Immersion microscope objective

An immersion microscope objective includes a system of several optical lenses or lens groups between which air spaces are provided and an adjusting device for adapting the immersion microscope objective to different immersion mediums for correcting imaging errors when utilizing the immersion microscope objective in connection with a cover glass, which closes off a specimen holder, and/or for correcting longitudinal chromatic aberrations. The adjusting device is configured to change two air spaces and especially the air spaces (A1, A2) are linearly changeable.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority of German patent application no. 10 2006 052 142.0, filed Nov. 6, 2006, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to an immersion microscope objective which includes a system of several optical lenses or lens groups between which air spaces are provided. An adjusting device is also provided for the following: adapting the immersion microscope objective to various immersion mediums; correcting imaging errors in the use of the immersion microscope objective in association with a cover glass which closes off the specimen holder; and/or, correcting longitudinal chromatic aberrations.

BACKGROUND OF THE INVENTION

The immersion microscope objective of the invention is assigned to the class known as “planapochromat”. A planapochromat is characterized in that the focus positions of the spectral lines e, C′ and F′ are coincident. The “plan” in planapochromat means “planar” and that the image field is flattened.

Water, glycerine and oil can be used as immersion mediums whereby the immersion microscope objective is especially suitable for live cell imaging methods. Here, it is necessary that the indices of refraction of the liquids on both sides of the cover glass approximate each other. The immersion medium “water” is suitable for the examination of living objects especially when the objective is to be immersed directly into the aqueous medium without cover glass. In contrast, for critical fluorescence examinations, a purified glycerine is preferable as the immersion medium because purified glycerine has virtually no inherent fluorescence.

Glycerine and water are preferably utilized in the microscopy of living objects because these objects are in a medium having a similar index of refraction.

Furthermore, it is desirable that the objective also is usable with oil as an immersion medium so that the objective can be used for other usual viewing. Furthermore, a large work distance is wanted because objectives having a large working distance ensure easy accessibility to the specimen.

Various immersion microscope objectives are known from the state of the art. Thus, a microscope objective having three different variations with respective numerical apertures of 1.15 is shown by way of example in U.S. Pat. No. 5,530,590. This objective comprises three lens groups. The second lens group can be displaced along the optical axis relative to the two other lens groups in order to adapt the objective to the thickness of the cover glass and to so compensate the spherical and chromatic aberration which varies with this thickness.

In United States patent publication US 2006/0087745 A1, an immersion microscope objective is likewise described which, however, does not yet satisfy the requirements in many applications with respect to the correction of the longitudinal chromatic aberration or the planapochromatic correction. Furthermore, this objective is not corrected for oil as an immersion medium.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the invention to provide an immersion microscope objective which can be used for various immersion mediums and which has an image contrast improved with respect to the state of the art as well as achieving a correction of the longitudinal chromatic aberration.

According to a feature of the invention, the adjusting device in an immersion microscope objective of the type referred to above is configured for changing two air spaces. The air spaces (A1, A2) are linearly changeable.

A linear change of the two air spaces (A1, A2) is provided for adapting to different immersion mediums in accordance with the function:

For correcting imaging errors when utilizing a cover glass, a linear change of the two air spaces (A1, A2) is provided according to the function:

A2,Imm,mD-A2,Imm,oDA2,Gly,oD-A2,Wat,oD=A1,Imm,mD-A1,Imm,oDA1,Gly,oD-A1,Wat,oD
wherein: the index “1 mm,mD” is for the particular air space when utilizing an immersion medium with a cover glass; “1 mm,oD” is for the particular air space when utilizing an immersion medium without cover glass; “Gly,oD” is for the corresponding air space when utilizing the immersion medium “glycerine” without cover glass; and, “Wat,oD” is for the particular air space when utilizing the immersion medium “water” without a cover glass.

In a specific embodiment, the immersion microscope objective viewed from the specimen comprises:(a) a two-lens composite member G1having a positive refractive power and formed from a fill lens L1and a parent spherical lens L2;(b) a biconvex lens L3;(c) a first meniscus lens L4having a positive refractive power;(d) a two-lens composite member G2having positive refractive power and comprising a biconcave lens L5and a biconvex lens L6;(e) a two-lens composite member G3having positive refractive power and comprising a biconvex lens L7and a second meniscus lens L8;(f) a third meniscus lens L9having negative refractive power; and,(g) a fourth meniscus lens L10having positive refractive power.

The air space A1between the composite member G1and the biconvex lens L3and the air space A2between the biconvex lens L3and the meniscus lens L4are changeable.

The front surface of the fill lens L1in the composite member G1is configured to be planar and the centers of curvature of the two surfaces of the parent spherical lens L2lie on the object side and the centers of curvature of the two surfaces of the meniscus lens L4lie on the image side and the centers of curvature of the two surfaces of the meniscus lens L8lie on the object side and the centers of curvature of two surfaces of the meniscus lens L9lie on the image side and the centers of curvature of the two surfaces of the meniscus lens L10lie on the object side.

For the lenses L1and L2, the following indices of refraction neand Abbe numbers νeare for the spectral line e (546.07 nm):ne, L1<1.50, νe, L1>70ne, L2>1.85, νe, L2<42

For the lenses L9and L10, the following indices of refraction neand Abbe numbers νeare for the spectral line e (546.07 nm):ne, L9>1.80, νe, L9>45ne, L10<1.60, νe, L10<40

The net transmission at the wavelength 365 nm is greater than 50% and is therefore ideal for fluorescence investigations and at a wavelength of 850 nm, the net transmission is greater than 84%.

In contrast to such multi-immersion objectives known previously, a planapochromatic correction over a wide spectrum from 450 nm to 850 nm is realized with this objective. All wavelengths of this range are corrected to be diffraction limited. The customer need not refocus when changing the wavelength within this spectrum.

In order to correct the spherical aberration, the longitudinal chromatic aberration, and some other imaging errors when changing the immersion medium, it is only necessary to change two air spaces in the optical system. In the specific case, these air spaces are A1and A2. These changes can be carried out in a simple manner with the aid of a correction ring.

Furthermore, the spherical aberrations can also be corrected with the immersion microscope objective of the invention. This spherical aberration occurs with the use with or without a cover glass. The corresponding correction is likewise achieved by changing the two air spaces.

The variations of the air spaces take place linearly whereby a simple construction of the adjusting device, that is, the correction ring, is possible.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIGS. 1aand1bshow an embodiment of an objective assembly. In bothFIGS. 1aand1b, a specimen P is indicated as the object to be examined and an immersion medium is identified as being immersion water.

Starting from the specimen P and the immersion medium, and going from left to right inFIGS. 1aand1b, the following are shown:(a) a two-fold composite lens G1having positive refractive power and formed from a fill lens L1and a parent spherical lens L2;(b) a biconvex lens L3;(c) a first meniscus lens L4having positive refractive power;(d) a two-fold composite lens G2having positive refractive power and comprising a biconcave lens L5and a biconvex lens L6;(e) a two-fold composite lens G3having positive refractive power comprising a biconvex L7and a second meniscus lens L8;(f) a third meniscus lens L9having negative refractive power; and,(g) a fourth meniscus lens L10having positive refractive power.

Spaces A1to A8are provided between the individual lenses and the composite lenses and the spaces A1and A2are changeable by means of correction rings (not shown inFIGS. 1aand1b).

The adjusting device for varying the spaces A1and A2includes correction rings and is provided on the frame of the objective as will be described hereafter with respect toFIG. 4.

A rear diaphragm follows the space A7and closes off the objective. The lens of a tube system (not shown here) follows the objective at a spacing A8. This lens of the tube system has a focal length of 164.50 mm.

The two configurations shown inFIGS. 1aand1bdiffer only in the spaces A1and A2from each other. These spaces are adjusted depending upon the thickness of the cover glass and the immersion medium in correspondence to the above-delineated conditions.

The immersion microscope objective ofFIGS. 1aand1bhas the system data for a spectral line e (546.07 nm) set forth in Table A which lists: radii; thicknesses and spaces; refractive indices neand Abbe numbers νe.

With water as the immersion medium, the immersion microscope objective of Table A has the following parameters: numerical aperture=0.8; the imaging scale=−24.7; and, the field of view number=18. With glycerine as the immersion medium, the following apply: numerical aperture=0.8; imaging scale=−25.0; and, the field of view number=18. With oil as the immersion medium, the following apply: numerical aperture=0.8; imaging scale=−25.2; and, the field of view number=18.

Table B sets forth the values which are applicable for the different immersion mediums:

The correction of longitudinal chromatic aberrations takes place in a spectral range of 450 nm to 1,000 nm. The deviation of the best focus position of the secondary wavelength from the principal wavelength lies within a depth of field. When using water as the immersion medium, this deviation lies in the range of 450 nm to 950 nm and when using oil as the immersion medium, this deviation lies in the range of 480 nm to 1,000 nm.

The transverse aberrations at different wavelengths in dependence upon the aperture for water as the immersion medium are shown inFIGS. 2ato2c. The transverse aberrations plotted as a function of the aperture for glycerine as the immersion medium are shown inFIGS. 2dto2f. Here, a subdivision of the vertical coordinate EX corresponds to 0.08 mm. The aperture is plotted on the abscissa PX.

FIG. 3ashows, by way of example, the field dependent imaging errors for water as the immersion medium andFIG. 3bshows the field dependent imaging errors for glycerine as the immersion medium at the wavelengths of 546.07 nm, 643.85 nm, 479.99 nm and 435.83 nm.

FIG. 4shows an immersion microscope objective incorporating an adjusting device including means for changing the two air spaces A1and A2inFIG. 1aorFIG. 1b.

The adjusting device comprises correcting rings4.1and4.2which hold optical units (not shown inFIG. 4) and the threaded rings5.1and5.2are connected by bolts6.1and6.2. The threaded rings5.1and5.2have outer threads8.1and8.2, respectively. The bolts6.1and6.2extend through axial breakthroughs3.1and3.2of the cylinder sleeve2and can, together with the threaded rings5.1and5.2and the correction rings4.1and4.2, only be adjusted or displaced in the direction of the optical axis7. The cylinder sleeve2is fixedly mounted in the main mount1.

A rotation about the optical axis7is not possible because the cylinder sleeve2is connected to sleeve12via threaded fastener15and the sleeve12is connected to the main mount1via the threaded pin9. With the rotation of an adjusting ring11about the optical axis7, the mutually connected entraining rings10.1and10.2are taken along and rotated about the optical axis7. The entraining ring10.1comprises two rings connected to each other with adhesive.

The two entraining rings10.1and10.2are connected fixedly to each other via the threaded pin13. With a rotation of the entraining rings10.1and10.2via the adjusting ring11, an axial displacement of the correction rings4.1and4.2and the optical elements held therein is realized. This takes place as a consequence of the coaction of inner threads of the entraining rings (10.1,10.2) with corresponding ones of the outer threads8.1and8.2of the threaded rings (5.1,5.2) which are mounted so that they are resistant to torsion.

Referring toFIGS. 1aand1band by way of example, the two-lens composite member G1comprising fill lens L1and parent spherical lens L2can be mounted in correction ring4.1and biconvex lens L3can be mounted in correction ring4.2. The adjusting device effects a shifting of the optical lenses to achieve a change of the spacings A1and A2. This involves axially displacing the two threaded rings5.1and5.2simultaneously which, in turn, causes the correction rings4.1and4.2to be displaced differently along the optical axis7. This is achieved by imparting different thread pitches to threaded rings5.1and5.2.

The adjusting device shown inFIG. 4and described above does the following:

(a) adapts the immersion microscope objective to different immersion mediums;

(b) corrects aberrations or imaging errors occurring because of the cover glass closing off a specimen vessel; and/or,

The immersion microscope objective described above with respect toFIGS. 1ato4can be used for various immersion mediums and provides an improved image contrast as well as achieving a correction of longitudinal chromatic aberration.