angle θ of the light beam directly emitted from the strobe flash tube 2 is set.
When 1 and the angle θ 2 of the light beam emitted after being reflected by the strobe reflector 1 are made equal to each other as the irradiation angle θ, the light utilization efficiency is the best. For this purpose, the depth of the strobe reflector must be equal to the major axis length a of the ellipse, and
The aperture diameter D in the strobe reflector 1 is 2 of the minor axis b of the ellipse.
Need to double. That is, a = b · sin θ and b = D / 2.

Therefore, for example, in order to obtain a stroboscopic flash device with an irradiation angle θ = 25 ° and an aperture diameter D = 12 mm, these values are substituted into the above formulas to determine the elliptical shape of the stroboscopic reflector 1. The axial length a is 14.197 mm and the minor axial length b is 6 mm. That is, it is understood that the depth of the strobe reflector 1 needs to be 14.197 mm, and must be considerably deep. As described above, in the conventional stroboscopic flash device using the elliptic mirror, in order to narrow the irradiation angle θ, the depth of the strobe reflector 1, that is, the major axis length a, must be made large, which hinders miniaturization. It was.

[0004]

OBJECT OF THE INVENTION It is an object of the present invention to downsize a strobe flash device. In particular, a convex Fresnel lens is attached to the front surface of the reflector to reduce the dimension of the reflector in the depth direction.

[0005]

SUMMARY OF THE INVENTION The stroboscopic flash device of the present invention is an ellipse whose reflective surface of a longitudinal section is represented by the formula x = a {1- [1- (y ² / b ² )] ^1/2 } (where a is A semi-elliptical cylindrical reflector consisting of the major axis length of the ellipse, and b the minor axis length of the ellipse; a cylindrical stroboscope located at the focal point of this reflector; at the front open end of the reflector A fixed Fresnel lens positioned fixedly;
The depth Dp of the reflector is less than the length of the major axis a, and the convex Fresnel lens is not reflected from the strobe flash tube at the reflecting surface of the reflector at the front open end in the longitudinal section of the reflector. The angle of irradiation of the light ray emitted from the strobe flash tube in the direction away from the optical axis and the angle of irradiation of the light ray emitted from the strobe flash tube in the direction approaching the optical axis through the post-convex Fresnel lens. Is characterized by being substantially equal.

The irradiation angle θ is preferably in the range of θ = ± 15 ° to ± 45 °, and Dp is preferably in the range of approximately 0.52a to 0.65a.

The convex Fresnel lens has less vignetting when the convex Fresnel groove is formed only on the surface opposite to the strobe flash tube. If a semi-cylindrical housing portion is formed at the apex of the reflector and the inner portion of the strobe flash tube is housed in the semi-cylindrical housing portion, further miniaturization can be achieved.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to illustrated embodiments. FIG. 1 and FIG. 2 show examples of the shape of the stroboscopic flash device according to the present invention. The longitudinal section has the formula x = a {1- [1- (y ² /
b ² )] ^1/2 }, the semi-elliptical cylindrical reflector 3 having a constant cross section represented by an ellipse has a convex Fresnel lens 4 at the front opening 3 a.
, And a cylindrical strobe flash tube (xenon flash tube) 5 is located at the internal focus position. The convex Fresnel lens 4 has a convex Fresnel groove 4a formed on its front surface, that is, on the surface opposite to the strobe flash tube 5. This lens 4 has less vignetting and has a higher light-collecting effect than a convex Fresnel lens of the same type in which the convex Fresnel groove 4a is formed on the strobe flash tube 5 side. Vignetting in the convex Fresnel lens means a portion that does not contribute to the light condensing action, and the state of the vignetting is shown in FIGS. 9 and 10. As shown in this figure, the convex Fresnel groove 4a formed on the side opposite to the flash tube 5 (subject side) (FIG. 9) has the convex Fresnel groove 4a formed on the strobe flash tube 5 side (FIG. It can be seen that vignetting is smaller than that in (See 10) and, as a result, the condensing effect is high.

A feature of the present invention is that the convex Fresnel lens 4 is arranged in the front opening 3a of the reflector 3 as shown in FIGS.
As shown in, the depth Dp of the reflector 3 is made smaller (shallow) than the length of the major axis a of the ellipse, and then the surface shape of the reflector 3, the position of the strobe flash tube 5, and the convex Fresnel lens 4 are provided.
By appropriately setting the power of the above, the upper and lower irradiation angles θ shown in FIG. 1 are made substantially equal. That is, at the front opening end 3a in the vertical cross section of the reflector 3, a light beam emitted from the strobe flash tube 5 through the convex Fresnel lens 4 in a direction away from the optical axis without being reflected by the reflecting surface of the reflector 3. And the irradiation angle θ of the light ray reflected from the strobe flash tube 5 by the reflector 3 through the post-convex Fresnel lens 4 toward the optical axis.
These elements are set so that are approximately equal to each other. Thus, if the irradiation angles θ in the vertical direction are equal, the light utilization efficiency is highest and the depth of the reflector 3 can be made much shallower than in the conventional case.

