JPS6052371B2 - Focal position measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focal position measuring device, particularly to a focal position measuring device suitable for use in adjusting the focal position when attaching an objective lens to a microscope lens barrel.

When assembling and adjusting a microscope, it is difficult to achieve accurate focusing, especially when the objective lens has a low magnification because the depth of focus is deep.

Particularly in microscopes, multiple objective lenses with different magnifications are installed, and even if these objective lenses are exchanged to change the magnification, the barrel of the objective lens is made so that the pits match, that is, they are parfocal. It is necessary to accurately expose the attached surface. Conventionally, in order to achieve parfocal alignment, an index is placed at a position corresponding to the object plane, an image of this index is projected, a focusing mirror or screen is placed at the focal position determined by the microscope, and the image is observed under the microscope or on the screen. While observing the image, the objective lens was moved on the optical axis, and the image formation state was observed and adjusted.

However, in this method, as described above, when the objective lens has a low magnification, the depth of focus is deep, so it is difficult to obtain an accurate focal position, which leads to a decrease in accuracy. The present invention provides a focal position measuring device which uses a split image method using polarized light and detects the focal position by lateral movement of an image, thereby enabling accurate and easy focusing. It is.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The focal position measuring device of the present invention will be described below based on the illustrated embodiments.

Figure 1 shows an optical system of a transmission type embodiment. 1 is a pupil splitting filter placed at the aperture stop position that is illuminated by an appropriate light source (not shown), and polarized light as shown in Figure 2. Two polarizing elements 1a and lb whose surfaces are orthogonal to each other are arranged on the left and right so that they touch at a boundary surface lc. Reference numeral 2 denotes an indicator having two arrows 2a and 2b facing each other as shown in FIG. 3, and this indicator can have various other suitable shapes.

This index 2 is illuminated by an illumination light beam whose polarization direction is determined by a pupil splitting filter 1, and is projected onto an object plane 4 by a lens 3. 5 is an objective lens for measuring the focal position;
Reference numeral 6 denotes a focus plate, and as shown in FIG.
These are placed above and below so that they touch at c, and this boundary 6
c is placed so as to be inclined by 90 degrees with respect to the boundary 1c of the pupil division filter.

Further, 7 is a crosshair provided on the focusing plate 6. Note that the focusing plate 6 is also generally called a focusing mirror. Next, we will explain how to adjust the objective lens 5 used in the microscope to make it parfocal in the optical system described above.The distance between the object plane 4 and the focusing plate 6 is fixed constant, and the objective lens is moved on the optical axis and adjusted so that the object plane 4 is projected onto the focusing plate 6.

In this case, the index 2 is illuminated by illumination light having two different polarization directions orthogonal to each other due to the presence of the pupil splitting filter 1, and is imaged on the object plane 4. On the focusing plate 6, if the pits are not aligned, the image of the index 2 is divided into the upper image 2a'' and the lower image 2a'' with the boundary surface 6c of the focusing plate 6 as a boundary, as shown in FIG. 5A. The image 2b'' is observed shifted laterally. Therefore, in order to align the parfocal, the objective lens 5
may be moved on the optical axis so that the aforementioned index images 2a'' and 2b'' coincide. This point will be explained in detail. FIG. 6 shows a perspective explanatory diagram in which a light ray is added to the above-mentioned optical system. The thick line is used as a representative of the light passing through the lower half (that is, the vertically polarized illumination light), and the thin line is used as a representative of the light passing through the lower half. Further, this figure shows a case where the focal position of the objective lens 5 is shifted to the rear of the focusing plate 6. First, consider imaging using horizontally polarized illumination light. The illumination light passes through the upper half of the pupil splitting filter 1, becomes horizontally polarized light, passes through one point of the index (in this case, the point of contact between the two arrows on the optical axis), passes through the lens 3, and reaches the object plane 4. Connect the statue with. Furthermore, the image is focused again through the objective lens 5. Here, since the focusing plate 6 is located in front of this image point, on this focusing plate 6, as is clear from the figure, the light passes through a point a above the optical axis. Therefore, arrow images facing each other with this point as the center are projected onto the focus plate 6 by light emitted from the same light source point. However, since this light beam is horizontally polarized, it passes only through the horizontal polarizing plate portion of the focus plate 6. That is, in this case, it is only the right half, and therefore only the image of the arrow on the right side passes through. Similarly, as for the image of the index formed by the vertically polarized illumination light, only the image of the lower left half of the arrow with point b as the apex of the arrow passes through the focus plate 6. Therefore, this is illustrated as shown in FIG. 5A. Thus, if the pits are not aligned, the pits will be aligned by moving the objective lens 5 on the optical axis so that the deviation of this arrow disappears. Note that since only a part of the light flux is considered here, only a part of the image that is actually visible is shown, but in reality, all the light flux enters and the arrow observed on the focus plate 6 is blurred. It becomes something that spreads.
However, blurring still causes two-splitting, and two arrows can be observed, which makes it possible to measure the focal point position. Next, FIG. 7 shows another embodiment of the present invention, which is an example of an epi-illumination type.

In this figure, 11 is a light source, 12 is a collector lens, and 14 is a pupil division filter placed at the position of the aperture stop 13, the structure of which is similar to that of the previous embodiment. Reference numeral 15 denotes a lens disposed near the aperture stop 13, and this lens 15 projects the exit pupil of the collector lens 12 into the vicinity of the field lens 6.

A field stop 17 and an index 18 are arranged near the field lens 16. The above optical elements constitute an illumination system. Furthermore, 19 is a semi-transparent mirror, 2
0 is an objective lens for determining the parfocal position, and 21 is a reflecting mirror member. This reflecting mirror member 21 is composed of a hemispherical reflecting mirror 23 embedded in a fixed base 22.
The plane 23a of the hemispherical reflector 23 is directed toward the objective lens 20, and the center of curvature 23b of the hemispherical reflector 23 is located on the optical axis, so that the surface 23a coincides with the object plane. Also 24
25 is a focusing plate, and 25 is an eyepiece. Among the optical elements used in these optical systems, the pupil division filter, index, and other structures are substantially the same as those used in the embodiment shown in FIG. A case where parfocal adjustment is performed using such an embodiment will be described. First, the distances from the center of curvature 23b of the hemispherical reflector 23 to the center of the focusing plate 24 and the center of the index 18 are adjusted to be optically equal, and the plane 23a of the hemispherical reflecting mirror 23 and the focusing plate 24 are spaced at a constant distance. After fixing it, measure as follows. Light from a light source 11 is focused by a collector lens 12 onto a pupil division filter 14 placed at an aperture stop 13 . Since this pupil division filter 14 has a structure as shown in FIG. 2, the light passing through it is divided into two different polarized lights that are perpendicular to each other. An indicator 18 as shown in FIG. 3 is illuminated by these two polarized lights having different vibration directions and being perpendicular to each other. This index 18 is imaged by the objective lens 20 once on the surface 23a of the hemispherical reflector 23, that is, on the object plane, is reflected by the reflecting surface of the hemispherical reflector, passes through the object plane again, and is then transferred to the focal plane by the objective lens 20. The image is formed on 24, and the eyepiece 25
observed by If the objective lens 20 is not focused accurately, the image on the focusing plate 24 observed at this time will be at the boundary between both polarizers of the focusing plate for the same reason as already explained based on FIG. Images of the index shifted in opposite directions are observed on both sides. Therefore, the correct focusing position of the objective lens can be determined by moving the objective lens 20 along the optical axis so that the optical edges of the index images are perfectly aligned. As explained above, according to the focal position measuring device of the present invention, the pit position is detected by the horizontal movement of the image using the split image method, so that it is possible to detect the pit position by moving the image horizontally. Accurate measurements are possible no matter what.

Among them, if the epi-illumination method is used, the focal position can be measured with twice the accuracy as the transmission method. In the focal position measuring device of the present invention, pit alignment is performed by keeping the distance between any two of the object plane, objective lens, and focusing plate constant and moving the remaining one. I can do it.

Also, since pit alignment can be performed with extremely high sensitivity, it can also be used for focus detection in autofocus.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the optical system of the measuring device of the present invention, Fig. 2 is a diagram showing the pupil division filter used in the measuring device of the present invention, Fig. 3 is a diagram showing indicators, and Fig. 4 is a diagram showing the focusing plate. FIG. 5 is a diagram showing an image of an index formed on the focus plate, FIG. 6 is a perspective view illustrating the above optical system with a light beam added, and FIG. 7 is an optical diagram of the measuring device of the present invention. FIG. 3 is a diagram showing another example of the system. 1... Pupil division filter 1, 2... Index, 3... Lens, 4... Object plane, 5...
...Objective lens, 6... Focus plate.

Claims (1)

[Claims] 1 A pupil splitting filter arranged with a boundary on the same plane so that the polarization planes are orthogonal to each other, and a pupil splitting filter arranged so that it is illuminated by the illumination light that has passed through the pupil splitting filter and is projected onto the object plane. A measuring lens comprising an index and a focus plate arranged with a boundary on the same plane so that the planes of polarization are orthogonal to each other, and the boundary is orthogonal to the boundary of the pupil splitting filter. is provided between the object plane and the focusing plate, and measures the focal position by adjusting the position of the measuring lens so that an image of the index is formed on the focusing plate.