JPH0610643B2 - Measuring method of lens axis tilt, etc. - Google Patents

Description

The present invention relates to a method for measuring the inclination of the axis of a lens, and more specifically, the inclination of the symmetry axis of the surface of an aspherical molded lens with respect to the optical axis of an optical system. , Eccentricity, etc. are optically measured.

BACKGROUND OF THE INVENTION The majority of lenses used in optical systems today have optical surfaces that are spherical. The point symmetry of the spherical surface of such a lens allows the positioning of the optical axes of these surfaces after they have been formed by simple mechanical methods (eg edging techniques). The symmetry of the spherical surface of such a lens makes the alignment of such a surface and the optical system relatively simple. This is because the only possible misalignment of the spherical surface is because it is due to eccentricity and can be corrected relatively easily.

An optical lens having an aspherical surface has a great optical advantage as compared with a spherical lens. For example, an aspherical lens can be designed so that spherical aberration and coma are not generated in the optical system. However, this aspherical lens is not yet widely used. One reason is
This means that it is difficult to manufacture a lens that has an aspherical surface that can be accurately positioned and is aligned (angled). This is because it was difficult to accurately position and align the axis of symmetry of the aspherical surface during manufacturing, testing, or final use of the aspherical lens.

Therefore, the only way to correctly position and align the aspheric surface involves measuring the exact shape of the aspheric surface (eg, with a mechanical needle or with an interferometer). Such measurements are inherently complex and time consuming to perform. Also, such measurements are often impossible to implement in some optics (due to space limitations). Therefore, other methods have been considered to accurately position and align the aspheric surface of the lens.

The present invention has been made in view of the above circumstances, and accurately positions and aligns the aspherical lens in the optical device to be used, and the inclination of the symmetry axis of the aspherical surface with respect to the optical axis of the optical system. It is an object to provide a method for optically measuring the eccentricity and the wedge angle of an aspherical lens.

(Means for Solving the Problem) The method of optically measuring the inclination of the symmetry axis of the surface of the aspherical molded lens with respect to the optical axis of the optical system according to the present invention is as follows: The step of molding a lens having a reference surface having a predetermined position and angle with respect to the step (b) directing the light directed to the optical axis of the optical system to the optical surface of the lens, and then performing (c) (1) caused by light reflected from the reference surface and light reflected by a reference surface arranged at a right angle to the optical axis of the optical system between the reference surface and the light source of the light. Interference pattern, or (2) a reflection angle when the light is reflected by the reference surface, or (3) a refraction angle when the light is refracted when passing through the reference surface And a step of observing.

Further, the method of optically measuring the eccentricity of the symmetry axis of the surface of the aspherical molded lens with respect to the optical axis of the optical system according to the present invention includes (a) a predetermined position and an angle with respect to the symmetry axis or the symmetry point of the optical surface. Performing a step of molding a lens having a reference surface having the final size and shape thereof, (b) directing light converging on the optical axis of the optical system to the optical surface of the lens, and then (c) (1) The light reflected by the reference surface and the light reflected by the reference surface whose rotation axis is located on the optical axis of the optical system between the reference surface and the light source of the light. Interference pattern, or (2) the reflection angle when the light is reflected by the reference surface,
Alternatively, (3) the step of observing the refraction angle when the light is refracted when passing through the reference surface, is included.

Further, the method of optically measuring the wedge angle of the aspherical molded lens according to the present invention includes (a) a reference plane having predetermined positions and angles with respect to the symmetry axis or the symmetry point of the two optical surfaces. Performing the step of shaping the lens into its final shape, (b) directing parallel light to the reference surface of the lens, and then (c) the interference caused by the light reflected at each reference surface. The step of observing a pattern comprises the following steps.

The aspherical molded lens used in the method of the present invention is a molded lens having at least one aspherical surface and at least one reference surface extending laterally to the axis of symmetry of the aspherical surface. In one embodiment, the aspherical lens has two aspherical surfaces and two reference planes on both sides in the longitudinal direction thereof, and the reference planes are disposed at substantially the same angle with respect to the axis of symmetry of the adjacent aspherical surface. Project in one direction. Therefore, these reference planes are substantially parallel. When viewed along the axis of symmetry of the aspherical surface, the two reference planes appear to substantially overlap. In this example, the angle between the axes of symmetry of the two aspheric surfaces of the lens, the wedge angle, is precisely determined by optical methods. As a result, the mutual position and angle of the two aspherical surfaces of the aspherical lens can be adjusted during the manufacturing process to give the aspherical surface the required position and angle.

