MXPA00000886A - Image quality mapper for progressive eyeglasses - Google Patents

Abstract

An instrument and method for optical testing of an eyeglass lens, including progressive addition lenses, to obtain image quality measurements includes an illumination system for presenting a beam of light to a test lens, a test lens positioning system for rotating the test lens so that different areas on the lens are illuminated, a zoom lens for focusing the beam at a constant effective focal length, a detection system for recording and measuring image quality of the test lens, and an alignment boom for conveying the zoom lens and the detection system such that the optical axis remains aligned with the beam exiting the test lens. The instrument is fully automated and capable of obtaining measurements of the power, astigmatism, prism and modulation transfer function at various locations on the surface of the lens.

Description

INSTRUMENT FOR THE OBTAINING OF MAPS AND IMAGE QUALITY GRAPHICS FOR ADEQUES OF PROGRESSIVE ADHESIVE CROSS REFERENCE WITH RELATED REQUESTS This application claims the priority of the provisional patent application No. 60 / 053,824 filed July 24, 1997, the material of which is incorporated herein by reference.

FIELD OF THE INVENTION The present invention relates to optical test instruments and very particularly to an automated optical test instrument capable of measuring the image quality on the surface of a lens for progressive addition glasses.

BACKGROUND OF THE INVENTION The optical design of a progressive addition lens (PAL) lens comprises changing the magnification evenly (inverse focal length) between the different regions of the lens, giving the lens an image quality that changes over the lens surface. This change introduces large amounts of astigmatism along with significant amounts of other aberrations. In this way, a PAL, even if it is manufactured to reproduce the optical design perfectly, will have significant variations in the image quality through the lens. In addition, glasses in general have defects associated with their manufacture, such as deviation from their design curvatures, variations in the refractive index, bubbles, inclusions, and scratches that can also alter the image quality. Because these manufacturing defects are difficult to model, it is necessary to be able to measure them. With the increasing popularity of PALs, there is a need for an optical test apparatus that measures the variation in image quality of different designs to provide an objective comparison. Currently, measurements of magnification, astigmatism and prism can be performed manually at certain sites on the lens (generally with a diameter of 3 mm under-aperture) using commercially available lenses, also known as focometers. The measurement of the resolution is usually done using a test equipment in the work table through the inspection of an image formed by a PAL of a white bar object of the Air Force at infinity using a microscope. Although these instruments and methods provide basic information about the PAL, they can not provide comprehensible accurate image quality information that would be very useful for the PAL designer and / or manufacturer. Furthermore, the known instruments and methods do not allow to automatically obtain maps of the magnification, astigmatism, prism and modulation transfer function (MTF) over the entire surface of a PAL.

As a consequence, there is a need for an improved optical test instrument, and particularly, an optical test instrument that allows to automatically obtain maps of magnification, astigmatism, prism and MTF on the total surface of a PAL.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides an improved instrument and method for measuring the image quality of lenses for eyeglasses, including PALs, designed to counteract the disadvantages associated with the prior art. In a preferred embodiment, an instrument for obtaining fully automated goggle image quality maps and graphs is provided for measuring magnification, astigmatism, prism and MTF at various sites through the surface of a spectacle lens. The instrument includes a lighting system to present a beam of collimated light of appropriate size to a test lens, a positioning system to rotate the test lens and that the different areas on the lenses are illuminated, a variable focus lens to focus the beam at a constant effective focal length of the system once it passes through a particular sub-aperture of the test lens, a detection system for recording and measuring the image quality of the lens, and an alignment boom for transporting the lens. variable focus lens and detection system so that the optical axis of the focus / detection system remains aligned with the beam that comes out of the test lens.

