JP7616218B2 - Variable magnification objective lens and photometric/colorimeter equipped with same - Google Patents

Description

The present invention relates to a variable magnification objective lens and a photometric and colorimeter equipped with the same.

Luminance meters, colorimeters, spectrophotometers, etc. are used in the quality control of display products. These devices measure the optical characteristics of displays and are used to manage or adjust the luminance and chromaticity of displays. One such optical characteristic measuring device is the optical characteristic measuring device disclosed in International Publication No. 2015/182571 (Patent Document 1).

Displays include, for example, micro OLEDs (Organic Light Emitting Diodes), micro LEDs (Light Emitting Diodes), smartphone displays, and television sets (e.g., 4K televisions, 8K televisions, etc.). Displays come in a variety of sizes depending on the type. If the size of the display to be measured is small, the measurement range of the luminance and chromaticity of the colorimeter must be small, and vice versa. For this reason, there is a demand for a colorimeter that can measure the luminance and chromaticity of any display and has an objective lens that can change the measurement diameter (diameter of the measurement area).

Patent document 1 discloses an optical property measuring device for measuring the luminance and chromaticity of a light-emitting body. This measuring device has a first optical system and a second optical system. The first optical system performs spectroscopic measurement of a certain measurement range within a measurement area of the object to be measured. The second optical system can perform two-dimensional measurement of the object to be measured with tristimulus values simultaneously with the measurement by the first optical system. The second optical system has only one variable magnification group, which allows the measurement diameter on the image side to be variable. In particular, in the second optical system, the collected measurement light passes through a filter with a spectral response approximating the CIE color matching function and is guided to the sensor. The luminance and chromaticity of the object to be measured are calculated based on the tristimulus values.

International Publication No. 2015/182571

In recent years, there has been an increasing need to measure the luminance and chromaticity of small-sized light emitters used in displays, such as micro OLEDs and micro LEDs. In addition, as the luminance range (dynamic range) of displays has expanded, measurement of the luminance on the low luminance side has also become important in gamma adjustment of displays.

For example, when measuring the brightness of a display using an objective lens without a zoom function, the measurement diameter can be changed by changing the extension amount of the lens. However, with this method, the F-number on the image side changes as the measurement diameter changes. Therefore, as the measurement diameter changes, the amount of light captured by the sensor of the measurement device decreases.

When the brightness of a display is low, if the sensor of the measuring device cannot receive a sufficient amount of light for measurement, the accuracy of the brightness measurement at low brightness decreases. For example, the signal-to-noise ratio in brightness measurement decreases. Therefore, the dynamic range of the measuring device becomes narrower. Because the dynamic range of the measuring device is narrow, it is expected that the dynamic range of the display product will be measured narrower than its original performance. In addition, it is difficult to significantly change the measurement diameter using only one magnification system.

The optical system disclosed in Patent Document 1 has one variable magnification group. In this optical system, the measurement diameter is variable. However, the measurement angle changes with the change in the measurement diameter. The change in the measurement angle changes the angle of incidence of light incident on the filter. In a measurement device, the closer the spectral sensitivity is to the color matching function, the closer the measured value is to the true value (the value calculated by the color matching function), so it is important that the spectral sensitivity of the filter is close to the color matching function. Generally, an interference filter is used as such a filter. When the angle of incidence of light incident on an interference filter changes, the optical path difference in the interference film changes. This causes a wavelength shift in the transmittance characteristics of the filter, so the spectral response of the optical characteristic measuring device deviates from the color matching function. This can lead to a problem of reduced accuracy in measuring the luminance and chromaticity of the object being measured.

Therefore, when the measurement diameter is varied using an objective lens, it is important that the variation in the F-number on the image side is as small as possible.

The present invention has been made in consideration of such problems, and aims to provide a variable magnification objective lens that can vary the measuring diameter while minimizing fluctuations in the image-side F-number, and a photometric and colorimetric meter equipped with the same.

A variable magnification objective lens according to one aspect of the present invention is a variable magnification objective lens that forms an intermediate image at a position conjugate with the image plane, and has, in order from the object side, a first lens group which is a variable magnification group, a second lens group which is also a variable magnification group, and a third lens group which does not substantially change magnification, and when the magnification is changed, the distance between two adjacent lens groups among the first lens group, the second lens group, and the third lens group changes, and an intermediate image is formed between the first lens group and the second lens group, and the third lens group has an aperture stop, and the aperture stop is positioned so that the conjugate image of the aperture stop is closer to the object side than the first lens group.

A photometric colorimeter according to one aspect of the present invention is provided with the above-described variable magnification objective lens.

According to the present invention, it is possible to provide a variable magnification objective lens that can change the measuring diameter while minimizing the variation in the image-side F-number, and a photometric and colorimetric meter equipped with the same.

1 is a block diagram showing an example of a photometric and colorimeter equipped with a variable magnification objective lens according to an embodiment of the present invention. FIG. 2 is a lens configuration diagram showing the configuration of a variable magnification objective lens according to the first example. FIG. 11 is a lens configuration diagram showing the configuration of a variable magnification objective lens according to a second example. FIG. 13 is a lens configuration diagram showing the configuration of a variable magnification objective lens according to a third example.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of a photometric colorimeter equipped with a variable magnification objective lens according to an embodiment of the present invention. The photometric colorimeter 10 according to this embodiment is used, for example, in an inspection process on a display manufacturing line, and measures the brightness (luminance) and chromaticity of the display surface 12 of the display.

For example, the photometric colorimeter 10 (hereinafter simply referred to as "colorimeter 10") according to the present embodiment is realized as a tristimulus value colorimeter. As shown in Fig. 1, the colorimeter 10 comprises a measurement probe unit 14 and a measurement device main body unit 16. The measurement probe unit 14 and the measurement device main body unit 16 are integrally configured.

The measurement probe 14 is disposed facing the display surface 12 of the display, which is the object to be measured, at a predetermined distance (for example, 3 cm). The measurement probe 14 photoelectrically converts the light from the display surface 12 into an electrical signal (analog signal) and transmits the electrical signal to the measuring device main body 16.

The measurement probe section 14 is composed of a measurement optical system 27 and a light receiving system 28. The measurement optical system 27 has a variable magnification objective lens 21 according to this embodiment and a light beam splitter member 24. The variable magnification objective lens 21 is provided as an entrance section for allowing light from the object to be measured to enter. In FIG. 1, the variable magnification objective lens 21 is shown as a single lens to indicate that the colorimeter 10 has the variable magnification objective lens 21. The detailed configuration of the variable magnification objective lens 21 according to this embodiment will be described in detail later.

The beam splitting member 24 is provided as a light guiding section that guides the light incident through the variable magnification objective lens 21. The beam splitting member 24 splits the beam that has passed through the variable magnification objective lens 21 into three beams.

The light receiving system 28 has a filter section 23, a photoelectric conversion section 25, and an amplifier section 26. The light beam split by the light beam splitting member 24 passes through the filter section 23 and enters the photoelectric conversion section 25. The photoelectric conversion section 25 has a light receiving sensor (not shown) for converting the incident light into an electrical signal. The filter section 23 has a spectral sensitivity correction filter (not shown) for giving the light receiving sensor of the photoelectric conversion section 25 the spectral sensitivity of the standard observer specified by the CIE. The spectral sensitivity correction filter is a filter having a spectral sensitivity close to the color matching function. An interference film filter can be used as the spectral sensitivity correction filter. The amplifier section 26 amplifies the electrical signal (voltage) output from the light receiving sensor of the photoelectric conversion section 25 to a predetermined level.

The measuring device main body 16 converts the electrical signal (analog signal) input from the measuring probe 14 into a digital signal and performs a predetermined calculation process. Through this calculation process, the measuring device main body 16 calculates tristimulus values (X, Y, Z), xyY (chromaticity coordinates, luminance) established by the CIE (International Commission on Illumination), TΔuvY (correlated color temperature, color difference from the blackbody locus, luminance), etc., and displays the calculation results on the display unit 34.

The measuring device main body 16 has an A/D conversion section 31, a data memory 32, a display section 34, an operation section 35, a control section 36, and a power supply section 37. The A/D conversion section 31 converts the received light signal input from the measuring probe section 14 into a digital signal (hereinafter referred to as measurement data). The data memory 32 stores the measurement data output from the A/D conversion section 31. The control section 36 controls the measurement operation by centrally controlling the operation of the measuring probe section 14 and the operation of each section in the measuring device main body 16. The control section 36 uses the measurement data stored in the data memory 32 to calculate tristimulus values (X, Y, Z), xyY established by CIE, TΔuvY, etc.

The display unit 34 displays the results of calculations performed by the control unit 36. Various information related to the measurement (measurement instructions, display mode settings, measurement range, etc.) is input to the operation unit 35. The power supply unit 37 transforms the voltage of the power supplied from an external AC adapter (not shown) and supplies power to each component via the control unit 36.

Although an example of a tristimulus value colorimeter has been described, the photometric colorimeter 10 according to this embodiment may be a spectrophotometer. In the case of a spectrophotometer, the filter section 23 shown in FIG. 1 is replaced with a spectroscopic section. Light emitted from the display surface 12 of the display is dispersed by the spectroscopic section and enters the photoelectric conversion section 25. Based on the spectral characteristics indicated by the signal output from the photoelectric conversion section 25, the control section 36 determines the tristimulus values by numerical calculation.

In this embodiment, the variable magnification objective lens 21 can change the diameter (measurement diameter) of the measurement area AR on the display surface 12 of the display. This allows the same colorimeter 10 to measure the brightness (luminance) and chromaticity of displays of various sizes. Furthermore, in this embodiment, the F-number on the image side can be kept constant even if the measurement diameter is changed. This allows the luminance on the low-luminance side of the display to be measured with high accuracy.

In this embodiment, the variable magnification objective lens 21 is a variable magnification objective lens that forms an intermediate image at a position conjugate with the image plane, and has, in order from the object side, a first lens group which is a variable magnification group, a second lens group which is a variable magnification group, and a third lens group which does not substantially change magnification, and when the magnification is changed, the distance between two adjacent lens groups among the first lens group, the second lens group, and the third lens group changes, and an intermediate image is formed between the first lens group and the second lens group, and the third lens group has an aperture stop, and the aperture stop is positioned so that the conjugate image of the aperture stop is on the object side of the first variable magnification group.

According to the above configuration, the first and second lens groups, which are variable magnification groups, form an afocal system, and an intermediate image is formed between the groups, making it an optical system that makes it easy to bring the conjugate image of the aperture to the object side. In this embodiment, the term "afocal system" refers to an optical system configured so that the composite focal length of the two variable magnification groups is at least twice the focal length of the entire optical system.

The image-side F-number can be made constant at all zoom positions by using a third variable magnification group that does not change magnification and an aperture diaphragm whose position and aperture diameter are fixed. Therefore, the deviation of the spectral response with respect to the color matching function can be reduced when the optical characteristics are measured at each measurement diameter. This enables highly accurate luminance and chromaticity measurements. Even when the measurement diameter is small, optical characteristics such as luminance can be measured without narrowing the dynamic range. The aperture diaphragm may be located in front of the third lens group (closer to the object than the lens in the third lens group that is closest to the object).

Furthermore, since the conjugate image of the aperture stop is located closer to the object side than the first lens group, the brightness unevenness of the object to be measured is not reflected on the image plane (the light receiving surface of the light receiving sensor). This makes it possible to configure an optical system that is not affected by the unevenness of the object to be measured. When the object plane and the image plane are in a conjugate relationship, as in an imaging optical system, the brightness unevenness of the object to be measured is reflected directly on the image plane, resulting in a decrease in measurement accuracy. On the other hand, according to this embodiment, such problems can be prevented. Furthermore, the aperture stop and the object plane may be in a conjugate relationship.