According to the present invention, the position and angle of the axis of symmetry of the aspherical surface can be determined quickly, easily and accurately by conventional optical test techniques.

(Structure and Action of the Invention) The aspherical lens molded in the present invention is optically transparent glass or plastic (preferably glass).
And the like, which are conventionally known lens materials. The aspherical lenses are described in U.S. Pat. Nos. 2,410,616 and 3,900.
1 by a suitable lens manufacturing process such as the molding method described in US Pat. Nos. 328 and 4139677.
It is configured to have one or more aspherical surfaces and one or more reference surfaces according to the present invention.

The aspherical lens used in the present invention is a "Process To Mo" filed in the United States on Oct. 30, 1981.
ld Precision Glass Artic
It is preferably molded to its final size and shape by the method and apparatus described in s "(Application No. 316861).
Such a method and apparatus provides a lens of a particular size and shape with an element such as a reference plane having a predetermined position and angle with respect to other elements such as the axis of symmetry of an aspheric surface. Is configured to make. Thus, the method and apparatus can be used to transfer the geometry of the lens molding surface of the apparatus to the manufactured lens so that the lens is free of optical irregularities.

1 and 2 show a double-sided aspherical lens of the present invention.
10 is shown. The lens 10 has two aspherical surfaces 11 and 12 in front of and behind each of the lenses. Aspherical surface
The axis of symmetry of 11 and 12 (not shown) is the optical axis 13 of the lens 10.
Almost matches. Located on each side of each aspheric surface 11 and 12 are adjacent flat reference surfaces 14 and 15, respectively. The side edge of the reference surface 1415 has a smooth, longitudinally extending lens 10
Are connected by a cylindrical surface 16 of which the axis is substantially coincident with the optical axis 13 of the lens.

Each of the reference surfaces 14 and 15 of the lens 10 has its adjacent aspherical surface.
It projects laterally of each axis of symmetry of 11 and 12. By using the term "lateral" with respect to the reference plane of this invention,
The term means a direction that forms an acute angle or a right angle with the axis of symmetry of the aspherical surface, so that the reference plane has a precise predetermined position and angle. In order to perform optical measurement of the inclination and eccentricity of the symmetry axis of the aspherical surface and the wedge angle of the aspherical surface according to the present invention, a reference surface (eg, the reference surface 14
Alternatively, the use of 15) is preferred over a longitudinally extending reference surface (eg cylindrical surface 16). According to the invention, in order to determine the wedge angle of the lens 10, a) each of the reference surfaces 14 and 15 should be at substantially the same angle, preferably at right angles to the axis of symmetry of the adjacent aspherical surfaces 11 and 12. It is preferred that they project laterally and therefore the reference surfaces 14 and 15 are substantially parallel, and b) that the reference surfaces 14 and 15 substantially overlap when viewed along the axis of symmetry of the aspherical surfaces 11 and 12.

Each of the reference surfaces 14 and 15 preferably contacts its adjacent aspherical surface 11 and 12 and projects around the axis of symmetry of its adjacent aspherical surface, as shown in FIGS.

The inclination of the symmetry axis (and the optical axis 13 of the lens) of the front aspherical surface 11 of the lens 10 with respect to the optical axis of the optical system is determined by a predetermined light which is incident on the front reference surface 14 and is reflected from the reference surface 14 or transmitted therethrough. Can be precisely determined by the behavior of. This determination is made, for example, by (a) being parallel to the optical axis of the optical system,
The interference pattern caused by the light reflected from the front reference surface 14 and the light reflected by the flat reference surface located in front of the front reference surface 14 and arranged at right angles to the optical axis of the optical system. By observing, or (b) by observing the reflection angle when such parallel light is reflected from the front reference plane (14), or (c) such parallel light is detected by the front reference plane 14 ( And at the refraction angle as it is refracted as it passes through the rear reference plane 15). Any of the above observations also accurately show whether there is a misalignment of the front reference plane 14 of the lens 10 with the direction perpendicular to the optical axis of the optical system, and thus the lens 10 relative to the optical axis of the optical system. The corresponding tilt of the symmetry axis of the front aspheric surface 11 is shown.

The tilt of the axis of symmetry of the front aspherical surface 11 of the lens 10 of FIGS. 1 and 2 within the optical system is determined interferometrically by a Fizeau interferometer 20, as shown in FIG. Third
As shown, the interferometer 20 includes a monochromatic light source 21, such as a laser,
Pinhole 22, beam splitter 23, collimator lens
24 (focus on pinhole 22 and focus divergent light 25 from pinhole into parallel light 25 '), flat reference surface 26
(Located in front of the lens 10 and arranged at a right angle to the optical axis 27 of the interferometer 20 and coated with an antireflection film), and is incident on the reference surface 26 and the front reference surface 14 of the lens 10 at a substantially right angle. , Collimated light 25 'from the collimator lens 24 reflected from it
It comprises means 28, such as a pinhole, which allows the observer 29 to observe the interference pattern formed by the. To make this determination, the optical axis 27 of the interferometer 20 preferably coincides with the optical axis (not shown) of the optical system in which the lens 10 is used.

The interference pattern observed by the interferometer 20 from the front reference plane 14 of the lens 10 is the front aspherical surface 11 of the lens in the optical system used in order to optimize the performance of the lens in the optical system. It can be used to minimize the tilt of the axis of symmetry (and the optical axis 13 of the lens). In this regard,
The observed interference pattern can be used to minimize misalignment of the front reference plane 14 of the lens 10 from a direction perpendicular to the optical axis 27 of the interferometer 20 and is related to the optical axis of the interferometer 20. The tilt of the symmetry axis of the front aspherical surface 11 of the lens 10 can be minimized. Especially, the inclination of the symmetry axis of the front aspherical surface 11 with respect to the optical axis of the optical system used is determined by the interferometer.
A minimum number of lines of interference, preferably 0, is observed via means 28, as it is minimized by the alignment of 20 lenses 10.

The reference planes 14 and 15 in front of and behind the lens 10 are
It is used to precisely measure the wedge angle of an optical method. This measurement is carried out by using a device such as the Fizeau interferometer 20A shown diagrammatically in FIG. This Fizeau interferometer 20A is different from the Fizeau interferometer of FIG. 3 in that it does not have a flat reference surface in front of the lens 10, but has the same structure as the others. Fourth
The illustrated apparatus 20A emits collimated light 25A 'which is incident on and reflected by the reference surfaces 14 and 15 of the lens 10. Light if necessary
25A 'can be parallel to one of the axes of symmetry of aspherical surfaces 11 and 12 of lens 10 (no member tilt) as shown in FIG. 4, but this is not required. The angle between the nearly parallel reference planes 14 and 15 and the two aspheric surfaces of the lens
The corresponding angle between the axes of symmetry of 11 and 12, namely the wedge angle, is determined by the collimated light 25A 'in the front and rear reference planes 14 and 15 respectively.
It can be measured from the interference pattern generated between them. The wedge angle measured from the interference pattern can be used to adjust the angle of the lens 10 in the optical system in which the lens 10 is used to optimize lens performance within the optical system. The lens 10 is aligned in the optical system to be used, so that the angle between the optical axis of the optical system and each of the axes of symmetry of the two aspherical surfaces 11 and 12 is minimal. The wedge angle measured in this manner is used to adjust the process and equipment as the optical member 10 is manufactured to minimize any wedge angle or to provide the necessary (and possibly large) wedge angle. It is preferable to obtain it.

Shown in FIGS. 5 and 6 is another double-sided aspherical lens 30 according to the present invention. The lens 30 has two aspherical surfaces 31 and 32 in the front and rear, respectively. Aspherical surfaces 31 and 32
The axis of symmetry (not shown) substantially coincides with and constitutes the optical axis 33 in the longitudinal direction of the lens. A spherical surface 34 is located in front of the lens 30 adjacent to the front aspherical surface 31 (spherical surface 34).
Constitutes the reference surface for the aspherical surface 31). Lens 30
Located at the rear of the table is a flat reference surface 35 adjacent the rear aspheric surface 32, similar to the flat reference surface 15 adjacent the rear aspheric surface 12 of the lens 10 of FIG.

Each of the spherical surface 34 and the flat reference surface 35 projects laterally of the axis of symmetry of the aspheric surfaces 31 and 32 to which they are adjacent.

According to the invention, the symmetry point (not shown) of the spherical surface 34 of the lens 30 is the axis of symmetry (not shown) of the adjacent front aspherical surface 31.
It is preferably above. Sphere 34 is also the front aspheric surface
Adjacent to 31, is located about the axis of symmetry of the front aspheric surface of FIGS.

The spherical surface 34 of the lens 30 is the symmetry axis (and the optical axis of the lens) of the front aspherical surface 31 of the adjacent lens 30 with respect to the optical axis of the optical system.
33) is used to precisely measure the eccentricity, and the eccentricity is
It is measured from the behavior of a given light incident on the spherical surface 34 and reflected or transmitted by it. This measurement includes, for example, a) the light converged on the optical axis of the optical system, the light reflected by the spherical surface 34, and the spherical surface positioned in front of the spherical surface 34 and having its rotation axis on the optical axis of the optical system. Observing an interference pattern due to interference with the spherical light reflected by the reference surface, or b) observing a reflection angle or bending angle when such a convergent spherical light is reflected or transmitted by the spherical surface 34. Can be done by. Such an observation precisely shows whether or not there is a distance between the symmetry point of the spherical surface 34 of the lens 30 and the optical axis of the optical system. It indicates eccentricity with respect to the optical axis.

The eccentricity of the symmetry axis of the front aspherical surface 31 of the lens 30 shown in FIGS. 5 and 6 is, for example, a Fizeau interferometer schematically shown in FIG.
By using 20B, it can be measured by an interferometric method. The interferometer 20B shown in FIG. 7 is similar to the interferometer 20 shown in FIG. 3, and is a lens that uses a monochromatic light source 21B, a pinhole 22B, a beam splitter 23B, and divergent light 25B from the pinhole 22B as convergent light 25B '. It consists of 24B. The interferometer 20B shown in FIG. 7 is also located in front of the lens 30 and is interferometer 20B.
The concave reference surface 26B whose optical axis 27B and the rotation axis coincide with each other, and the reference surface 26B incident from the lens 24B 'and the spherical surface 34 of the lens 30.
Means 28B for the observer 29B to observe the interference pattern due to the convergent light 25B 'reflected by. When performing this measurement, the optical axis 27B of the interferometer 20B preferably coincides with the optical axis of the optical system (not shown) in which the lens 30 is arranged.

The interference pattern when observing the spherical surface 34 of the lens 30 with the interference system 20B is the aspherical surface in front of the lens 30 used in the optical system.
It is used to minimize the eccentricity of the 31 axis of symmetry (and the optical axis 33), which allows for maximum lens performance in the optical system. The observed interference pattern is the symmetry point of the spherical surface 34 of the lens 30 and the interferometer 20.
It is used to minimize the distance between the axes of rotation of the B reference surface 26B and minimizes the eccentricity of the axis of symmetry of the aspherical surface 31 in front of the lens 30 with respect to the optical axis 27B of the interferometer 20B. In particular, the eccentricity of the symmetry axis of the front aspherical surface 31 with respect to the optical axis 27B of the interferometer 20B is as follows: Or 2) Interferometer 20B lens 30
Can be minimized by aligning.

The flat reference surface 35 of the lens 30 can be used to precisely measure the tilt of the symmetry axis of the rear aspheric surface 32 adjacent to the optical axis of the optical system. This can be done in the same manner, for example, using the same interferometer 20 shown in FIG. 3 for measuring the tilt between the front reference surface 14 of the lens 10 and the front aspheric surface 11 of the lens 10.

According to the present invention, the inclination of the optical axis 13 of the lens 10 of FIGS. 1 and 2 with respect to the optical axis of the optical system is located on the side of the lens 10 and extends in the longitudinal direction along a cylindrical surface 16 Can be measured more accurately. The cylindrical surface 16 has a predetermined position and angle with respect to the axes of symmetry of the aspherical surfaces 11 and 12 of the lens 10 and constitutes the reference surface of the present invention.

