KR20170057615A

KR20170057615A - Apparatus and method for measuring focal points of convergent lens

Info

Publication number: KR20170057615A
Application number: KR1020150160941A
Authority: KR
Inventors: 남기봉; 이재현
Original assignee: 한림대학교 산학협력단
Priority date: 2015-11-17
Filing date: 2015-11-17
Publication date: 2017-05-25
Also published as: KR101754196B1

Abstract

The present invention relates to an apparatus and method for measuring a focal point of a converging lens. The apparatus for measuring a focal point of a converging lens is configured to irradiate light onto a lens whose focal point is to be measured and to measure the strength of light passing through a pin hole moving on an optical axis. The present invention is able to determine the position of a pin hole of a part, where the strength of light is meaningfully strong, as a focal distance, and to measure the relative efficiency of light concentration between several focal points.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an apparatus and a method for measuring a focal point of a converging lens,

The present invention relates to an apparatus and method for measuring a focus of a converging lens, and more particularly to an apparatus and method for measuring a focus of a converging lens, And the intensity of light passing through the pinhole is measured by moving the pinhole in the direction of the optical axis of the lens and analyzing the intensity of the light according to the position of the pinhole to determine one or a plurality of focal lengths And more particularly to an apparatus and method for measuring a focus of a converging lens.

Cataracts are diseases in which the lens becomes hazy and does not pass the light properly, so that the field of vision becomes cloudy as if the fog is covered. The eyes that develop cataracts are scattered or blocked by protein molecules that are deposited, so that the visual field is blurred as if looking in the fog, and there are various degrees of visual loss depending on the position, degree and extent of lens opacity. Although it is generally known to be a disease with age, there are also congenital cataracts and cataracts caused by trauma or inflammation.

Treatment of these cataracts includes drug therapy and surgery. Surgery is a method of inserting an intraocular lens into the eye. It is also called an intraocular lens (IOL) by inserting a lens into the eye after intraocular lens or extracapsular surgery. And is divided into a front lens, an iris supporting lens, and a rear lens depending on the supporting method. It is preferred because it is a more convenient and permanent method than glasses or contact lenses.

Open Patent Application No. 2011-0125652 discloses a diffractive trifocal lens that includes a plurality of annular concentric regions on the lens surface and monotonically changes the optical thickness between adjacent regions. In this patent, one lens has multi-focal points by having diffraction orders corresponding to near, medium, and far vision. However, in order to realize such a multifocal lens, it is important to obtain an accurate focal distance during development and fabrication.

In general, the MTF measurement method is widely used as a method of evaluating the performance of a multifocal lens including a guide lens. The MTF (Modulation Transfer Function) measurement method is a method of analyzing the loss of contrast through an image projected by a lens. However, in order to measure only the actual focal length, which is basic information necessary for the study of the guide lens, a simpler method than the MTF measurement method is necessary.

Therefore, it is required to develop an apparatus and method for measuring the focal length of a converging lens including a multifocal lens by a simpler method. Further, when a plurality of focal points are spaced apart from each other as in the case of a multifocal lens, it is difficult to accurately determine the position of the light passing through each focal point because the light passing through each focal point functions as a background light at another focal point. It is necessary to develop an apparatus and a method for measuring the focal length of a multi-focal lens.

Patent Document: Korean Published Patent Application No. 2011-0125652 (Published on November 21, 2011)

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus and method for focusing a converging lens that can easily and accurately measure the focal length of a converging lens by moving the pinhole in the direction of the optical axis.

It is an object of the present invention to provide an apparatus and method for focusing a converging lens capable of accurately measuring a plurality of foci not only for a short focal lens but also for a multifocal lens, and also for measuring a relative light condensing efficiency at a focal point.

According to an aspect of the present invention, there is provided an apparatus for focusing a converging lens, including a light source, a lens holder, a pinhole, and an optical sensor. The lens fixing part is spaced apart from the light source and fixes the lens. The pinhole is located on the optical axis of the lens and is movable in the optical axis direction of the lens. The optical sensor measures the intensity of light passing through the pinhole.

The converging lens focus measuring apparatus according to another embodiment of the present invention may further position the beam expander between the light source and the lens holding section.

The apparatus for focusing a converging lens according to another embodiment of the present invention may further include a controller for controlling the movement of the pinhole and determining the focal distance by analyzing the intensity of the light measured by the optical sensor according to the movement of the pinhole.

The method of measuring a focus of a converging lens according to an embodiment of the present invention includes the steps of irradiating light toward a lens, moving the pinhole in the direction of the optical axis of the lens, measuring the intensity of light passing through the pinhole, And determining the focal distance by analyzing the intensity of the light.

The convergent lens focus measuring method according to another embodiment of the present invention further includes the step of re-measuring the focal distance by adjusting the moving speed of the pinhole according to the calculated difference of the plurality of focal lengths when the plurality of focal points are calculated can do.

According to another aspect of the present invention, there is provided a method for measuring a focus of a converging lens, comprising the steps of: measuring an intensity of light passing through a pinhole according to a difference between a plurality of calculated focal lengths, The method may further comprise the step of measuring.

The converging lens focus measuring apparatus and method of the present invention can accurately measure the focus of a short focus lens and the plurality of focuses of a multifocal lens with a simple configuration.

1 is a block diagram showing a focus measuring apparatus for a converging lens according to an embodiment of the present invention.
2 is a view showing a focus measuring apparatus for a converging lens according to an embodiment of the present invention.
FIG. 3 is a view showing the measurement of the focal length of the focusing lens by the focusing device of a converging lens according to the embodiment of the present invention.
Fig. 4 (a) shows the focus measurement result of this focus lens, and Fig. 4 (b) shows the focus measurement result of the short focus lens.
5 is a view showing a focus of the Fresnel lens by the convergent lens focusing apparatus according to the embodiment of the present invention.
6 is a view showing a focus measurement result of the Fresnel lens.
7 is a view showing the focus of the Fresnel lens for condensing by the converging lens focus measuring apparatus according to the embodiment of the present invention.
8 is a flowchart showing a method for measuring a focus of a converging lens according to an embodiment of the present invention.
Fig. 9 is a diagram showing a focusing state in a converging lens having a Fresnel lens structure of an axisymmetric structure. Fig.
10 is a result of measuring the surface shape of the lens with a surface analyzer.
11 is a view showing a focus measurement result of a converging lens having a Fresnel lens structure of an axisymmetric structure according to an embodiment of the present invention.
12 is a view showing a focus measurement result of a comparison object lens according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that, in the drawings, the same components are denoted by the same reference symbols as possible. Further, the detailed description of known functions and configurations that may obscure the gist of the present invention will be omitted. For the same reason, some of the components in the drawings are exaggerated, omitted, or schematically illustrated.

FIG. 1 is a block diagram showing an apparatus for measuring a focus of a converging lens according to an embodiment of the present invention, FIG. 2 is a view showing an apparatus for measuring a focus of a converging lens according to an embodiment of the present invention, and FIG. FIG. 4A is a view showing the focus measurement result of the focus lens, FIG. 4B is a view showing a focus measurement result of the converging lens according to the example, Fig. 8 is a view showing a focus measurement result of the lens. Fig.

1, a focus measuring apparatus 1000 for a converging lens according to an embodiment of the present invention includes a light source 1100, a lens fixing unit 1200, a pinhole 1300, and an optical sensor 1400 .

The light source 1100 is not limited to the type that irradiates parallel light, and a laser is used in this embodiment. The laser used the 633nm wavelength laser. The beam expander 1120 can be positioned in front of the light source 1100 so that the laser can be incident on the focus measurement object lens 1220 with a large light beam. The beam expander 1120 can adjust the magnification of the light beam so that light can be incident on the front surface of the incident portion of the focus objective lens 1220.

The lens fixing unit 1200 fixes the focus measurement objective lens 1220. [ The lens fixing part 1200 is spaced apart from the light source 1100 and the beam expander 1120 in the irradiation direction of the light source 1100. The lens fixing unit 1200 can fix only the edge of the lens so as not to block the entrance surface and the exit surface of the lens 1220 to be focused. For example, the periphery of the focus objective lens 1220 can be fixed in the form of a ring. The material is not limited, but it is preferable to use a transparent material. And may be designed to be resilient or resizeable to accommodate various lens sizes. The focus objective lens 1220 may be a monofocal or a multifocal lens, and a convergent lens may be used to measure the focus.

The pinhole 1300 is located on the optical axis of the focus objective lens 1220. The pinhole 1300 can move in the optical axis direction of the focus objective lens 1220. [ The diameter of the pinhole 1300 may be 10 to 30 占 퐉, preferably 20 占 퐉. The pinhole 1300 passes only the light passing through the aperture and blocks the remaining light. Light emitted from the lens travels through the pinhole 1300. As shown in FIG. 2, the present invention irradiates light and moves the pinhole 1300 in the optical axis direction. The pinhole 1300 can be mounted on the one-dimensional scanner 1320 in order to move the pinhole 1300. The pinhole 1300 is mounted on the scanner 1320 and moves on the optical axis at a constant speed.

The optical sensor 1400 measures the intensity of light passing through the pinhole 1300. The optical sensor 1400 is a sensor that converts input optical information into an electrical signal and measures the strength of the optical signal. In this embodiment, the optical sensor 1400 can use, for example, photodiode, CCD, CMOS, avalanche photodiode, and PMT (light pipe). The light sensor 1400 is located on the same optical axis as the lens and pinhole 1300. [

Since the diameter of the pinhole 1300 is very small, only a part of light emitted from the lens passes through. As shown in FIG. 3, it is assumed that the light passing through the lens is refracted and proceeds, and the pinhole is located at positions A to E. When the pinhole is in the A position, only a part of the light passing through the lens center passes through the pinhole. When the pinhole is in the B position, light passing through the outer periphery of the lens passes through the pinhole through the optical axis. When the pinhole is at the C position, only a part of the light passing through the center of the lens passes through the pinhole, and the light that does not reach the optical axis or passes through the optical axis is blocked by the pinhole. When the pinhole is in the D position, light passing through the center of the lens passes through the pinhole through the optical axis. When the pinhole is at the E position, only a part of the light passing through the center of the lens passes through the pinhole, and the light passing through the optical axis is blocked by the pinhole.

4A shows changes in the intensity of light according to the position of the pinhole. It can be seen that when the pinhole is at the positions B and D, the intensity of the light has a peak. In comparison with this, FIG. 4 (b) shows the experimental result in the short focus lens, and it can be seen that only one peak appears.

That is, only the light passing through the optical axis and the optical axis of the focus objective lens 1220 passes through the pinhole 1300, and when the intensity of the light sensed by the optical sensor 1400 is greatest, It can be judged. In the present invention, the intensity of light passing through the pinhole 1300 is measured, and the intensity of the light according to the position of the pinhole 1300 is analyzed. The position of the pinhole 1300 measured as the light intensity is significantly significant is determined as the focal distance.

A control unit (not shown) controls the movement of the pinhole 1300 in the optical axis direction. The moving speed of the pinhole 1300 can be determined according to known focal information of the lens, and the moving speed of the secondary measurement can be adjusted as necessary after the primary focus measurement. The optical sensor 1400 measures the intensity of light incident on the optical sensor 1400 continuously or at regular intervals while the pinhole 1300 is moving. For example, it can be set to measure the light intensity at a moving distance of 2 mu m of the pinhole 1300. [ The control unit records the intensity of the measured light.

The controller calculates the focal distance by analyzing the point at which the peak appears. When the noise is severe, the focus can be calculated by judging only the light intensity (intensity of the light at the peak) over a specific value as a significant value. On the other hand, when the noise is severe at the point excluding the peak value, the control unit can recognize that the influence of the background light is large at a point other than the focus point, and the influence of the noise can be minimized by reducing the opening of the pinhole. Conversely, when the peak value itself is low, the aperture of the pinhole may be enlarged to adjust the intensity of the light passing through the pinhole to be large.

FIG. 5 is a view showing a focus measurement of a Fresnel lens by a focus measuring apparatus for a converging lens according to an embodiment of the present invention, FIG. 6 is a view showing a focus measurement result of a Fresnel lens, Fig. 8 is a view showing the focus of the Fresnel lens for condensing by the converging lens focus measuring device according to the embodiment of the present invention. Fig.

The following is the result of an experiment using a Fresnel lens as a focusing objective lens by an apparatus according to the present invention.

The Fresnel lens is a condenser lens that is divided into several or several ring-shaped bands to reduce the thickness of the lens, thereby reducing the thickness of the central part. A lens having a large diameter can be manufactured without increasing the thickness of the lens. However, in the present embodiment, an experiment was conducted by using, as an objective lens, not a Fresnel lens generally used for light focusing, but using a lens borrowing the structure of a Fresnel lens as a focus measurement target lens.

As shown in Fig. 5, the Fresnel lens focuses the light on each focal point in the portion of each ring-shaped band. Therefore, theoretically, the point at which the peak is the maximum should exist as many as the number of the circular bands. However, it is not easy to produce a clear focal length in the production of an actual multifocal Fresnel lens. The focal point can be measured using the converging lens focus measuring apparatus according to the present invention in order to design the Fresnel lens to have an accurate focus in the process of manufacturing the Fresnel lens.

FIG. 6 shows the result of measuring the intensity of light passing through the pinhole with respect to the Fresnel lens of FIG. As shown in FIG. 6, the intensity of the light is peaked at a plurality of points, and the focus position can be determined through the pinhole positions of the peaks. If the noise is severe at the point excluding the peak value, it can be understood that the influence of the background light is large at a point other than the focus point, and the influence of the noise can be minimized by reducing the aperture of the pinhole. Conversely, when the peak value itself is low, the aperture of the pinhole may be enlarged to adjust the intensity of the light passing through the pinhole to be large.

7 is a view showing the measurement of the focus of a general Fresnel lens for light focusing. The present invention is also effective for examining the performance of a light-converging lens as well as an image-forming lens. As shown in FIG. 7, the Fresnel lens condenses the incident light. It is important to make each of the annular bands have the same focal point in manufacturing such a condensing Fresnel lens. However, when an error occurs in the lens manufacturing process, the focus of each circular band does not coincide, and a peak may appear at a plurality of points as a result of focus measurement. Therefore, it is possible to correct the focal distance and aberration through repetitive focus measurement so that the number of focal points becomes one in the manufacturing process of the Fresnel lens for condensing, that is, the maximum peak appears at one point.

8 is a flowchart showing a method for measuring a focus of a converging lens according to an embodiment of the present invention.

In order to measure the focus of the converging lens, light is irradiated toward the lens (S8100). The light to be irradiated may be a laser but is not limited thereto. A single light may be used as the light source, such as a laser, but it is not particularly limited as long as it is parallel light. In this embodiment, a laser is used, and a beam expander is further placed in front of the light source in order to thicken the beam of the laser beam.

Next, the pinhole is moved in the optical axis direction of the lens (S8200). The pinhole is mounted on a one-dimensional scanner and can be moved on the optical axis at a constant speed. The diameter of the pinhole opening may be 10 to 30 占 퐉, preferably 20 占 퐉. The pinhole passes only the light passing through the aperture and blocks the remaining light. The light incident on the lens through the beam expander is refracted and travels through the pinhole.

The intensity of the light passing through the pinhole is measured by the optical sensor (S8300). The optical sensor measures the intensity of light passing through the pinhole on the optical axis, such as the lens to be focused and the beam expander. Measurements may be made continuously or at regular intervals depending on the spacing of the pinholes.

The intensity of light according to the position of the pinhole is analyzed to determine the focal length of the lens (S8400). The control unit records the intensity of light with respect to the moving distance of the pinhole. By analyzing the intensity of the light according to the pinhole position, the position of the center pinhole with the intensity of the first light is determined as the focal distance. In the case of a multifocal lens, a plurality of points having a high intensity are provided, and a plurality of focal positions can be accurately determined through the pinhole positions of these points.

In the case of a multifocal lens, the distance between adjacent foci may be very small depending on the type of lens and the manufacturing process. In this case, the focus can be re-measured by moving the pinhole again to avoid errors. For example, it may be set to re-measure the focal distance if the distance between the initially measured focal points is less than 1 mm. In the case of re-measurement, the moving speed of the pinhole can be adjusted to achieve more precise scanning. If the distance between focal points is too close, the movement speed of the pinhole can be adjusted more slowly. The re-measured results are judged to be more accurate than the first-order results, and can be compared with the first-order results to determine whether there is an error.

In another embodiment, the light intensity measurement interval of the light sensor may be adjusted during remeasurement. The optical sensor can continuously measure the intensity of light, but it can also be measured at intervals of 2 to 10 μm when the pinhole moves. For example, if the distance between foci measured for the first time (measured at 5 占 퐉 intervals) is 1 mm or less, the moving distance of the pinholes may be set shorter (measured at 2 占 퐉 intervals) to remeasure the focal distance.

The present invention is more effective when there are a plurality of focal points or a short distance between the in-focus points. In addition to being able to determine the positions of the two focal points using accurate quantitative signals, The efficiency can also be measured.

[Example]

Fig. 9 is a view showing a focusing state in a converging lens having a Fresnel lens structure of an axisymmetric structure, Fig. 10 is a result of measuring the surface shape of the lens with a surface analyzer, Fig. FIG. 12 is a view showing focus measurement results of a converging lens having a Fresnel lens structure of an axisymmetric structure according to an embodiment of the present invention. FIG.

The guide lens is inserted into the eye to correct the visual acuity, but since there is no perspective adjustment function, a multifocal guide lens is used as an alternative thereto.

The multifocal guide lens is made of a basic monofocal lens structure with a supplementary structure that can realize different focal lengths. As shown in Fig. 9, this auxiliary structure may borrow a Fresnel lens structure having an axisymmetric structure. In this embodiment, the focal length of the multifocal lens is measured. In the case of the short focal lens, it is relatively easy to measure the focus. However, in the case of the multifocal lens, especially when the two focal lengths are close to each other, it is difficult for the experimenter to judge the magnitude of the focal spot objectively on the optical bench. This is because the energy of the light gathered at the adjacent different focus is observed overlapping with the focus to be measured.

The beam expander is placed in front of the laser light source, the focus is fixed to the lens fixing portion, and then the light is irradiated. Then, the pinhole was moved in the direction of advance of the laser, and the change in brightness of the light passing through the pinhole was observed to obtain the focal distance of interest. The wavelength of the laser used in this embodiment is 633 nm.

In this embodiment, in order to confirm that two focal points are formed by the lens as shown in FIG. 9, a pinhole is spaced apart from the emitting portion of the focus objective lens and is slowly moved forward and backward in the laser advancing direction, We chose to record. It is expected that when the pinhole aligned on the optical axis moves, the transmission energy increases when the focus is focused. A diameter of 20 mu m was used as the pinhole. The pinhole was mounted on a one-dimensional scanner so that it could be moved back and forth.

10 is a result of measuring the surface shape of the used lens with a surface analyzer (Zygo surface profiler), and it can be confirmed that the Fresnel lens structure is padded on the basic shape of the curved surface.

