1. Plug connector for light conductors, comprising two connector parts  which can be plugged together and locked to one another and of which at least one connector part is provided with at least one optical ferrule, wherein a locking device is provided, via which the ferrule which is associated with a first connector part can be locked with the other connector part; in that the first connector part comprises a base part which accommodates the ferrule, a housing which is movable in the plugging or axial direction over a definite range relative to the base part and a locking element which is movable in the plugging or axial direction in each case over a definite range both relative to the base part and relative to the housing said locking element being resiliently supported at the base part and being urged by a spring force into a forward securing position when viewed in the plugging direction in which it secures the locking of the ferrule when the connector parts are plugged together, with the locking element first being moved out of its securing position against the spring force during the plugging together of the two connector parts in order to enable a locking of the ferrule , and assuming its securing position again only after the completion of the locking, and with the locking element being movable out of its securing position during the separation of the two connector parts with a drawing back of the housing relative to the base part against the spring force in order to enable an unlocking of the ferrule .

2. Plug connector in accordance with claim 1, wherein the housing is coupled preferably via flexible latching elements to the base part in such a manner that the base part can be moved together with the housing during the plugging together of the two connector parts and, during the separation of the two connector parts , can first be moved back relative to the base part over a definite range while taking along the locking element .

3. Plug connector in accordance with claim 1, wherein the locking element is urged into its securing position through a compression spring which is supported at the base part.

4. Plug connector in accordance with claim 1, wherein the locking element is formed by a preferably ring-shaped slider element.

5. Plug connector in accordance with claim 1, wherein the locking device comprises at least one resilient locking arm which is associated with the other connector part and which in the course of a relative displacement between the ferrule and the other connector part is first deflectable against the spring force by the ferrule and can then be brought into engagement with a locking surface which is provided at the ferrule .

6. Plug connector in accordance with claim 5, wherein at least two mutually oppositely lying locking arms are provided.

7. Plug connector in accordance with claim 5 or claim 6, wherein the locking surface is formed by a groove which is provided at the ferrule.

8. Plug connector in accordance with claim 7, wherein the groove is formed by a peripheral groove.

9. Plug connector in accordance with claim 1, wherein during the plugging together of the two connector parts the locking element first comes to an abutmenet at the deflected locking arm and can thereby be moved out of its securing position, and then assumes its securing position again after a latching in of the locking arm into the locking surface as a result of the spring force in order to hold the locking arm  in engagement with the locking surface .

10. Plug connector in accordance with claim 1, wherein the locking element is executed in ring shape and can be at least partly pushed over the locking arm after a latching in of the locking arm into the locking surface as a result of the spring force.