The inclination of the optical axis 13 of the lens 10 with respect to the optical axis of the optical system can be precisely determined by the behavior of predetermined light that is incident on the cylindrical surface 16 and is reflected or transmitted through this surface. This determination is, for example, a) the cylindrical light that converges along the optical axis of the optical system and is reflected by the cylindrical surface 16 of the lens 10, and the axis in front of this cylindrical surface 16 is i) the light of the optical system. On-axis and ii) by observing an interference pattern formed by a cylindrical wave reflected by a cylindrical reference surface arranged at a right angle to the convergent light, or b) by this converging cylindrical light This can be done by observing the reflection angle or the refraction angle when reflected or transmitted through the ten cylindrical surfaces 16. Such observation is performed in the direction parallel to the optical axis of the optical system and the cylindrical surface 16 of the lens 10.
Shows whether or not there is a misalignment of the axes, and shows the corresponding tilt of the optical axis 13 of the lens 10 with respect to the optical axis of the optical system.

For example, a Fizeau interferometer 20C as shown in FIG. 8 can determine the tilt of the optical axis 13 with respect to the optical system in which the lens 10 is to be used, by an interferometric method. The interferometer of FIG.
20C is the first except that its optical axis is perpendicular to the optical axis of the optical system used and has a cylindrical reference surface 26C having that axis on the optical axis of the optical system used. It is similar to the interferometer 20 in FIG.

The interference pattern observed by the interferometer 20C on the cylindrical surface 16 of the lens 10 is the direction perpendicular to the optical axis of the interferometer 20C (and parallel to the optical axis of the optical system used), and the cylindrical surface 16
To minimize the misalignment and to minimize the tilt of the optical axis 13 of the lens 10 with respect to the optical axis of the optical system used. In particular, the optical axis 13 of the lens 10 with respect to the optical axis of the optical system used
The tilt of can be minimized by aligning the lens 10 in the interferometer 20C, and is preferably zero.
The number of interference lines is observed by the observation means 28C.

In the present invention, as described above, the double-sided aspherical lenses 10 and 30 have one or a plurality of reference surfaces on each aspherical surface of the lens. The aspherical lens of the present invention has one or more aspherical surfaces on the front part and / or the rear part of the lens, and, for example, as shown in FIGS. It is intended to have a reference surface either on the rear side or / or the side of the lens as shown in FIG. The reference surface of the present invention is provided on one side of the lens or around the aspherical surface in order to predetermine the precise predetermined position and angle between the plurality of aspherical surfaces to which it relates.

In the above description, the use of a Fizeau interferometer is mentioned as an example of an interferometric means for measuring the position and angle of the axis of symmetry of an aspherical lens with a reference surface according to the invention and the wedge angle of the aspherical lens. It was Suitable Fizeau interferometers include those manufactured by Zygo Corporation of Middletown, Connecticut, USA, which use a helium neon gas laser as the monochromatic light source. However, in the practice of this invention,
Other suitable means may be used to implement such interferometric measuring means.

From the above description, various advantages are found from the present invention and matters associated with the present invention, but various modifications can be made to the shape, structure and arrangement of the aspherical lens portion of the present invention, and Various modifications may be made to the steps of the process for measuring the position and angle of the aspheric lens symmetry axis according to the present invention, and the order of execution of the steps of this process may be modified. Therefore, the above description is merely the description of some embodiments, and various modifications and changes can be made without departing from the technical idea of the present invention and without diminishing the effects obtained from this. That is clear.

For example, the lens according to the invention can have one spherical surface in addition to the aspherical surface. In the present invention, the reference surface having a precise predetermined position and angle with respect to the symmetry point of the spherical surface can be provided on the spherical surface as an independent reference surface.

The front reference surface 14 and the rear reference surface 15 of the lens 10 shown in FIGS. 1 and 2 have predetermined precise positions with respect to the symmetry axes of the adjacent front and rear aspherical surfaces 11 and 12, respectively. It is possible to have a fine groove pattern having an angle. For example, the grooves can be concentric grooves, each of which is centered on the axis of symmetry of the adjacent aspheric surfaces 11 and 12. This groove can be used to measure the precise position and angle of the aspherical surfaces 11 and 12 of the lens 10. this is,
It is measured by the moire interference pattern, which is the behavior of light incident on this groove and reflected or transmitted.

Furthermore, the front reference plane 14 of the lens 10 of FIGS.
Can project rearward (as a continuation of the rearward curvature of the front spherical surface 11), and the rear reference surface 15 of the lens 10, which is preferably parallel to this front reference surface 14, can also project rearward. Alternatively, the front reference surface 14 can project forward and the parallel rear reference surface 15 can project forward (as a continuation of the forward curve of the rear aspherical surface 12). In either case, parallel front and rear reference planes 14 and 15 are useful for measuring tilt as well as wedge angle in lens 10 according to the present invention. Front and rear reference planes 14 and 15 if required
Can also project in opposite longitudinal directions, which are not parallel and are not useful for defining the wedge angle of the lens 10.