The lens used in the experiment is Alcon's Acrysof IQ ReSTOR IOL model. The focal distance data provided by the manufacturer is 20.0 D + 3.0 add. If the refractive power of the IOL is 20D, the focal length should be 50mm, but the measured focal distance is only 24mm. That is, the diopter value of 20D specified in the product is expected not to be the refractive performance in the air, but to be the refractive index expected in the case where the refractive index around the lens is close to 1.33. Only one focal point was observed in the naked eye, and it was not confirmed whether two focal points were produced. FIG. 11 shows the result of z-scan for this lens, and it can be seen that two foci clearly appear along the z-axis direction. In other words, since the two focal points are formed at a distance of 1.48 mm, it is considered that the two focal points were observed as one long focal point when observed with the naked eye. However, it can be seen that the two focal points are clearly separated and observed in the measurement result of the pinhole transmitted light measured at intervals of 2 탆 in the optical axis direction of the lens. Figure 11 shows not only the number of focuses clearly but also the relative intensity of the two foci, so that in the case of the lenses used, the respective focus intensities are observed to be approximately equal. These data can be used as data to predict the clarity of the visual field corresponding to each focus when the guide is used.

FIG. 11 shows the result of four measurements at the same setting at the same time. In addition to the peak as the main observation target, attention is paid to the similarity of the baseline. That is, the baseline is generally considered to represent noise, but the baseline of Figure 11 shows that all four measurements are of a similar type, so that each of these measurements is not random noise. That is, the signals observed in the vicinity of 12 ~ 18, ~ 42 ~ ~ 53 on the z - axis are not simple noise but verifiable with reproducible values. These are, of course, supposed to be secondary signals made by IOL-padded Fresnel lens structures.

As a comparative object, experiments were repeated using Nikon Tessar Lens 50 mm, which is a lens for a camera. As shown in FIG. 12, strong signals were observed only in one focus, and it was confirmed that signal values corresponding to noise were observed in the other regions. The periodic signal appearing at the baseline is considered to be an interference effect by the experimental setup, which is considered a technical factor to be removed in the future.

In this embodiment, the intensity of the light transmitted through the pinhole is measured while moving the pinhole in the direction of the optical axis in order to measure the focal position of the lens. As a result, only one peak is observed in the case of a lens for a commercial camera And the other parts were not measured. When we measured the multifocal guide lens, we could observe two focal points that were not distinguished by the naked eye. The two focal points were separated by 1.48mm . It was also found that some of the various small signals appearing on the baseline were reproducibly observed repeatedly in four measurements, and that these values were not random in the case of simple lenses (camera lenses) It can be confirmed that the result is due to the redundant Fresnel structure.

It should be noted that the embodiments of the present invention disclosed in the present specification and drawings are only illustrative of the present invention in order to facilitate description of the present invention and to facilitate understanding of the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

1000: focus measuring device 1100: light source
1200: lens fixing part 1220: lens to be focused on
1300: pinhole 1320: one-dimensional scanner
1400: Light sensor

Claims

Light source;
A lens fixing unit positioned apart from the light source and fixing the lens;
A pinhole located on an optical axis of the lens and movable in an optical axis direction of the lens; And
And an optical sensor for measuring the intensity of light passing through the pinhole.

The method according to claim 1,
And a beam expander positioned between the light source and the lens fixing unit.

3. The method according to claim 1 or 2,
Further comprising a controller for controlling the movement of the pinhole and analyzing the intensity of light measured by the optical sensor according to the movement of the pinhole to determine a focal distance.

Irradiating light toward the lens;
Moving a pinhole in a direction of an optical axis of the lens;
Measuring the intensity of light passing through the pinhole; And
And determining a focal distance by analyzing the intensity of light according to the position of the pinhole.

5. The method of claim 4,
When a plurality of focal lengths are calculated in the step of determining the focal distance by analyzing the light intensity according to the position of the pinhole,
And measuring the focal distance by adjusting a moving speed of the pinhole according to the calculated difference of the plurality of focal lengths.

5. The method of claim 4,
When a plurality of focal lengths are calculated in the step of determining the focal distance by analyzing the light intensity according to the position of the pinhole,
And measuring the focal distance by adjusting an interval of measuring the intensity of the light passing through the pinhole according to the calculated difference of the plurality of focal lengths.