High aperture immersion objective

The present application is a National Phase entry of PCT Application No. PCT/EP2013/068325, filed Sep. 5, 2013, which claims priority from DE Patent Application No. 10 2012 018 698.3, filed Sep. 21, 2012, said applications being hereby incorporated by reference herein in their entirety.

The invention relates to a high-aperture immersion objective, in particular for applications in confocal microscopy using oil as an immersion liquid, the objective being made up of three subsystems comprised of lenses and/or lens groups.

The performance of a microscope depends primarily on the performance data and correction quality of the microscope objective being used.

In confocal microscopy, a great deal of value is placed on as perfect a parfocality as possible over an extremely large spectral range of 365 nm to 900 nm. This property being sought should if possible also be combined with the requirement of large objective fields, which is very important as well.

An apochromatically corrected microscope objective with a high aperture, a large object field and apochromatic correction in a wavelength range from ultraviolet to infrared is described in DE 102005027 423 A1, for example. However, water is used in this case as the immersion medium.

Known immersion objectives that use water as known solutions have the disadvantage that the numerical aperture is limited to about 1.2. However, higher numerical apertures and thereby a higher resolution capability require an oil immersion as a necessity.

In DE 102009037743 A1, a high-aperture immersion objective of an oil immersion for confocal applications in microscopy is described, the objective consisting of subsystems comprising three lenses and/or lens groups. In this solution, the disadvantage is that no parfocality is achieved in the UV range from 400 nm to 365 nm.

Starting with these disadvantages, the object of the invention is to further improve a high-aperture immersion objective with oil as the immersion liquid, in particular for confocal microscopy applications, in such a way that apochromatic correction in a range of 365 to 900 mm is achieved at high-resolution numerical apertures of 1.3 to 1.4 and an object field of 0.4 to 0.625 mm, and such that the immersion objective also possesses sufficiently good transparency up to a wavelength of 340 nm.

According to the invention, this object is achieved with an immersion objective of the type described above by way of the features of patent claim 1 , wherein the immersion objective is made up of three optical subsystems. Advantageous embodiments are described in the dependent claims 2 through 11 .

Starting from the object side, the

first subsystem comprises a cemented element followed by two collecting lenses, wherein the cemented element comprises a flat surface facing the object side and consists of a collecting lens and a meniscus that is curved toward the object side, the meniscus having a negative refractive power, the second subsystem comprises three optical elements, the first optical element being designed as a collecting element and consisting of a collecting lens and a diverging lens, the second optical element consisting of a diverging triple cemented element with a collecting lens enclosed by two highly-refractive diverging lenses, and the third optical element being designed as a collecting element and consisting of a diverging lens and a collecting lens and the third subsystem comprises two meniscuses whose hollow surfaces face one another, wherein the first meniscus is designed as a cemented element with a collecting lens and a diverging lens and the second meniscus consists of a split cemented element comprising a diverging lens and a collecting lens.

An advantage is that the cemented member of the first subsystem has a weakly negative refractive power, with both collecting lenses being made of a fluoro-crown glass.

Another advantage is to make the collecting lens of the first optical member of the second subsystem out of fluorspar (CaF2) or a fluoro-crown glass.

Also advantageous is to make the collecting lens of the second optical member of the second subsystem of fluorspar (CaF2) or a fluoro-crown glass.

It is expedient for the diverging lenses of the second optical element of the second subsystem to be made of a highly-refractive lanthanum glass.

In another advantageous embodiment, the diverging lens of the third optical member of the second subsystem is made of a short flint glass.

Also advantageous is to make the collecting lens (S 4 ) of the third optical member (G 3 ) of the second subsystem (T 2 ) of fluorspar (CaF2) or a fluoro-crown glass.

It makes sense for the meniscuses of the third subsystem to have weak refractive forces, wherein the last collecting lens of the second meniscus has an Abbe number of less than 34.

The immersion objective according to the invention enables apochromatic correction in a range of 365 to 900 mm at high-resolution apertures of 1.3 to 1.4 and an object field of 0.4 to 0.625 mm. Moreover, the objective has good transparency up to a wavelength of 340 nm.

The invention is explained in more detail below with the aid of exemplary embodiments. Shown are:

FIG. 1 : A representation of the subsystems of the immersion object according to the invention according to a first exemplary embodiment

FIG. 2 : A representation of the immersion objective according to the invention according to FIG. 1 with construction data references,

FIG. 3 : A representation of the subsystems of the immersion objective according to the invention according to a second exemplary embodiment,

FIG. 4 : A representation of the immersion objective according to the invention according to FIG. 3 with construction data references,

FIG. 5 : A representation of the subsystems of the immersion objective according to the invention according to a third exemplary embodiment and

FIG. 6 : A representation of the immersion objective according to the invention according to FIG. 5 with construction data references.

FIGS. 1, 3 and 5 show the lens arrangements of the three optical subsystems of all three exemplary embodiments as seen from the object side, the subsystems identified by T 1 , T 2 and T 3 .

The first subsystem T 1 comprises a cemented element followed by two collecting lenses S 2 and S 3 , wherein the cemented element comprises a flat surface facing the object side OS and consists of a collecting lens S 1 and a meniscus M 1 that is curved toward the object side OS, the meniscus having a negative refractive power.

The second subsystem T 2 is characterized by three optical elements G 1 , G 2 and G 3 , wherein the first optical element G 1 is designed as a collecting element and is made of a collecting lens S 4 and a diverging lens Z 1 .

The second optical element G 2 is made of a diverging triple member comprising a collecting lens S 3 enclosed by two highly-refracting diverging lenses Z 2 and Z 3 . The third optical member G 3 is designed as a collecting member and is made of a diverging lens Z 4 and a collecting lens S 4 .

The third subsystem T 3 is made of two meniscuses M 2 and M 3 whose hollow surfaces face one another, wherein the first meniscus M 2 is designed as a cemented element with a collecting lens S 5 and a diverging lens Z 5 . The second meniscus M 3 is characterized by a diverging lens Z 6 and a collecting lens S 6 representing a split cemented element.

FIGS. 2, 4 and 6 show the lens arrangements of FIGS. 1, 3 and 5 with radii of curvature r 1 to r 24 and thicknesses, or air gaps, d 1 to d 23 of the arrangements according to FIGS. 1, 3 and 5 .

For the first exemplary embodiment according to FIGS. 1 and 2 , the following construction data result at a magnification of 40×, an image field diameter of 25 mm, a numerical aperture of 1.3, a working distance of 0.247 mm, a cover glass thickness of 0.17 mm, refractive indices n e , Abbe numbers v e and oil immersion:

When using the following construction data of a tubular lens unit not shown in more detail:

For the second exemplary embodiment according to FIGS. 2 and 3 , the following construction data result at a magnification of 63×, an image field diameter of 25 mm, a numerical aperture of 1.4, a working distance of 0.201 mm, a cover glass thickness of 0.17 mm, refractive indices n e , Abbe numbers v e and oil immersion:

When using the following construction data of the tubular lens unit not shown in more detail:

For the third exemplary embodiment according to FIGS. 5 and 6 , the following construction data result at a magnification of 63×, an image field diameter of 25 mm, a numerical aperture of 1.4, a working distance of 0.173 mm, a cover glass thickness of 0.17 mm, refractive indices n e , Abbe numbers v e and an oil immersion:

When using the following construction data of the tubular lens unit not shown in more detail: