JPS6353510A - Optical system for focus detection - Google Patents

Abstract

PURPOSE:To detect the focal point of an image forming lens through simple comparison and operation, by providing a beam splitter and band-pass filter and obtaining divided luminous fluxes as a visible light detecting luminous flux and near infrared or near ultraviolet ray detecting luminous flux. CONSTITUTION:The luminous flux 32e transmitted through the splitting plane 34a of a beam splitter 34 is a near infrared flux having a wavelength range of 700-800mm and the other luminous fluxes reflected by the plane 34a have wavelength ranges of <=700mm which are lower than visible light. Therefore, the luminous flux 32e is condensed to a light receiving element 36 as a detecting luminous flux and the luminous flux 32b of the luminous flux 32c which is passed through a band-pass filter 38 and has a peak wavelength band of 550mm is condensed to another light receiving element 35 as a detecting luminous flux. Therefore, the output of the element 35 shows a peak value at the focusing time and the output of the element 36 shows a peak value at the time of front focus. Both contrasts becomes lower at the time of rear focus. When the output relation between each light receiving element 35 and 36 is compared and operated with a microcomputer, focusing states can be judged whether a focused state is proper, front focus, or rear focus.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention detects the image formation state by an imaging lens on a light receiving element as a difference in the image formation state of two detection light beams of different wavelength bands obtained from an imaging light beam. It relates to an optical system used for observation and detecting focus, and is used in projection equipment such as micro leagues and micro reader printers, and photographic equipment such as ordinary cameras and video cameras.

(Prior art) Conventionally, this type of focus detection device uses a separate lens to form an image on a plane equivalent to the image plane at two locations on the light receiving element, and then uses contrast to detect differences in the image formation state. This is obtained as a waveform phase difference (Conventional Example 1), and a combination of a vibrating grating and a relay lens is used instead of a separate lens to image the beams from both sides that have passed through a ticking lens on a light receiving element. The difference in the formation status is obtained as the difference in the imaging position (Example 2), and the light bundle from the photographic eyepiece lens, which can be seen with a biological microscope as another one, is alternately blocked by a chopper. By changing the image formation state on the light receiving element and obtaining the difference in the image formation state as a phase difference (conventional example 3), the light beam from the ticking lens is transferred to the film equivalent surface and before and after it using a half mirror. A light beam splitting method is known in which spectral images are formed on each of the provided light receiving elements, and the difference in the imaging state is obtained as a difference in the contrast of the image formed on each light receiving element (Conventional Example 4). Another method known for use in video cameras is to use a filter to extract a specific frequency from the image information obtained from the image sensor to obtain a waveform that has a peak at the time of focusing, and then scan and detect the peak (conventional example) 5) Also, sandwich the last piece of the photographic lens between piezoelectric elements,
A method in which the voltage is changed to cause the element to vibrate, and the accompanying slight reciprocating movement of the lens is used to obtain the difference in contrast depending on the focusing state as a difference in the size of the vibration waveform, and the minimum vibration waveform corresponding to the peak of the contrast waveform is obtained by scanning. (
There is also a conventional example 6).

As in Conventional Examples 1 to 4, in order to obtain a plurality of light beams with different contrasts and phase differences from the image-forming light beam, the focusing state of the image-forming lens is different. When dealing with optical conditions, the imaging distance and position are made to differ depending on the optical method, which tends to complicate the optical system and complicate calculations for phase difference detection. In addition, although the optical system of conventional examples 5 and 6 is not complicated, the peak corresponding to the focus of the contrast waveform must be detected by scanning by focusing the imaging lens, so that the in-focus state can be obtained. It takes time.

Therefore, detection light beams in different wavelength bands are extracted from the imaging light beam that has passed through the imaging lens, and the difference in the imaging state due to longitudinal chromatic aberration of each detection light beam is observed as a difference in contrast using a light receiving element to detect the focus. Conceivable.

As a result, extraction of the two light beams for focus detection, comparison, and calculation can be quickly performed using simple means.

