JPH0718969B2 - microscope - Google Patents

Description

The present invention relates to an automatic focus detection device used in an optical system such as a camera or a microscope.

No conventional automatic focus detection device considers an optical system with different color correction. For example, in the case of a TTL automatic focus detection device for a single-lens reflex camera, the lens may be replaced, but the color correction of the interchangeable lens is almost the same, and even if the amount of correction is slightly different, the focus of the camera will change. Since there is almost no problem when considering the depth, conventionally, an infrared light cut filter was placed in front of the image sensor to remove the harmful influence of infrared light. Therefore, if optical systems with different color corrections are exchanged for use, they will not be in focus or the accuracy will deteriorate, which is a problem. It has also been found that there is a problem in that the focus is lost when a color filter is used or the wavelength distribution of the light source is changed.

Hereinafter, these points will be described in detail.

Among the elements constituting the automatic focus detection device, those related to light include a light source, an optical system, and a light receiving element. Among these, the light source and the optical system can be changed. For example, in the case of a light source, it is possible to change from natural light to artificial light such as a halogen lamp, and in the case of an optical system, a camera has various interchangeable lenses, and a microscope has various objective lenses. Since each element, that is, the light source, the optical system, and the light receiving element have wavelength dependences such as spectral distribution, chromatic aberration, and spectral sensitivity, accurate focusing can be achieved in the case of a certain set of light source and optical system combination. The focus position is adjusted so that it can be performed. Therefore, for example, if the optical system is replaced with an optical system having a different color correction, the focal position becomes different.

Figure 1 shows CIE daylight D ₆₅ specified by CIE (International Commission on Illumination).
This is used when displaying an object color illuminated by daylight with a color temperature close to 6504K (New Color Science Handbook, Tokai University Press). Also, the second
The figure shows an example of the spectral sensitivity of a MOS type linear image sensor. Generally, this type of sensor has a high sensitivity on the infrared side. As described above, the light-emitting side and the light-receiving side usually have a spectral distribution, and the spectral distribution cannot be flat with respect to all wavelengths even if limited to all visible wavelengths.

FIG. 3 is a diagram showing the color correction state of spherical aberration of two types of objective lenses of a microscope as an example of an optical system with different color correction. In FIG. 3, (a) is an objective lens with achromatic correction, In the respective cases, b) is an apochromat objective lens for color correction different from that of (a). Comparing the chromatic aberration correction states of (a) and (b), the aberration amount itself is extremely smaller in (b). In addition, it can be seen that the balance of color correction is not corrected because the short wavelength side is neglected in (a), but is corrected similarly to the long wavelength side in (b).

FIG. 4 is a diagram showing the state of color correction of numerical aperture × 0.7 in FIG. 3 with the horizontal axis representing wavelength. (A) shows the case of an achromat, and (b) shows the case of an apochromat, where the achromat is C, F and the apochromat is C, d, F.
It can be seen that each is corrected.

FIG. 5 shows a relative luminous efficiency curve representing the spectral sensitivity of the eye, which has a mountain-shaped distribution shape centered at a wavelength of 555 nm. FIG. 6 shows the spectral sensitivities of the color film and the black and white film.

FIG. 7 shows the spectral sensitivity when a near infrared cut filter is used for correction in the linear image sensor of the light receiving element.

As shown in FIG. 5 and FIG. 7, the spectral distribution of the eye sensitivity and the spectral distribution of the sensor are quite different, and therefore the focus positions when actually focusing are different. This is shown in FIG. 8, and the focal position when the light is adjusted is at a position determined by the aberration near the wavelength of 555 nm, but when it is adjusted by the sensor, it is affected by a wide range of wavelengths. When the degree of correction of chromatic aberration is almost the same, it suffices to install a sensor in consideration of the difference in focal position in advance. However, as shown in FIGS. 8A and 8B, optical systems with different color corrections are used. In the case of, it is not possible to satisfy both at the same time because the amount of difference is quite different. According to FIG. 6, the spectral sensitivity of the color film is closer to the spectral sensitivity of the sensor than the relative visual sensitivity, so it seems that focusing by the sensor is more suitable for taking a picture, but when looking at a photo After all, it depends on the relative luminosity, so it is better to shoot with a focus that matches your eyes.

FIG. 9 shows the spectral distribution of the light source when the color temperatures are 4000K, 5500K, and 7000K, respectively. When the spectral distribution of the light source changes in this way, the relative luminosity is narrow band when adjusted by eye, and the aberration near that wavelength (near 555 nm) is generally well corrected by the optical system, and the aberration due to the wavelength change. Since there is little fluctuation in the
In the case of a sensor, the range of spectral sensitivity is wide and the optical system cannot completely correct chromatic aberration in a wide range, so the focus moves significantly. Therefore, when the spectral distribution of the light source changes, the amount of difference between the focal position of the eye and the focal position of the sensor changes as shown in Fig. 10 (a), and the sensor is installed by correcting the difference in advance. Moving the focus is inevitable. For example, when taking a picture of a microscope, a light source of 5500K is generally used, but as shown in Fig. 10 (b), the sensor position is adjusted by α so that the eye focus position matches the sensor focus position. Even if it is kept, if the color temperature of the light source changes to 7000K for some reason, the focus will shift by β in the automatic focus detection device. In this way, even if the color correction of the optical system does not change, if the spectral distribution of the light source changes, out of focus occurs.

In the case of a black-and-white film at the time of photographing with a microscope, a green filter is inserted to improve the contrast. The spectral transmittance of this green filter is almost the same as the spectral distribution of the relative luminous efficiency shown in FIG. Therefore, when such a narrow band filter enters the optical path, the spectral sensitivity of the sensor becomes similar to the relative luminous efficiency, and there is no difference in the focal position at each color temperature. Therefore, if the sensor installation position is corrected by α in advance as in the previous example, the focus will be out of focus by −α.

In view of the above problems, the present invention arranges a bandpass filter having a narrow band in the detection optical path to limit the band of light received by the light receiving element, thereby performing color correction of the optical system or spectral distribution of the light source. Although it is intended to provide an automatic focus detection device capable of performing accurate focusing regardless of changes, if this is explained based on one embodiment shown in FIG. 11 and FIG. 12 below. FIG. 11 shows an optical system of a microscope automatic focus detection device, 1 is a light source, 2 is a condenser lens, 3 is a stage on which a sample is placed, 4 is an objective lens,
5 is a half mirror, 6 is an eyepiece, 7 is a photographic eyepiece, and 8 is a film. Reference numeral 9 denotes a green filter used when photographing a black and white film, for example, which can be placed in the optical path. Reference numeral 10 is a MOS type linear image sensor for obtaining image information. A magnifying optical system may be arranged in front of the sensor. Reference numeral 11 is a signal processing circuit, which performs processing by the so-called contrast method. 12
Is a stage drive circuit, which receives a signal from the signal processing circuit 11 to drive the stage 3 for focusing.
The light source 1 is adjusted to a color temperature of 5500K at the time of taking a photograph by a light balance filter and an appropriate applied voltage. Generally, the brightness of the light source is arbitrarily adjusted so that the user of the microscope can observe it, so that the color temperature is not constant. Of course, the color temperature may be kept constant by adjusting the brightness of the light source with the ND filter. Reference numeral 13 is a narrow band bandpass filter, and in this embodiment, the image sensor 10 is used.
Is provided in the detection optical path immediately before. Of course, as in the case of the green filter 9, it is possible to use a system in which the light is only put into the optical path when focusing.

Since the automatic focus detection device according to the present invention is configured as described above, the band of light received by the image sensor 10 is limited by the action of the bandpass filter 13. Therefore, whether the objective lens 4 is an achromat or an apochromat, the color temperature of the light source 1 is changed, the green filter 9 is inserted in the optical path, and the bandpass filter is within a predetermined wavelength range. Using only the light of
Since focus detection is performed, focus detection can always be performed while maintaining a constant relationship with the case of focusing with eyes. When the green filter 9 is inserted in the optical path, the amount of light changes abruptly. Therefore, the feedback time of the sensor signal should increase the accumulation time of the image sensor 10 and automatically increase the applied voltage of the light source 1. It is convenient to keep it.