[Brief description of drawings]

FIG. 1 is a configuration side view of a double-sided aspherical lens used in the present invention. The lens has an optical aspherical surface on its front and rear surfaces, and has a pair of parallel flat reference surfaces that are located around this aspherical surface and serve as reference surfaces. FIG. 2 is a top view of the lens shown in FIG. 1, and FIG. 3 is a configuration diagram of the optical system, which shows a portion between the symmetry axis of the front aspherical surface of the lens of FIG. 1 and the optical axis of the optical system. The angle, or tilt, is accurately determined by the interference of light incident on and reflected from the reference plane in front of the lens. FIG. 4 is a block diagram of an optical system, in which the wedge angles at the time of alignment of the front and rear aspherical surfaces of the lens of FIG. 1 are incident on the reference surfaces in front of and behind the lens and are reflected. Accurately determined from the interference of light. FIG. 5 is a configuration side view of another double-sided aspherical lens used in the present invention. The lens shown in FIG. 5 is similar to the lens of FIG. 1 except that the front reference plane of the lens of FIG. 1 has been replaced by a spherical surface in the lens of FIG. This spherical surface is located around the front aspherical surface of the lens of FIG. 5 and constitutes the reference surface. Figure 6 shows
6 is a top view of the lens of FIG. 5. FIG. FIG. 7 is a plan view of the optical system. The distance between the symmetry axis of the front aspherical surface of the lens of FIG. 5 and the optical axis of the optical system, that is, decentering, is incident on the front spherical surface of the lens and is reflected. Accurately determined from the interference of light. FIG. 8 is a plan view of the optical system, and the inclination of the optical axis of the lens in FIG. 1 with respect to an axis perpendicular to the optical axis of the optical system is incident on the cylindrical surface of the side surface of the lens and reflected. It can be accurately determined from the interference of light. 10,30 …… Aspherical lens 11,12 …… Aspherical surface, 13 …… Optical axis 14,15 …… Reference plane, 16 …… Cylinder surface 20,20A, 20B, 20C …… Interferometer 21,21A, 21B , 21C …… Monochromatic light source 22, 22A, 22B, 22C …… Pinhole 24, 24A, 24B, 24C …… Collimating lens 25, 25A, 25B, 25C …… Divergent light 26, 26B, 26C …… Reference surface 34… … Spherical

Claims (1)

[Claims] 1. A method for optically measuring an inclination of a symmetry axis of a surface of an aspherical molded lens with respect to an optical axis of an optical system, comprising: (a) a predetermined position and an angle with respect to the symmetry axis or a symmetry point of an optical surface. Molding a lens with a reference surface having a final size and shape thereof, (b) directing light directed to the optical axis of the optical system toward the optical surface of the lens, and (c) (1) An interference pattern generated by the light reflected from the reference surface and the light reflected by the reference surface arranged at a right angle to the optical axis of the optical system between the reference surface and the light source of the light, or (2) A method of observing a reflection angle when the light is reflected by the reference surface, or (3) a refraction angle when the light is refracted when passing through the reference surface. . (2) In a method of optically measuring the eccentricity of the symmetry axis of the surface of the aspherical molded lens with respect to the optical axis of the optical system, (a) having a predetermined position and angle with respect to the symmetry axis or the symmetry point of the optical surface. Molding a lens having a reference surface into its final size and shape, (b) directing light converging on the optical axis of the optical system toward the optical surface of the lens, and (c) (1) the reference surface. Interference pattern generated by the light reflected from the light and the light reflected by the reference surface whose rotation axis is arranged on the optical axis of the optical system between the reference surface and the light source of the light, or ( 2) A method of observing a reflection angle when the light is reflected by the reference surface, or (3) a refraction angle when the light is refracted when passing through the reference surface. (3) In a method for optically measuring the wedge angle of an aspherical molded lens, (a) a lens having a reference surface having a predetermined position and an angle with respect to the symmetry axis or symmetry point of two optical surfaces, respectively. Shaping into its final shape, (b) directing parallel light to the reference plane of the lens, and (c) observing the interference pattern caused by the light reflected at the angular reference plane. And how to.