DE20207780U1 - Afocal zoom for use in microscopes - Google Patents

Description

Leica Microsystems AG L 008 U-DE

CH-9435 Heerbrugg 10.05.2002/cb/sg/mg

Afocal zoom for use in microscopes

The invention relates to an afocal zoom for use in microscopes with a tube lens, wherein the zoom consists of four consecutive optical assemblies as seen from the object side, wherein the first group has a positive focal length, the second group has a negative focal length, the third assembly has a positive focal length and the fourth assembly has a negative focal length, and wherein the first and fourth assemblies are arranged in a fixed position and the second and third assemblies are arranged to be movable in order to change the magnification of the zoom, wherein the zoom magnification decreases with increasing distance between the second and third assemblies. The invention further relates to a microscope and a stereomicroscope with such an afocal zoom.

Microscopes, especially stereomicroscopes, with an afocal zoom of the type mentioned are used wherever a high object magnification is required, such as in technology companies for the manipulation and inspection of small objects, such as semiconductor structures or micromechanical objects, in research institutes in the life sciences and materials science, and for the examination and manipulation of cells or for surgical purposes. As miniaturization and research into ever smaller specimens progress, the requirements for the resolution of these microscopes are increasing on the one hand, while on the other hand the size of the field of view is increasing with weak light.

Magnification for rapid positioning of specimens and for improved overview during inspections is becoming increasingly important.

In order to increase the magnification of a microscope and to be able to change it continuously over a certain range, these are equipped with a zoom. An afocal zoom projects an object at infinity into an image at infinity. If wE is the angle to the optical axis at which an object point appears at infinity, and wA is the exit angle after passing through the zoom at which the image point appears at infinity, the magnification of the zoom is VZO = tan(wA)/tan(wE). The zoom system allows magnification to be varied without changing the object and image position. The ratio of maximum to minimum zoom magnification is called the zoom factor ζ.

Figure 1 shows an afocal zoom 1 constructed according to the preamble of claim 1. Such a zoom construction is known, for example, from "Optical Designs for Stereomicroscopes", K.-P. Zimmer, in International Optical Design Conference 1998, Proceedings of SPIE, Vol. 3482, Pages 690 - 697 (1998) or from the patent specification US-6,320,702. The known zoom type consists of four optical assemblies Gl, G2, G3 and G4 as seen from the object, with the groups Gl and G4 being arranged in a fixed position. The group Gl has a positive focal length fl, the group G2 has a negative focal length f2, the group G3 again has a positive focal length f3 and the fourth group G4 again has a negative focal length f4. To change the magnification of the zoom, the movably arranged groups G2 and G3 are moved. In Figure la) the position of the highest magnification is indicated, in Figure lb) the position of the lowest magnification. The change in position of the assemblies G2 and G3 is cam-controlled along the optical axis 2. The

The Wüllner equations known from the literature allow the calculation of the corresponding distances, namely the distance D12 between the assemblies Gl and G2, the distance D23 between the assemblies G2 and G3 and the distance D34 between the assemblies G3 and G4, from a known distance between the focal points of the assemblies Gl and G4, from the known focal lengths f2 and f3 and from a selected magnification (of the groups G2 and G3).

As shown in Figure 1, D23 is minimal at the highest magnification and increases from there with decreasing zoom magnification, so that D12 and D34 become minimal at the lowest zoom magnification. The zoom factor of such a system is only limited by the fact that the assemblies G2 and G3 must not penetrate each other at maximum magnification and the assemblies G1 and G2 and G3 and G4 must not penetrate each other at minimum magnification.

ENP is the diameter of the entrance pupil of the zoom 1 at the highest magnification (Figure Ia). The diameter EP of the entrance pupil of the zoom is maximum at the highest zoom magnification. The entrance field angle wE of the zoom is the angle of view at which an object appears at infinity. This angle is maximum at the lowest zoom magnification and takes on the value wl, as can be seen from Figure Ib). The overall length L of the zoom corresponds to the distance between the outer vertices of the assemblies G1 and G4.

Figure 2 shows a schematic diagram of a microscope with an afocal zoom 1. An object 9 is arranged in the front focal point of the objective 10 and is imaged by this towards infinity. The subsequent afocal zoom 1 changes the magnification in a selectable range and again images the object towards infinity. Behind the

·

A tube lens 11 is arranged in the zoom 1, which produces an intermediate image 12, which in turn is visually viewed by the eye 17 through an eyepiece 13. EP denotes the diameter of the entrance pupil of the zoom 1. AP denotes the diameter of the exit pupil of the microscope after the eyepiece 13. As is known, the resolution of the microscope depends on the numerical aperture nA of the objective 10, which is defined as the sine of half the opening angle α of the cone with a tip in the center of the object, which is limited by the entrance pupil EP. For well-corrected optical systems that satisfy the sine condition, the relationship EP = 2 × fO nA applies, where fO denotes the focal length of the objective 10. At a wavelength of λ = 550 nm, the rule of thumb for the resolving power is 3000 × nA (in line pairs per millimeter). Since the numerical aperture increases with the diameter of the entrance pupil, it is obvious that a large diameter EP is required to achieve high resolution.

