Optical system and surgical microscope

Abstract

An optical system images an object region with an optical beam path in an image plane of an image acquisition system. The optical system includes a first optical assembly through which the optical beam path passes and a second optical assembly arranged in the optical beam path on the side of the first optical assembly facing away from the object region. The second optical assembly is a system at least partly compensating longitudinal chromatic aberrations of the first optical assembly occurring in the wavelength range 625 nm850 nm of the light.

Claims

1. A surgical microscope comprising: an image acquisition system defining an image plane; an optical system defining an optical beam path and being configured for imaging an object region into said image plane via said optical beam path; said optical system including a first optical assembly mounted in said optical beam path so as to permit said optical beam path to pass therethrough; said first optical assembly having an end facing away from said object region; said optical system further including a second optical assembly mounted in said optical beam path at said end of said first optical assembly; said second optical assembly being configured as a compensation system to at least partially compensate for longitudinal chromatic aberrations of said first optical assembly occurring in a wavelength range of light of 625 nm850 nm; said first optical assembly being configured as an achromatic system corrected for the light of a first wavelength and a second wavelength; said first wavelength being preferably 486 nm and said second wavelength being preferably 656 nm; said achromatic system including lenses made exclusively of normal or standard glasses to provide achromatization with said normal or standard glasses having chromatic aberrations for light in the near infrared and infrared which are approximately five times larger than chromatic aberrations in the visible spectral range; the chromatic aberrations in the near infrared and infrared having a sign opposite to the sign of the chromatic aberrations in the visible spectral range; and, said second optical assembly being an apochromat or semi-apochromat corrected for the light of said first wavelength, which is preferably 486 nm, and for the light of said second wavelength, which is preferably 656 nm, as well as the light of a third wavelength which is preferably 588 nm to reduce the chromatic aberration in the near infrared and infrared of the image of the object region supplied to said image acquisition system.

2. The surgical microscope of claim 1, wherein: said second optical assembly has a first lens of positive refractive power, a second lens of negative refractive power and a third lens of positive refractive power; said first lens being made from a first glass material and said second lens being made from a second glass material and said third lens being made from said first or a third glass material; wherein the differences P.sub.dc of partial dispersions of said first glass material or of the third glass material in relation to the partial dispersion of the second glass material and the differences v of the Abbe numbers of said first glass material or said third glass material in relation to the Abbe number of said second glass material are related to one another in a ratio |P.sub.dc/v|, for which |P.sub.dc/v|0.1 applies.

3. The surgical microscope of claim 2, wherein: said differences P.sub.dc of partial dispersions of said first glass material or of said third glass material in relation to the partial dispersion of said second glass material and the differences v of the Abbe numbers of said first glass material or said third glass material in relation to the Abbe number of said second glass material are related to one another in a ratio of |P.sub.dc/v|for which |P.sub.dc/v|0.03 applies.

4. The surgical microscope of claim 2, wherein: said first lens of positive refractive power and said second lens of negative refractive power are combined to form a cemented member; and/or, said first lens of said second optical assembly is mounted at the end thereof facing toward said first optical assembly in said optical beam path; and/or, said third lens of said second optical assembly is mounted so as to face toward said image plane of said image acquisition system in said optical beam path.

5. The surgical microscope of claim 2, wherein said first lens of said second optical assembly and/or said third lens of said second optical assembly are made of a lens material which has anomalous partial dispersion.

6. The surgical microscope of claim 1, wherein said first optical assembly includes an afocal zoom system.

7. The surgical microscope of claims 1, wherein said second optical assembly has a positive refractive power.

8. The surgical microscope of claim 1, wherein said second optical assembly is an objective effecting an imaging of said object region into said image plane of said image acquisition system.

9. The surgical microscope of claim 1, wherein said second optical assembly has at least one lens displaceable in said optical beam path relative to said image plane of said image acquisition system.

10. The surgical microscope of claim 9, wherein said second optical assembly is displaceably mounted so as to permit adjustment of the optical wavelength of said optical beam path from said object region into said image plane of said image acquisition system.

11. The surgical microscope of claim 1, wherein said image acquisition system includes a color camera configured as a three-chip camera; and, a plurality of image sensors arrayed in said image plane of said image acquisition system.

12. The surgical microscope of claim 11, further comprising an illumination unit defining an illumination beam path for exciting fluorescence of a dye in said object region; and, including a filter system for filtering out light having a wavelength corresponding to the wavelength of the fluorescence light of the fluorescing dye.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described with reference to the drawings wherein:

(2) FIG. 1 shows a surgical microscope with an optics system for visualizing an object region in eyepieces and imaging of the object region in an image plane of an image acquisition system with an optical beam path;

(3) FIG. 2 shows a first optical assembly in the optics system of the surgical microscope, which contains a microscope main objective system and an afocal zoom system;

(4) FIG. 3 shows a longitudinal chromatic aberration of this first optical assembly in the optics system of the surgical microscope, which longitudinal chromatic aberration is dependent on the wavelength of the light;

(5) FIG. 4 shows a second optical assembly embodied as a camera objective in the optics system of the surgical microscope;

(6) FIG. 5 shows a longitudinal chromatic aberration of the second optical assembly in the optics system, which longitudinal chromatic aberration is dependent on the wavelength of the light; and,

(7) FIG. 6 shows a resultant longitudinal chromatic aberration of the first and second optical assemblies as a function of the wavelength of the light.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

(8) The surgical microscope 10 shown in FIG. 1 enables an observer to observe, with magnification, an object region 12 in a left-hand and right-hand eyepiece (14L, 14R) of a binocular tube 15 with a stereoscopic optical beam path (16L, 16R). In the surgical microscope 10, the light from the object region 12 is guided through an optics system which contains, arranged in a microscope main body 17, a first optical assembly 18 with a microscope main objective system 20 and an afocal zoom system 22R and which has a second optical assembly 24, which acts as the camera objective of an image acquisition system in the form of a color camera 26 with image planes (27a, 27b, 27c), to which the light is guided from the beam path 16R by means of a beam splitter 28. In the image planes (27a, 27b, 27c) of the color camera 26 there are a splitter prism arrangement 25 and different image sensors (29a, 29b, 29c) which serve to register the different light lying in the red, green and blue spectral ranges. The image sensor 29a configured for registering light in the red spectral range also enables the registration of light with a wavelength lying in the near infrared and infrared spectral ranges, that is, light with a wavelength in the range from 0.7 m to 5 m and light with a wavelength of 5 m to 50 m.

(9) As an alternative to the above, it is also possible especially to configure the splitter prism arrangement 25 in such a way that the image sensor 29c, which is configured for registering light in the blue spectral range, can also register the light with wavelengths in the near infrared and infrared spectral ranges.

(10) The observation beam path 16L in the surgical microscope passes through a zoom system 22L which corresponds to the configuration of the zoom system 22R.

(11) The surgical microscope 10 is accommodated on a stand (not shown here), which has adjustable articulated arms. On the stand, the surgical microscope 10 can be displaced over the object region 12 by adjusting the articulated arms.

(12) The surgical microscope 10 contains an illumination device 30 with a light source 32 and illumination optics 34, through which the light from the light source 32 can pass. The illumination optics provide an illumination beam path 36 via which the object region 12 can be illuminated.

(13) The illumination device 30 is configured to excite one or more dyes, such as, for example, indocyanine green (ICG) dye, 5ALA dye or protoporphyrin IX dye, to fluoresce. To this end, light having a wavelength in the blue spectral range is provided by the light source 32 of the illumination device 30. In order to prevent light having a wavelength corresponding to the wavelength of the light of the dye, which is excited to fluoresce and arranged in the object region 12, from being guided in the illumination beam path 36 to the object region 12, there is a fluorescence excitation filter 40 in the illumination device 30. The fluorescence excitation filter can be introduced into the illumination beam path 36 in accordance with the double-headed arrow 38 so as to filter out the spectral range of the illumination light which is released when a dye in the object region 12, which is excited to fluoresce, fluoresces.

