JP5008625B2 - Evaluation method of mold press lens and evaluation method of lens mold - Google Patents

Description

  The present invention relates to a mold press lens evaluation method for evaluating a lens surface shape error of a mold press lens molded by the lens mold at the stage of processing a lens mold for molding a mold press lens. The present invention also relates to a lens mold evaluation method for evaluating a lens mold using such a mold press lens evaluation method.

  Image pickup lens systems used in image pickup optical systems such as digital cameras are highly demanded for downsizing and compactness as well as higher pixels. In recent years, aspherical lenses are frequently used in image pickup lens systems in order to satisfy such demands. . A mold press lens made of a glass material is known as an aspheric lens. If the shape error of the aspherical surface of the aspherical lens is large, desired optical characteristics cannot be obtained as the entire imaging lens system. Therefore, it is necessary to accurately measure the aspherical shape of the aspherical lens after manufacture, and to remove the one having a large shape error.

  Conventionally, for measuring the aspherical shape of an aspherical lens, a contact-type measuring device that measures the shape of the aspherical surface by bringing a contactor into contact with the aspherical lens (for example, a form-talissurf manufactured by Taylor Hobson, Inc. Matsushita Electric Industrial Co., Ltd. UA3P) is used. The shape measurement using such a surface shape measuring apparatus has a problem that it takes time to measure the shape of the entire aspheric surface. Therefore, it is conceivable to measure the shape of the aspherical surface using an interferometer such as a Fizeau interferometer that is frequently used for measuring the shape of the spherical lens.

  As an interferometer, a transmitted wavefront interferometer that measures a lens transmitted wavefront is known. The transmitted wavefront measuring method is disclosed in Patent Documents 1 and 2. As described in these patent documents, in the transmitted wavefront measurement method, interference fringes or wavefront aberrations are measured using a null lens and an interferometer.

Here, in the mold press lens, the yield of the molded mold press lens is poor unless the lens mold can be manufactured with high accuracy. Therefore, it is necessary to evaluate the shape error of the mold press lens itself and to evaluate the shape error of the lens mold and use a lens mold that meets the standards. In Patent Document 3, a correction wavefront aberration amount that cancels the wavefront aberration amount of an optical element molded by a temporary mold is calculated, and the optical design of the optical element having a shape that generates the correction wavefront aberration amount is performed again. An optical element mold designing method for designing a regular mold based on the above is disclosed. In this method, the wavefront aberration of the optical element is measured using an interferometer.
JP 2002-214076 A JP 2000-227313 A JP 2004-299934 A

  Since an imaging lens used for a digital camera or the like is generally used as a combined lens, a large aberration exists in the transmitted wavefront of a single lens. Therefore, when a null lens capable of nullifying aberration is inserted, the transmitted wavefront can be made non-aberrated. If such a null lens system can be configured, if there is a shape error in the lens to be inspected, the error component appears as a wavefront aberration. Therefore, the lens performance can be evaluated by measuring the wavefront aberration value. Even if the null lens is not actually manufactured, if there is optical design software and shape error data of the lens to be inspected, the wavefront aberration value can be calculated by simulation. However, a null lens design that is close to the optical characteristics of the actual assembled lens is ideal, and in pass / fail judgment based on the wavefront aberration value, check the correlation between the mounting resolution evaluation result and the simulation wavefront aberration calculation value. Therefore, it is necessary to determine a reference value (wavefront aberration value) for pass / fail judgment.

  Here, in the case of a mold press lens, the transfer characteristics of the lens mold can be grasped, and if the variation in the lens shape of one lens mold is sufficiently small, the shape of the lens surface molding surface of the lens mold Based on the error, the shape error of the mold press lens molded using the lens mold can be accurately predicted. Therefore, it is possible to evaluate the wavefront aberration without actually molding the mold press lens at the stage of processing the lens mold.

  An object of the present invention is to provide a mold press lens capable of evaluating a lens surface shape error of a mold press lens molded by the lens molding die at a stage of processing a lens molding die for molding a mold press lens based on such knowledge. To propose an evaluation method.

  Another object of the present invention is to propose a lens mold evaluation method for evaluating a lens mold using such a mold press lens evaluation method.

In order to solve the above problems, the evaluation method of the mold press lens of the present invention is:
Produce a lens mold for molding mold press lenses,
Measuring a shape error of the first lens surface molding surface and the second lens surface molding surface for molding the first and second lens surfaces of the mold press lens in the manufactured lens molding die;
Based on the measured shape error of the first and second lens surface molding surfaces, calculate the expected shape error of the first and second lens surfaces of the mold press lens molded using the mold,
Designing a null lens for nulling wavefront aberration appearing in a transmitted wavefront of light after passing through the mold press lens having the first and second lens surfaces without a shape error,
Calculating an expected wavefront aberration appearing in a transmitted wavefront of light after passing through the mold press lens and the null lens having the first and second lens surfaces including the expected shape error;
The pass / fail of the mold press lens molded using the lens mold is evaluated based on the calculated expected wavefront aberration.

  Here, it is possible to perform the design of the null lens and the calculation of the predicted wavefront aberration by using an optical design apparatus including a computer in which an optical design program and a wavefront aberration calculation program are installed.

  Further, the present invention is suitable for use in the evaluation of an aspheric mold press lens that is difficult to manufacture compared to a spherical lens or the like.

  Furthermore, in order to easily design a null lens, rather than designing a null lens system using a plurality of spherical lenses, the null lens is designed so that one lens surface is a convex or concave aspheric surface and the other lens surface is It is desirable to design as a single lens that is flat.

Next, the present invention is a lens mold evaluation method using the above-described mold press lens evaluation method,
A plurality of first lens molding dies having the first lens surface molding surface for molding the first lens surface of the mold press lens, and a second lens surface of the mold press lens for molding the second lens surface. Producing a plurality of second lens molding dies having the second lens surface molding surface;
For each of the lens molds composed of a combination of one of the first lens molds and one of the second lens molds, an evaluation is performed by the evaluation method of the mold press lens.
The combination of the first lens mold and the second lens mold that have passed the evaluation result is evaluated as an acceptable product as the lens mold.

  In the mold press lens evaluation method of the present invention, the shape error of the molding surface of the lens mold is actually measured, and both lenses of the mold press lens molded using the lens mold based on the measurement shape error. The predicted shape error of the surface is obtained by calculation. Therefore, it is possible to evaluate the shape error of the mold press lens obtained by molding before actually molding the mold press lens, that is, at the stage of processing the lens mold. Therefore, there is an advantage that generation of a defective lens can be prevented in advance.

  In the lens mold evaluation method of the present invention, the first lens mold and the second lens mold are individually evaluated for a lens mold composed of a pair of upper and lower first and second lens molds, for example. Rather, they can be evaluated for their combination. Even if the shape error of the molding surface is within the allowable range for a single lens mold, if the mold press lens is molded in combination, the shape error of both molding surfaces will overlap and deviate from the allowable range. There is a possibility that a mold press lens having such a large shape error may be molded. According to the method of the present invention, the effect that the lens mold in the combined state can be evaluated is obtained. For example, the lower mold is circulated at regular intervals along the circulation path, the heated glass material is supplied to the molding surface of the lower mold, and then the upper mold is set against the lower mold with the glass material sandwiched and pressed. In a mold press molding apparatus that performs molding, the method of the present invention can eliminate combinations of defective molds in advance and prevent defective lenses from being formed in advance.

  Hereinafter, an evaluation method for an aspheric mold press lens and an evaluation method for a lens mold according to an embodiment of the present invention will be described with reference to the drawings.

(Evaluation method of aspheric mold press lens)
FIG. 1 is a schematic process diagram showing a method for evaluating an aspheric mold press lens according to the present embodiment, and FIGS. 2 to 4 are explanatory diagrams for explaining each process.

  First, in step ST1 of FIG. 1, a lens mold for molding a mold press lens is manufactured. Here, the design of the lens surface molding surface of the master lens mold is performed by a design method generally performed based on the optical parameters of the mold press lens.

  That is, in the mold press molding of the mold press lens, the lens surface molding surface shape of the lens mold does not match the lens surface shape of the mold press lens due to heat shrinkage during the cooling period after molding. In addition, due to non-uniform distribution of the internal temperature of the molding glass material at the time of molding and differences in the thickness of each part of the molded mold press lens, there is a difference in the amount of thermal shrinkage of each part of the mold press lens. Therefore, the surface shape of the lens mold and the lens surface shape of the mold press lens are often not similar.

  Therefore, in the production of the master lens mold, the lens surface shape of the mold press lens obtained by molding is measured, the shape change during molding is predicted based on the measured value, and the molding surface of the mold is estimated. A design method is adopted in which the shape of the molding surface is optimized while correcting.

  Each lens mold is manufactured to have the molding surface shape determined in this way. Therefore, the relationship between the lens surface molding surface shape of the lens mold and the lens surface shape of the mold press lens molded using the lens molding die is known.

  Examples of the mold press lens include a biconvex lens 1 having both aspheric surfaces shown in FIG. 2A and a concave meniscus lens 2 having both aspheric surfaces shown in FIG. 2B. The mold press lenses 1 and 2 are used as constituent lenses of a combined lens used as an imaging optical system such as a digital camera.

  Further, as shown in FIG. 3, for example, a lens mold 3 for mold press molding the concave meniscus lens 2 includes an upper mold 4 and a lower mold 5 and a cylindrical body 6. Is done. A first lens surface molding surface 4 a for molding the first lens surface 2 a of the concave meniscus lens 2 is formed on the lower end surface of the upper mold 4, and the concave meniscus lens 2 is formed on the upper end surface of the lower mold 5. A second lens surface molding surface 5a for molding the second lens surface 2b is formed.

  Next, in step ST2 of FIG. 1, the first lens surface molding surface 4a and the second lens surface molding surface of the manufactured lens molding die, for example, the upper molding die 4 and the lower molding die 5 shown in FIG. The shape error of 5a is actually measured. For measuring the shape error, a contact-type measuring device that measures the shape of the aspheric surface by bringing a contact member into contact with the aspheric lens (for example, Foam Talisurf manufactured by Taylor Hobson or UA3P manufactured by Matsushita Electric Industrial Co., Ltd.) Can be used.

  Next, in step ST3 of FIG. 1, based on the shape error measurement values of the first and second lens surface molding surfaces 4a and 5a, a mold press lens, for example, a concave meniscus lens 2 molded using the lens molding die 3 is used. The expected shape errors of the first and second lens surfaces 2a and 2b are calculated. As described above, the shape of the first and second lens surface forming surfaces 4a and 5a having no shape error and the shape of the first and second lens surfaces 2a and 2b of the concave meniscus lens 2 having no shape error. The relationship between is known. Therefore, based on these known relationships, the shape error (predicted shape error) that will occur on the first and second lens surfaces 2a and 2b of the concave meniscus lens can be calculated.

  Next, in step ST4 of FIG. 1, wavefront aberrations appearing on the transmitted wavefront of light after passing through the concave meniscus lens (mold press lens) having the first and second lens surfaces 2a and 2b having no shape error are calculated. Design a null lens to nullify.

  Since the concave meniscus lens 2 (mold press lens) of this example is used as a combined lens of an imaging system optical system, the lens alone has aberration. Therefore, the transmitted wavefront after removing the aberration using a null lens is measured, and the shape error is calculated based on the wavefront aberration included therein. The transmissive null lens system used in this example is designed so that the parallel light incident on the lens to be examined gathers at one point through the null lens. In the transmission type null lens, the wavefront transmitted through both the first and second lens surfaces 2a and 2b of the concave meniscus lens 2 (mold press lens) which is a test lens is measured. This is “the combined shape error of the first and second lens surfaces” and “inter-surface eccentricity”.

  Next, the required number of null lenses is roughly determined by the type of mold press lens and the evaluation target items, and whether the null lens is spherical or aspheric. In the table of FIG. 4A, the column “Aspherical” of “Null lens required number” is an example in which the aspherical null lens is a plano-convex aspherical surface. FIG. 4B shows a plano-convex aspherical null lens in which, when the lens to be examined is a concave meniscus lens 2, one first lens surface 6a is a convex aspheric surface and the other second lens surface 6b is a flat surface. 6 shows an example of an optical system for transmitted wavefront measurement when 6 is used.

  The reason for adopting a plano-convex aspherical surface is that it is easier to manufacture than both aspherical surfaces. This is because it is realistic to manufacture an aspherical null lens by grinding, considering the cost. This is because a plano-convex surface having a flat surface on one side is easier to process, and if both aspheric surfaces are used, the influence of manufacturing errors increases.

  As shown in the table of FIG. 4A, when the test lens is a concave meniscus lens 2, the design difficulty is higher than that of the biconvex lens 1, and the required number of null lenses is also increased. In addition, when the evaluation target is “shape”, a larger number of sheets is required than when “eccentric”. This is because in the case of “shape” evaluation, it is necessary to make the light flux pass through the entire effective diameter, but in the case of “eccentricity” evaluation, this is not necessary. That is, as the luminous flux increases, the amount of aberration to be corrected increases, so that more null lenses are required.

  In designing a null lens, it is not easy to say which is better for a spherical system or an aspheric system because of the relationship between design availability and error sensitivity. However, in terms of ease of design, it is desirable to adopt a design procedure in which a plano-convex aspheric surface is used first, and if a plano-convex aspheric surface design is impossible, a spherical group lens is employed.

  Here, the null lens can be designed by performing a simulation evaluation on commercially available optical design software without actually manufacturing the null lens. That is, it can be performed by using an optical design apparatus mainly composed of a computer in which an optical design program is installed.

  Next, in the process ST5 of FIG. 1, the concave meniscus lens 2 (mold press lens) provided with the first and second lens surfaces 2a and 2b including the predicted shape error calculated earlier, and the above-described design are performed. The wavefront aberration that appears in the transmitted wavefront of the light after passing through the null lens 6 is obtained by calculation. Also in this case, on the optical design software installed in the optical design apparatus, the expected shape error data of the lens surfaces 2a and 2b of the concave meniscus lens 2 is input, the wavefront aberration calculation program is started, and both lenses are started. A wavefront aberration (such as third-order spherical aberration) obtained by combining the error components of the surface is calculated. That is, on the optical design software, an optical system including the concave meniscus lens 2 and the null lens 10 shown in FIG. 4B is configured, and the wavefront aberration appearing in the transmitted wavefront is calculated based on the expected shape error of the concave meniscus lens 2. To do.

  Thereafter, in step ST6 of FIG. 1, the pass / fail of the concave meniscus lens 2 (mold press lens) molded using the lens mold 3 is evaluated based on the calculated wavefront aberration (expected wavefront aberration). Here, it is desirable to determine the wavefront aberration value standard as an evaluation criterion in consideration of the correlation with the mounting resolution evaluation result when the concave meniscus lens 2 is actually mounted as a combined lens. Such a wavefront aberration value standard may be stored in the memory of the optical design apparatus, and the calculated wavefront aberration may be compared with the standard value to evaluate pass / fail.

(Evaluation method of lens mold)
Next, a method for evaluating a lens mold using the above-described method for evaluating an aspheric mold press lens will be described.

  For example, in the lens mold 3 provided with the upper and lower pair of upper mold 4 and lower mold 5 shown in FIG. 3, even if the shape error of the lens surface molding surface of one mold is within the standard error, When the concave meniscus lens 2 is molded by combining these molds, the wavefront aberration of the concave meniscus lens 2 may exceed the allowable range. In other words, the shape error of the lens surfaces 2a and 2b of the concave meniscus lens 2 may exceed the allowable range. Therefore, in the case of such a pair of lens molds 3, it is desirable not to evaluate each lens mold individually but to evaluate their combination.

  For example, the lower molding die 5 is circulated along a circulation path at a constant pitch, and the heated glass material is supplied to the molding surface 5a of each lower molding die 5 at a predetermined position. In a mold press molding apparatus in which 4 is set in a lower mold and press molding is performed, a large number of lens molds 3 are used.

  In the case of such a mold press molding apparatus, after manufacturing a large number of upper molds 4 and a large number of lower molds 5, an arbitrary set of upper molds 4 and lower molds 5 is selected, and these lenses are selected. By measuring the shape error of the surface molding surface with Talysurf and evaluating the concave meniscus lens 2 to be molded in accordance with the process shown in FIG. 1, a defective lens is formed by the combination of the selected upper molding die 4 and lower molding die 5. It can be determined whether or not it is molded. By eliminating the combination of the upper mold 4 and the lower mold 5 in which the defective lens is molded, the lens mold 3 composed of the combination of the upper mold 4 and the lower mold 5 capable of molding a non-defective lens is selected. Can do.

It is process drawing which shows the procedure of the evaluation method of the mold press lens of this invention. (A) And (b) is explanatory drawing which shows two examples of a mold press lens. It is explanatory drawing which shows an example of the lens shaping die for shape | molding a mold press lens. (A) is a chart showing the relationship between the type of lens to be tested and the required number of null lenses, and (b) is a transmission type for measuring the wavefront aberration of the transmission wavefront of a concave meniscus lens using a planoconvex aspherical null lens. It is explanatory drawing which shows an optical system.

Explanation of symbols

1 Biconvex lens (Mold press lens)
2 Concave meniscus lens (mold press lens)
2a First lens surface 2b Second lens surface 3 Lens molding die 4 Upper molding die 4a First lens surface molding surface 5 Lower molding die 5a Second lens surface molding surface 6 Null lens 6a First lens surface (convex aspherical surface)
6b Second lens surface (plane)

Claims (5)

Produce a lens mold for molding mold press lenses,
Measuring the shape error of the first and second lens surface molding surfaces for molding the first and second lens surfaces of the mold press lens in the manufactured lens mold;
Based on the measured shape error of the first and second lens surface molding surfaces, calculate the expected shape error of the first and second lens surfaces of the mold press lens molded using the mold,
Designing a null lens for nulling wavefront aberration appearing in a transmitted wavefront of light after passing through the mold press lens having the first and second lens surfaces without a shape error,
Calculating an expected wavefront aberration appearing in a transmitted wavefront of light after passing through the mold press lens and the null lens having the first and second lens surfaces including the expected shape error;
A method for evaluating a mold press lens, wherein pass / fail of the mold press lens molded using the lens mold is evaluated based on the calculated expected wavefront aberration. In the evaluation method of the mold press lens according to claim 1,
An evaluation method for a mold press lens, wherein the null lens is designed and the predicted wavefront aberration is calculated using an optical design apparatus including a computer in which an optical design program and a wavefront aberration calculation program are installed. In the evaluation method of the mold press lens according to claim 1 or 2,
The mold press lens is characterized in that at least one lens surface is aspherical. In the evaluation method of the mold press lens according to any one of claims 1 to 3,
One of the lens surfaces of the null lens is a convex or concave aspherical surface, and the other lens surface is a flat surface. A method for evaluating a lens mold using the method for evaluating a mold press lens according to any one of claims 1 to 4,
A plurality of first lens molding dies having the first lens surface molding surface for molding the first lens surface of the mold press lens, and a second lens surface of the mold press lens for molding the second lens surface. Producing a plurality of second lens molding dies having the second lens surface molding surface;
For each of the lens molds composed of a combination of one of the first lens molds and one of the second lens molds, an evaluation is performed by the evaluation method of the mold press lens.
A method for evaluating a lens mold, comprising: evaluating a combination of the first lens mold and the second lens mold that has passed the evaluation result as an acceptable product as the lens mold.