(Problems to be Solved by the Invention) However, it is difficult to obtain two detection beams with different imaging states, that is, large longitudinal chromatic aberrations, using different optical paths for sufficient focus detection. ! This method tends to become complicated and is difficult to apply to small devices.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a beam splitter having a beam splitting surface that splits an imaging light beam into a transmitted light beam and a reflected light beam, and The present invention is characterized in that it includes a bandpass filter that transmits a predetermined wavelength band, and by their cooperation, the divided light flux is obtained as a visible light detection light flux and a near-infrared or near-ultraviolet light detection light flux.

When the imaging beam reaches the beam splitting surface of the beam splitter,
Depending on the splitting characteristics of the beam splitting surface, it is possible to divide the reflected beam into a reflected beam and a split beam, allowing each beam to take a different optical path.

The transmitted and reflected light beams of each wavelength band that take these different optical paths are converted into visible light and near-infrared to near-ultraviolet light by a bandpass filter that works on the imaging light beam or the divided light beam, and are In addition to exhibiting longitudinal chromatic aberration, visible light exhibits the same imaging characteristics as the imaging light flux,
Due to the difference between the imaging state of near-infrared or near-ultraviolet light, the focus of the imaging lens can be detected by simple comparison and calculation of the contrast on each light-receiving element.

(Example) An embodiment of the present invention shown in FIG. 1 will be described.

This embodiment shows a case where it is applied to a micro league, a micro league printer, etc. (hereinafter referred to as a micro league, etc.). The imaging light beam 32 that has passed through the projection lens 31 is transformed into an imaging light beam 32a for autofocus by a half mirror 33.
and a practical luminous flux 32b. The practical light beam 32b is used as a projection light path onto a screen or the like.

The imaging light beams 32a pass through the beam splitter 34 and are separated from each other by 9
The light beams are split into light beams 32c and 32e directed to optical paths that differ by 0 degrees. On the optical path of each of the light beams 32c and 32e, light receiving elements 35 and 36 are provided at positions where the imaging light beam 32 and the imaging surface formed by the imaging lens 31 are equally damaged.

Since a halogen lamp is used as the light source, a cold filter 37 is placed in front of the projection lens 31 to prevent heat effects, so that wavelengths of 800 mm or less are transmitted, and wavelengths longer than that, that is, infrared wavelengths, are reflected. ing. The wavelength transmission characteristics of this cold filter 37 are shown in FIG.

Next, a beam splinter 340 splits the imaging light beam 32a into light beams 32c and 32e, and the dividing surface 34a has a beam of 700
It is coated to reflect the following wavelength ranges and to transmit the above wavelength ranges, so that it has the spectral and reflectance characteristics shown in Fig. 3. As a result, the light beam 32e that passes through the dividing surface 34a has a wavelength range of near infrared light ranging from 700 to 800 m, and the other reflected light flux 32c has a wavelength range below visible light of 700 +n.

Furthermore, a bandpass filter 38 is provided in the optical path of the reflected light beam 32c to transmit a wavelength band around 550 nm, which is the peak wavelength band of visible light. 70ON~8001 indicated by
A light beam 32e in the 111 wavelength band is collected as a detection light beam, and a light beam 32d in the 550 Tsuru peak wavelength range, which is shown by the shaded area B in FIG. The light is focused as

Here, the detection light beam 32d has the peak wavelength of visible light in the imaging light beam 32 and exhibits the same focusing characteristics as the imaging light beam 32. When the imaging light beam 32 is focused, the light beam 32d also passes through the light receiving element 35. The light is condensed upward in a focused state as a luminous flux 32dl in FIG. Further, in the front bin state, the luminous flux is 32d2, and in the rear bin state, the luminous flux is 32d3.

The corresponding outputs of the light-receiving element 35 are as shown in FIG.
2d + s.

On the other hand, the detection light beam 32e is used as a reference light beam to judge the degree of focus of the light beam 32d, and because it has a longer wavelength than the light beam 32d, when the imaging light beam 32 is focused, The light beam 32e is focused on the light receiving element 36 in a slightly backward bin state. In addition, luminous flux 3 corresponds to the front bin state.
2e2, the light receiving element 36 is brought into focus. Corresponding to the rear bin state, the light beam 32e enters a strong rear bin state with respect to the light receiving element 36. Light receiving element 36 corresponding to them
The outputs are as shown in FIG.
The contrast waveform at the rear bin becomes 32e I 3.

Therefore, the output of the light receiving element 35 shows a peak value when in focus, and the output of the light receiving element 36 shows a peak value during the front bin. Also, in the case of the rear bin, both contrasts are low.

By comparing and calculating the output relationship of each of the light receiving elements 35 and 36 using a microcomputer, it is possible to determine whether the object is in focus, front focus, or rear focus.

Note that if the beam splitter 34 to each light receiving element 35 and 36 shown in FIG. 1 are treated as a unit 39, it will be easy to use as a focus detection device for small optical equipment other than Microleague or the like.

In addition, in the embodiment of the present invention, focus detection is performed by comparing the imaging states of each of the near-infrared and visible light fluxes, but the imaging states of the near-ultraviolet and visible light fluxes are compared. The focus may be detected by doing this, an example of which is shown in FIGS. 9 and 10. To explain this, the dividing surface 34a of the beam splitter 34 is a simple half mirror without color coating, and it divides the imaging optical system 32a into a reflected light beam 32c and a transmitted light beam 32f, and the transmitted light beam 32f is divided into a reflected light beam 32c and a transmitted light beam 32f, as shown in FIG. The near-ultraviolet detection light beam 32g is obtained by passing it through a band-pass filter 40 having transmittance characteristics, and is imaged on the light-receiving element 36. As a result, the wavelengths of the visible light detection light beam 32d and the near-ultraviolet detection light beam 32g are changed. The difference in image formation state due to the difference is obtained on the light receiving elements 35 and 36, and focus detection can be performed by comparing them. The near-ultraviolet detection light flux can also be obtained by a color-coating coating on the splitting surface 34a of the beam subrifter 34 or a combination thereof with a band-pass filter.

(Effects of the Invention) According to the present invention, two detection light beams of different wavelength bands for detecting the degree of focus are separated into a transmitted light beam and a reflected light beam by a splitting surface, and in a predetermined optical path. By collaborating with a bandpass filter that transmits a predetermined wavelength band in the light beam, visible light and near-infrared or near-ultraviolet light are separated in wavelength, so the structure is simple and accurate focus detection is possible. You can make it happen. In addition, visible light exhibits the same imaging characteristics as the imaging light flux from an imaging lens, and the focus can be detected by simpler comparison and calculation of the imaging state with near-infrared or near-ultraviolet light. Detection processing speed may also be improved.

[Brief explanation of drawings]

Fig. 1 is a side view of one embodiment of the present invention, Fig. 2 is a graph showing the reflectance characteristics of the cold filter, Fig. 3 is a graph showing the reflectance at the beam splitter splitting plane, and Fig. 4 is the graph showing the reflectance characteristics of the cold filter.
A graph showing the wavelength band focused on each light receiving element in the figure, Figure 5 is a side view showing the imaging state of the short wavelength side light beam on the light receiving element, and Figure 6 corresponds to each imaging state in Figure 5. Figure 7 is a side view showing the imaging state of the long wavelength side light beam on the light receiving element, and Figure 8 is the contrast of the light receiving element corresponding to each imaging state in Figure 7. FIG. 9 is a graph showing the output waveform, FIG. 9 is a side view showing another embodiment, and FIG. 10 is a graph showing the reflectance characteristics of the bandpass filter shown in FIG.

Claims (1)

[Claims] (1) A beam splitter having a beam splitting surface that divides the imaging light beam into a transmitted light beam and a reflected light beam, and a bandpass filter that transmits a predetermined wavelength band in a predetermined light beam, and by their cooperation, the divided light beam is 1. An optical system for focus detection, characterized in that a visible light detection light flux and a near-infrared or near-ultraviolet light detection light flux are obtained.