Figure 3 shows the schematic structure of a telescope-type stereomicroscope. The stereomicroscope enables the observer to obtain a spatial impression of the object 9 being observed. To this end, the object 9, which is located in the front focal point of the objective 10, is imaged via two separate observation channels. The two observation channels 15L and 15R are constructed in the same way and each contain a zoom system IL, IR, a tube lens HL, HR and an eyepiece 13L and 13R. Image inversion systems 16L, 16R arranged behind the tube lenses HL, HR ensure laterally correct upright intermediate images 12L and 12R, which are visually observed with the pair of identical eyepieces 13L, 13R by a pair of eyes 17L and 17R. The two zoom systems IL and IR change

optionally the magnification, but in the same way for the right and the left channel.

The two intermediate images 12L and 12R are different images of the object 9, since the object 9 is viewed in the left channel 15L at the angle wL and in the right channel 15R at the angle wR. In this way, a stereoscopic view of the object 9 is possible, in the same way as when viewing an object through the pair of eyes. The two different images are processed in the brain to form a three-dimensional image.

EP is again the name of the diameter of the entrance pupil of the zoom, where EP is the same for both zooms IL and IR, which can be adjusted in the same way. uL and uR are the half opening angles of the cones with a tip in the center of the object, which are limited by the entrance pupil. uL and uR are the same size, since the microscope is symmetrical to the axis 14 of the objective 10. uL and uR can therefore be named together with u. Since wR and wL are not large, the relationship EP = 2 × fO × sin(u) = 2 × fO × nA applies, analogous to the microscope in Figure 2, where nA again represents the numerical aperture, but this time related to the entrance pupil of the zoom downstream of the objective 10 in each channel.

In the article by K.-P. Zimmer "Optical Designs for Stereomicroscopes" (1998) mentioned above, a zoom for a stereomicroscope as described above is presented, as shown schematically in Figure 4. The applicant launched such a zoom on the market on April 3, 1995 under the name "MZ 12". This zoom is constructed according to the preamble of claim 1. At the highest magnification VZO of the zoom, the entrance pupil diameter ENP is 20 mm, the distances between the optical components

Gl, G2, G3, G4 are D12 = 33.53 mm, D23 = 2.99 mm and D34 = 36.82 mm. The focal lengths of the groups are fl = 65.47 mm, f2 = -15.30 mm, f3 = 32.17 mm and f4 = -43.65 mm. At its smallest magnification setting (see Figure 4b)) the distances are D12 = 7.51 mm, D23 = 62.82 mm, D34 = 3.01 mm. The zoom shown in Figure 4 has a zoom factor ζ of 12.5. It is | fl/f2| = 4.28.

The zoom shown in Figure 4 can be increased to a larger zoom factor ζ in accordance with the Wüllner equations known from the literature by moving the optical assemblies G2 and G3 further along the optical axis 2 without the lens groups penetrating each other. As can be seen from Figure 5a), the assembly G2 is moved by 0.12 mm in the direction of G3 and the assembly G3 is moved by 0.8 mm in the direction of G2, so that the distance D23 = 2.07 mm and accordingly D12 = 33.65 mm and D34 = 37.62 mm. In this setting, the zoom magnification VZO is = 5.2. In Figure 5b), in comparison to the position in Figure 4b), the assembly G2 is moved by 2.27 mm in the direction of Gl and G3 is moved by 0.85 mm in the direction of G4. The zoom magnification VZO in this position is 0.3517. For the zoom shown in Figure 5, the resulting zoom factor is ζ = 14.8. Furthermore, Ifl/f2I = 4.28 and furthermore |z/(fl/f2)| = 3.46.

The disadvantage of the configuration shown in Figure 5 is that increasing the zoom range towards higher magnifications does not lead to higher resolution. Higher resolution can only be achieved by using larger entrance pupil diameters, which leads to large dimensions, particularly in stereomicroscopes (see Zimmer: "Optical Designs for Stereomicroscopes", 1998, page 693). When the resolution limit is reached, increasing microscope magnification leads to what is known as empty magnification,

where no further details can be seen despite increasing magnification.

Finally, US 6,320,702 Bl protects an afocal zoom for microscopes, which also consists of four optical assemblies Gl to G4, which have alternating positive and negative focal lengths. Zooms with a zoom factor ζ > 14 and a focal length ratio of the focal length groups Gl and G2 with | fX/f2| > 3.9 are claimed there. A further advantageous condition is specified there: 3 < |z/(fl/f2) < 5. This limitation is intended on the one hand to prevent excessive zoom lengths, and on the other hand to prevent penetration of the first and second lens groups Gl and G2.

The zoom according to US 6,320,702 Bl contains more lenses overall than the zoom shown in Figures 4 and 5 and also has the disadvantage shown in connection with Figure 5 that a higher zoom factor alone is not suitable for increasing the resolution of the microscope. In addition, a higher zoom magnification is disadvantageously coupled with a reduction in the diameter of the exit pupil of the microscope at maximum magnification.

The object of the present invention is therefore to provide an afocal zoom of the type mentioned at the beginning for high-resolution microscopes with a high zoom factor, which enables continuously variable magnification over the largest possible range while at the same time providing the greatest possible resolution. In addition, the requirements for increasing fields of view should be met.

This object is achieved by the features of independent claims 1 and 2. Advantageous embodiments emerge from the respective subclaims and the following description.

The condition VZO < 41 x ENP/fT, referred to below as (Bl), specifies an upper limit for the zoom magnification, which is proportional to the ratio of the diameter ENP of the zoom entrance pupil at maximum zoom magnification to the focal length fT of the tube lens of the microscope. In this way, the performance data of the zoom are linked to the optical parameters of the microscope. Fulfillment of (Bl) guarantees that the high microscope magnification lies in the range of beneficial magnification and limits the drop in contrast with small exit pupils.

The useful magnification of a microscope is defined as the range of microscope magnification within which all object structures are resolved, magnified and recognized by the human eye. Higher magnification is possible, but not useful, as no further details can be recognized that cannot be imaged by the microscope objective due to limited resolution (empty magnification, which produces a larger image but no finer structures). The ability to recognize details also depends on the contrast of the image. The exit pupil diameter of the microscope plays a role here, as an increasing diameter produces brighter images and the loss of contrast due to diffraction in the eye and irregularities in the vitreous body of the eye is reduced.

Fulfillment of the inventive condition (Bl) ensures for high-resolution microscopes with ENP > 21 mm that with increasing zoom magnification VZO the detail recognizability also increases and that at the same time the contrast loss, which counteracts the detail recognizability, remains limited.

While (Bl) defines a condition for the afocal zoom at maximum magnification, the following condition (B2) specifies a requirement for the zoom at the lowest magnification. According to the invention, (B2) is: tan(wl) > 0.268 x z/ENP. Here, wl is defined as the entrance field angle of the zoom at minimum magnification, as can be seen from Figure Ib), ζ represents the zoom factor, i.e. the ratio of maximum zoom magnification to minimum zoom magnification, where ζ > 15. ENP (to be specified in mm units) again designates the diameter of the zoom entrance pupil at maximum magnification (cf. Figure Ia)), where ENP > 21mm. Fulfillment of (B2) guarantees, like (Bl), that work is carried out in the range of beneficial magnification, and also that a field of view diameter (diameter of the intermediate image) of at least 22 mm can be used even at the lowest magnification. This advantageous property for a microscope formulates condition (B2) based on the required performance of the zoom with regard to the field angle wl at minimum magnification, taking into account the zoom factor ζ and the maximum diameter ENP of the entrance pupil. In an advantageous way, this means that with zooms with a given diameter ENP of the entrance pupil, a larger field of view can be used with increasing zoom factor ζ. This avoids vignetting at the smallest magnifications and thus enables rapid positioning of the specimens and/or an improved overview during inspections.

It is advantageous to simultaneously fulfill conditions (B1) and (B2), since this ensures that when working with the zoom according to the invention, the microscope magnification is in the range of the beneficial magnification, and that a large field of view is available at low magnifications and sufficient resolution is available at highest magnifications.

It has proven to be advantageous if the diameter of the zoom entrance pupil at maximum magnification satisfies the condition 21 mm < ENP < 27 mm. Such entrance pupil diameters are particularly suitable in practice for fulfilling the condition (Bl). In practice, larger entrance pupil diameters lead to large structural dimensions, especially in stereo microscopes, and also to increasing optical imaging errors. On the other hand, smaller entrance pupil diameters lead to reduced resolution.

Furthermore, for the zoom factor ζ, it is advantageous to meet the condition 15 < ζ < 20. In conjunction with conditions (B1) and (B2), working in the range of beneficial magnification with a sufficiently large field of view in the range of low magnification is easily achievable in practice with these zoom factors.

The overall length of the zoom is of great importance for ergonomic and manufacturing reasons. A long zoom results in a large overall height of the microscope and makes it difficult to view without fatigue. Large entrance pupil diameters EP and large zoom factors ζ are difficult to achieve in zooms with a short overall length. It has proven advantageous for the zooms according to the invention to limit the zoom length L upwards by the following condition (B3):

L/ENP < k × Vz < 1.37 Vz

where L is the length of the zoom, measured between the outer lens vertices of the assemblies G1 and G4, and k is a length factor which lies in the range 1.34 and 1.37. For the embodiments according to the invention described below, an upper limit of k = 1.34 can be maintained.

According to the above, high-resolution microscopes require a large entrance pupil diameter ENP of the zoom at maximum zoom magnification. In order to still be able to achieve a short overall length of the zoom, the construction of the assembly Gl should advantageously be designed in such a way that the focal length fl of the assembly Gl remains small despite the large ENP. The following inequality can be set up as a particularly favorable condition (B4):

fl/ENP < 3.5.

Embodiments of zooms according to the invention are presented which satisfy the condition (B4) with an upper limit of 3.3 instead of 3.5 and thus advantageously contribute to a short overall length and good imaging performance with large ENPs.

An upper limit on the number of lenses is advantageous in terms of manufacturing technology and limits costs. Zooms according to the invention with a maximum of eleven lenses are particularly advantageous in this respect.

It is particularly advantageous for the manufacturing costs of the zoom if the assembly G4 consists of a maximum of two lenses cemented together. It is also sensible for the assembly Gl to be constructed from a cemented element followed by a single lens, whereby the cemented element consists of two lenses cemented together, and whereby the single lens is biconvex and in the cemented element the lens with positive refractive power points towards the object.

A particularly advantageous embodiment of an afocal zoom according to the invention is given in Table 1 for the embodiment

1. This embodiment is described in more detail below.

In the following, embodiments of the invention and its advantages are explained in more detail with reference to the accompanying drawings.

Show it

Figure 1 shows a known zoom explained in the introduction to the description in a schematic representation,

Figure 2 shows a microscope explained in the introduction to the description with an afocal zoom according to Figure 1 in a schematic representation,

Figure 3 shows a stereomicroscope of the telescope type explained in the introduction to the description in a schematic representation,

Figure 4 shows a state-of-the-art afocal zoom,

Figure 5 shows the afocal zoom from Figure 4 in slight modification,

Figure 6 shows a schematic representation of an afocal zoom according to the invention in a first embodiment,

Figure 7 shows the imaging performance of the zoom according to Figure 6 at maximum and minimum magnification,

Figure 8 shows a schematic representation of a zoom according to the invention in a second embodiment,

Figure 9 shows the imaging performance of the zoom shown in Figure 8 at maximum and minimum magnification,

Figure 10 shows a schematic representation of a zoom according to the invention in a third embodiment,

Figure 11 shows the imaging performance of the zoom shown in Figure 10 at maximum and minimum magnification,

Figure 12 shows a schematic representation of a zoom according to the invention in a fourth embodiment and

Figure 13 shows the imaging performance of the zoom shown in Figure 12 at maximum and minimum magnification.

Figures 1 to 5 have already been discussed in connection with the prior art in the introduction to the description. Four embodiments of a zoom according to the invention for use in a microscope, in particular a stereo microscope, are presented below. The zooms shown, in combination with a tube with a focal length fT = 160 mm, illuminate an intermediate image diameter of 22 mm. However, the invention is in no way limited to this tube focal length.

First embodiment

The zoom 1 shown in Figure 6 consists of four optical assemblies Gl, G2, G3 and G4, of which Gl and G4 are fixed in position, while G2 and G3 can be moved along the optical axis 2 to adjust the magnification VZO of the zoom 1. Figure 6a) shows the zoom

position with a maximum zoom magnification VZO = 5.66, for which the diameter of the entrance pupil is maximum with ENP = 22.5 mm. Figure 6b) shows the zoom setting at the lowest magnification with VZO = 0.35, so that the zoom factor ζ = 16 results. At minimum magnification, the entrance field angle of the zoom is wl = 11.23°.

This results in the condition (Bl): VZO < 41 x ENP/fT = 41 x 22.5 mm/160 mm = 5.77, so that the zoom with its maximum magnification of 5.66 fulfills the condition (Bl).

For the second condition (B2) we get: tan(wl) = 0.20 ^ 0.268 × z/ENP = 0.268 × 16/22.5 = 0.19, so that condition (B2) is also fulfilled.

In the example shown, the ratio of the overall length L of the zoom 1 to the maximum entrance pupil diameter ENP is L/ENP = 5.33, so that condition (B3) with 5.33 < 1.37 × Vz = 1.37 × 4 = 5.48 is also fulfilled.

With a focal length fl = 73.06 mm for the optical assembly Gl of zoom 1, the condition (B4) is: fl/ENP = 3.25 < 3.5.

In summary, it can be stated that all four conditions (B1) to (B4) are met for the embodiment shown, so that the zoom according to the invention guarantees a strong microscope magnification that is in the range of beneficial magnification and enables the object image to be viewed with a usable field of view diameter of 22 mm and sufficient contrast. The overall length of the zoom is L = 120 mm, smaller than comparable zooms and thus sufficiently small to ensure ergonomic and

to ensure a microscope height that is favorable for positioning. This is also supported by the relatively short focal length of fl = 73.06 mm at ENP = 22.5 mm.

As can be seen from Figure 6a, the optical assembly G1, viewed from the object side, initially has a cemented element in which a lens 57 with positive and a lens 58 with negative focal power are cemented, and a subsequent individual lens 59. In the cemented element, the lens 57 with positive refractive power faces outwards. The individual lens 59 is biconvex. This structure results in a total of five lens surfaces. The optical assembly G2 consists of an individual lens and a cemented element (surface numbers 6 to 10), the assembly G3 also consists of an individual lens and a cemented element (surface numbers 11 to 15) , but in contrast to the assembly G2 has positive refractive power. The assembly G4 is finally designed as a single two-lens cemented element with negative refractive power (surface numbers 16 to 18) . Table 1 below gives the numerical data for this zoom.

Table 1

Areas
number radius
[mm] Distance [mm] 1.49700 Vd Pg, F Pc, t 1 61.31 4.55 1. 74400 81 .6 0.5375 0.8236 2 -42.17 2.0 44.8 0.5655 0.7507 3 -775.05 0.1 1.49700 4 92.37 3.35 81.6 0.5375 0.8236 5 -92.37 Dl 41.59 + 5.51 1.48749 6 -42.45 1.5 70.2 0.5300 0.8924 7 23.20 1.72 1.62041 8th -57.04 1.2 1.78470 60.3 0.5427 0.8291 9 12 .31 2.6 26.3 0.6135 0.6726 10 30.51 D2 5.31 H-78.67 1.49700 11 44.65 2.46 81.6 0.5375 0.8236 12 -44.65 0.2 1.74950 13 26.40 2.1 1.49700 35.3 0.5869 0.7140 14 13.95 5.1 81.6 0 .5375 0.8236 15 94 .46 D3 42.84 H-5.56 1.67270 ■16 -26.60 2 .2 1.51633 32.1 0.5988 0.7046 17 -14.16 1.2 64.1 0.5353 0.8687 18 45 . 96

In the rows of the table, from left to right, the surface number, the radius of curvature, the distance to the next surface, the refractive index n _d , the dispersion v _d and the partial dispersions P _9/F and P _C/C are listed. Where na is the refractive index, Vd = (rtd -1) / (n _F - n _c ) is the Abbe number, P _9/F = {n _g - n _F ) / (n _F - n _c ) is the relative partial dispersion for the wavelengths g and F ₁ and P ₀ ,t = ( ⁿ c - ⁿ t) I (n _F - n _c ) is the relative partial dispersion for the wavelengths C and t. An air distance is indicated by a blank line in the material information. Dl, D2 and D3 are the variable distances.

The wavelengths are defined as follows: the yellow helium line d with &lgr; = 587.56 nm, the blue mercury line
g with &lgr; = 435.83 nm, the blue hydrogen line F with &lgr; = 486.13 nm, the red hydrogen line C with &lgr; = 656.27
nm and the infrared mercury line t with λ = 1013.98 nm.

·

Figure 7 now shows the imaging performance of the zoom from Figure 6. Figure 7a) shows the imaging performance at maximum zoom magnification of VZO = 5.66, while Figure 7b) shows the imaging performance at minimum zoom magnification VZO = 0.35. Spherical aberration, astigmatism and distortion are plotted for two wavelengths, namely the d-line at λ = 587.56 nm and the g-line with λ = 435.83 nm. The aperture error is given in diopters as a function of the pupil height. The image shells and the distortion are plotted over the field angle in diopters or percent. In the case of astigmatism, a distinction is also made between the meridional and the sagittal shell.

The zoom has a good correction of the aperture error (spherical aberration) and a good correction of the color errors (chromatic aberration), in particular a clear reduction of the secondary spectrum, as can be seen from the course of the aberration curves for the wavelength 435.83 nm. Astigmatism, field curvature and distortion are designed in such a way that the usual imaging errors of the tube lens and eyepiece are compensated. The structure of the optical assembly Gl already described makes it possible to correct the aperture error with a large diameter ENP in the case of maximum magnification and the astigmatism for a large field angle wl in the case of the weakest magnification. By suitably arranging an aperture in the zoom, it can be advantageously achieved that as the magnification VZO increases, the numerical aperture of the microscope and thus the resolution of the microscope coupled to it, as explained above, increases steadily.

iö* ^# -

Second embodiment

Figure 8 shows the schematic representation of another zoom 1 according to the invention with an entrance pupil diameter at maximum zoom magnification of ENP = 27 mm, at a maximum zoom magnification of VZO = 5.66. The entrance field angle wl of the zoom 1 at minimum magnification is 11.14° at VZO = 0.35, so that a total zoom factor of ζ = 16 results.

From this, the following is calculated for condition (Bl): VZO ^ 41 × ENP/fT = 41 × 27/160 = 6.92, so that the maximum magnification of VZO = 5.66 satisfies this condition. Furthermore, tan(wl) = 0.20 > 0.268 × 16/27 = 0.16, which satisfies condition (B2).

The overall length of the zoom shown in Figure 8 is L = 140 mm, so that L/ENP = 5.19 < 1.37 x Vz = 5.48, which satisfies condition (B3). Finally, for a focal length fl = 76.43 mm, the ratio fl/ENP = 2.83, which also satisfies condition (B4). The zoom shown in Figure 8 therefore has all the advantages associated with the satisfaction of the above conditions, as already explained for the first embodiment.

Table 2 below gives the numerical data of the zoom from Figure 8, whereby the area numbers are the same as those stated in connection with Figure 6.

Table 2

Areas
number radius
[mm] Distance [mm] n _d Vd Pq, F Pc. t 1 95.60 9.17 1.49700 81.6 0.5375 0.8236 2 -40 . 60 2.0 1.74400 44 . 8 0.5655 0.7507 3 -308.35 0.1 4 72.31 4.09 1.49700 81 .6 0.5375 0.8236 Ul -98.39 Dl43.98 -^
7.94 6 -82.59 1.5 1.48749 70.2 0.5300 0.8924 7 17.46 2.34 8th -27.87 1.2 1.62041 60 .3 0.5427 0.8291 9 17. 84 2.67 1.78470 26.3 0.6135 0.6726 10 113.74 D2 5.12 ■*-
84.85 11 48 .45 2.31 1.49700 81.6 0.5375 0.8236 12 -64.60 0.1 13 38.96 5.56 1.74950 35.3 0.5869 0.7140 14 17.14 2.82 1.49700 81.6 0.5375 0.8236 15 -269.15 D3 49.25 -7-
5.56 16 -33.02 4.26 1.67270 32.1 0.5988 0.7046 17 -17.55 3.53 1.51633 64.1 0.5353 0.8687 18 52.77

In the rows of the table, from left to right, the surface number, the radius of curvature, the distance to the next surface, the refractive index n _d , the dispersion v _d and the partial dispersions P _9iF and P _C/t are listed. Here , na is the refractive index, v _d = (nd -1) / {n _F - n _c ) is the Abbe number, P _9/F = (n _g - n _F ) / (n _F - n _c ) is the relative partial dispersion for the wavelengths g and F ₁ and P _c ,t = (-^c - ^t) / (n _F - n _c ) is the relative partial dispersion for the wavelengths C and t. An air distance is indicated by a blank line in the material information. Dl, D2 and D3 are the variable distances.

Figure 9 shows the imaging performance of the zoom according to the invention in accordance with the second embodiment at the maximum magnification of VZO = 5.66 (Figure 9a)) and at the minimum magnification of VZO = 0.35 (Figure 9b)). For details, please refer to the information already provided in connection with

Figure 7 explained in the first embodiment.

Third embodiment

Figure 10 shows a zoom according to the invention in a further embodiment in a schematic representation. Both the maximum zoom magnification and the maximum diameter of the entrance pupil are significantly increased in this zoom. The maximum diameter of the entrance pupil of the zoom 1 at a maximum zoom magnification of VZO = 6.76 is ENP = 27 mm. At a minimum zoom magnification of VZO = 0.34, the zoom entrance angle wl = 11.59°, so that the following results:

(Bl) VZO < 41 &khgr; ENP/fT = 41 &khgr; 27/160 = 6.92. With a maximum magnification of VZO = 6.76, the upper limit of (Bl) is exceeded.

(B2) tan(wl) = 0.2 > 0.268 xz/ENP = 0.268 &khgr; 20/27 = 0.20, so that condition (B2) is also satisfied.

The overall length of the zoom in this case is 140 mm, so that L/ENP = 5.19 < 1.37 × -Jz = 6.13, which satisfies condition (B3). The optical assembly Gl of the zoom shown in Figure 10 has a focal length of fl = 79.86 mm, so that fl/ENP = 2.96 < 3.5, which also satisfies condition (B4).

The advantages resulting from the fulfilment of the above conditions apply as already stated above. The following table shows the numerical data of the zoom shown in Figure 10 for each individual area number.

&bull; · &bull; ·

Table 3

Areas
number radius
[mm] Distance [mm] n _d Vd P ₃ . F Pc, t 1 102.52 5.07 1.49700 81.6 0.5375 0.8236 2 -42.42 2.0 1.74400 44.8 0.5655 0.7507 3 -312.91 0.1 4 76.50 4.05 1.49700 81.6 0.5375 0.8236 5 -102.65 Dl49.35 +
9.02 6 -46.18 1.5 1.48749 70 .2 0.5300 0.8924 7 20.39 1.96 8th -46.61 1.2 1.62041 60.3 0.5427 0.8291 9 13.60 2.67 1.78470 26.3 0.6135 0.6726 10 40.59 D2 5.26 +
88.89 11 44.20 2.35 1.49700 81.6 0.5375 0.8236 12 -58.28 0 . 1 13 32.66 5.13 1.74950 35.3 0.5869 0.7140 14 15.09 2.99 1.49700 81.6 0.5375 0.8236 15 437.12 D3 50.13 -r
6.83 16 -29.87 4.95 1.67270 32.1 0.5988 0.7046 17 -15.67 1.2 1.51633 64.1 0.5353 0.8687 18 43.26

In the rows of the table, from left to right, the surface number, the radius of curvature, the distance to the next surface, the refractive index n _d , the dispersion v _d and the partial dispersions P _9iF and P _c ,t are listed. Where n _d is the refractive index, v _d = (n _d -1) / (n _F - n _c ) the Abbe number, P _9/F = {n _g - n _F ) / {n _F - n _c ) the relative partial dispersion for the wavelengths g and F ₁ and Pc,t = ( ⁿ c - n _t ) / (n _F - n _c ) the relative partial dispersion for the wavelengths C and t. An air distance is indicated by a blank line in the material information. Dl, D2 and D3 are the variable distances.

Figure 11 shows the imaging performance of the third embodiment of the zoom according to the invention, with spherical aberration, astigmatism and distortion being shown in Figure 11a) at a maximum magnification of VZO = 6.7 6 and in Figure 11b) at a minimum magnification of VZO = 0.34.

For details of this representation and the properties resulting from it, please refer to the similarly constructed zoom of the first embodiment (see Figure 7).

Fourth embodiment

Figure 12 finally shows a fourth embodiment of the zoom 1 according to the invention, again in a similar structure to the previous embodiments, whereby in this example a high zoom factor of ζ = 20 is linked to a smaller maximum entrance pupil diameter of ENP = 22.5 mm. The maximum zoom magnification is VZO = 5.66, as shown in Figure 12a), the maximum entrance field angle of the zoom at minimum magnification is wl = 13.88°. The focal length fl of the first optical assembly Gl is fl = 73.48 mm. This results in:

(Bl) VZO < 41 × ENP/fT = 41 × 22.5/160 = 5.77, so that the maximum zoom magnification of 5.66 remains below this upper limit.

(B2) tan(wl) = 0.25 > 0.268 x z/ENP = 0.268 &khgr; 20/22.5 = 0.24.

(B3) L/ENP = 5.78 < 1.37 &khgr; Vi = 6.13.
(B4) fl/ENP = 3.27 < 3.5.

Thus, the zoom according to the invention shown in Figure 12 also combines all the advantages that are provided by fulfilling the conditions (B1) to (B4). Table 4 below shows the numerical data for each of the 18 surfaces of the zoom structure from Figure 12.

Table 4

Areas
number radius
[mm] Distance [mm] n _d Vd P ₃ . F Pc, t 1 70.76 4.39 1.49700 81.6 0.5375 0.823S 2 -42.39 2.0 1.74400 44.8 0.5655 0.7507 3 -478.21 0 . 1 4 78 .22 3.37 1.49700 81.6 0.5375 0.8236 5 -104.35 Dl 44 . 01 -T-
5.4 6 -133.05 1.5 1.48749 70 .2 0.5300 0.8924 7 15.41 3 .22 8th -26.68 1.2 1.62041 60.3 0.5427 0.8291 9 15.90 2.70 1.78470 26.3 0.6135 0.6726 10 79.38 D2 5.11 *
86.89 11 46.72 4.40 1.49700 81.6 0.5375 0.8236 12 -75.42 0.1 13 37.82 3.20 1.74950 35.3 0.5869 0.7140 14 17.47 2.90 1.49700 81.6 0.5375 0.8236 15 -126.80 D3 48.67 -&tgr;-
5.5 16 -32.81 1.94 1.67270 32.1 0.5988 0.7046 17 -16.80 1.2 1.51633 64.1 0.5353 0.8687 18 47.26

The rows of the table list from left to right the surface number, the radius of curvature, the distance to the next surface, the refractive index n _d , the dispersion v _d and the partial dispersions P _9/F and P _C/t . Where n _d is the refractive index, v _d = {n _d -1) / (n _F - n _c ) is the Abbe number, P _9iF = (n _g - n _F ) / {n _F - n _c ) is the relative partial dispersion for the wavelengths g and F, and P _C/t = (n _c - n _t ) / {n _F - n _c ) is the relative partial dispersion for the wavelengths C and t. An air distance is indicated by a blank line in the material information. Dl, D2 and D3 are the variable distances.

Figure 13 shows the imaging performance of the zoom according to the fourth embodiment in the usual representation for a zoom magnification of VZO = 5.66 in Figure 13a) and for a zoom magnification of VZO = 0.28 in Figure 13b). Since the zoom is constructed similarly to that described in the first embodiment, the analogous explanations also apply here.

List of terms

1 - Afocal zoom

2 - Optical axis of the zoom

5 - Upper marginal ray

6 - Lower marginal ray

9 - Object in the front focal point of the lens

10 - Lens

11, HL and HR - tube lens, in stereo microscopes in the left or right channel

12, 12L and 12R - intermediate image, in stereo microscopes in the left or right channel

13, 13L and 13R - Eyepiece, for stereo microscopes in the left or right channel

14 - Axis of the lens 10

15L and 15 R- Left and right viewing channels for stereo microscopes

16L and 16R image inversion systems in the left and right observation channels
17, 17L and 17R - Eye, left and right eye

55, 56 - cemented lenses of assembly G4 57, 58 - cemented lenses of assembly Gl 59 - single lens of assembly Gl

AP - diameter of the exit pupil of a microscope

D12 - Distance between zoom elements Gl and G2 D23 - Distance between zoom elements G2 and G3 D34 - Distance between zoom elements G3 and G4

EP - diameter of the entrance pupil of the zoom

ENP - Diameter of the entrance pupil of the zoom at maximum magnification

fl - focal length of the 1st lens group Gl f2 - focal length of the 2nd lens group G2 f3 - focal length of the 3rd lens group G3 f4 - focal length of the 4th lens group G4 fO - focal length of the lens
fT - focal length of the tube lens

Gl - optical assembly of the 1st zoom element

G2 - optical assembly of the 2nd zoom element

G3 - optical assembly of the 3rd zoom element

G4 - optical assembly of the 4th zoom element

k - length factor

L - mechanical length of the zoom, given by the distance between the outer vertices of the groups Gl and G4

nA - numerical aperture of the lens

u, uR, uL - half the opening angle of the beam cone with tip in the object center, which is limited by ENP

VZO - Zoom magnification

wA - exit field angle from a telescope/zoom wE - entrance field angle into a telescope/zoom wl - entrance field angle of the zoom at minimum zoom magnification

wL, wR - angle to the optical axis 14 of the beam, which after refraction in the objective 10 forms the optical axis of the left or right observation channel 15L and 15R.