Furthermore, according to this embodiment, the variable magnification objective lens has two variable magnification groups. This allows the range of magnification to be expanded.

In this embodiment, if the composite focal length of the first lens group and the second lens group at the d-line is f12, the focal length of the entire optical system of the variable magnification objective lens 21 is FL, and η = FL/f12, it is preferable that -0.5 < η < 0.5.

As described above, in this embodiment, "afocal system" refers to an optical system configured such that the combined focal length f12 of the two variable magnification groups is at least twice the focal length FL of the entire optical system. The above conditions are the conditions for the two variable magnification groups (the first lens group and the second lens group) to form an afocal system in this embodiment. By forming the first lens group and the second lens group into an afocal system, the light rays incident on the third lens group become closer to parallel light. This makes it easier to correct aberrations on the image surface of the third lens group.

In this embodiment, it is preferable that the first lens group has, in order from the object side, an eleventh lens group having negative power and a twelfth lens group having positive power.

With the above configuration, it is possible to give the first lens group as a whole a positive power. This makes it possible to configure an afocal system that forms an intermediate image between the first lens group and the second lens group.

In this embodiment, it is preferable that the second lens group has, in order from the object side, a 21st lens group having positive power and a 22nd lens group having negative power.

With the above configuration, it is possible to give the second lens group as a whole a positive power. This makes it possible to configure an afocal system that forms an intermediate image between the first lens group and the second lens group.

In this embodiment, when the magnification β1 of the first lens group is defined as β1 = ft1/fw1 based on the focal length ft1 at the telephoto end of the first lens group and the focal length fw1 at the wide-angle end of the first lens group, and the magnification β2 of the second lens group is defined as β2 = ft2/fw2 based on the focal length ft2 at the telephoto end of the second lens group and the focal length fw2 at the wide-angle end of the second lens group, it is preferable that the magnification β1 of the first lens group is 1 < β1 < 2.5 and the magnification β2 of the second lens group is 0.2 < β2 < 0.8.

According to the above configuration, the first and second lens groups, which are variable magnification groups, form an afocal system in order to collimate the light emitted from the aperture stop on the measurement surface side. By forming an intermediate image between the first and second lens groups, it is possible to reduce the magnification of each of the first and second lens groups, which are variable magnification groups.

Desirably, the magnification of the first lens group is 1.5≦β≦2 and the magnification of the second lens group is 0.5≦β≦0.7.

When the magnification of the first lens group is 2<β1, the distance from the first lens group to the intermediate image becomes short, making it more difficult to correct aberrations in the second lens group. On the other hand, when 1<β1<1.5, the variable range of the focal length of the first lens group becomes narrow, so the range of magnification change of the entire optical system becomes narrow. Similarly, when the magnification of the second lens group is β2<0.5, the distance from the second lens group to the intermediate image becomes short, so it becomes difficult to correct aberrations in the first lens group. On the other hand, when β2 is 0.8<β2, the magnification becomes 1x as β2 approaches 1, so the variable range of the focal length of the second lens group becomes narrow, as in the case of the first lens group. This narrows the range of magnification change of the entire optical system. When the magnification β1 of the first lens group is 1.5≦β1≦2 and the magnification β2 of the second lens group is 0.5≦β2≦0.7, the distance from the front group of the first lens group to the object side can be secured at the wide-angle end, so the angle of incidence to each magnification change group becomes small. This makes it easier to correct aberrations, and also makes it possible to widen the range of magnification change of the entire optical system.

In this embodiment, when the magnification ratio γ is defined as γ=β1*β2 based on the magnification β1 of the first lens group and the magnification β2 of the second lens group, it is preferable that 0.5≦γ≦1.5.

By configuring as described above, each lens group has a magnification ratio, so that the range of magnification of the measuring diameter can be expanded while simplifying the configuration or mechanism for zooming.

It is preferable that 1≦γ≦1.2. When 1≦γ≦1.2 is satisfied, the focal length variation of each variable power group becomes equal or nearly equal, making it easier to correct aberrations.

In this embodiment, it is preferable that the absolute value |Fno| of the image-side F-number Fno at each zoom position of the variable magnification objective lens satisfies 1 < |Fno| < 6, and the difference in F-number Fno between each zoom position is 3.5 or less.

By configuring it as described above, it is possible to suppress the reduction in the amount of light reaching the image plane caused by reducing the measurement diameter. Therefore, the dynamic range of measurement can be kept constant even if the measurement diameter changes.

In this embodiment, it is preferable that the angle of incidence of the chief ray on the image surface side is 5 degrees or less.
With the above-described configuration, the angle of incidence on the image plane can be kept constant at any angle of view, so that a decrease in the amount of light guided to the image side due to changes in the angle of view can be suppressed.

In this embodiment, the aperture system of the aperture stop is variable. By configuring in this way, the measurement diameter can be further reduced. In this embodiment, it is also possible to reduce the measurement diameter to φ1 mm. This makes it possible to measure the luminance and chromaticity of light-emitting elements used in small-sized displays, such as micro OLEDs or micro LEDs.

In this embodiment, the photometric colorimeter includes any one of the variable magnification objective lenses described above. This makes it possible to realize a photometric colorimeter that can vary the measurement diameter while minimizing the variation in the image-side F-number.

Specific examples of the variable magnification objective lens according to the present invention will be described below with reference to Figs. 2 to 4 and a table. Figs. 2 to 4 are lens configuration diagrams showing the configuration of the variable magnification objective lens 21 according to the first to third examples, respectively. In Figs. 2 to 4, the first to third examples will be denoted as "EX1", "EX2", and "EX3", respectively.

In Figures 2 to 4, "AX" indicates the optical axis, "STO" indicates the aperture stop, "I11" indicates the position of the intermediate image, "IM" indicates the imaging surface or image plane of the light receiving sensor, and "AR" represents the position of the measured area.

In the following explanation, Z1 to Z4 refer to zoom positions. In each of Figures 2 to 4, (Z1), (Z2), and (Z3) show lens cross-sectional views at the telephoto end, the intermediate focal length state, and the wide-angle end, respectively. (Z4) shows a lens cross-sectional view at the same zoom position as (Z3), but with the aperture stop diameter reduced. The measurement diameters at (Z1) to (Z4) are 10 mm, 5 mm, 2.5 mm, and 1 mm, respectively.

Example 1
As shown in Fig. 2, the variable magnification objective lens 21 is an objective lens that forms an intermediate image at a position conjugate with the image surface IMG. The variable magnification objective lens 21 has, in order from the object side, a first lens group G1 that is a variable magnification group, a second lens group G2 that is a variable magnification group, and a third lens group G3 that does not substantially change magnification. During magnification change, the interval between two adjacent lens groups among the first lens group G1, the second lens group G2, and the third lens group G3 changes. Specifically, the third lens group G3 is fixed, and the first lens group G1 and the second lens group G2 move along the optical axis AX.

The first lens group G1 has, in order from the object side, an eleventh lens group G11 having negative power and a twelfth lens group G12 having positive power. The eleventh lens group G11 is composed of one negative lens L1. The twelfth lens group G12 is composed of two positive lenses L2 and L3. This gives the first lens group G1 a positive power overall.

The second lens group G2 is composed of, in order from the object side, a 21st lens group G21 having positive power and a 22nd lens group G22 having negative power. The 21st lens group G21 is composed of one positive lens L4. The 22nd lens group G22 is composed of one negative lens L5. This gives the second lens group G2 a positive power overall.

The third lens group G3 has, from the object side, an aperture stop STO, a positive lens L6, and a positive lens L7.

The first lens group G1 and the second lens group G2 form an afocal system, and an intermediate image is formed at an imaging position I11 between the first lens group G1 and the second lens group G2. The conjugate image of the aperture diaphragm STO is closer to the object side than the first lens group G1. The third lens group G3 does not change magnification, and the position of the aperture diaphragm STO is fixed. Furthermore, the aperture diameter of the aperture diaphragm STO is fixed in the zoom positions Z1 to Z3. As a result, the F-number on the image side does not change in the zoom positions Z1 to Z3. The variable magnification objective lens 21 can reduce the measurement diameter by reducing the aperture diameter of the aperture diaphragm STO from the state shown in (Z3) (see (Z4)).

