JPS6217721A - Projector - Google Patents

Abstract

PURPOSE:To assemble easily the titled device to a camera by dividing a paraboloid of revolution by a face containing its revolving shaft, forming a half or below of its one side to a specular surface, and providing a light source in the vicinity of the focus of a parabolic mirror so that the center luminous flux of emitted light is made incident on the parabolic mirror. CONSTITUTION:As for a focusing optical system, the paraboloid of revolution is divided by a plane containing its revolving shaft (x), and by using a reflecting mirror 12 on which a half of its one side or a part thereof has been formed to a specular surface, the center of a light emitting part of an LED 1 is placed in a focus of a parabolic mirror 12 or its vicinity. Also, the LED 1 is placed so that the center light of the LED 1 is made incident on the reflecting mirror 12. In such a way, the constitution of the optical system is simplified, such as it is converted to a block, etc., a light source 1 is placed without causing a problem for shielding a luminous flux, etc., and the assembly to a camera, etc. can also be executed easily. Furthermore, the utilization efficiency of a luminous flux energy can be raised.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a light projecting device, particularly to a light projecting device suitable for autofocusing of a camera.

(Prior Art) FIG. 7 shows the general light distribution characteristics of an LED used as a light source in a light projecting device for light emitting/receiving type autofocus of a camera, a light projecting device for a bar code reader, and the like. This generally belongs to a characteristic called omnidirectionality, and if ft1θ is the emission intensity in the direction along the generatrix of a cone with the 0 direction as the axis and the light emitting point as the apex and the half apex angle θ, then IO is the emission intensity in the 0 direction. It can be approximately expressed as 1θ=100080.

FIG. 8 shows an example of the optical system of a conventional light projector. 1 is an LED as a light emitting light source, a 2Fi floodlight lens, 16 is a light emitting point, 3.3 is a ray that passes through the periphery of the floodlight lens 2 among the nine luminous fluxes emitted from the light emitting point 1a, and 3 is a central ray. The figure shows a typical example of such an optical system, where the focal length of lens 2 is f = 20 tw, and the radius is 16. In this case, the F number is f4 =
1.25, which is almost the limit of the brightness that can be obtained with this type of device. However, the half-vertex angle of the cone of the luminous flux that is effective KW in this projector is θ#21.8°, and the ratio of light energy included in this angle range is 1 to the total luminous energy.
- (!O82θ)/2, which is only 13.8%.

Cameras with automatic focus devices mounted on amateur still cameras and video cameras are required to be small and low in cost due to their portability and other reasons.

Light emitting/receiving type AF devices can easily satisfy such requirements and are therefore relatively commonly used.

This method has the great advantage of being usable even when there is insufficient external illumination, but on the other hand, it has the fatal drawback of not being able to measure distances when photographing distant objects due to insufficient reflected light energy. With a camera equipped with a relatively long focal length, so-called telephoto lens, the subject distance is 10 m or more! T! It is necessary to perform focusing separately from (7) and (2). However, in a typical example of an autofocus device of this type that is currently in practical use, the limit detection distance is only about 5 mK.

(Problem to be solved by this invention) In a light emitting/receiving type autofocus device, the light energy Pi returning to the light receiving element is as follows, where Po is the light emitting energy of the LED: R: Subject reflectance D: Light receiving lens Aperture F: F number of the light projection lens t: Expressed by subject distance.

Therefore, for example, when trying to set the limit detection distance to Iom of 2@, if this is done only by increasing the light emitting energy of the LED, the light reception Wkwo cannot be made the same unless the light emitting energy is at least 4@.

Also, if you want to solve the problem by making the projection lens brighter, you need to set the F number to I/2.

There are three ways to achieve this: by setting the aperture of the light projection lens to 2@, by reducing the focal length of the light projection lens to 1/2, or by combining both at the ratio of t-i. be.

Another possible solution is to double the aperture of the light receiving lens.

However, even in the above example, the limit of the emission energy of the LED is
Therefore, the apertures of the light projecting lens and the light receiving lens were increased to the maximum extent possible due to the appearance.

Furthermore, if the focal length of the projection lens is made shorter than this, the curvature of a single lens becomes too large, and the reflection of peripheral light increases, making it impossible to expect an increase in the projection energy. This problem can be temporarily solved by increasing the number of lens elements, but this results in a large increase in cost despite the small effect. For these reasons, the above-mentioned conventional examples have not been able to exceed the limit of distance detection ability.

This invention aims to increase the utilization efficiency of the emitted light flux of 1 dLED, but the half-apex angle θ of the cone with the light emitting point as the apex is
The table below shows the light utilization efficiency and the corresponding F number in the case of .