Further, the bandpass type filter 13 is ideally a filter having characteristics similar to the relative luminous efficiency. By doing so, the focus position that is in focus with the eye and the position that is adjusted by the sensor match, and it is not necessary to correct the difference in advance.
FIG. 12 shows an example of the filter used in this embodiment. The spectral sensitivity of the sensor is practically (the spectral distribution of the light source)
× (filter transmittance) × (spectral sensitivity of sensor), but it can be considered that the filter transmittance corresponds to the spectral sensitivity of the sensor near the wavelength of 555 nm.
This will be explained with reference to FIG.

The characteristics are very similar to the relative luminous efficiency characteristics of G-530 and G-533.
(Hoya Glass) Although it is a filter, it needs a bright light source because of its poor transmittance. Further, it is not suitable to reduce the thickness of the filter to increase the transmittance because the wavelength band becomes wider. IF550 is an interference bandpass filter with a peak at 550 nm. CM500 + Y46 (Hoya Glass) is an infrared cut filter (CM500) and a yellow filter (Y4).
Although the one using 6) is advantageous in terms of light quantity, it is not suitable for a large change in color temperature of the light source due to its wide band.

The present invention is applicable regardless of the principle of focusing, as long as it is a device having a light receiving element as a focus detection unit. For example, FIGS. 13 and 14 show a second embodiment in which two detectors (image sensors) detect the focus by comparing the contrasts of the two detectors before and after the virtual focus. The half mirror 15
Is used to split the light and two image sensors 10, 10 'are placed before and after the virtual focus 14. The signal processing in this case is performed by the image sensor 10, 10 'as shown in FIG.
Is performed by searching for a position where the contrasts 16 and 16 'from are equal.

The above is the embodiment of the so-called contrast method, but since the present invention is also effective for the so-called phase difference method, the embodiment of the phase difference method by the pupil division method, that is, the third embodiment will be described below with reference to FIGS. An example will be described.

FIG. 15 shows the principle of the pupil division method. In FIG. 15 (a), 21 is an imaging lens, 22 is a light shielding plate having an opening 22a arranged in the vicinity of the pupil in front of the imaging lens 21. , 23 are image planes, and the image Q is formed on the image plane 23 at the time of focusing, but at the time of non-focusing, in the directions perpendicular to the optical axis O with respect to the image Q corresponding to the front focus and rear focus. Blurred image Q ₁ in the opposite direction,
Q ₂ is formed on the image plane 23. FIG. 15 (b) shows a case where the opening 22a of the light shielding plate 22 is moved to the opposite side with respect to the optical axis O. An image Q'is formed on the image plane 23 at the time of focusing, but it is out of focus. each front focus, the image Q blurred corresponding to the rear pin _'1, Q' ₂ is formed on the image plane 23 upon focusing. Therefore, if the aperture of the light shielding plate 22 is moved from the position shown in FIG. 15 (a) to the position shown in FIG. 15 (b), the images Q and Q'are not at the same position during focusing, but the image does not move. In case of pins the image is Q ₁
Image in the case of moving the Q _'1 position also the rear pin from Q ₂
To move to Q _'2 of the position from.

FIG. 16 shows an example in which the pupil division method is applied to a microscope. The members 1 to 13 are the same as those in the first embodiment (FIG. 11), and the processing method performed by the signal processing circuit 11 is different. It is connected.
Reference numeral 17 denotes an image forming lens for forming an image of the sample on the image sensor 10. Reference numeral 18 denotes a pupil division member placed at the pupil position, which is composed of a rotatable light shielding plate 22 having an opening 20 as shown in FIG. Is designed to be split. Therefore, the timing of image pickup of the light shielding plate 22 and the sensor 10 is matched by the synchronizing signal from the signal processing circuit 11 to obtain a set of image signals described in FIG. Then, the phase difference between the obtained two image signals is obtained by, for example, the calculation of correlation to calculate the direction and amount of defocus, and the signal corresponding to this is input to the stage drive circuit 12 to focus. To do.

In this case, a half mirror may be provided at the position of the pupil so that the image in the state (a) and the image in the state (b) in FIG. 15 are picked up by the two image sensors 10 and the same processing is performed. it can. Further, since it suffices to detect the displacement of the image position, if a semiconductor position detector is used instead of the image sensor 10, processing such as correlation calculation becomes unnecessary, which is convenient.

Thus, also in the case of the third embodiment, since the band of light received by the image sensor 10 is limited by the action of the bandpass filter 13, even if a lens having different color correction is used as the objective lens 4, the light source 1 Even if the color temperature of is changed, accurate focusing can be performed even if the green filter 9 is inserted in the optical path. Further, if the transmission characteristic of the bandpass filter 13 is set to be similar to the relative luminous efficiency characteristic, it is not necessary to previously correct the difference between the focal position adjusted by the eye and the focal position adjusted by the sensor 10.

As described above, the automatic focus detection device according to the present invention has a very important advantage that accurate focusing can be performed irrespective of the color correction of the optical system or the change of the spectral distribution of the light source.

[Brief description of drawings]

FIG. 1 is a diagram showing the spectral irradiance of CIE daylight D ₆₅ , FIG. 2 is a diagram showing the spectral sensitivity of the image sensor, and FIG. 3 is a diagram showing the color correction state of spherical aberration of two types of objective lenses. FIG. 4 is a diagram showing the state of color correction of numerical aperture × 0.7 in FIG. 3 based on wavelength, FIG. 5 is a diagram showing relative luminous efficiency, FIG. 6 is a diagram showing film spectral sensitivity, FIG. 7 is a diagram showing the spectral sensitivity of the image sensor when a near-infrared cut filter is used, and FIG. 8 is a diagram showing the difference between the focal position in the case of visual adjustment and the focal position in the case of the sensor. FIG. 9 is a diagram showing the spectral distribution of the light source when the color temperature is different, FIG. 10 is a diagram showing the change in the amount of difference between the focal position with the eye and the focal position with the sensor, and FIG. 11 is the present invention. FIG. 12 is a diagram showing an optical system of one embodiment of the automatic focus detection device, and FIG. 12 is a bandpass filter used in the above embodiment. FIG. 13 is a diagram showing a transmission characteristic, FIG. 13 is a diagram showing an optical system of a second embodiment, FIG. 14 is a diagram showing a contrast from the image sensor of the second embodiment, and FIG. 15 is a third diagram. FIG. 16 is a diagram showing the principle of the embodiment, FIG. 16 is a diagram showing the optical system of the third embodiment, and FIG. 17 is a front view of the pupil division member used in the third embodiment. 1 ... Light source, 2 ... Condenser lens, 3 ... Stage, 4
… Objective lens, 5… Half-meer, 6… Eyepiece,
7 ... Photo eyepiece, 8 ... Film, 9 ... Green filter, 10 ... Image sensor, 11 ... Signal processing circuit, 12
… Stage drive circuit, 13… Band pass type filter.

Claims (4)

[Claims] 1. A microscope comprising an illumination light source, an observation object placing means for placing an observation object illuminated by the illumination light source, and an objective lens for forming an image of the observation object illuminated by the illumination light source, A splitting means for splitting the image-forming light flux formed by the objective lens into an observation light path and a detection light path, a focus detection means having a light receiving element for receiving the light flux in the detection light path, the objective lens and the light receiving element. 550n provided in the connecting optical path
a bandpass filter having a transmission wavelength band close to the relative luminous efficiency centered around m, and the relative position between the observation object mounting means and the objective lens at the focus position detected by the focus detection means. A microscope having a focus position moving means for moving the position. 2. The transmission wavelength band of the bandpass filter is
The microscope according to claim 1, which has a wavelength of 450 nm to 650 nm centered around 550 nm. 3. The microscope according to claim 1, wherein the bandpass filter is an interference bandpass filter. 4. The microscope according to any one of claims 1 to 3, wherein the light source is an illumination light source whose spectral distribution varies.