as shown in fig1 , the ophthalmoscope 10 according to the invention comprises a lower housing part 14 in which an observing unit is arranged behind a central glass pane 42 . the observing direction of the observing unit can be set by a setting rod 26 . provided above the glass pane 24 is an upper housing part 12 in which an illuminating unit with an illuminating source , for example leds , is accommodated . although it is not shown in the drawings for reasons of clarity , in the case of the ophthalmoscope according to the invention , as in the case of the opthalmoscope known from u . s . pat . no . 4 , 684 , 227 , there is firstly arranged between the light source and the observing unit an adjustable diaphragm means , after which there is arranged a filter means with optical filters in the illuminating path . the diaphragm means can be set by a swivel lever means 16 via a mechanism that is not shown . the setting of the filters is enabled by a swivel lever means 17 via a mechanism ( likewise not shown ). two swivel lever means 16 , 17 are of identical design . for this reason , the construction of the swivel lever means 16 , 17 is described with the aid of the swivel lever means 16 for the diaphragm means . a circular bearing opening 32 is provided in the corresponding sidewall 28 of the top housing part 12 . an overall cylindrical bearing section 34 of a rotary element 33 is rotatably supported in the bearing opening 32 . by means of a coaxial screw 36 , the bearing section 34 is connected inside in a rotationally fixed fashion to the diaphragm means in order to adjust it . guided in the bearing section 34 such that it can be displaced in the radial direction of the bearing section 34 is a locking body 40 of a locking element 41 that extends beyond the outside of the bearing section 34 and has on its outside a fluted gripping surface 42 . upwardly extending outside the upper housing part 12 from the bearing section 34 is a lever 38 that has in the region of the locking body 40 a downwardly extending shoulder 46 that , in the unlocking position , shown in fig2 , of the locking body 40 , engages in a recess 44 on the top side of the locking body 40 , and bears against the base thereof . extending radially downward approximately from the axis of rotation of the bearing section 34 at a distance from the vertically running inside of the locking body 40 is a narrow latching slide 52 designed integrally with the locking body 40 . there is formed as a result between the locking body 40 and latching slide 52 a downwardly open u - shaped cutout 48 that extends radially downward and extends longitudinally . the latching slide 52 is guided radially at the side in a slot 59 in the bearing section 34 . as is to be seen in fig4 , there are formed in the edge 35 of the bearing opening 32 a number of latching depressions 54 a , 54 b , 54 c , 54 d that are open toward the axis of rotation and outwardly and have sidewalls 64 , 66 that are inclined to the radial of the bearing opening 32 through the middle of the corresponding latching depression 54 a , 54 b , 54 c , 54 d at an angle α , and are bounded by a tangentially running base 70 . at its tip , the latching slide 52 has lateral surfaces 62 , 68 that are inclined at the same angle as the lateral surfaces 64 , 66 of the latching depressions 54 a to 54 d . it is to be seen in fig3 that a transversely running blind hole 37 in which a helical spring 39 is arranged is formed in the locking body 40 . it is shown in fig6 , in which the locking body 40 is omitted for the purpose of clarity , that there is fastened at the end of the helical spring 39 a ball 43 which projects from the blind hole 37 in the unloaded state . arranged at a distance from one another in the bearing section 34 in a fashion opposite the ball 43 are two substantially concave recesses 51 , 53 in the displacement direction of the locking body 40 , in which the ball 43 engages in the unlocking position or in the locking position of the locking body 40 . the ball 43 biased by the spring 39 ensures that the locking body 40 automatically latches in the unlocking position or in the locking position as soon as the ball 43 has overstepped the edge of the corresponding recess 51 , 53 . if the diaphragm is to be fixed in a specific position , for the purpose of locking the swivel lever means 16 the locking body 40 is displaced downward in the radial direction until the tip of the latching slide 52 strikes the base of the corresponding latching depression 54 a to 54 d , and the sidewalls 62 , 68 of the latching slide 52 bear against the sidewalls 64 , 66 of the corresponding depressions 54 a to 54 d . the swivel lever means 16 is thereby locked . as a result , an inadvertent misadjustment of the swivel lever means 16 , and thus of the diaphragm is prevented . the inclination of the lateral surfaces 62 , 64 , 66 , 68 , and the resistance of the locking body 40 in the radial direction are , however , selected such that in the event of a force that exceeds a previously determined force , the latching slide 52 is moved out of the corresponding latching depression 54 a or 54 d . this prevents damage to the swivel lever means 16 . the inclination angle α is a function of the coefficient of friction between the lateral surfaces 62 , 64 , 66 , 68 and the force that is required in order to move the locking body 40 in the unlocking direction . the angle α is preferably between 10 and 80 degrees . as the swivel lever means 17 is designed like the swivel lever means 16 , the filters can be fixed in the same way as described above .
an ophthalmoscope includes a housing in which there are arranged an observing unit and a light source between which there are / is arranged a diaphragm and / or a filter device that can be set via a swivel lever device mounted outside on the housing . the swivel lever device can be locked in respective latch stages by a locking device .