(14) So that only the fluorescent light released by a fluorescing dye in the object region 12 can be guided to an observer and the color camera 26 in the fluorescence operating mode of the surgical microscope 10, the optics system in the surgical microscope 10 contains adjustable filter elements 42 which, in accordance with the double-headed arrow 44, can be arranged in the stereoscopic observation beam paths (16L, 16R) on the end of the zoom systems facing away from the object region. The filter elements 42 can ensure that the light with the wavelength of the light exciting the fluorescence does not reach the eyepieces (14L, 14R) of the binocular tube 15 and the color camera 26.

(15) FIG. 2 shows the first optical assembly 18 in the optics system of the surgical microscope 10. The microscope main objective system 20 is a cemented member with the optically effective surfaces 101, 102 and 103. The afocal zoom system 22R has four members (110, 112, 114, 116.) The members (110, 116) of the zoom system 22R have positive refractive power and are in each case configured as cemented members. The members (112, 114) in the afocal zoom system 22R are arranged so as to be displaceable. Here, the member 112 is likewise embodied as a cemented member. The zoom system 22R has the optically effective surfaces (120, 121, 123, 124, 125, 126, 127, 128, 129, 130 and 131).

(16) The optical assembly 18 is an achromat which completely compensates the longitudinal chromatic aberration CHL of the wavefront for the light with the wavelength =486 nm (F-line) in relation to the light with the wavelength =656 nm (C-line), that is, CHL.sup.18.sub.FC=0.

(17) FIG. 3 shows the longitudinal chromatic aberration CHL.sup.18.sub.xC, related to the C-line and dependent on the wavelength of the light (x-line), of this first optical assembly in the optics system of the surgical microscope.

(18) The configuration of the optics system in the surgical microscope 10 is based on the consideration that the longitudinal chromatic aberration CHL.sup.18.sub.xC, related to the C-line and dependent on any wavelength of the light (x-line), of the wavefront in relation to the C-line can be estimated to a good approximation as follows:

(19) ${\mathrm{CHL}}_{\mathrm{xC}}^{18}={}_{\mathrm{xC}}.Math.\underset{i}{.Math.}\frac{1}{2}{y}_i^2.Math.{}_i+\underset{i}{.Math.}{}_{\mathrm{xC},i}.Math.\frac{1}{2}{y}_i^2.Math.\frac{{}_i}{v_i}$
where .sub.xC denotes the gradient of the normal line related to the C-line for the light with a wavelength x, .sub.xC,i denotes the distance of a specific glass of a lens i from this normal line, y.sub.i denotes the marginal ray height, v.sub.i denotes the Abbe numbers of the materials v=(n.sub.d-1)/(n.sub.F-n.sub.C), and .sub.i denotes the refractive powers of the lenses i.

(20) The inventors discovered that, if only normal glasses are used in the optical assembly 18 for achromatization (that is, .sub.xC,i=0), the chromatic longitudinal aberrations, related to the C-line, for the light with a wavelength =588 nm (d-line) and =850 nm (s-line), with
CHL.sub.dC.sup.18=.sub.dC.Math..sub.iy.sub.i.sup.2.Math..sub.i .sub.dC=+0.00046173
CHL.sub.sC.sup.18=.sub.sC.Math..sub.iy.sub.i.sup.2.Math..sub.i .sub.sC=0.002304493
are related to one another as follows:

(21) $\frac{{\mathrm{CHL}}_{\mathrm{sC}}}{{\mathrm{CHL}}_{\mathrm{dC}}}=\frac{{}_{\mathrm{sC}}}{{}_{\mathrm{dC}}}-5$

(22) That is, the chromatic aberrations for the light in the near infrared and in the infrared are approximately 5-times larger than in the visible spectral range in the optical assembly 18; the sign of these chromatic aberrations is, however, opposite to the sign of the chromatic aberrations in the visible spectral range.

(23) The second optical assembly 24 in the optics system of the surgical microscope 10 serves to reduce the chromatic aberration of the image of the object region, supplied to the color camera 26, in the near infrared and in the infrared.

(24) This is achieved by virtue of the chromatic aberrations of the optics group 24 being completely compensated for simultaneously, preferably for light with the wavelength =656 nm (C-line), =588 nm (d-line) and =486 nm (F-line). This is because the chromatic aberration of the optical assembly 24 for the wavelength =850 nm (s-line) then has the opposite sign to the corresponding chromatic aberration of the optical assembly 18. As a consequence, the chromatic aberration in the near infrared and in the infrared of the optical assembly 18 is at least partly lifted by the chromatic aberration of the optical assembly 24 in the near infrared and infrared. Since the optical assembly 18 and the optical assembly 24 are in each case completely compensated for the light in the visible spectral range, the combination of the optical assembly 18 with the optical assembly 24 in the optics system of the surgical microscope 10 can supply the color camera 26 with an image which does not have any chromatic aberrations in the visible spectral range either.

(25) FIG. 4 shows the second optical assembly 24 in the optics system of the surgical microscope 10. The optical assembly 24 has a positive refractive power. It contains three lenses 200, 202 and 204. The lenses (200, 202) form a cemented member with positive refractive power. The refractive power of the lens 204 is positive. The lenses 200 and 204 consist of a lens material, the partial dispersion of which is anomalous in the visible spectral range. The lens 202 in the cemented member consists of one of the materials mentioned above, which fits with the material of the positive lenses. The optical assembly 24 has the optically effective surfaces 206, 207, 208, 209 and 210. It is a two-member apochromat which, in relation to the light with the wavelength =656 nm (C-line), completely compensates the longitudinal chromatic aberration CHL.sup.24 of the wavefront for the light with the wavelength =486 nm (F-line) and for the light with the wavelength =588 nm (d-line), that is, CHL.sub.FC.sup.24=0 and CHL.sub.dC.sup.24=0. This is ensured by the aforementioned glass selection.

(26) FIG. 5 shows the longitudinal chromatic aberration CHL.sub.xC.sup.24, related to the C-line and dependent on the wavelength of the light (x-line), of this second optical assembly 24 in the optics system of the surgical microscope 10.

(27) The inventors have discovered that the residual error of the two-member apochromat into the near infrared in the case of light with the wavelength =852 nm (s-line) can be estimated to a good approximation as follows:

(28) ${\mathrm{CHL}}_{\mathrm{sC},\mathrm{Apo}}=\frac{1}{2}.Math.y_0^2.Math..Math.\frac{P_{\mathrm{sC}}}{v}$
where y.sub.0 is the marginal ray height and is the refractive power of the two-member apochromat. The variable P.sub.sC denotes the difference of the relative partial dispersions of the two employed glass types in the wavelength range between the s-line and the C-line, the variable v describes the difference in the Abbe numbers of the two glasses.

(29) As can be gathered from the following table, the values of the variable P.sub.sC/v vary between +0.00051 and +0.00042 for some of the aforementioned glass pairs.

(30) TABLE-US-00001 Table of values of the variable P.sub.sC/v for different glass pairs P P/v Glass pair sC v sC S-FPL51/N-KZFS2 0.01410 27.54 0.000512 S-FPL53/N-BK7 0.01290 30.78 0.000419 N-PK51/N-SK11 0.00760 16.18 0.000470

(31) The variations of the values of the variable P.sub.sC/v for different glass types are used by the invention in order thereby to at least partly compensate the longitudinal chromatic aberration CHL.sub.xC of the first optical assembly 18 by way of a suitable selection of the glass types of the lenses (200, 202, 204) in the optical assembly 24. To this end, an allowance with a sign opposite to the sign of the longitudinal chromatic aberration of the first optical assembly is set for the longitudinal chromatic aberration of the second optical assembly in the infrared spectral range.

(32) FIG. 6 shows the resultant longitudinal chromatic aberration CHL.sub.xC.sup.18+24 of the first optical assembly 18 and second optical assembly 24 depending on the wavelength of the light.

(33) Therefore, in the optics system of the surgical microscope 10, the second optical assembly 24 compensates the longitudinal chromatic aberration of the first optical assembly 18 except for a residual error, which does not have an effect for the imaging of the object region 12 on the image sensor of the camera with light in the infrared spectral range.

(34) A configuration example for the first optical assembly 18 and the second optical assembly 24 in the optics system of the surgical microscope 10 is reproduced in the following tables:

(35) TABLE-US-00002 Table Optical Assembly 18 Optically Free effective Thickness or diameter Medium surface Radius r/mm air gap d/mm d.sub.F/mm (glass type) 12 Object 195.154 25 AIR 101 187.4 2 25 BAF3 102 75.6 8 25 CAF2 103 111.5 12.407 AIR 120 32.181 1.2 12 S-NBH8 121 16.404 2.2 12 S-PHM53 123 180.98 0.986 12 AIR 124 19.376 1.4 7 N-SF6 125 9.183 1 7 N-SK16 126 41.591 1.6 7 AIR 127 41.591 1 7 N-SK16 128 41.591 29.808 7 AIR 129 180.98 2.2 12 S-PHM53 130 16.404 1.2 12 S-NBH8 131 32.181 2 AIR

(36) TABLE-US-00003 Table Optical Assembly 24 Optically Free effective Thickness or diameter Medium surface Radius r/mm air gap d/mm d.sub.F/mm (glass type) 205 Pupil 10-60 12 AIR 206 33.978 3 12 S-FPL51 207 18.260 1.5 12 N-KZFS2 208 56.630 0.1 12 AIR 209 25.489 2 12 S-FPL51 210 732.328 46.65 12 AIR 211 Image

(37) Here, the following applies:

(38) TABLE-US-00004 Refractive index Abbe number Medium (glass type) ne at 546 nm ve at 546 nm BAF3 1.585650 46.17 CAF2 1.434966 94.69 S-NBH8 1.725384 34.47 S-PHM53 1.605199 65.15 N-SF6 1.812659 25.16 N-SK16 1.622863 60.08 S-FPL51 1.498454 81.14 N-KZSF2 1.560823 53.83 AIR 1

(39) It should be noted that, in principle, as lens material for the lenses with anomalous partial dispersion in the second optical assembly, use can also be made of glasses N-FK58, N-FK51A, N-PK52A, N-PK51 from Schott, the glasses S-FPL53, S-FPL-51, S-FPL51Y, S-FPM3 or else S-FPM2 from Ohara, or glasses which have optical properties corresponding to the optical properties of the aforementioned glasses and an anomalous partial dispersion.

(40) It should be noted that, in principle, the microscope main objective system 20 in the above-described surgical microscope 10 can also be embodied as a focusable microscope main objective. The configuration of the optical assembly 24 according to the table reproduced above ensures that an image of the object region 12 is respectively generated even when focusing the microscope main objective in the image planes 27a, 27b and 27c, which image does not lose sharpness only for light in the visible spectral range but does not lose sharpness for the light in the near infrared either, without this requiring a displacement in the beam path 16R of the optical assembly 24 as a whole or of the lenses in this optical assembly.

(41) In conclusion, the following, in particular, should be registered: The invention relates to an optics system for imaging an object region 12 with an optical beam path (16R, 16R) in an image plane (27a, 27b, 27c) of an image acquisition system. The optics system contains a first optical assembly 18, through which the optical beam path 16R passes, and a second optical assembly 24 arranged in the optical beam path 16R on the side of the first optical assembly 18 facing away from the object region 12. The second optical assembly 24 is embodied as a system at least partly compensating longitudinal chromatic aberrations of the first optical assembly 18 occurring in the wavelength range 625 nm850 nm of the light.

(42) It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

LIST OF REFERENCE SIGNS

(43) 10 Surgical microscope 12 Object region 14L Left-hand eyepiece 14R Right-hand eyepiece 15 Binocular tube 16L Left-hand beam path 16R Right-hand beam path 16R Right-hand beam path 17 Microscope main body 18 First optical assembly 20 Microscope main objective system 22L, 22R Zoom system 24 Second optical assembly 25 Splitter prism arrangement 26 Color camera 27a, b, c Image planes 28 Beam splitter 29a, b, c Image sensors 30 Illumination device 32 Light source 34 Illumination optics 36 Illumination beam path 38 Double-headed arrow 40 Fluorescence excitation filter 42 Filter element 44 Double-headed arrow 101, 102, 103 Optically effective surface 110, 112, 114, 116 Member 120, 121, 123, 124, 125, 126, 127, 128, 129, 130, 131 Optically effective surface 200, 202, 204 Lens 205 Pupil 206, 207, 208, 209, 210 Optically effective surface 211 Image