At a certain sub-aperture on the test lens the increase in best focus, magnitude and direction of astigmatism, magnitude and direction of prism and MTF of best focus are measured. The MTF is obtained through a Fourier transform of the measured point distribution function (PSF). Thus, a map of a lens is constructed by the lens test in a plurality of subaverage sites. Graphs of surface, contour, and text of magnification, astigmatism, prism, and MTF are made, as well as astigmatism and prism vector graphics.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features and advantages of the present invention will be apparent as best understood with reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein: Figure 1 is a schematic view of the procurement instrument of maps and image quality graphics for eyeglasses (EIQM) according to the present invention; Figure 2 is a graph illustrating the radial variance against the increase of the test lens, generated by the EIQM of Figure 1 and used to measure the best focus gain; Figure 3 is a graph that exemplifies the ratio of the maximum image width to the minimum image width versus the magnification of the test lens, generated by the E1QM of Figure 1 and used to measure the magnitude of astigmatism; Figure 4 is a schematic view illustrating the two axes of rotation of the mounting / positioning system of the test lens, the two axes of rotation of the alignment boom, and the two linear movements of the variable focus lenses; Figure 5 is a schematic view of a PAL illustrating the plurality of sites or sub-openings on the lenses in which the image quality measurements are made using the EIQM of Figure 1; Figure 6A is a series of schematic views of a test lens under rotation, illustrating the deflection of the beam that results when the back and front surfaces of a PAL are not parallel to each other; Figure 6B is a series of schematic views of a test lens under rotation, similar to that of Figure 6A, illustrating the use of a boom assembly in the EIQM of Figure 1, whose point of rotation is on the surface back of the PAL and carrying the variable focus lens and detection system; Figure 7 is a graph of the position of the variable focus lens against the magnification of the test lens for the EIQM of Figure 1, for each of the lenses comprising the variable focus lenses; Figures 8 and 9 are examples of images through focus of a minimal astigmatic region and an astigmatic region of the PAL, respectively, generated by the EIQM of Figure 1; Figure 10 is a schematic view of a PAL, illustrating the PSF on the surface of the lens at several sites; Figures 11 A, 11 B, 11 C, 11 D, 11 E and 11 F, respectively, are a contour plot of the best focus magnification, a contour plot of the magnitude of astigmatism, a vector graph of the angle of astigmatism, a contour plot of the magnitude of the prism, a vector graph of the angle of the prism, and a contour plot of the MTF normalized to 20/20 for LENS A, generated by the EIQM of Figure 1; Figures 12A, 12B, 12C, 12D, 12E and 12F, respectively, are a contour plot of the best focus magnification, a contour plot of the astigmatism magnitude, a vector graph of the astigmatism angle, a contour plot of the magnitude of the prism, a vector graph of the angle of the prism, and a contour graph of the MTF normalized to 20/20 for LENS B, generated by the EIQM of Figure 1; Figures 13A and 13B are complete graphs of the MTF of different sub-apertures of LENS A, generated by the EIQM of Figure 1; and Figures 14A and 14B are, respectively, a three-dimensional map of the MTF normalized to 20/20, and a numerical graph of MTF normalized to 20/20 against the location of subaverage, generated by the EIQM of Figure 1.

DETAILED DESCRIPTION OF THE INVENTION With reference to Figure 1, the optical test instrument 10 or the instrument for obtaining image maps and graphics for eyeglasses (EIQM) according to the present invention generally includes: (a) a lighting system 12 for presenting a beam of collimated light of appropriate size to a test lens; (b) a mounting / positioning system 14 of a test lens capable of rotating the test lens so that the different areas on the lens are illuminated; (c) a variable focus lens 16 for focusing the beam at a constant effective focal length of the system (EFL) once it has passed through a particular under-aperture of the test lens; (d) a detection system 18 for recording and measuring the image quality of the lens; and (e) an alignment boom 20 for transporting the variable focus lens and detection system so that the optical axis of the focusing / detection system remains aligned with the beam exiting the test lens. Additionally, because one of the advantages of the present invention is that the EIQM is fully automated, the instrument 10 is preferably coupled to a microprocessor-controlled computer system 22 to control the quality mapping and graphing instrument. of image and analyze the obtained data. Each of the components of the EIQM is described in more detail below. First, however, a brief description of the types of image quality measurements available using the system is provided.

I. Image Quality Measurements A. Improved Focus Increase The increase of a PAL is determined from the position of the variable focus lens that produces the best image quality. During the test, the variable focus lens moves through a series of positions and the image quality is measured at each position. A useful indication of the image quality is the dot distribution function produced by a lens. 1. Point distribution function One of the unique characteristics of the EIQM is the ability to measure the dot distribution function (PSF) produced by a sub-aperture of the test lens. The PSF is a measurement of the light intensity distribution. In general, a lower PSF indicates a better image quality than a larger PSF, because a larger PSF results in higher aberrations in the lens. A useful measure of the size of a PSF is the radial variance, which describes the size of the light distribution around its average position. The following procedure describes how the radial variance can be calculated. First, there is the centroid of a certain image. Radial variance is a measure of how closely the light is distributed around the centroid as a function of the radial distance from the centroid. This quantity, or rather, its average square root (RMS), is widely used in both the lens design and the lens test to find the best focus location. After the radial variance is found for each plurality of images taken through the focus for a certain sub-aperture on the test lens, a polynomial is fitted to the data, and the increase in the variable focus lens is recorded where the radial variance It is minimal. This increase is the best focus increase, and this is when the final PSF is recorded. A plot of the radial variance against the increase is illustrated in Figure 2. A minimum in the radial variance can be clearly seen at around 0.35 D. The analysis program used in the EIQM has adjusted a curve in the data and calculated the minimum to make it 0.3449141 D. This is the best approach increase.

B. Astigmatism The EIQM is also capable of performing astigmatism measurements for PALs, both in terms of magnitude and in terms of orientation. When there is significant astigmatism in a particular site on the test lens, two line images will be formed, one in one magnification fix and the other in another. The difference in magnification between the two line images is defined as the magnitude of astigmatism. The angle of the line image of least magnification gives the angle, or axis, of astigmatism. To determine the locations of the line images, a measurement of the width of the image in one direction is used, instead of the two-dimensional radial variance used to find the best approach. If the width of the single-dimension image along a line through the centroid of an image is measured as a function of the angular orientation of the line, a maximum width will be obtained (along the line image) ) and a minimum width (through the line image). The ratio of minimum width to maximum width for the plurality of images through focus taken at a given sub-aperture on a lens can be plotted against magnification, as seen in Figure 3. The ratio varies from 0 for a line image, to 1 for a circular image. Therefore, when there is astigmatism, the two locations on the graph where the ratio approaches 0 correspond to the two line sources. From these two locations, the magnitude of astigmatism can be calculated using the increasing difference. With reference to figure 3, it is possible to observe the two minima corresponding to two foci of different lines. The difference between them is around 0.35 D. This is the magnitude of astigmatism. The analysis programs used in the EIQM adjust a curve to the data around each minimum to more accurately determine astigmatism. For pure astigmatism, the best focus gain is in between the two line foci. However, when other aberrations occur (for example, spherical aberrations, coma, etc.), the location of the best focus increase may not be exactly at the midpoint and should be found using the minimum radial variance presented previously.

C. Prism Another important characteristic of the PAL that the EIQM is able to measure is the prism of the lens. The lens prism is a measure of how much a beam deviates from its original path after passing through a certain point on the lens. The traditional measurement unit is the prism diopter, which is defined as the lateral displacement of the beam, measured in centimeters, from its original location on a surface that is 1 m behind the lens. In other words, 1 diopter of prism is equal to 10 milliradians of angular deviation. The EIQM determines the prism at any test site by recording the angular position of the boom with respect to the axis or zero position (see Figure 6B). D. Modulation transfer function Another unique aspect of the EIQM is the ability to perform modulation transfer function (MTF) measurements. Once the EIQM has measured the PSF produced by a lens as described above, a Fourier transform is performed on the PSF to obtain the MTF. The MTF is the magnitude of the Fourier transform of the 2-dimensional PSF. The MTF is usually plotted against spatial frequency in cycles / mm. The MTF can also be plotted against angular frequency in cycles / mrad. In a focusing system, this is done by multiplying the spatial frequency values by the focal length of the system. In one embodiment of the invention, the EIQM graphs the MTF of the lens against the angular frequency, because visual acuity is generally expressed in angular units. To make it easier to evaluate the MTF of a given lens, graphs of several slices are made through the center of the PSF. Generally, four slices are drawn to different spatial orientations or angles, such as 0, 45, 90 and 135 degrees. Using the procedure described above, the MTF is obtained simultaneously for all spatial orientations and all spatial frequencies up to the Nyquist limit of the detector used to register the PSF. For example, in a prototype of the EIQM, the detectors have a width of 19 microns, so that the largest spatial frequency detected is 1 / (2 x 0.019 mm) = 26.3 cic / mm. With a focal length of the system of 600 mm, this translates to 0.6m x 26.3 cic / mm = 15.8 cic / mrad. Since the best thing that the lens with a 5 mm pupil can do is D /? = 5mm / 543nm = 9.2 cic / mrad, the detector is more than adequate to register all spatial or angular frequencies. II. The EIQM lumination system begins with an illumination system 12 designed to present a collimated beam of appropriate size to test lens 24 from a light source 26. In one embodiment of the EIQM, a laser green HeNe 543 is used nm as the source and spatially filtered using a 5 micron orifice. A non-limiting example of a laser suitable for use in the EIQM is a 543 nm green linear-polarized He-Ne laser of 1 mW available from Melles Griot, Irvine, California. It should be noted that a broadband source such as a white light source (eg, a quartz halogen lamp) or a light emitting diode (eg, a green LED) can alternatively be used as the light source. In those alternative embodiments, a narrow-band interference filter (e.g., a 550 nm filter) may be used to select the test wavelength. Using a laser as the light source offers certain advantages over a wide band light source, including easier alignment, higher magnification, and a more uniform beam. However, because the laser produces so much magnification, a neutral density filter is preferably placed in the lighting system in order to attenuate the beam and avoid saturation of the detection system. During the initial EIQM test, the spectral bandwidth of the light source was originally set at 550 ± 10 nm using a wide band light source and a filter, because most of the tests with glasses are done at or near 550 nm in order to provide consistency throughout the field. Subsequently, it was decided to change to the 543 nm laser. A collimator 28 is used to present a collimated beam to the test lens. In one embodiment, the collimator includes a 20x30 microscope objective, followed by a hole, and then an achromatic lens 32. The achromatic lens 32 used in a prototype of the EIQM is an achromatic doublet which is a combination of a positive element of low dispersion and a high dispersion negative element, cemented together to form a positive lens that essentially does not present dispersion in the visible spectrum. In addition to exhibiting less chromatic aberration, achromatic doublets present significantly lower amounts of other aberrations (spherical aberration, coma, astigmatism, etc.) than singlet ones. However, those skilled in the art should know that another lens, such as an imperfect spherical singlet or an air-separated doublet, can alternatively be used for collimation. Suitable components for the collimator described above are available from Newport, in Irvine California and Splinder-Hoyer, in Milford, Massachusetts. The diameter of the collimated beam is fixed using an adjustable aperture 34. For example, the beam can be fixed using one of four openings (2,3,5 and 7mm) on a slide plate. These beam diameters cover the typical scale of pupil sizes for the human eye under different lighting conditions. Tests with smaller pupil diameters can be performed to simulate bright view conditions or simply to obtain an image quality graph in greater detail through the test lens. Testing with larger pupil diameters will simulate darker conditions. Alternatively, an adjustable or adjustable aperture wheel can be used in place of the adjustable aperture plate to fix the beam diameter. III. Mounting system / positioning of the test lens. The test lens 24 after the lighting system is supported by a mounting / positioning system 14, and illuminated by the collimated beam. A primary objective of the EIQM is to model the manner in which the eyeglass lens is used by the human eye. The human eye has a center of rotation, and as the eye rotates, the light that passes through the lens for eyeglasses and the pupil form a series of beams that revolve around the center of rotation of the eye. To simulate this, the mounting / positioning system is designed to rotate the lens around a point of rotation 35 behind the back surface of the test lens. In a preferred embodiment, a radius of 27 mm is used for the rotation of the test lens. The radius of 27 mm was selected because it is consistently used in the relevant literature as an average distance between the center of rotation of the eye and the posterior vertex of the eyeglass lens; however, the EIQM is capable of making measurements with a varying rotation distance. To allow this rotation, a mounted lens 36 is coupled to a two-axis turntable system used to position the test lens so that the different areas on the lens are illuminated for measurement. In a preferred embodiment, the two-axis turntable system comprises two motorized turntables. Suitable low capacity motorized rotating platforms are available from Velmex in Bloomfield, New York. The two-axis turntable system is designed so that, if the z-axis is the optical axis, the test lens is able to rotate around a line parallel to the x-axis and a line parallel to the y-axis in order to simulate the human eye as described above. In Figure 4, the arrows 40, 42 indicate the rotation of two lens axes. In an EIQM modality, a three-projection auto-centered lens holder is used for lens assembly (the test lenses typically have no edge and have a diameter of about 76 mm). An adjustment screw is used in the assembly to prevent the projections from exerting excessive force on the lens. A self-centering lens assembly of three projections of 80 mm diameter is available from Melles Griot in Irvine, California. The two-axis turntable system for the test lens mounting / positioning system is used to sequentially place the test lenses in a predetermined list of sites or sub-slots on the test lens to perform image quality measurements. The specific sites on the test lenses are determined by the properties of the lens that will be tested, the size of the test beam, and the desired information on the test lens. For example, with a typical PAL and a 5 mm diameter test beam, the EIQM used 103 measurement sites that are spaced more roughly in the upper distance zone and more finely around the transition and aggregation zones (Figure 5). ). The list of lens positions is simply a list of angles (a horizontal angle and a vertical angle for each position) provided to the computer. The angles define how the two-axis turntable system 38 should rotate around the eye's rotation point for each position. At each lens position, the magnification, astigmatism (magnitude and angle), prism (magnitude and angle and MTF are calculated and used to measure the image quality on the lens.) When using a 3mm diameter test beam, it is convenient to increase the total number of measurement points (ie to decrease the space between the adjacent points) in order to obtain better maps of the lenses, in any case, the space between the measurement points should preferably be fixed so that the traces of the beam The above procedure is completely automatic and controlled by the EIQM computer 22. The two rotation axes for the test lens are motorized with limit detection switches and controlled by the computer. Lens positions where the tests will be performed are loaded into the computer.The computer directs the motorized turntable system 38 to position the objects sequentially in each of the specified positions so that appropriate measurements can be made before the lens is rotated to the next position. IV. Gable alignment One of the main problems occurs when a PAL is rotated in the manner described above. With reference to Figure 6A, the test beam generally does not impinge on the anterior surface of the PAL. As the lens under test moves, the test beam is deflected to the back surface of the PAL and swept by a significant angle as it exits the lens. In other words, the incident collimated beam 37 and the refracted beam through the lens under test 39 are not parallel to each other. The EIQM counteracts this problem by rotating the focusing system of the lens / detector on a boom around the point of deflection of the beam 41 on the test lens (Figure 4). In other words, both the variable focus lens system and the detector system are attached to the boom and rotate together around the test lens so that the light transmitted through the lens under test is transmitted along, or near the axis of the lens. variable focus lens and be incident close to the middle part of the detection system. After the test lens moves to a new measurement point, the boom is rotated until the image refocuses on the detector. To allow the focusing / detector system to align with and focus on the beam emerging from the test lens, the alignment boom is coupled to a two-axis turntable system. In a preferred embodiment, the two-axis turntable system comprises two motorized turntables. Suitable high-capacity motorized rotating platforms are available at Velmex in Bloomfield, New York. One of the challenges in designing the boom system is that vibration-free and stable movement over large angular trajectories is required. Most of the boom structure was made from aluminum to reduce weight, with steel brackets used to attach the boom to the rotating platforms. Due to the load of relatively heavy brackets, large commercial rotating platforms were selected for the two axes of rotation of the boom. Additionally, a counter weight was designed to protect the bearings on the rotating lifting platform against excessive wear due to excessive loading. In Figure 4, the arrows 46, 48 indicate the two axes of rotation of the boom. As described above, the operation of the boom system is completely automated and controlled by computer 22 of the EIQM. The two axes of rotation for the boom are motorized with limit detection switches and controlled by the computer. Once the test lens rotates from one measurement point to the next, the boom is moved by the motorized two-axis turntable system 44 to re-center the image on the detection system. Sometimes, particularly with high magnification lenses, the beam will move completely away from the active surface of the detection system as the lens moves to the next measurement point. To avoid this, it will be necessary to follow the beam. This refers to the practice of moving only part of the trajectory to the next measurement point, stopping, adjusting the boom to re-center the image, and then continuing until the next measurement point is reached without losing the beam. For the lenses that have been tested with the EIQM, only two steps were needed between any two measurement points; however, for high-magnification lenses more steps may be needed to avoid losing the beam. It is possible to use other means to solve the problem of deflection of the beam and replace the boom system. For example, an adjustable prism can be placed directly behind the lens to return the beam to its original axis, or a variable focus lens with a wide field of view can be used to capture the outgoing beam without the need to move the detection system .

V. Variable focus lens The measurement of image quality is also complicated because PALs have a spatially variable magnification or focal length. That is, different parts of the lens focus at different distances from the progressive lens. In addition, some test lenses may have negative magnifications. Therefore, an additional optical system is used to provide light to the focus. Although the problem of varying the gain could be counteracted by using an adjustable translation system to move the detection system along the optical system and focus the image during the test, this is a costly and complex solution. In addition, if the PAL increase varies but the increase in the variable focus lens is set, then the effective focal length (EFL) of the optical system consisting of the PAL and the variable focus lens also vary. The size of a PSF for a given number of aberrations varies in proportion to the EFL system. Therefore, if the EFL system varies, it becomes difficult to directly compare the PSFs of several sites on the lens. To solve this problem, a single variable focus lens is designed to focus the beam on the detector system to a constant EFL system. This allows the detection system to be placed at a fixed distance from the PAL. Additionally, because the EFL system remains constant for any test location on the PAL, the scale of the PSFs for direct comparison is avoided. In a preferred embodiment, the slow variable focus includes two elements, a positive achromatic 50 followed by a biconcave singlet 52.

Suitable elements for variable focus lenses, including an 80 mm EFL achromatic doublet and a 20 mm EFL biconcave lens, are available from Spindler-Hoyer in Milford, Massachusetts. Additionally, the variable focus lens includes two motorized linear translation platforms mounted on the boom. The anterior achromatic lens of the variable focus lens is coupled with a first, longer platform, while the rear biconcave lens engages a second shorter platform, which in turn is coupled with the longer platform. This arrangement provides the adjustment of axial spacing between the PAL and the achromatic, and between the achromatic and the biconcave lens independently, so that the EFL system is constant to vary the PAL increases. In other words, the linear platforms allow the two elements of the variable focus lens to move along the optical axis through their centers as the focus varies, to keep the EFL system constant. Suitable motorized linear translation platforms are available from Velmex in Bloomfield, New York. In a preferred embodiment, the variable focus lens is used to focus the beam on the detection system to a constant EFL system of 605 mm. This focal length produces a limited diffraction PSF that is large enough for accurate sampling by the detection system. The variable focus lens used in the EIQM can accommodate any increase in PAL on the scale of -0.5 to +2.8 diopters. The variable focus system was designed in CodeV ™, by Optical Research Associates, Pasadena, California, optimizing the axial locations of the two variable focus lenses for a series of paraxial lenses of different magnifications located at the position of the test lens so that the complete EFL system remains at 605 mm with good image quality (in an image plane fixed with respect to the PAL). Thirteen magnifications were used in the lens (giving 13 different focus positions) to obtain sufficient data to adjust a high order polynomial in the individual trajectories of the variable focus lenses. The trajectories along which these variable focus lenses move with respect to the test lens are not linear, as shown in Figure 7. In Figure 4, arrows 58 and 60 indicate the linear translation of the variable focus lens and its individual elements. As described above, the operation of the variable focus lens is fully automatic and controlled by computer 22 of the EIQM. The two linear translation axes for the variable focus lens are motorized with limit detection switches and controlled by the computer. Once the boom rotates to bring the optical axis of the variable focus lens substantially parallel with the light beam exiting the test lens, the variable focus lens moves through a plurality of assigned test positions for each subarea over the lens, and the image quality is measured by the detection system. Those skilled in the art will understand that it is possible to have other lens designs for the variable focus system. For example, currently a three-element variable focus lens with a higher magnification scale is being developed for the EIQM. SAW. Detection system Different methods and detection systems can be used with the EIQM to measure the image quality. In a preferred embodiment, the detection system includes a camera 62 for measuring the intensity distribution of light, commonly referred to as the PSF. The camera used in the detection system is preferably a load-coupled device (CCD) camera, which is made of a two-dimensional array of pixels or detectors. The true PSF of an optical system is a continuous two-dimensional distribution of light intensity. However, when a CCD is used to measure the PSF, intensity values of a two-dimensional arrangement are obtained, one for each pixel. The spacing and size of the pixels used to test the PSF should be taken into account when performing calculations on the PSF, such as those used to obtain the MTF. Another type of detector that can be used is a charge injection device (CID). The main requirements of the disposition detector are that they have very low noise and a large dynamic scale so that the fine characteristics of the PSF can be seen. An accurate PSF leads to an exact MTF. In a preferred embodiment, a 512x512, 14-bit cooled CCD camera is used with the EIQM. A CCD camera for use in the EIQM is available from Photometrics in Tuscon, Arizona. In another embodiment, the detection system is a scrolling knife edge in front of a single detector element for measuring the line distribution function (LSF) of an image. The LSF provides a measurement of the width of the image along an axis. Single-element detectors, such as silicon photodiode, photomultiplier tubes, thermoelectric detectors, and thermopile detectors have a single detection surface with only one output, not an array of detectors such as the CCD, and, by themselves, do not the spatial distribution of an image. Therefore, a blade edge, slot, or hole should move through the image in front of said single element detectors while the output is tested to be able to determine the spatial distribution of the light. In addition, the MTF for a single orientation but at all spatial frequencies can be obtained from a Fourier transform of the LSF. Generally, the scrolling knife edge test should be repeated for various orientations (eg 0, 45, 90 and 135 degrees) of the knife edge in the transverse plane to obtain data representative of the image quality. The best approach can be localized by repeating a series of four measurements of the LSF as a fixation of planes along the optical axis, and locating the plane where the average width of the LSF is brought to the minimum. The same data can be used to determine the magnitude and orientation of astigmatism. In another embodiment, the detection system includes an interferometer capable of measuring the image quality associated with a focus near the beam, such as a shear interfering interferometer or a Smartt dot diffraction interferometer (PDI). These interferometers measure the aberration of the wave front associated with an image by interfering with two wave fronts derived from the same light source. From the measurement of aberration of the wavefront, the average square root (RMS) of aberration of the wave front can be determined. The best approach can be determined by finding the plane where the aberration RMS of the wave front is minimized. In a preferred embodiment, all components of the EIQM are mounted on an aluminum base plate. A light-tight black plexiglass cover is designed to cover the system during operation. At the top of the cover is an access panel that provides access to the test lenses. Vile. Calibration of the EIQM After assembling and aligning the system, the EIQM must be calibrated. For that purpose, after the initial assembly and alignment system, the EIQM was verified for measured magnification, image quality / MTF, image centering, and EFL system through the focus scale using a series of high laboratory lenses. quality. The measured increases were around 1% of the certified values, the images were limited to diffraction, and remained centered through the focus for each lens within about ± 20 pixels, and the EFL system remained constant at around ± 5 mm The EFL of the system was measured through the focus scale using a 300 line / inch grid placed before the calibration lenses. The separation of the orders of 0 and ± 1 on the CCD was used to calculate the EFL.

Then the instrument was checked for measured astigmatism. Two single vision lenses with 1.0 D of determined astigmatism were used. The astigmatism at the geometric center of each lens was first measured with a workbench test of lens quality at an average of ± 0.05 D. The astigmatism values measured by the EIQM were within ± 0.1 D of the calibrated values. The PSF / MTF of the instrument were taken, without placing the test lenses and the focus was set to 0 D, for all the bin fixations (1, 2, 4, &10) (see Section VIII). It was found that the instrument was limited to diffraction for "bin" factors of 1 & 2. The "aliasing" of the MTF measures for the "bin" factors of 4 & 10 coincided with those predicted by the theory. However, using the "bin" selection rules, the cutoff frequency for any image must be less than the "aliasing" frequency for the "binning" used. The above calibration procedure is preferably performed on a periodic basis to ensure continuous accuracy of the instrument. VIII. Illustrative test procedure using the EIQM The uncut test lenses are received with marks indicating the sites of the optical center, the zone of aggregation or reading, as well as the appropriate horizontal orientation of the lens. Using these marks, a series of alignment marks are made on the edge of the lens so that fabrication marks can be removed from the face of the lens. Then the lens is mounted on the EIQM in its normal orientation using the edge marks as a guide.

The desired test opening diameter is set. The cover closes and the control program of the main instrument is run. The first step in the program is to initialize all the platforms. Limit switches are used to house the platforms, and then the PAL is fixed with the first test point (at the geometric center of the lens), the focus system is set at -0.5 D, and the boom is adjusted to center the image in the CCD. In each of these test points or subartars, 20 images are taken, equally spaced on the scale of -0.5 to + 2.8D of the focusing optics. For each of the acquired focus images (see figures 8 and 9 for example), the following parameters are recorded or calculated: the increase corresponding to the position of the focus, the location of the centroid of the image, the radial variance of the image , the widths of the image along and through a line adjusted to the image (for measurement of astigmatism), the line angle of the image, the maximum value of the pixel, and the sum of all the pixel values. The best focus location is calculated from the radial variances by focus. A parabola is fitted to the data surrounding the minimum radial variance of the 20 images measured through focus (see figure 2). The minimum of this adjusted curve will then be the best approach (in diopters) for this subaverage. The focusing system moves to this position, the magnification is recorded, and an image of the PSF is taken. The angular position of the boom is recorded to determine the prism. Depending on the size of the best focus image (as determined by the radial variance), the final image taken was made "bin" (up to a factor of 10). The "binning" adds the adjacent pixel values grouped to produce a smaller image grid. During the initial test, all the images taken were grouped appropriately to give a 50x50 grid for analysis. When a binning factor is used, only the central 50x50 pixels of the CCD are used. This gives the highest resolution for smaller images. When a binning factor of 10 is used, the full active area of the CCD is used, but with less resolution. This is done in larger images with high aberrations. Figure 10 shows the degree to which a better focus image can vary through a typical PAL. The binning is set to avoid any degradation (ie "aliasing") in the MTF and to be calculated subsequently from the PSF. So the PAL is transported to the next test point, the image is refocused on the CCD, and the procedure is repeated. To register / center, the full active area 512x512 of the CCD can be used ("binned" 10 times in each direction). The tests can be performed on any desired group of sites on the PAL. Figure 5 shows an illustrative map consisting of 103 sub-sections. A denser sample is preferably used in the smaller portion of the PAL, where the image quality changes more rapidly. For initial testing, the entire test sequence is controlled by a Visual Basic ™ program that interacts with the motor controller and the detection system. To complete a test with 103 sub-sections, approximately two hours are required. The resulting output consists of an ASCII test file that contains all the data through the focus for each subarea and a PSF image file for each subarea. IX. Data analysis using the EIQM As mentioned above, the increase for each test subarea is calculated and recorded during the test. The additional data analysis is done to determine the astigmatism (magnitude and orientation), prism (magnitude and orientation) and MTF in each subarea. The data obtained can be graphed to produce a lens map for easy interpretation. For the initial test, only PAL without specific astigmatism was used, in order to measure the unwanted astigmatism presented in the lenses. Line image information through focus is used to determine the location, in diopters, of the two line images formed by an astigmatic region of the PAL. This line image is the width of the image through a better adjusted line divided by the width of the image along the line. This gives a value of 0 for a perfect line, and a value of 1 for a perfect circle. For astigmatic images, a graph of this line image width as an augmentation function produces a curve with two minima located in the two astigmatic focus lines (see figure 3). The difference in diopters between the minimum sites gives the magnitude of astigmatism. The angle of the low magnification line image gives the angle, or axis, of astigmatism. The magnitude and direction of the prism of the local lens is calculated from the angular positions of the two boom platforms. The gable positions are in degrees, and are converted to diopters from prism to sample. Next, a two-dimensional Fourier transform is performed on each individual PSF to produce the MTF of said sub-aperture. The MTF is calculated, with appropriate scales, as an angular frequency function (for example cycles / mrad). The value of the MTF (normalized to the value limited to diffraction) at an angular frequency corresponding to the vision /20 (one-minute arc-line widths) is recorded for each subarea. From these numerical data, the 2-D and 3-D contour graphs, or maps, of magnification, magnitude of astigmatism, magnitude of prism, and 20/20 MTF normalized across the surface of the PAL are generated. (see figures 11-14). The vector graphics of the astigmatism axis and direction of the prism are also generated (see figures 1 1 C, 1 1 E and 12C, 12E). In addition, the numerical data can be graphed as a function of the location of the sub-aperture (see Figure 14C). The data analysis and the obtaining of graphs described above have been done using Mathematica 3.0.1 ™ and require approximately half an hour per lens. Those skilled in the art, however, should take into account that it is possible to use other suitable programs to perform the necessary data analyzes. X. Examples of graphs and maps for lenses generated by the EIQM A large variety of lenses has been tested with the EIQM. In this section examples of the results of the instrument are given. The PAL used for this test, cataloged as "LENS A" and "LENS B", were obtained from different vendors, with both lenses designed to have a distance correction of 0 D and an addition increase of +2 D. It should be noted that contour graphics are generated and printed normally in color to make interpretation easier, however, the graphics included in this one are in black and white, and therefore are more difficult to read. However, it is possible to observe the general characteristics. The contour plot in Figure 12A shows the best focus increase of LENS B on the surface. It is possible to clearly see how the magnification changes from 0 D in the distance zone of vision greater than slightly above +2 D in the reading zone, or aggregation, in the lower left side. The magnification map for LENS A is similar (figure 1 1 A). As stated earlier, this transition from low to high increase produces large amounts of astigmatism. This is very evident in the contours of magnitude of astigmatism shown in figures 1 1 B (LENS A) and 12B (LENS B). It can be seen that LENS B has a greater area of high astigmatism and more astigmatism in the area of aggregation. The astigmatism vector graph shows continuous and light transitions of magnitude and angle between the upper and lower portions of the lenses (Figures 1 1 C and 12C). Additionally, from the contours of MTF normalized to 20/20 shown in figures 1 1 D and 12D, it is possible to observe that LENS A shows better performance than LENS B. For LENS A, the MTF it can be seen higher in the upper portion of the lens and in the center of the aggregation zone. It falls in a certain way in the "channel" that connects to these two regions and is very poor in the "wings" on any of the sides of the channel. For LENS B, the high MTF zone in the upper portion is much smaller and does not recede much in the aggregation zone. Figures 13A and 13B show two complete MTF graphs for LENS A, one of a good portion of the distance zone and another from a highly asygmatic region. There is a total of four curves in each graph for 3-D slices of the MTF at 0, 90 and ± 45 degrees. The diffraction-limited MTF for a pupil diameter of 5 mm at 543 nm is shown as the dotted line. Other maps and graphs that can be automatically generated by the EIQM are shown in Figures 14A and 14B. The value of EIQM is evident from the maps and graphs described above, because the image quality changes drastically from one lens design to another. This allows the lens designer, the lens manufacturer, and / or the doctor who recommends it to accurately and objectively establish the quality of any eyeglass lens. These graphs can be generated for any measurable quality. Although several embodiments of the invention have been described and shown, it will be apparent to those skilled in the art that various modifications are possible without departing from the concept of the invention presented and described herein. For example, although EIQM was described as an instrument capable of measuring increases in the scale from -0.5 to +2.8 D, the variable focus lens can be modified to increase measurable increases. Additionally, although the EIQM is particularly suited to measure the image quality of PALs, it can certainly be used to measure the image quality of any type of eyeglass lens, as long as the magnification and astigmatism of the lens are within the system's measurement scale. Therefore, it should be understood that within the scope of the appended claims, it is possible to practice this invention in a manner different from that specifically described.

Claims (24)

NOVELTY PE THE INVENTION CLAIMS

1. - An automated optical test instrument for measuring the image quality of a spectacle lens, said instrument comprising: a lighting system for presenting a test beam to the lens; a positioning system for rotating the lenses so that the different areas on the lens are illuminated and thus measuring the image quality of said lens area; a detection system for recording and measuring the image quality of the lens; and a variable focus lens to focus the beam through the detection system at a constant effective focal length once the beam passes through the lens.

2. The optical test instrument according to claim 1, further characterized in that the positioning system rotates the lens around a fixed rotation point behind the lens.

3. The optical test instrument according to claim 1, further characterized in that the variable focus lens can be moved along an optical axis of the system with respect to the lens.

4. The optical test instrument according to claim 3, further characterized in that the variable focus lens comprises a first lens and a second lens, and wherein the second lens can be moved along the optical axis with respect to the first lens. lens.

5. The optical test instrument according to claim 1, further characterized in that the detection system is located at a fixed distance from the lens.

6. The optical test instrument according to claim 1, further characterized by comprising an alignment boom, wherein the variable focus lens and the detection system are coupled with the alignment boom, and wherein the boom of Alignment rotates around the lens to realign the test beam with the detection system as the lens is rotated by the positioning system.

7. The optical test instrument according to claim 1, further characterized in that it comprises a microprocessor to control the operation of the optical test instrument.

8. The optical test instrument according to claim 1, further characterized in that the detection system comprises means for automatically measuring the dot distribution function produced by a site on the lens.

9. The optical test instrument according to claim 1, further characterized in that the detection system comprises means for automatically calculating the modulation transfer function of a location on the lens.

10. An automated optical test instrument for measuring the image quality of a spectacle lens, said instrument comprising: a light source for presenting a test beam to the lens; a positioning system for rotating the lens and for the different areas on the lens to be illuminated and thus measure the image quality of said lens area; a detection system for recording and measuring the image quality of the lens; a variable focus lens to focus the beam on the detection system; and an alignment boom, wherein the variable focus lens and detection system are coupled with the alignment boom, and wherein the alignment boom rotates around the lens to realign the test beam with the detection system as the lens is rotated by the positioning system. 1.

The optical test instrument according to claim 10, further characterized in that it comprises a microprocessor for controlling the operation of the optical test instrument.

12. The optical test instrument according to claim 1 1, further characterized in that the positioning system rotates the lens around a fixed rotation point behind the lens.

13. The optical test instrument according to claim 12, further characterized in that the variable focus lens focuses the test beam at a constant effective focal length once the beam passes through the lens.

14. The optical test instrument according to claim 13, further characterized in that the detection system comprises means for automatically measuring the magnification, astigmatism, prism and modulation transfer function at a site on the lens.

15. An automated optical test instrument for measuring the image quality of a spectacle lens, said instrument comprising: a lighting system for presenting a test beam to the lens; a positioning system for rotating the lens and for the different areas on the lenses to be illuminated and thus measure the image quality of said lens area; a detection system for recording and measuring the image quality of the lens; a variable focus lens to focus the beam on the detection system; an alignment boom; and a microprocessor for controlling the operation of the optical test instrument, wherein the variable focus lens and the detection system are coupled with the alignment boom, and wherein the optical test instrument is capable of measuring the magnification, astigmatism, prism and lens modulation transfer function.

16. The optical test instrument according to claim 15, further characterized in that the positioning system rotates the lens around a fixed rotation point behind the lenses.

17. The optical test instrument according to claim 16, further characterized in that the variable focus lens focuses the test beam at a constant effective focal length once the beam passes through the lens.

18. A method for measuring the image quality of a lens for glasses, said methods comprises the steps of: (a) illuminating a site on the lens with a test beam from a light source; (b) focusing the test beam on a detection system at a constant effective focal length after the beam passes through the site on the lens; and (c) measuring the image quality of the site on the lens.

19. - The method according to claim 18, further characterized in that it comprises rotating the lens to illuminate a different site on the side, and repeating steps (a) to (c) cited above.

20. The method according to claim 19, further characterized in that the rotation step comprises rotating the lens around a fixed rotation point behind the lenses.

21. The method according to claim 18, further characterized in that the focusing step comprises rotating the detection system around the lens to realign the test beam with the detection system as the lens rotates.

22. The method according to claim 21, further characterized in that the focusing step also comprises moving a variable focus lens along an optical axis of the system with respect to the lens to maintain the effective focal length constant.

23. The method according to claim 18, further characterized in that the measurement step comprises measuring the magnification, astigmatism, prism and modulation transfer function at the location of the lens.

24. The method according to claim 18, further characterized in that the measurement step comprises measuring the distribution function of points at the lens site. The method according to claim 23, further characterized in that the measurement step comprises transforming the point distribution function to obtain the modulation transparency function at the location of the lens.