Next, the ellipse is expressed by the equation x = y ² / R [1+ {1- (1 + K) y ² / R ² }.
^1/2 ] (where K is a cone constant and R is a radius of curvature of the reference spherical surface), the focal length f of the convex Fresnel lens 4, the depth Dp of the reflector 3, the apex and the focus position of the reflector 3 An example of a specific method for obtaining the distance Fp and the coefficients K and R representing the cross-sectional shape of the reflector 3 will be described. First, it is assumed that the focal length f of the convex Fresnel lens is within the range of the following relational expression with respect to the aperture diameter D of the reflector 3. 1.5D <f <3D When the focal length f of the convex Fresnel lens is shorter than this range, vignetting at the end of the convex Fresnel lens becomes large, which is not preferable. Further, when the focal length f of the convex Fresnel lens is longer than this range, the depth Dp of the reflector 3 cannot be made so shallow. In the following calculation, f = 2D was used in principle.

Next, with respect to the depth Dp of the reflector 3, the distance Fp between the apex of the reflector 3 and the focus position, and the coefficients K and P representing the cross-sectional shape of the reflector 3, an ideal allowable range is obtained. As shown in FIG. 3, in order to obtain these numerical values by calculation, assuming that the angle of the prism 4a is σ, the refractive index is n, and the incident angle with respect to the first surface is θ1, the deflection angle ε of the light beam is expressed by the following equation. It ε = θ1 + sin ^-1 [nsin {σ-sin ^-1 (sin θ1 / n)}]-σ (a) First, the prism angle σ at the end of the convex Fresnel lens is obtained from the focal length f of the convex Fresnel lens. As shown in FIG. 4, the deflection angle δ of the light ray at the end of the convex Fresnel lens is calculated by the following equation. δ = tan ⁻¹ (D / 2f) Therefore, by substituting θ1 = 0 and ε = δ in the equation (a) and solving for σ, the following equation is obtained. σ = sin ^-1 (sin δ / [n ² -2ncos δ + 1] ^1/2 ) (b)

The prism angle σ at the end of the convex Fresnel lens is obtained by this equation. Next, as shown in FIG. 5, the emission angle ε1 of the light beam emitted from the focal point F of the reflector 3 and passing through only the convex Fresnel lens and illuminating the subject at the end of the convex Fresnel lens coincides with the irradiation angle θ. Find the angle ψ at. Substituting ε = φ−ε1 = φ−θ and θ1 = φ into the equation (a), φ−θ = φ + sin ⁻¹ [nsin {σ-sin ⁻¹ (sin φ / n)]} − σ Become. Arranging this, θ = σ−sin ⁻¹ [nsin {σ-sin
^-1 (sin φ / n)}] and solving this for φ gives the following equation. φ = sin ^-1 [nsin {σ-sin ^-1 (sin (σ−θ) / n)}] (c)

Next, referring to FIG. 5, a convex Fresnel lens 4 is emitted from the focal point F of the reflector 3 and reflected by the rear reflector 3.
The angle ρ when the exit angle ε2 of the light ray at the end of the convex Fresnel lens, which is refracted by and is irradiated on the subject, coincides with the irradiation angle θ is obtained. The angle ρ is the angle of incidence of the light rays reflected by the reflector 3 on the convex Fresnel lens 4. In equation (a) above, ε =
Substituting ε2 = θ and θ1 = ρ, θ = ρ + sin ^-1 {nsin (σ-sin ^-1 (sin ρ / n))}-σ (d) (d) is transformed into f ( ρ) = 2ρ−σ−θ + sin ⁻¹ {nsin (σ−sin ⁻¹ (sinρ / n)} (e), and ρ for f (ρ) = 0 is obtained by the so-called midpoint method. The method is a method of repeatedly calculating the root of a complicated equation and can be easily performed by a computer etc. For example, calculation is performed with initial values ρ1 = 0 °, ρ2 = 90 °, and error δ = 0.001 °. .

