Abstract:
The invention relates to an apparatus for tilting a carrier for optical elements with two optical faces which are arranged together on a carrier and are fixed at a fixed angle to one another, the carrier being fastened on a base plate via articulated connections. The carrier can be pivoted about three tilting axes, a first tilting axis preferably being located in the plane of the first optical face and extending normal to the plane of the second optical face, the second tilting axis preferably being located in the plane of the second optical face and extending normal to the plane of the first optical face, and the third tilting axis being located parallel to the line of intersection between the two planes of the optical element.

Description:
RELATED APPLICATION 
     This application relates to and claims priority to corresponding German Patent Application No. 101 18455.7 filed on Apr. 12, 2001. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an apparatus for tilting a carrier for optical elements with two optical faces which are arranged together on a carrier and are fixed at a fixed angle to one another, the carrier being fastened on a base plate via articulated connections. 
     More specifically the invention refers to two mirrors, e.g. plane mirrors as optical elements and also for a beam splitter as optical element. 
     2. Description of the Related Art 
     In the case of optical systems with a plurality of optical axes, the light beams are deflected by mirrors, prisms or beam splitters. For this purpose, it is known, for example, for two plane mirrors, which form a fixed angle between them, to be arranged on a common carrier. The optical elements adjacent to the carrier have to be aligned precisely in relation to one another, this also requiring, for example, precise air clearances to be maintained. If the air clearances are co-ordinated, and the three dihedral angles of the mirror carrier are pre-adjusted, problems arise for the precision adjustment of the dihedral angle. If the tilting angle of one of the two mirrors changes, then this change likewise results in a change in tilting and air clearance for the other mirror, since the two mirrors are fixed to one another. For this reason, in some circumstances, a number of high-outlay follow-up adjustments are then necessary. The mirror carrier thus has to be adjusted in at least five degrees of freedom. If the precise location of the mirror carrier is adjusted beforehand, the latter just has to be tilted about three spatially arranged axes for an orientation adjustment. 
     In the case of known tilting apparatuses, then, a change in tilting angle in the case of one of the two mirrors is also associated with a change in location of the mirror carrier. The location of the mirror carrier is designed, for example, via a reference point RP which is spaced apart from an adjacent optical element by a certain distance a and from another optical element by a certain distance b. In the case of known changes in tilting angle for a mirror, the reference point is displaced, as a result of which the values a and b also change, as does the location of the mirror carrier. It is thus disadvantageously necessary for the location of the mirror carrier and the values a or be to b corrected again. 
     This means that there are two problems. If the air clearances are left unchanged or are included in the calculation, then the location of the apparatus has to be adjusted precisely beforehand. The advantage of this configuration is that there is no need for any reference point for adjustment purposes. 
     In the case of a second, more straightforward type of adjustment, in contrast, a reference point is required. In this case, however, the air clearances are not yet provided and adjustment via an image or via optical imaging is not possible, in some circumstances, due to the lack of imaging. In order to co-ordinate the air clearances, the mirror carrier then also has to be rotated correspondingly about the defined reference point RP. In the case of the first-mentioned possibility, in which case the air clearances are included in the calculation, an optical image may already be present for the precision adjustment of the tilting. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a tilting apparatus for carriers for a plurality of optical elements in the case of which a change in tilting on one optical element, e.g. a plane mirror or a beam splitter only insignificantly affects, if at all, the other optical element or elements. It is intended here for it to be possible for the carrier to be adjusted in three directions in space and, if appropriate, for there to be no change in the location of the carrier or the air clearances in relation to the adjacent optical elements, with the results that there is no need for any follow-up adjustments. 
     A first solution proposes that the carrier can be pivoted about three tilting axes, a first tilting axis, for tilting the first optical face, extending normal to the plane of the second optical face, the second tilting axis, for tilting the second optical face, extending normal to the plane of the first optical face, and the third tilting axis being located parallel to the line of intersection between the two planes of the optical element. 
     A very advantageous configuration of the invention may provide that the first tilting axis is located at the point at which the optical axis passes through the plane of the first optical face, and that the second tilting axis is located at the point at which the optical axis passes through the plane of the second optical face. 
     By virtue of this configuration, only extremely small displacement distances are necessary for the optical element. 
     If the above mentioned three conditions are fulfilled, tilting adjustment of one of the two optical faces is possible without the other face in each case being adjusted out of line and without any change in air clearance. Purely from a design point of view, it is possible, for this purpose, for the carrier, for example, to be fastened cardanically on a base plate. The optical element can be a mirror structure with two mirrors as optical faces or a beam splitter. 
     An advantageous configuration of the invention may provide that the tilting articulations are formed by solid-state articulations. 
     Since only small distances are necessary for adjustment, solid-state articulations are suitable here in particular since they allow very precise and reproducible displacements. 
     Since only very small adjusting angles occur in practice, the adjustment may be regarded as being linear and, in a simplified embodiment of the invention, it is thus possible for the tilting axes to be designed in the form of four-bar mechanisms, it being possible for the instantaneous centre of rotation to be located on the desired axes in each case. 
     A second solution according to claim  9  describes a simplified tilting apparatus, wherein the carrier is arranged to be pivot about a plurality of tilting axes which all run through a reference point. 
     In the case of this solution according to the invention, there are then no translatory displacements, which would mean a change in location, at the reference point RP. In order to define the air clearances, the carrier then has to be rotated from the reference point RP. In this case, however, the installation values a and b are maintained since the carrier is no longer displaced. 
     The simplified tilting apparatus can be used for all components which have to be adjusted in at least five degrees of freedom. This is thus also possible, for example, for prisms and beam splitter cubes. 
     It is advantageously provided here that the vertex of the carrier or the point of intersection between the two mirror planes is used as the reference point RP. 
     It is also advantageously possible here to provide solid-state articulations for adjusting the tilting axes. 
     In comparison with the solution mentioned in claim  1 , the tilting apparatus here is indeed more straightforward but since possibly even in the case of small amounts of tilting decentring of the carriers there is still no image or optical imaging provided, the apparatus can only be adjusted by trial or measurement of the tilting angles. 
     Additional advantages of the present invention will become apparent to those skilled in the art from the following detailed description of exemplary embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an apparatus according to the prior art with two plane mirrors arranged on a mirror carrier, 
         FIG. 2  shows a mirror with an illustration of different movement directions, 
         FIG. 3  shows a diagram with a mirror tilted about one tilting axis, 
         FIG. 4  shows a diagram with the second mirror tilted about one tilting axis, 
         FIG. 5  shows a diagram with the first mirror tilted about a further tilting axis, 
         FIG. 6  shows a diagram with tilting about the tilting axis according to  FIG. 5 , the tilting axis being located at a different location, 
         FIG. 7  shows a section through the apparatus according to the invention along the line VII—VII from  FIG. 8 , 
         FIG. 8  shows a view according to the invention as seen in the direction according to arrow VIII in  FIG. 7 , 
         FIG. 9  shows a view as seen in the direction according to arrow IX from  FIG. 7 , 
         FIG. 10  shows a mirror carrier with two plane mirrors with different movement directions illustrated, 
         FIG. 11  shows an apparatus according to the prior art, 
         FIG. 12  shows a mirror carrier according to  FIG. 10  with a reference point (RP), 
         FIG. 13  shows a design of the apparatus according to  FIG. 11  in accordance with the section along line XIII—XIII from  FIG. 14 , 
         FIG. 14  shows a view of the apparatus according to the invention from  FIG. 13  as seen in arrow direction XIV, 
         FIG. 15  shows a view of the apparatus according to the invention from  FIG. 13  as seen from arrow direction XV, and 
         FIG. 16  shows a beam splitter cube mounted on a manipulator for adjusting and tilting. 
     
    
    
     DETAILED DESCRIPTION 
     Two plane mirrors  1  and  2 , according to  FIG. 1 , are fixed on a carrier, namely a mirror carrier  3 , at a fixed angle to one another. The mirror carrier  3  is connected firmly to a top plate  4 . The top plate  4  is mounted on a ball  5  and adjusting screws  6 ,  7  and  8  such that an adjusting screw  6  can be used to adjust tilting about the φ x  axis. The adjusting screw  7 , which is offset depthwise in relation to the drawing plane, is used to adjust tilting about the φ y  axis and the adjusting screw  8  is used to adjust tilting about the φ z  axis. All three tilting axes run through the center point of the ball  5 . The ball  5  and the adjusting screws  6 ,  7  and  8  are mounted in the base plate  9  which, in turn, is connected firmly to the outside, e.g. the mount of a lens system. By means of a tension spring  10  between the top plate  4  and the base plate  9 , the top plate  4  is pressed against the ball  5  and the adjusting screws  7  and  8 . 
     The mirror carrier  3 , then, is intended to be aligned in relation to the optical axes  11 ,  12 ,  13  and  14 , in which case it is also necessary to maintain the air clearances  21 ,  22 ,  23  and  24  in relation to the adjacent optical elements, e.g. lenses  15 ,  16 ,  17  and  18 . 
     If the optical axes  11 ,  12 ,  13  and  14  are located in one plane, the mirror carrier  3  has to be aligned in five respects, two air clearances and the three dihedral angles φ x , φ y  and φ z . Since, in  FIG. 1 , all the optical axes  11  to  14  are intended to be located in one plane, a displacement of the mirror carrier normal to the drawing plane causes he mirrors  1  and  2  to be replicated as before, with the result that there is no need to co-ordinate the location of the mirror carrier  3  perpendicular to the drawing plane. There is thus only a need for co-ordination in five, instead of six, respects. 
     The location of the mirror carrier  3  in the drawing plane is only determined by two air clearances, the other two air clearances resulting automatically because the optical elements  15  to  18  adjacent to the mirror carrier  3  have to be aligned precisely in relation to one another. 
     If the air clearances  21  to  24  are coordinated and the three dihedral angles of the mirror carrier  3  are pre-adjusted, it is beneficial, for the precision adjustment of the three dihedral angles, for it to be possible for the mirror carrier  3  to be tilted without any change in the air clearances  21  to  24 , since, otherwise, there is a need for a new change in air clearance and, resulting from this, possibly also a new angle adjustment. 
     During tilting adjustment of the mirror  1 , changes in tilting to the other mirror  2 , and vice versa, have a similarly disruptive effect. 
     As can be seen from  FIG. 1 , which describes the prior art, up until now, a change in tilting angle in the case of one of the two mirrors was accompanied by a change in tilting and air clearance of the other mirror, since the two mirrors are fixed in relation to one another on the mirror carrier. That is to say, if the tilting of one mirror is adjusted, the tilting and the air clearance of the other mirror has to be corrected again, which results in a new adjustment operation. 
     This means, in the case of the known apparatus, that a change in tilting angle in the case of one mirror is also associated with a change in the air clearances  21  to  24  and with a change in tilting of the other mirror. 
     If, for example, the φ z  tilting angle of the mirror  1  is adjusted, then the air clearances  21 ,  22 ,  23  and  24  nevertheless also change because the point  19 , the point of intersection between the optical axis  11  and the mirror plane  1 , and the point  20 , the point of intersection between the optical axis  13  and the mirror plane  2 , are displaced in accordance with the vector v 19z  and v 20z , respectively. 
     The normal component of the displacement c 19z  in relation to the mirror plane  1  results in changes in length in the air clearances  21  and  22 ; the normal component of the displacement c 20z  in relation to the mirror plane  2  results in changes in length in the air clearances  23  and  24 . 
     On account of being firmly interconnected by the mirror carrier  3 , the φ z  tilting angle adjustment of one mirror is inevitably accompanied by the φ z  tilting angle adjustment of the other mirror. In the case of the two mirrors having a common carrier, separation of the φ z  tilting movement is not possible. 
     The only possible improvement in the case of the φ z  tilting angle adjustment is to avoid changes in air clearance. 
     In the case of the φ x  and φ y  tilting angle of one of the two mirrors being adjusted, changes in tilting, in addition to changes in air clearance, to the other mirror occur since the respective tilting axes are not oriented normal to the mirror surface which is not to be tilted. 
     For a more straightforward adjustment here, it is necessary to suppress, in addition to the changes in air clearance, also the tilting movements of the mirror which is not to be tilted. 
     According to the invention, then, the intention is to isolate from one another the degrees of freedom for adjusting the pair of mirrors  1 ,  2  and/or the mirror carrier  3 . 
     This is achieved, in the case of small tilting movements, by utilizing sensitive and insensitive movements of an individual mirror. If the tilting of one of the two mirrors is changed, then the other mirror only executes movements which do not result in any change in tilting and air clearance to said mirror (insensitive movement). 
     Taking, for example, the point of intersection  19  between the optical axis  11  and the mirror  1  there are three sensitive movements for the point  19 :
         translation z normal to the mirror plane  1     tilting α x  about an axis in the mirror plane  1     tilting α y  about an axis in the mirror plane  1 , but perpendicular to the tilting α x .       

     Translation normal to the mirror plane  1  at the point of intersection  19  means a change in air clearance  21  and  22 . 
     Tilting actions in the mirror plane  1  give rise to different deflecting angles for the beam on the optical axis  11 , with the result that, following reflection on the mirror  1 , the light beam deviates from the desired optical axis  12 . 
     There are also three insensitive movements, in the case of which the mirror plane  1  is replicated as before:
         translation x in the mirror plane  1     translation y in the mirror plane  1 , perpendicular to the translation x   tilting α z  about the axis normal to the mirror plane  1 .       

     In  FIG. 2 , sensitive movement directions for the mirror  1  are illustrated by solid lines and insensitive movement directions for the mirror  1  are illustrated by dashed lines. 
     For the mirror  2 , analogously to mirror  1 , there are also sensitive and insensitive movements. The insensitive movements cause the mirror  2  to be replicated as before. 
     As can be seen from  FIG. 3 , for the precision tilting adjustment of the mirrors  1  and  2 , a first tilting axis  31  runs through the point of intersection  19  between the optical axis  11  and the mirror  1 , the direction thereof being oriented normal to the mirror  2 . 
     Rotation of the mirror  1  about the tilting axis  31  causes the mirror plane  2   a  to be replicated as before, with the result that neither changes in tilting nor changes in air clearance occur at the mirror  2 . 
     It is also possible here for no changes in air clearance to occur for the mirror  1 , since the tilting axis  31  runs through the point of intersection  19  between the optical axis  11  (or the optical axis  12 ) and the mirror plane  1   a.    
     If the mirrors  1  and  2  do not enclose a right angle, a tilting movement  31   a  for the mirror  1  divides up into tilting  31   b  in the mirror plane  1  and tilting  31   c  normal to the mirror plane  1 . 
     The tilting  31   c  causes the mirror  1  to be replicated as before. The mirror  1  is thus effectively tilted only by the tilting component  31   b  in the mirror plane  1 . 
     As can be seen from  FIG. 4 , in a manner analogous to the first tilting axis  31 , the second tilting axis  32  runs normal to the mirror plane  1   a  through the point of intersection  42  between the optical axis  13  or  14  and the mirror  2 , in order to achieve the situation where it is only the mirror  2  which tilts, without any changes in tilting or air clearance in the case of the mirror  1 . 
     According to  FIG. 5 , the third tilting axis  33  runs parallel to the line of intersection between the mirror  1  and the mirror  2 . In the case of this tilting, the mirror  1  and the mirror  2  are tilted at the same time, it being the intention for no change in the air clearances  21  to  24  to occur both in the case of the mirror  1  and in the case of the mirror  2 . 
     In order for no change for the air clearances  21  and  22  to occur at the mirror  1 , the third tilting axis  33  would have to run through the point of intersection  19  since, in this case, the point of intersection  19  is not displaced in a translatory manner. 
     It would likewise be necessary, however, for the third tilting axis  33  also to pass through the point of intersection  20 , in order that no changes for the air clearances  23  and  24  occur at the mirror  2 . 
     Since, however, the third tilting axis  33  cannot run through the points of intersection  19  and  20  at the same time, a compromise has to be found. 
     In  FIG. 5 , the mirror  1  is tilted at the tilting axis  33 , which is spaced apart from the mirror plane  1  by the distance a and of which the normal to the mirror plane  1  is spaced apart from the point of intersection  19  by the distance d, through the angle φ into the position  1 ′. 
     In the process, the point of intersection  19  moves along the optical axis  11  into the position  19 ′. 
     By virtue of the mirror  1  being tilted through the angle φ, the optical axis  12 ′ reflected on the tilted mirror plane  1 ′ deviates by the angle  2 φ from the original optical axis  12 , the optical axis  12 ′ nevertheless being spaced apart from the original point of intersection  19  by the distance u. 
     An optical axis  12 ″, which intercepts the mirror  1  at the point of intersection  19  and runs parallel to the optical axis  12 ′, would be desirable. 
     The lateral offset u of the optical axis  12 ′ in relation to the desired optical axis  12 ″ may be approximated, for small tilting angles φ, by the following formula. The angle c here is the original angle of incidence of the optical axis  11  in relation to the mirror  1 . 
       μ   =         (       αφ   2     +     2   ⁢           ⁢   d   ⁢           ⁢   φ       )     ·     sin   ⁡     (       2   ⁢   ɛ     +     2   ⁢   φ       )           2   ⁢     (       cos   ⁢           ⁢   ɛ     -     φ   ⁢           ⁢   sin   ⁢           ⁢   ɛ       )             
 
     The distance d of the normal of the tilting axis  33  in relation to the mirror plane  1  has a linear influence on the tilting angle φ, and thus contributes the most to the lateral offset u in the case of small tilting angles φ. In order for this disruptive lateral offset u to be reduced as far as possible, the tilting axis  33  has to be located such that the normal of the tilting axis  33  in relation to the mirror plane  1  intersects the mirror  1  at the point of intersection  19  (see  FIG. 6 ). 
     The lateral offset u is then simplified to the minimal lateral offset u mln : 
         μ   min     =         αφ   2     ·     sin   ⁡     (       2   ⁢   ɛ     +     2   ⁢   φ       )           2   ⁢     (       cos   ⁢           ⁢   ɛ     -     φ   ⁢           ⁢   sin   ⁢           ⁢   ɛ       )             
 
     On account of the quadratic dependence of the axial offset u min  on the tilting angle φ, very small tilting angles φ only result in small values for the lateral offset u min , which may still be located within the tolerance range. 
     In a manner analogous to the mirror  1 , it would also be necessary for the tilting axis  33  to be located on the normal to the mirror plane  2 , at the point of intersection  20  between the optical axis  13  or  14  and the mirror  2 . 
     The tilting axis  33  is thus obtained from the point of intersection between the normal to the mirror  1  at the point of intersection  19  and the normal to the mirror  2  at the point of intersection  20  ( FIG. 6 ). 
     The lateral offset w min  at the mirror  2  (not illustrated) is calculated in a manner analogous to that for the mirror  1 , b being the distance between the point of intersection  20  and the tilting axis  33  and η being the angle of incidence at the mirror  2 . 
         W   min     =       b   ⁢           ⁢       φ   2     ·     sin   ⁡     (       2   ⁢   η     +     2   ⁢   φ       )             2   ⁢     (       cos   ⁢           ⁢   η     -     φ   ⁢           ⁢   sin   ⁢           ⁢   η       )             
 
       FIGS. 7 to 9  show an example of the design of an apparatus for tilting the mirror carrier  3  with the mirrors  1  and  2 , the position of the three tilting axes  31 ,  32  and  33  in space having been selected in accordance with the abovedescribed criteria. 
     The surfaces  1  and  2  of the mirror carrier  3  are mirror-coated and form the mirrors  1  and  2 . Since the mirrors  1  and  2  enclose a right angle, the tilting axis  31  is located in the mirror plane  1   a  and the tilting axis  32  is located in the mirror plane  2   a.    
     The mirror carrier  3  is connected firmly, via its rear side, to a solid-state articulation  41 , of which the articulation axis coincides with the desired tilting axis  33 . Adjusting screws  43  can be used to adjust the tilting angle about the axis  33  and fix the same. 
     The solid-state articulation  41  is connected firmly, on the other side, to a frame  42  which, in turn, is connected firmly, by way of a connection surface  46 , to the outside, e.g. a lens-system housing part  49 . Two solid-state tilting articulations are accommodated in the frame  42 . 
     The articulation axis of one solid-state articulation coincides with the desired tilting axis  32 , it being possible for adjusting screws  44  to be used to adjust the tilting about the axis  32  and to fix the same  FIG. 8 ). 
     The articulation axis of the other solid-state articulation is located on the tilting axis  31 . Adjusting screws  45  can be used to adjust the tilting about the axis  31  ( FIG. 9 ). 
     The configuration of the tilting apparatus which is shown is only by way of example, so it is also possible for the solid-state articulations to be replaced by other rotary articulations. The essence of the invention is the position of the tilting axes  31 ,  32 ,  33  in relation to the mirror planes  1   a  and  2   a,  which allow tilting adjustment of one of the two mirrors  1  or  2  without the other mirror in each case being adjusted out of line and without any change in air clearance. 
     On account of the small angle-adjusting range, it is also possible for the tilting axes  31  to  33  to be approximated by four-bar mechanisms, of which the instantaneous center of rotation is located on the desired axes (not illustrated). 
     A simplified form of a tilting apparatus is described herein below, with reference to  FIGS. 10 to 15 , as an alternative to the exemplary embodiment explained above,  FIG. 11  serving to explain the prior art. 
     For the sake of simplicity, the same designations have been retained for the same parts in this exemplary embodiment, too. 
       FIG. 10  shows the mirror carrier  3  with the two plane mirrors  1  and  2  with an indication of the degrees of freedom and the tilting possibilities.  FIG. 11 , in this respect, illustrates an apparatus according to the prior art. The mirror carrier  3  is intended to be aligned in relation to the optical axes  11 ,  12 ,  13  and  14 , it also being intended to maintain the air clearances  21 ,  22 ,  23  and  24  in relation to the adjacent optical elements  15  to  18 . 
     For this purpose, the mirror carrier  3  has to be adjusted in all six degrees of freedom, the three translatory degrees of freedom defining the location of the mirror carrier and the three rotary degrees of freedom defining the orientation of the mirror carrier. 
     If the location of the mirror carrier  3  has already been adjusted, the mirror carrier  3  may thus be tilted, for an orientation adjustment, about three spatially arranged axes such that its location is not lost during tilting. 
     According to  FIG. 11 , the mirror carrier  3 , as with the first exemplary embodiment, is connected firmly to the top plate  4 . 
     The top plate  4  is likewise mounted on the bowl  5  and the adjusting screws  6 ,  7  and  8  such that the adjusting screw  6  can be used to adjust the tilting about the φ x  axis, the adjusting screw  7 , which is offset depthwise in relation to the drawing plane, can be used to adjust tilting about the φ y  axis, and the adjusting screw  8  can be used to adjust tilting about the φ z  axis. As in the first exemplary embodiment, all three tilting axes thus run through the center point of the bowl  5 . The bowl  5  and the adjusting screws  6 ,  7  and  8  are mounted in the base plate  9  which, in turn, is connected firmly to the outside. 
     By means of the tension spring  10  between the top plate  4  and base plate  9 , the top plate  4  is pressed against the bowl  5  and the adjusting screws  7  and  8 . 
     In the case of the apparatus illustrated in  FIG. 11 , which corresponds to the prior art, a change in tilting angle in the case of one mirror is also accompanied by a change in location of the mirror carrier  3 . 
     In  FIG. 11 , the location of the mirror carrier  3  is defined, by way of example, via the reference point RP on the mirror carrier  3  in relation to the reference surface  15   a  on the mount of the lens  15  and to the reference surface  16   a  on the mount for the lens  16 . The reference point RP is intended to be spaced apart from the surface  15   a  by the distance a and from the surface  16   a  by the distance b. 
     If, for example, the mirror carrier  3  is adjusted by the φ z  tilting angle, then the reference point RP is displaced in accordance with the vector v φz  shown, since the point of rotation is located at the center point of the bowl  5  rather than at the reference point RP. 
     The displacement of the reference point RP results in a change in the values a and b and thus in the location of the mirror carrier  3 . It is thus necessary for the location of the mirror carrier  3  and the values a and b to be corrected again. 
     The location of the mirror carrier  3  is defined by a reference point RP on the mirror carrier  3 , which has to be easily accessible for measuring operations, in relation to one or more adjacent optical elements. Specific surfaces on the optical elements themselves, mounts or some or other component may be used as the reference point for the location of the mirror carrier. 
     In  FIG. 12 , for example, the surface  15   a  on the mount for the lens  15  and the surface  16   a  on the mount for the lens  16  serve as reference planes for the location of the reference point RP on the mirror carrier. The reference point RP is intended to be spaced apart from the surface  15   a  by the distance a and from the surface  16   a  by the distance b. 
     The location of the prism reference point RP perpendicular to the drawing plane is not taken into consideration since a displacement of the mirror carrier  3  in this direction causes the mirrors  1  and  2  to be replicated as before, no optical effects occurring as a result. 
     As an alternative to the reference surfaces  15   a  and  16   a , of course, it is also possible to select surfaces on the mounts for the lenses  17  and  18  or else on other components. 
     During the subsequent tilting adjustment of the mirror carrier  3 , the location must not be adjusted out of line. It is thus necessary for all three tilting axes  31 ,  32  and  33 , which are linearly independent of one another, to run through the reference point RP on the mirror carrier  3 . There are then no translatory displacements, which would mean a change in location, at the reference point RP. 
       FIGS. 13 ,  14  and  15  show an example, in order to fulfil this condition, of an apparatus for adjusting a mirror carrier  3  with the mirrors  1  and  2 . 
     The frame  42  is connected firmly, by way of its connection surface  46  and an adjusting plate  47 , to the outside, e.g. the housing part  49  of a lens system. The adjusting plate  47  serves for adjusting the value b. 
     For adjusting the value a, use is made of an adjusting screw  48 , of which the nut thread is connected firmly to the outside or to the lens-system housing part  49 . 
     The frame  42  also has the solid-state tilting articulation  41  connected to it. Two solid-state articulations are accommodated in the frame  42 , one allowing tilting about the axis  32  and the other allowing tilting about the axis  31 . 
     The adjusting screws  44  are used to adjust the tilting about the axis  32  and to fix the same, and the adjusting screws  45  are used to adjust tilting about the axis  31  and to fix the same. 
     Webs  50  and  51  in the solid-state tilting articulation  41  are aligned in relation to the reference point RP such that they form a four-bar mechanism. The instantaneous center of rotation of the four-bar linkage is located at the reference point RP, with the result that the tilting axis  33  is located perpendicularly to the drawing plane, at the reference point RP. The adjusting screws  45  can be used to adjust tilting about the axis  33  and to fix the same. 
     The mirror carrier  3  is connected firmly, via its rear side, to the solid-state tilting articulation  41 . 
     The tilting axes  31 ,  32  and  33  are linearly independent and always pass through the reference point RP on the mirror carrier  3 . The tilting axis  31  runs randomly through the mirror plane  1   a , and the tilting axis  32  also runs randomly through the mirror plane  2   a.    
     The essence of the invention is the arrangement of the tilting axes  31 ,  32  and  33 , which are linearly independent of one another and all run through the reference point RP. This allows tilting and adjustment of the mirror carrier  3  in three directions in space without the location of the mirror carrier  3  changing and having to be readjusted. 
     Of course, it is also possible for the solid-state articulations in the apparatus, which are illustrated here by way of example, to be replaced by others, e.g. by rotary articulations, provided they allow tilting of the mirror carrier about three independent axes (cardanic suspension) which all intercept at a defined point of the mirror carrier  3 . This defined point serves, at the same time, as the reference point RP for determining the location of the mirror carrier  3 . 
       FIG. 16  shows a beam splitter in the form of a beam splitter cube  300  which corresponds to the carrier  3  with the two mirror planes  1  and  2 . Beam splitters are well known in the art, see for example the U.S. Pat. No. 6,252,712. The apparatus for tilting as described in the following can be used in an optical system as disclosed in the U.S. Pat. No. 6,252,712. The beam splitter cube  300  is mounted on a manipulator  400  which corresponds to the top plate  4  of  FIG. 1 . For adjusting and tilting the beam splitter cube  300 , the manipulator  400  is connected with a base plate  9  in an accurate way as described in  FIGS. 1 to 15 , especially in  FIG. 1 . 
     By tilting the manipulator  400  against the base plate  9 , the beam splitter cube  300  can be tilted and adjusted in the same way as the mirror carrier  3  with the mirror planes  1  and  2  as optical faces. 
     The optical faces of the beam splitter cube  300  are the entrance and exit surfaces for the beams.