The configuration of Example 1 will be explained in more detail below, using construction data, etc. The definitions described below also apply to Examples 2 and 3.

In the construction data, the surface data, from the left column, shows the surface number (OBJ: object surface, STO: aperture stop, IMG: image surface), radius of curvature r, axial surface spacing d, refractive index nd of the lens material at the d-line (wavelength 587.56 nm), Abbe number νd of the lens material at the d-line, and effective diameter eff. dia. Surfaces with an * next to surface number i are aspheric, and the shape of the aspheric surface is expressed by the following "Equation 1" with the vertex of the surface as the origin, the X-axis in the direction of the optical axis, and h as the height perpendicular to the optical axis.

however,
Ai: ith-th aspheric coefficient, R: radius of curvature, K: conic constant.

The fundamental wavelength assumed for use in the lenses of each example is 587.56 nm (d-line), and the unit of the surface shape such as the radius of curvature is mm. Furthermore, a power of 10 (for example, 2.5×10 ⁻⁰⁰² ) is expressed using E (for example, 2.5E-002). Lens data of the variable magnification objective lens according to Example 1 is shown in Table 1.

The surface spacing of the lens surfaces of the variable magnification objective lens of Example 1 is shown in Table 2 below. In Table 2, Z1 to Z4 correspond to Z1 to Z4 shown in FIG. 2, respectively, and a1 to a5 correspond to a1 to a5 shown in Table 1, respectively.

Tables 3 and 4 show the aspheric coefficients of the lens surfaces of the variable magnification objective lens of Example 1 as aspheric data. Note that the coefficients of terms not listed in the aspheric data are 0.

Table 5 shows the characteristics of the variable magnification objective lens of Example 1. FL means the focal length of the entire variable magnification objective lens system, Fno means the image side F-number, BF means the back focus, TL means the overall system length, Ymax means the radius of the beam splitter member, f12 means the composite focal length of the first lens group G1 and the second lens group G2 at the d line, and η is defined by FL/f12. The units of FL, BF, TL, Ymax, and f12 are mm. From Table 5, it can be seen that the image side F-number is constant between positions Z1, Z2, and Z3.

Table 6 shows the lens data of the single lenses that make up the variable magnification objective lens of Example 1. Lens numbers 1 to 7 correspond to the symbols L1 to L7 shown in Figure 2, respectively.

Example 2
As shown in Fig. 3, the variable magnification objective lens 21 is an objective lens that forms an intermediate image at a position conjugate with the image surface IMG. The variable magnification objective lens 21 has, in order from the object side, a first lens group G1 that is a variable magnification group, a second lens group G2 that is a variable magnification group, and a third lens group G3 that does not substantially change magnification. During magnification change, the interval between two adjacent lens groups among the first lens group G1, the second lens group G2, and the third lens group G3 changes. Specifically, the third lens group G3 is fixed, and the first lens group G1 and the second lens group G2 move along the optical axis AX.

The first lens group G1 has, in order from the object side, an eleventh lens group G11 having negative power and a twelfth lens group G12 having positive power. The eleventh lens group G11 is composed of one negative lens L1. The twelfth lens group G12 is composed of two positive lenses L2 and L3. This gives the first lens group G1 a positive power overall.

The second lens group G2 is composed of, in order from the object side, a 21st lens group G21 having positive power and a 22nd lens group G22 having negative power. The 21st lens group G21 is composed of one positive lens L4. The 22nd lens group G22 is composed of one negative lens L5. This gives the second lens group G2 a positive power overall.

The third lens group G3 has, from the object side, an aperture stop STO, a positive lens L6, and a positive lens L7.

The first lens group G1 and the second lens group G2 form an afocal system, and an intermediate image is formed at an imaging position I11 between the first lens group G1 and the second lens group G2. The conjugate image of the aperture diaphragm STO is closer to the object side than the first lens group G1. The third lens group G3 does not change magnification, and the position of the aperture diaphragm STO is fixed. Furthermore, the aperture diameter of the aperture diaphragm STO is fixed in the zoom positions Z1 to Z3. As a result, the F-number on the image side does not change in the zoom positions Z1 to Z3. The variable magnification objective lens 21 can reduce the measurement diameter by reducing the aperture diameter of the aperture diaphragm STO from the state shown in (Z3) (see (Z4)).

The lens data for the variable magnification objective lens of Example 2 is shown in Table 7.

The surface spacing of the lens surfaces of the variable magnification objective lens of Example 2 is shown in Table 8 below. In Table 8, Z1 to Z4 correspond to Z1 to Z4 shown in FIG. 3, respectively, and a1 to a6 correspond to a1 to a6 shown in Table 7, respectively.

Tables 9 and 10 show the aspheric coefficients of the lens surfaces of the variable magnification objective lens of Example 2 as aspheric data. Note that the coefficients of terms not listed in the aspheric data are 0.

Table 11 shows the characteristics of the variable magnification objective lens of Example 2. From Table 11, it can be seen that the image side F-number is constant between positions Z1, Z2, and Z3.

Table 12 shows the lens data of the single lenses constituting the variable magnification objective lens of Example 2. Lens numbers 1 to 7 correspond to the symbols L1 to L7 shown in Figure 3, respectively.

Example 3
As shown in Fig. 4, the variable magnification objective lens 21 is an objective lens that forms an intermediate image at a position conjugate with the image surface IMG. The variable magnification objective lens 21 has, in order from the object side, a first lens group G1 that is a variable magnification group, a second lens group G2 that is a variable magnification group, and a third lens group G3 that does not substantially change magnification. During magnification change, the interval between two adjacent lens groups among the first lens group G1, the second lens group G2, and the third lens group G3 changes. Specifically, the third lens group G3 is fixed, and the first lens group G1 and the second lens group G2 move along the optical axis AX.

The first lens group G1 has, in order from the object side, an eleventh lens group G11 having negative power and a twelfth lens group G12 having positive power. The eleventh lens group G11 is composed of one negative lens L1. The twelfth lens group G12 is composed of two positive lenses L2 and L3. This gives the first lens group G1 a positive power overall.

The second lens group G2 is composed of, in order from the object side, a 21st lens group G21 having positive power and a 22nd lens group G22 having negative power. The 21st lens group G21 is composed of one positive lens L4. The 22nd lens group G22 is composed of one negative lens L5. This gives the second lens group G2 a positive power overall.

The third lens group G3 has, from the object side, an aperture stop STO, a positive lens L6, and a positive lens L7.

The first lens group G1 and the second lens group G2 form an afocal system, and an intermediate image is formed at an imaging position I11 between the first lens group G1 and the second lens group G2. The conjugate image of the aperture diaphragm STO is closer to the object side than the first lens group G1. The third lens group G3 does not change magnification, and the position of the aperture diaphragm STO is fixed. Furthermore, the aperture diameter of the aperture diaphragm STO is fixed in the zoom positions Z1 to Z3. As a result, the F-number on the image side does not change in the zoom positions Z1 to Z3. The variable magnification objective lens 21 can reduce the measurement diameter by reducing the aperture diameter of the aperture diaphragm STO from the state shown in (Z3) (see (Z4)).

The lens data for the variable magnification objective lens of Example 3 is shown in Table 13.

The surface spacing of the lens surfaces of the variable magnification objective lens of Example 3 is shown in Table 14 below. In Table 14, Z1 to Z4 correspond to Z1 to Z4 shown in FIG. 4, respectively, and a1 to a6 correspond to a1 to a6 shown in Table 13, respectively.

Tables 15 and 16 show the aspheric coefficients of the lens surface of Example 3 as aspheric data. Note that the coefficients of terms not listed in the aspheric data are 0.

Table 17 shows the characteristics of the variable magnification objective lens of Example 3. From Table 17, it can be seen that the image side F-number is constant between positions Z1, Z2, and Z3.

Table 18 shows the lens data of the single lenses constituting the variable magnification objective lens of Example 3. Lens numbers 1 to 7 correspond to symbols L1 to L7 shown in Figure 4, respectively.

Next, Table 19 shows the values corresponding to the conditional expressions in each embodiment. In Table 19, η _max in each embodiment means the value of η that has the maximum absolute value among the values of η at positions Z1 to Z4 (see Tables 5, 11, and 17). In embodiment 1, η _max is the value of η at position Z2, and in embodiments 2 and 3, η _max is the value of η at position Z1.

Although the embodiments and examples of the present invention have been described, the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, and it is intended to include all modifications within the meaning and scope of the claims.

10 photometric colorimeter, 12 display surface, 14 measurement probe section, 16 measurement device main body, 21 variable magnification objective lens, 23 filter section, 24 beam splitting member, 25 photoelectric conversion section, 26 amplifier section, 27 measurement optical system, 28 light receiving system, 31 A/D conversion section, 32 data memory, 34 display section, 35 operation section, 36 control section, 37 power supply section, AR measured area, AX optical axis, G1 first lens group, G2 second lens group, G3 third lens group, G11 eleventh lens group, G12 twelfth lens group, G21 twenty-first lens group, G22 twenty-second lens group, I11 imaging position of intermediate image, L1, L5 negative lenses, L2, L3, L4, L6, L7 positive lenses, Z1 to Z4 zoom positions.

Claims (10)

A variable magnification objective lens that forms an intermediate image at a position conjugate with an image plane,
From the object side,
a first lens group which is a magnification varying group;
a second lens group which is a magnification varying group;
and a third lens group that does not substantially change magnification.
During magnification change, a distance between two adjacent lens groups among the first lens group, the second lens group, and the third lens group changes,
the intermediate image is formed between the first lens group and the second lens group,
the third lens group has an aperture stop,
A variable magnification objective lens, wherein the aperture stop is disposed so that a conjugate image of the aperture stop is located on the object side of the first lens group. a composite focal length of the first lens group and the second lens group at the d line is f12;
The focal length of the entire optical system of the variable magnification objective lens is defined as FL,
If η=FL/f12,
2. The variable magnification objective lens according to claim 1, wherein −0.5<η<0.5. The first lens group is
From the object side,
an eleventh lens group having negative power;
a twelfth lens group having a positive power;
3. The variable magnification objective lens according to claim 1. The second lens group is
From the object side,
a 21st lens group having a positive power; and
and a second lens group having a negative power.
The variable magnification objective lens according to claim 1 . A magnification β1 of the first lens group is defined as β1=ft1/fw1, where ft1 is a focal length at a telephoto end of the first lens group and fw1 is a focal length at a wide-angle end of the first lens group,
When the magnification β2 of the second lens group is defined as β2=ft2/fw2, where ft2 is the focal length of the second lens group at the telephoto end and fw2 is the focal length of the second lens group at the wide-angle end,
the magnification β1 of the first lens group is 1<β1<2.5,
5. The variable magnification objective lens according to claim 1, wherein the magnification β2 of the second lens group satisfies 0.2<β2<0.8. the magnification β1 of the first lens group; and
When the magnification ratio γ is defined as γ=β1*β2 based on the magnification β2 of the second lens group,
6. The variable magnification objective lens according to claim 5, wherein 0.5≦γ≦1.5. the absolute value |Fno| of the F-number Fno on the image side at each zoom position of the variable magnification objective lens satisfies 1<|Fno|<6;
7. The variable magnification objective lens according to claim 1, wherein a difference in the F-number Fno between each of the zoom positions is 3.5 or less. A variable magnification objective lens according to any one of claims 1 to 7, in which the angle of incidence of the chief ray on the image plane is 5 degrees or less. 9. The variable magnification objective lens according to claim 1, wherein the aperture diameter of the aperture stop is variable. A photometric colorimeter equipped with a variable magnification objective lens according to any one of claims 1 to 9.

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