If we want to increase the light utilization efficiency to 50%, we must use the luminous flux up to the half-vertex angle of 45, and the 8th
Considering the normal optical system as shown in the figure, the F number is 1/2.
If tanθ is 0.5, it is impossible to realize it based on common sense.

This invention aims to dramatically improve the efficiency of light use without increasing the size and cost of the projector.

Structure of the Invention (Means for Solving the Problem) As shown in FIG. 1, the basic structure of the light projecting device of the present invention is such that the focusing optical system has a paraboloid of rotation with an axis of rotation f
Using a reflecting mirror 12 divided by f and having one half or a part thereof mirrored, the center of the light emitting part of the LED l is placed at or near the focal point of the parabolic bell, and the center ray of the LED is directed to the reflecting mirror 12. The LEDI is arranged so that the light is incident on the light.

(Function) The light projection device configured as described above is arranged at the focal point so that the central light beam of the LEDI is emitted perpendicularly to the rotation axis 128 of the parabolic mirror 12, and the light beam path of the limit of the usable luminous flux is set. is 13
', 13, these reflected rays travel by the parabolic mirror 12 in the direction of its axis of symmetry 12aK. 1st
In the figure, if the width of the emitted light beam (@ in the y-axis direction) is 16 mm, which is the same as that of lens 2 in Figure 8, and the beam is converged on an object at a distance of 10 m, the angle that the rays at both limits make with the principal ray is It is only 245, and can be considered to be essentially the chief ray and the mo line. If the focal length of the lens is 20 dragons in Figure 8,
The difference in the position of the light emitting point 1a between the case of focusing 10 m ahead and the case of directing the light beam is only 40 μm, which is the same level of error or less than the error caused by manufacturing variations in parts and LED installation. You can think of it as placing it at the focus of a parabolic mirror.

In Figure 1(a), the equation of a parabola is generally
It can be set as y2=4PX. Due to the size constraints of the device, if the axis of y of the aperture is constant, then X will be inversely proportional to P, and that X will be a paraboloid @i! 12! It represents the depth of L, that is, the distance from the apex of the parabola to the opening.

Therefore, the smaller P is, the deeper the depth is, and the larger P is, the shallower the depth is, and this makes the embodiments different.

In the optical system shown in Fig. 1, the aperture is 16 sow, and P
= 3.2 tm, the depth will be 20 tm, which corresponds to the conventional example shown in Figure @8. At this time, the critical angle of the light beam exiting the aperture, that is, the half-vertex angle of the cone, is approximately 46.4, and the light flux utilization efficiency is a little more than 52 inches, which is more than 3 times the utilization efficiency of the conventional example.

(Example) FIG. 1(b) shows the spread of a conical light beam taken at every half apex angle of 10 from the center ray of the LED at 13&-13f.

Therefore, considering the effective range of the parabolic mirror, it can be made into any shape, such as by cutting along the chain line in the figure. An example of a cut piece like this is shown in a perspective view in Figure 2. In the explanation so far, the light emitting point 1a has been treated as a point with no size, but in an actual LED, the size of the light emitting part is a radius. It is normal that the length is 083 to 0.5m. Naturally, if the light emitting section has a certain size, a corresponding spread of the luminous flux will occur on the subject surface as well. In a normal lens system as shown in Figure 8, its expansion can be found by calculating the f-factor.If the focal length of the lens is 20 m and the radius of the light emitting part is 0°3, then at a subject position of 10 m, It has a radius of 150u. When using the same optical system on the light receiving side as on the light emitting side, the size of the reflected light obtained on the light receiving element is:
Unless the size is the same as that of the light emitting part, the spread of the luminous flux due to the size of the light emitting part does not originally cause loss of light quantity. However, if the spread of the light beam becomes larger than the target object, more energy will be returned as reflected light.
This will result in a loss of light quantity. When a person is assumed as the main subject, the above-mentioned radius of 150 degrees is a sufficiently small one shift, and a radius of up to 2,501 degrees is acceptable. In the example of the floodlight device shown in Figure 1 with the above configuration, if the light emitting part has a size of half TL 0.3 m, the spread of the luminous flux will be an ellipse with a short axis of 700 m and a long axis of 1400 m5 at a subject distance of 10 m. become.

This condensed state is shown in a spot diagram in FIG. 1(e). In the figure, the coordinate origin is aligned with the optical axis of the light projecting side (the water line passing through the center of the aperture of the reflecting mirror). The radius of the two circles centered on the origin is 25011, which is within the allowable range.
i! The outside is a reference mill with a radius of 300fl.

Of the total luminous flux reaching the subject plane at a distance of 10 m,
Approximately 69% of the energy enters the allowable mill above, and LE
This is approximately 36.3% of the total luminous energy of D. With this configuration, an improvement in efficiency of about 2.6@ is obtained compared to the one shown in FIG. 8, and the measurable distance of the autofocus device becomes approximately 8 mfM degrees at 16@.

In the example shown in Figure 3, the center axis of the LED is approximately 20 degrees from the vertical.
The paraboloid is tilted toward the opening side. With this configuration, the luminous flux utilization efficiency is improved to 38.3%.

Figure 4 is an example using a shallow paraboloid, where υ and P are 71111.
In this case, LED 1 is tilted 20 degrees counterclockwise from the perpendicular direction to the optical axis. (in the same figure) is shown by a single spot diagram on its condensing shape f14. In this example, the luminous flux utilization efficiency F
i44.1%.

In FIG. 5, P=14.8, the LED angle is 65, and the optical system is formed as one block from a transparent material such as resin or glass. The block 22Fi has a paraboloid of revolution 22C as a reflective surface at one end thereof, and its rotation axis 22
The incident surface 22b of the light flux is formed on the top a, and the other end is the rotation axis 22
The output surface 22d is perpendicular to &. Figure (b) is a perspective view of this block.

The condensed light a' by this light projecting device is shown in a spot diagram in FIG. 2(e). Approximately 6 of the luminous flux emitted from the LEDl
0 beams are emitted from the exit surface 22d, and the efficiency of use of luminous energy is 51 beams, which is 3.7 meters in the conventional example shown in FIG. 8, thereby extending the measurable distance to approximately 9.6 meters.

Comparing the spot diagrams of FIG. 1(e) and FIG. 5(C), it is clear that there is a slight difference in the way the light beam spreads. This is due to the so-called difference in magnification. The magnification of the reflecting mirror used in this invention is the ratio of the distance from the light source to the mirror surface to the distance from the mirror surface to the subject, and the deviation from the focal point due to the size of the light source etc. is reflected on the subject plane at this magnification. It's coming out. In the embodiment shown in FIG. 1, the rate varies from 230 to 2300 depending on the location of the reflecting mirror, and the distribution of points in the spot diagram is widened. In the embodiment shown in FIG. 5, the @ ratio is relatively uniform at 520 to 660 times, and therefore the spread of the light beam is small.

In the above embodiment, the light emitting surface of the LED 1 and the incident surface 22b'l!
: Both are child beams, but in the case shown in Fig. 6, the entrance plane 22
When b is left unchanged and the LED l is tilted slightly clockwise by 0, for example, by 5, the luminous flux energy utilization efficiency is 50.2%, and the decrease in efficiency is extremely small. Moreover, the result is almost the same even if the light emitting surface of LEDl is left as is and the incident surface 22b is slightly tilted to either side.

This means that even if there are manufacturing errors and assembly errors regarding the angular changes of the LED light emitting surface and the incident surface, the luminous flux energy utilization efficiency Fi
This means that it has the advantage of not changing much. In addition, the entrance surface 22b is not a flat surface but a gently concave surface t'! ! This is advantageous in correcting aberrations. However, if the surface is concave, the assembly precision V will be slightly stricter.

Effects of the Invention As described above, this invention uses a parabolic mirror of revolution, and instead of directing the central ray of the light source to the vertex of the parabolic mirror as is commonly used, the parabolic mirror of revolution is directed toward the axis of rotation. The mirror is divided by a plane containing the mirror, and one half or part of it is used to direct the central ray of the central light source of this partial parabolic mirror, making it easier to configure the optical system by making it into blocks. There is no problem of arranging the light source or blocking the light beam, and it is easy to assemble it into a camera or the like.

In addition, it is approximately the same size as a conventional optical system, and can improve the efficiency of using luminous flux energy to a point that cannot be achieved with a normal lens system, and can be used in autofocus cameras, etc. to almost double the measurable distance. A mouth that has a remarkable effect of drying.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the basic configuration of a light projecting device of the present invention;
@2 Figure 5 (b) is a perspective view of the embodiment, Figure 3, Figure 4 (a), Figure 5 (a), and Figure 6 are sectional views showing respective modified embodiments. Figure 4 (b) Figure 5 (11 is the spot diagram, Figure 7 is the LED light distribution characteristic diagram, Figure 8 is
The figure is an optical arrangement diagram of a conventional example. [ bl Figure 2 Figure 1 So' [el C Figure 3 Figure 4 [bl Figure 6

Claims (1)

[Claims] A paraboloid of revolution is divided by a plane including its axis of rotation, less than half of one side thereof is made into a mirror surface, and a light source is provided so that the central beam of the emitted light enters the parabolic mirror near the focal point of the paraboloid. A floodlighting device characterized by the following: