EP3558092A1

EP3558092A1 - Arrangement for adapting the focal plane of an optical system to a non-planar, in particular spherical object

Info

Publication number: EP3558092A1
Application number: EP17835624.2A
Authority: EP
Inventors: Andrea Berner; Ingo Koschmieder; Dietrich Martin
Original assignee: Carl Zeiss Meditec AG
Current assignee: Carl Zeiss Meditec AG
Priority date: 2016-12-22
Filing date: 2017-12-15
Publication date: 2019-10-30
Also published as: CN110113986B; WO2018114636A1; DE102016226002A1; US11234592B2; US20190374101A1; CN110113986A

Abstract

The invention relates to a solution with which a focal plane (or an image field) of an optical system can be adjusted to a non-planar, in particular spherical object (5). The arrangement is used for adapting the focal plane (4) of an optical system to a non-planar, in particular spherical object (5), wherein the optical system has a positive total refractive power and generates a real image. According to the invention, the optical system also comprises an optical element (3) with a negative refractive power. Although the proposed solution can principally be used in all technical fields with the corresponding requirements relating to a curved focal plane, it is particularly useful in opthalmologic devices. The eye which is to be examined is the spherical object (5) and in particular, is regarded as the front of the eye which has radii of between 5 and 10 mm of small dimensions.

Description

Arrangement for adapting the focal plane of an optical system to a non-planar, in particular spherical object

The present invention relates to a solution with which the focal plane (or image field) of an optical system can be adapted to a non-planar, in particular spherical object. This makes it possible in optical lighting or imaging systems to target and illuminate non-planar objects in a targeted manner and up to the edge.

Basically, in simple optical systems that produce a real image and thus have a positive Gesamtbrech force, the image field curved concavely in the direction of the object. The field curvature of the system is therefore negative.

1 shows an example of the course of the image field curvature of a simple optical system. The image field curvature course of the sagittal and tangential image shells is shown on a plane reference image plane. The result is a curved ideal focal plane FCideai which lies between the sagittal focal plane FCsag and the tangential focal plane FCtan. The ideal focal plane FCideai is curved concavely in the direction of the object.

According to the known state of the art, lighting and imaging systems are known which are optimized in such a way that a planar focal plane is created or used.

Illuminating or imaging spherical objects with such a system does not necessarily lead to a qualitative performance reduction of the optical image because the object does not fulfill the implicit assumptions of the design. Projected structures thus have only in the middle of the image field, z. B. on the vertex of the spherical curvature on the required focus. In the outer and peripheral areas, especially fine structures are out of focus and clearly lose their intensity. An evaluation of these structures is thus difficult or even possible only in a limited area. By alternatively focusing on the edge region, although the structures are sharply imaged there, the focus of the image is inevitably blurred.

This has a particularly disadvantageous effect if measurements are based on the evaluation or representation of structures over the entire field area of the non-planar surfaces.

If the spherical objects tend to have small radii, it can be stated that the optical systems used hitherto only permit a very good optical imaging in the area of the limited depth of field.

The illumination systems used in ophthalmic devices typically produce focal planes that are curved opposite the surface of the cornea of the eye. This leads to structures and in particular fine structures, such. As lines, only in a small area, d. H. either only at the edge or only around the vertex sharp and can be detected.

A uniformly sharp imaging of an optical gap on the cornea of the eye over its entire length is not possible with such an optical system without the use of special measures.

In the current ophthalmic devices, a straight or even oppositely curved image plane of the illumination or irradiation components has a disadvantageous effect. As a result, the structures projected in or onto the eye have the required image sharpness only in the center of the image field, on the visual axis. In the outer and peripheral areas, the fine structures unfold, become blurred and lose their intensity. A Evaluation of the structures is thus difficult or even possible only in a limited area.

In a slit lamp, this is expressed by the fact that the gap image projected onto the eye does not appear sharp over its entire length, and therefore the edge sharpness required for measurement purposes can not be used over the entire length of the gap.

In the patents US 5,404,884; No. 5,139,022 and US Pat. No. 6,275,718 describe methods and arrangements for illuminating the anterior eye segments, in which a planarly configured laser is used as the light source. A disadvantage of these solutions, the physically limited depth of field of the receiving system for the reflected light from the eye diffuse, whereby the expansion range of the sharp laser slice image can not be fully detected.

According to the known state of the art, solutions are known with which image fields are specifically shaped in order to adapt them to different curvatures of the objects.

Thus, for example, in DE 103 07 741 A1, an arrangement is improved with which the image field of the illumination or irradiation components of ophthalmic diagnostic and therapeutic devices. The arrangement is particularly suitable for ophthalmological devices in which a consistently high imaging quality over wide areas of the eye is of interest. For this purpose, a diffractive optical element (DOE) is arranged in the illumination beam path of the irradiation unit in order to achieve a targeted shaping of the image plane. The diffractive optical element may be located on the surface of another optical element or be formed as a separate element. Although both the type of light source used and the type of beam shaping, ie the pattern or pattern generation irrelevant, but the diffractive effect is wavelength dependent. This has a disadvantage, in particular in the different lighting and observation modes of ophthalmological devices. In addition, the production of the diffractive structures is demanding and expensive.

The present invention has for its object to overcome the known from the prior art disadvantages and to propose a solution with which the focal plane of an optical system to a non-planar, in particular spherical object is adaptable, so that projected structures, images, characters o ä. have a consistently high image quality over wide areas of the object. In addition, the proposed solution should be equally suitable for both illumination and imaging systems.

This object is achieved with the arrangement for adjusting the focal plane of an optical system to a non-planar, in particular spherical object in which the optical system has a positive Gesamtbrech power and generates a real image thereby achieved that at least one additional optical element with negative Refractive power is present.

According to the invention, preferred developments and refinements are the subject of the dependent claims.

Although the proposed solution for adapting the focal plane of an optical system to a non-planar, in particular spherical object of different dimensions can be used in principle in any technical field with the corresponding requirements for a curved focal plane, an application in ophthalmological devices is particularly suitable. As a spherical object here is the eye to be examined and to look particularly at the front of the eye, which has radii between 5 and 10 mm rather small dimensions. The invention will be described in more detail below with reference to exemplary embodiments. Show this

Figure 1: the course of field curvature of a simple optical

Systems,

FIG. 2 shows the course of the field curvature of an optical system according to the invention,

Figure 3: the schematic structure of an inventive

Lighting Systems,

Figure 4: the schematic structure of an inventive

Lighting system for a slit lamp and

Figure 5: the course of field curvature of the invention

optical system for a slit lamp.

In the arrangement for adjusting the focal plane of an optical system to a non-planar, in particular spherical, object, the optical system has a positive overall refractive power and produces a real image. According to the invention, the optical system has at least one additional optical element with negative refractive power.

It is of particular advantage that the optical system can be used both in a lighting arrangement and in an imaging arrangement. For this purpose, the focal plane of an optical system is optimized so that it adapts as precisely as possible to the curved surface of the object to be illuminated or imaged. As an additional optical element with negative refractive power corresponding lenses and / or mirrors are used here.

According to the invention, the negative refractive power of the additionally present optical element is dimensioned so that the sum of the sagittal and tangential Bildfeldwölbungsanteile the entire optical system is positive. In the design of the negative refractive power of the additional optical element, in particular, its material coefficients are taken into account.

The following explains the relationships for lighting curved objects. It should be noted, however, that the same conditions apply mutatis mutandis to the imaging of curved objects on a plane plane, such as a detector.

The illumination system is intended to illuminate a convexly curved object (viewed from the light source). For this purpose, the focal plane of the illumination system is consciously also curved convexly.

This is possible in accordance with the lens contributions for the sagittal and tangential field curvature FCsag and FCtan, by the deliberate addition of negative powers. The consideration of the material coefficients and selection of the corresponding type of glass is also important.

The lens contributions for the sagittal and tangential field curvature are calculated as follows:

FCsag = S3 + S4 (1)

FCtan = 3S3 + S4 (2) with S ₃ = H ² F

S ₄ = H ² F / n where S3 is the Seidel coefficient for astigmatism,

S4 the Seidel coefficient for the Petzval field curvature,

H the Lagrange invariant of the system (H = nuy = n'u'y '), n the refractive index of the lens and

F correspond to the refractive power of the lens.

For a convexly curved ideal image plane, FCsag and FCtan must be negative. Through the deliberate addition of negative refractive powers, in addition to the positive portions of the existing collecting lenses, shares of negative effect with regard to field curvature are now added up. With targeted use of an optical element with negative refractive power, the sum of the sagittal and tangential Bildfeldwölbungsanteile the entire optical system can thus be negative, which also creates a convexly curved ideal trapping plane between the sagittal and tangential field curvature shell. The focal plane of a lighting or imaging system is optimized so that it adapts as precisely as possible to the curved outer contour of the object to be illuminated or imaged.

For this purpose, FIG. 2 shows, by way of example, the profile of the field curvature of an optical system according to the invention. Also shown here is the field curvature course of the sagittal and tangential image shells on a plane reference image plane. This also results in a curved ideal (not shown) focal plane FCideai which is also located between the sagittal focal plane FCsag and the tangential focal plane FCtan. However, in contrast to the field curvature of a simple optical system shown in FIG. 1, the ideal focal plane FCideai is negative, ie. H. curved convexly according to the object curvature.

FIG. 3 shows the corresponding schematic structure of an illumination system according to the invention, which has a light source 1 and a lens system consisting of two convergent lenses 2.1 and 2.2. When additional optical element with negative refractive power is in this case a lens 3 is used, which is assigned to the two converging lenses 2.1 and 2.2. Preferably, the curvature of the focal plane 4 of the overall optical system serving lens 3 is disposed between the two converging lenses 2.1 and 2.2. 5 denotes the object to be illuminated with a spherical curvature. The double arrow 6 is intended to document the interchangeability of the lenses with negative refractive power for adaptation to spherical objects with different radii. The plane of the light source 1 is thus ideally imaged on the convexly curved object 5, since the resulting focal plane 4 is also convexly curved. It should also be noted that the schematic structure of an illumination system shown in FIG. 3 applies mutatis mutandis to an imaging system under the same conditions. The reflected light from the curved object would be imaged by the two converging lenses and the additional negative power lens disposed therebetween on a (plane) detector which would be at the location of the light source.

The use of the optical system according to the invention for both illumination and imaging is particularly advantageous. This makes it possible to illuminate a curved object with the aid of a planar illumination source (with an adapted curved focal plane) and to image the light reflected by the curved object (with a matched planar focal plane) onto a planar image detector.

According to an advantageous embodiment, a plurality of additional optical elements in the form of lenses with negative refractive power are present and interchangeably arranged to adapt to spherical objects with different radii.

According to a further advantageous embodiment, a lens is used to adapt the optical system to spherical objects with different radii, whose optical properties can be varied. This even offers the possibility of being able to adapt the optical system not only to spherical objects with different radii, but also to flat objects. Conceivable here are electro-optical systems or variable lenses, z. As liquid or rubber lenses or gel-based lenses.

In this case, the choice of the corresponding lens or its optical properties can be made by specific manual selection. But it is also possible to automate the selection with the help of a camera and a corresponding image analysis.

The additional optical element in the form of a lens also has the advantage that it can be used for correcting the optical system with respect to chromatic aberrations, distortion errors or the like.

According to a further embodiment, the use of the optical system according to the invention in an ophthalmological device is particularly advantageous. The non-planar, in particular spherical object corresponds to the eye. Even in an ophthalmic device, the optical system can be used both as a lighting and as an imaging system.

If the optical system is to be used, for example, in a slit lamp to illuminate the cornea, then additional additional boundary conditions result, such as ensuring a sufficient working distance and a given pupil position. The consideration of these conditions requires a corresponding adjustment of the optical system.

For the application of the optical system in a slit lamp is to ensure a sufficient working distance to the eye an additional imaging optics available. Preferably, the additional imaging optics for the movement of the gap image along the optical axis designed to be displaceable.

FIG. 4 shows the corresponding schematic structure of an illumination system according to the invention for a slit lamp, which has a light source 1 and a lens system consisting of two convergent lenses 2.1 and 2.2. As an additional optical element with negative refractive power in this case a lens 3 is used, which is associated with the two converging lenses 2.1 and 2.2. Preferably, the curvature of the focal plane 4 of the overall optical system serving lens 3 is disposed between the two converging lenses 2.1 and 2.2. In addition, FIG. 4 shows the eye 6 to be illuminated and the imaging optics 8 which are additional to ensure a sufficient working distance. The double arrow 9 is intended to document that the imaging optics 8 is designed to be displaceable along the optical axis for the movement of the gap image.

According to an advantageous embodiment of the illumination system according to the invention for a slit lamp according to FIG. 4, the individual lenses or the lens system have focal lengths from the following ranges:

• Lens 3: f = -5 to -30 mm

• lens system (2.1, 2.2 and 3): f = 50 to 150 mm

• Imaging optics 8. f = 25 to 125 mm

According to a particularly preferred embodiment, the individual lenses or the lens system focal lengths from the following areas:

• Lens 3: f = -10 to -20 mm

• lens system (2.1, 2.2 and 3): f = 80 to 120 mm

• Imaging optics 8. f = 50 to 100 mm Again, the plane of the light source 1 is thus ideally imaged on the convex curved eye 7, since the resulting focal plane 4 is also convex curved. It should also be noted here that the schematic structure of a lighting system for a slit lamp shown in FIG. 4 also applies mutatis mutandis to an imaging system under the same conditions.

The use of the optical system according to the invention for both illumination and imaging is particularly advantageous. This makes it possible to illuminate an eye with the aid of a planar illumination source (with an adapted curved focal plane) and to image the light reflected by the eye (with a matched plane focal plane) onto a planar image detector.

According to an advantageous embodiment, the additional optical element in the form of a lens with negative refractive power is designed so that

Gap images can be reproduced up to a length of 16 mm.

In accordance with a further embodiment, it is advantageous to design the additional optical element in the form of a lens with negative refractive power such that at a field diameter (or even illumination field diameter) of 5-20 mm radii of curvature R of the cornea of the eye are covered between 5 mm and 10 mm.

According to a last embodiment, it is advantageous to design the additional optical element with negative refractive power such that the ideal focal plane FCideai lies in the middle between the sagittal focal plane FCsag and the tangential focal plane FCtan and thereby minimizes deviations from the non-planar, in particular spherical, object. having. The minimum deviations are particularly advantageously within the depth of field of the system. Finally, FIG. 5 shows the profile of the field curvature of the inventive optical system for a slit lamp.

Shown here is the course of field curvature for the system of Figure 4, but in contrast to the illustrations of Figures 1 and 2 measured on a curved trailing plane with a radius of 8 mm.

It can be seen here that the ideal trapping plane, which is also located between the sagittal focal plane FCsag and the tangential focal plane FCtan, has a minimum deviation of 0, which corresponds to minimal deviations from the non-planar, in particular spherical object.

This shows that the optical system is ideally suited for lighting tasks on a spherical object with a radius of 8 mm.

With the solution according to the invention, an arrangement for adapting the focal plane of an optical system to a non-planar, in particular spherical object is provided with which the focal plane of an optical system can be adapted to a non-planar, in particular spherical object. This makes it possible in optical lighting or imaging systems to target and illuminate non-planar objects in a targeted manner and up to the edge. The proposed solution is equally suitable for both illumination and imaging systems.

Although the proposed solution can be used in principle in any technical field with the corresponding requirements for a curved focal plane, it is particularly suitable for use in ophthalmic devices with object radii between 5 and 10 mm.

The proposed solution can be optimized not only on monochromatic but also on spectrally broad light source (white light).

Claims

claims

1 . Arrangement for adapting the focal plane of an optical system to a non-planar, in particular spherical object, in which the optical system has a positive overall refractive power and produces a real image, characterized in that at least one additional optical element with negative refractive power is present and in one Illumination, and an imaging arrangement is applicable, wherein the at least one additional optical element is a lens and / or a mirror whose negative refractive power is dimensioned such that the sum of the sagittal and tangential Bildfeldwölbungsanteile the entire optical system are negative.

2. Arrangement according to claim 1, characterized in that in the design of the negative refractive power of at least one, additionally existing optical element and its material coefficients are taken into account.

3. Arrangement according to claim 1, characterized in that a plurality of additional optical elements are provided with negative refractive power and arranged to adapt to spherical objects with different radii interchangeable.

4. Arrangement according to claim 1, characterized in that for adapting the optical system to spherical objects with different radii optical elements are used, whose optical properties can be varied.

5. Arrangement according to claim 1, characterized in that the at least one additional optical element is also usable for correcting the optical system with respect to color or distortion errors or the like.

6. Arrangement according to claim 1, characterized in that the optical system is used in an ophthalmological apparatus, wherein the non-planar, in particular spherical object corresponds to an eye.

7. Arrangement according to claim 5, characterized in that the optical system in an ophthalmic device both as a lighting and as an imaging system is used.

8. Arrangement according to claim 6, characterized in that the optical system is used in a slit lamp and to ensure a sufficient working distance to the eye an additional imaging optics is available.

9. Arrangement according to claim 7, characterized in that the additional imaging optics for the movement of the gap image along the optical axis is designed to be displaceable.

10. Arrangement according to claim 7, characterized in that the at least one, additional optical element with negative refractive power is designed so that gap images can be imaged up to a length of 20mm.

1 1. Arrangement according to claim 7, characterized in that the at least one additional optical element with negative refractive power is designed so that at a field diameter of 5-20 mm radii of curvature R of the cornea of the eye between 5 mm and 10 mm are covered.

12. Arrangement according to claim 7, characterized in that the at least one additional optical element with negative refractive power is designed so that the ideal focal plane of the overall system FCideai, which in the midpoint between the sagittal focal plane FCsag and the tangential focal plane FCtan has minimal deviations from the nonplanar, in particular spherical, object.

13. Arrangement according to claim 7, characterized in that the minimum deviations are within the depth of field of the system.