ζ - Zoom factor = maximum zoom magnification/minimum zoom magnification

Conditions used

(Bl) VZO < 41 x ENP/ft (B2) tan(wl) ^ 0.268 &khgr; z/ENP (B3) L / ENP < 1.37 &khgr; Vz (B4) fl / ENP < 3.5

Claims (13)

1. Afocal zoom ( 1 ) for use in microscopes with a tube lens ( 11 ), wherein the zoom consists of four consecutive optical assemblies (G1, G2, G3, G4) when viewed from the object side, wherein the first assembly (G1) has a positive focal length (f1), the second assembly (G2) has a negative focal length (f2), the third assembly (G3) has a positive focal length (f3) and the fourth assembly (G4) has a negative focal length (f4), and the first and fourth assemblies (G1, G4) are arranged in a fixed position, and wherein the second and third assemblies (G2, G3) are arranged to be movable in order to change the magnification of the zoom ( 1 ), wherein the zoom magnification decreases with increasing distance (D23) between the two assemblies (G2, G3), characterized in that
that the magnification (VZO) of the zoom meets the following condition:
VZO ≤ 41 × ENP/fT,
where ENP is the diameter of the zoom entrance pupil at maximum zoom magnification and fT is the focal length of the tube lens ( 11 ) of the microscope, and where ENP > 21 mm. 2. Afocal zoom ( 1 ) for use in microscopes with a tube lens ( 11 ), wherein the zoom consists of four consecutive optical assemblies (G1, G2, G3, G4) when viewed from the object side, wherein the first assembly (G1) has a positive focal length (f1), the second assembly (G2) has a negative focal length (f2), the third assembly (G3) has a positive focal length (f3) and the fourth assembly (G4) has a negative focal length (f4), and the first and last assemblies (G1, G4) are arranged in a fixed position, and wherein the second and third assemblies (G2, G3) are arranged to be movable in order to change the magnification of the zoom ( 1 ), wherein the zoom magnification decreases with increasing distance (D23) between the two assemblies (G2, G3), characterized in that
that the entrance field angle (w1) of the zoom ( 1 ) at minimum zoom magnification satisfies the following condition:
tan(w1) ≥ 0.268 × z/ENP,
where z is the zoom factor and ENP is the diameter of the zoom entrance pupil in mm units at maximum zoom magnification, and where ENP > 21 mm and z > 15. 3. Afocal zoom ( 1 ) according to claim 1, characterized in that the entrance field angle (w1) of the zoom ( 1 ) at minimum magnification satisfies the condition
tan(w1) ≥ 0.268 × z/ENP
where z is the zoom factor and ENP is in mm units, and where z > 15. 4. Afocal zoom ( 1 ) according to one of claims 1 to 3, characterized in that the diameter of the zoom entrance pupil (ENP) at maximum zoom magnification satisfies the condition 21 mm < ENP ≤ 27 mm. 5. Afocal zoom ( 1 ) according to one of claims 1 to 4, characterized in that the zoom factor (z) satisfies the condition 15 < z ≤ 20. 6. Afocal zoom ( 1 ) according to one of claims 1 to 5, characterized in that the following condition is met for the length (L) of the zoom:
L/ENP ≤ 1.37 × &radic;z,
where z is the zoom factor and L is the length of the zoom measured between the outer lens vertices of the stationary assemblies (G1, G4). 7. Afocal zoom ( 1 ) according to one of claims 1 to 6, characterized in that it satisfies the condition
f1/ENP ≤ 3.5
Fulfills. 8. Afocal zoom ( 1 ) according to one of claims 1 to 7, characterized in that the zoom ( 1 ) is composed of a maximum of 11 lenses. 9. Afocal zoom ( 1 ) according to one of claims 1 to 8, characterized in that the fourth assembly (G4) consists of at most two lenses ( 55 , 56 ) cemented together. 10. Afocal zoom ( 1 ) according to one of claims 1 to 9, characterized in that the first assembly (G1) consists of at most one cemented element made of two lenses ( 57 , 58 ) cemented together and a single lens ( 59 ), wherein, viewed from the object side, the cemented element is arranged first and then the single lens ( 59 ), wherein the single lens ( 59 ) is biconvex and the lens ( 57 ) with positive refractive power is arranged in the cemented element towards the object side. 11. Afocal zoom ( 1 ) according to one of claims 1 to 10, characterized by a lens arrangement specified by the following table, wherein the surface numbers 1 to 5 are assigned to the first assembly (G1), the surface numbers 6 to 10 to the second assembly (G2), the surface numbers 11 to 15 to the third assembly (G3) and the surface numbers 16 to 18 to the fourth assembly (G4), and wherein ENP = 22.5 mm and z = 16:


where the surface number of a lens or cemented element, the radius of curvature of the respective surface, the distance to the next surface, the refractive index (n _d ), the dispersion (ν _d ) and the partial dispersions (P _g,F and P _C,t ) are listed in the columns of the table and n _{d is} the refractive index, ν _d = (n _d - 1)/(n _F - n _C ) is the Abbe number, P _g,F = (n _g - n _F )/(n _F - n _C ) is the relative partial dispersion for the wavelengths g and F, and P _C,t = (n _C - n _t )/(n _F - n _C ) is the relative partial dispersion for the wavelengths C and t, and where an air distance is further indicated by a blank line in the material information and D1, D2 and D3 denote variable distances. 12. Microscope with an afocal zoom ( 1 ) according to one of claims 1 to 11. 13. A telescope-type stereomicroscope with an afocal zoom ( 1 ) according to any one of claims 1 to 11.