Automatic focusing method for an optical instrument for magnified viewing of an object

1. A method of focusing an optical instrument for magnified viewing of an object, the optical instrument comprising instrument optics, an adjusting unit for adjusting the focal position when viewing the object by means of the instrument optics, and a recording unit which records the object by means of the instrument optics, the method comprising the steps of:

a) producing at least two images with different focal positions;

b) applying several different sharpness functions to each of the at least two images, each of the several different sharpness functions having an absolute extremum which specifies the optimum focal position to be set for the viewing and which lies in a close focus range of the sharpness function adjoined on both sides by a far focus range which is more susceptible to interferences during recording than the close focus range and therefore contains local secondary extrema, with the focal position as a variable such that a sharpness function variation direction of the focal position is calculated for each sharpness function in order to arrive at the optimum focal position;

c) determining a main variation direction by simultaneously utilizing together all sharpness function variation directions such that the main variation direction is calculated based on all of the sharpness function variation directions; and

d) using the determined main variation direction during further focusing.

2. The method according to claim 1 , wherein the sharpness function variation direction in step b) is determined by means of a gradient calculation.

3. The method according to claim 2 , wherein, in step c) the main variation direction is determined by a majority decision or a weighted majority decision from among all sharpness function variation directions.

4. The method according to claim 3 , wherein, in step c) it is ascertained, based on all sharpness function variation directions, whether the focal positions of the at least two images lie in one of the far focus range and in the close focus range, and this is taken into account during further focusing.

5. The method according to claim 4 , wherein, during further focusing, the step size for changing the focal position for further images is set higher if the far focus range has been ascertained compared with the case where the close focus range has been ascertained.

6. The method according to claim 2 , wherein, in step c) it is ascertained, based on all sharpness function variation directions, whether the focal positions of the at least two images lie in the far focus range or in the close focus range, and this is taken into account during further focusing.

7. The method according to claim 6 , wherein, during further focusing, the step size for changing the focal position for further images is set higher if the far focus range has been ascertained compared with the case where the close focus range has been ascertained.

8. The method according to claim 1 , wherein, in step c) the main variation direction is determined by one of a majority decision and a weighted majority decision from among all sharpness function variation directions.

9. The method according to claim 8 , wherein, in step c) it is ascertained, based on all sharpness function variation directions, whether the focal positions of the at least two images lie in one of the far focus range and in the close focus range, and this is taken into account during further focusing.

10. The method according to claim 9 , wherein, during further focusing, the step size for changing the focal position for further images is set higher if the far focus range has been ascertained compared with the case where the close focus range has been ascertained.

11. The method according to claim 1 , wherein, in step c) it is ascertained, based on all sharpness function variation directions, whether the focal positions of the at least two images lie in one of the far focus range and in the close focus range, and this is taken into account during further focusing.

12. The method according to claim 11 , wherein, during further focusing, the step size for changing the focal position for further images is set higher if the far focus range has been ascertained compared with the case where the close focus range has been ascertained.

13. An optical instrument for magnified viewing of an object, comprising:

instrument optics;

an adjusting unit for adjusting the focal position when viewing the object by means of the instrument optics,

a recording unit which records the object by means of the instrument optics; and

an evaluation and control unit, the evaluation and control unit configured:

to be fed at least two images with different focal positions;

to apply several different sharpness functions to each of the at least two images, each of the several different sharpness functions having an absolute extremum which specifies the optimum focal position to be set for the viewing and which lies in a close focus range of the sharpness function adjoined on both sides by a far focus range which is more susceptible to interferences during recording than the close focus range and therefore contains local secondary extrema, in each case to each of the at least two images, and evaluate them with the focal position as a variable such that for each sharpness function a sharpness function variation direction of the focal position is calculated in order to arrive at the optimum focal position;

to determine a main variation direction by simultaneously utilizing together all sharpness function variation directions such that the main variation direction is calculated based on all of the sharpness function variation directions; and

to use the determined main variation direction during further focusing.