A flowchart of this calculation is shown in FIG.
The flowchart shown in FIG. 8 will be briefly described. First, it is assumed that the initial values ρ1 and ρ2 of ρ are 0 ° and 90 °, respectively, and f (ρ1) and f (ρ2) are calculated based on these values, and the product f (ρ1) · f (ρ2) of these is calculated. Is always negative, that is, each f (ρ1), f (ρ2) approaches 0,
The value of (ρ1 + ρ2) / 2 is replaced with ρ1 or ρ2 one after another, calculation is performed until the value of | ρ2-ρ1 | becomes δ or less, and the value of ρ1 at that time is obtained as ρ. . The thus obtained ρ becomes the approximate solution of the equation (d).

Next, the shape of the reflector 3 is obtained from φ and ρ thus obtained. In FIG. 6, first, the major axis length a of the ellipse representing the shape of the reflector 3 is obtained. Due to the nature of the ellipse, FP + PF '= FP' + P'F = 2a. Therefore, FP + PF '=
D / 2sinφ + D / 2sinρ = 2a holds. Therefore, a = (D / 4) (1 / sinφ + 1 / sinρ) (f) Further, the minor axis length b of the ellipse representing the shape of the reflector 3 is obtained. From FIG. 6, 2ae = D / 2tan φ + D / 2tan ρ holds. Therefore, e = (D / 4a) (1 / tan φ + 1 / tan ρ) (g) where e is the eccentricity e = (a ² −b ² ) ^1/2 / a. Substituting (f) and (g) and substituting a and b thus obtained in the equation of b = a (1-e ² ) ^1/2 (h) ellipse, the reflector 3 Shape is required. The ellipse formula can be expressed as follows. x = a (1- (1- y 2) 1/2 / b 2) (i) ellipse, conic constant K = -e ^2, the reference spherical curvature radius R =
From the relationship of b ² / a, it can be expressed as an expression of conical curvature. That is, x = (y ² / R) / [1+ {1- (1 + K) y ² / R ² }] ^1/2 (j) Further, the distance Fp between the vertex of the reflector 3 and the focal point is Fp = a
(1-e), the depth Dp of the reflector 3 is Dp = Fp + D /
It can be obtained by the formula of 2 tan φ.

By performing the above calculation, if the aperture diameter D of the vertical cross section of the reflector 3, the vertical illumination angle θ of the strobe, and the refractive index n of the convex Fresnel lens 4 are input, the convex Fresnel lens 4 The focal length f and the coefficient representing the shape of the reflector 3 (conical constant K, radius of curvature R of the reference spherical surface), the depth Dp of the reflector 3 and the distance Fp between the apex of the reflector 3 and the focus can be easily obtained. .

Next, concrete numerical examples will be shown. [Example 1] Aperture diameter D of vertical section of reflector D = 12 Vertical irradiation angle θ = 25 ° Refractive index of convex Fresnel lens n = 1.49136 Here, if focal length f of convex Fresnel lens is f = 2D = 24 ,
The following results are obtained. Cone constant K = −0.85922 Radius of curvature of reference spherical surface R = 2.66777 Depth of reflector Dp = 8.782 Distance between vertex of reflector and focal point Fp = 1.384

[Embodiment 2] D = 12, θ = 33.5 °, n =
In the case of 1.49136, the following result is obtained. With f = 2D = 24, K = -0.711558, R = 3.56901 Dp = 7.054, Fp = 1.936

[Embodiment 3] D = 12, θ = 15 °, n = 1.49
In the case of 136, the following result is obtained. When f = 2D = 24, K = -0.99010, R = 1.54765 Dp = 12.099, Fp = 0.76

[Embodiment 4] D = 12, θ = 45 °, n = 1.49
In the case of 136, the following result is obtained. When f = 2D = 24, K = -0.46357, R = 4.79809 Dp = 5.354, Fp = 2.855

Table 1 shows a comparison between the depth Dp of the reflector of Examples 1 to 4 and the depth Dp 'of the reflector of the conventional example.

[Table 1] D θ Dp '(= a = b / sin θ) Dp Dp / Dp' 12 25 ° 14.179 8.782 0.619 12 33.5 ° 10.871 7.054 0.649 12 15 ° 23.182 12.099 0.522 12 45 ° 8.485 5.354 0.631

The following conditions are as follows: when the vertical irradiation angle θ of the strobe flash device is ± 15 ° to ± 45 ° and the refractive index n of the convex Fresnel lens is in the range 1.4 to 2, This is a condition for making the dimension in the depth direction about half of the conventional one. Focal length f1.5D <f <3D of convex Fresnel lens ... Coefficient K-1 <K <-0.4 which represents the shape of a reflector Coefficient RD / 10 <R <D / 2 which represents the shape of a reflector Depth of reflector Dp 0.4D <Dp <1.2D ... Distance Fp D / 20 <Fp <D / 3 ... between apex of reflector and focus

In the above embodiment, the case where the convex Fresnel groove of the convex Fresnel lens is on the side opposite to the strobe flash tube has been described. However, when the convex Fresnel groove of the convex Fresnel lens is on the strobe flash tube side, or The shape of the reflector can be obtained by the same method even when it is on both sides.

In FIG. 7, a semi-cylindrical storage portion 3a having a radius d, which is substantially equal to the radius of the strobe flash tube 5, centered on the axis x is formed at the apex a of the reflector 3. Three
The present invention is applied to a strobe flash device of the type in which the inner half of the strobe flash tube 5 is housed in a. F in the figure
The coefficients K and R representing the shapes of p and Dp and the reflector 3 are determined in the same manner as in the first embodiment described above. According to this embodiment, the focus F can be brought close to the apex a of the reflector,
It is possible to further reduce the size of the reflector 3. Moreover, since the light emission center of the strobe flash tube 5 is located in front of the reflection surface of the reflector 3, the light emission efficiency is not affected at all.

[0025]

According to the present invention, a convex Fresnel lens is mounted on the front surface of a reflector whose longitudinal section is a part of an ellipse, and a reflector from a strobe flash tube is installed at the front open end of the reflector in the longitudinal section. The irradiation angle θ of the light beam emitted in the direction away from the optical axis through the convex Fresnel lens without being reflected by the reflecting surface, and the optical axis after being reflected by the reflector from the strobe flash tube to the optical axis through the convex Fresnel lens. Since the irradiation angles θ of the light rays irradiated in the approaching direction are made substantially equal to each other, a small stroboscopic flash device in which the size of the reflector in the depth direction is reduced can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view taken along the line II of FIG. 2 showing an embodiment of a strobe flash device of the present invention.

FIG. 2 is a front view of the same.

FIG. 3 is an optical path diagram showing a refraction state of a convex Fresnel lens.

FIG. 4 is an optical path diagram for obtaining a prism angle at an end of a convex Fresnel lens in a vertical sectional view of the convex Fresnel lens.

FIG. 5 is an optical path diagram of light emitted from a strobe flash tube directly through a convex Fresnel lens and light emitted from a strobe flash tube through a reflector and a convex Fresnel lens.

FIG. 6 is an explanatory diagram for obtaining the major axis length and the minor axis length that form the ellipse of the reflector from the property of the ellipse.

FIG. 7 is a cross-sectional view showing another embodiment of the present invention.

FIG. 8 is a flowchart of a calculation formula for obtaining an incident angle at the end of a convex Fresnel lens of a ray passing through a reflector and a convex Fresnel lens.

FIG. 9 is a cross-sectional view showing one mode of vignetting in a convex Fresnel lens.

FIG. 10 is a cross-sectional view showing another embodiment.

FIG. 11 is a vertical cross-sectional view showing a conventional strobe flash device.

[Explanation of symbols]

 3 Reflector 4 Convex Fresnel lens 5 Strobe flash Dp Depth of reflector

Claims (4)

(57) [Claims] 1. A reflective surface having a vertical cross section has the formula x = a {1- [1- (y ² / b ² )].
Ellipse represented by ^1/2 } (where a is the major axis length of the ellipse,
b is the semi-elliptical cylindrical reflector consisting of the minor axis length of the ellipse);
A cylindrical stroboscopic light tube located at the focal point of this reflector; and a convex Fresnel lens fixed to the front open end of the reflector; and the depth Dp of the reflector is the major axis a. Less than the length and at the front open end in the longitudinal section of the reflector,
The irradiation angle θ of the light beam emitted from the strobe flash tube in the direction away from the optical axis through the convex Fresnel lens without being reflected by the reflecting surface of the reflector, and the post-convex Fresnel reflected by the reflector from the strobe flash tube. A strobe flash device characterized in that the irradiation angles θ of light rays irradiated in a direction approaching the optical axis through a lens are substantially equal. 2. The irradiation angle θ according to claim 1, wherein θ =
Within the range of ± 15 ° to ± 45 °, Dp is about 0.52a
Strobe flash in the range of ~ 0.65a. 3. The strobe flash device according to claim 1, wherein the convex Fresnel lens has a convex Fresnel groove formed only on the surface opposite to the strobe flash tube. 4. The reflector according to claim 1, wherein a semi-cylindrical housing portion is formed at the apex of the reflector, and the interior of the strobe flash tube is housed in the semi-cylindrical housing portion. Strobe flash that is being used.