Proceeding in a same way as for visual is a deliberated choice of my own. There are other ways and this choice raises more from the habit and the confidence acquired with numerous filar micrometer sessions.

If the gaps are too important, we can think that it occurred something wrong during the session and that the reduction will probably give bad results.

The most frequent problem concerns the angles of position. A bad polar alignment or an inopportune rotation of the camera (ie. when refocusing) can reduce all the imaging session to nothing.

However we can take care to record a trail on the visited stars. This is an alternative way to determine the orientation of the camera by measuring the position of several points on this trail. A linear regression permits to deduct the leading coefficient that is the tangent of the shift angle. The rest of the reduction is identical to what is said otherwise, the only difference is that the shift angle is provided by the trail and not by the calibration stars.

The process described here is a process by default that need probably to be deepened on some points.

It goes from the assumption that the projection of the celestial sphere on the narrow field is assimilated to a plan. Nothing is less sure, but while waiting better, it is the one that is usually used. The coordinates of the centroids kept preciously will always undergo the test of new algorithms in the future.

The following table show all steps of a reduction :

What | How | |

0 | Capture the images | |

1 | Select the best ones | |

2 | Measure of the centroïds | IRIS (PSF function) |

3 | Eventual correction for rectangular pixels | X = X * 8.2/7.6 (case of the Quickcam VC) |

4 | Calculation of the differences of rectangular coordinates (only the differences is of interest) | dX = Xb - Xa dY = Yb - Ya |

5 | Determination of the position angle on the matrix | a = arctg(dY/dX) |

6 | Determination of the position angle on the sky (d=shift in relation to the true North) | t = a + d |

7 | Determination of the distance (e = sampling) | r = e * square root
(dX^{2} + dY^{2}) |

8 | Determination of the the angle of position for the observation | theta_{i} = Average
(t) |

9 | Determination of the distance for the observation | rho_{i} = Average (r) |

10 | The averages of three close evenings give the definitive values of the measure | theta = Average
(theta_{i})rho = Average (rho _{i}) |

The principle remains the same that in the table, but step 6 is replaced by the calculation of the shift as follow: d = angle of position of the calibration star - a and the step 7 determines the sampling as follows e = separation of the calibration star / square root (dX

the d and e values are reintroduced in the formulas for the reduction of the stars of the program.

It integrates in a single environment the stages 1 to 9 the previous table.

Its main functionalities are therefore:

- Sorting of the pictures

- Calibration on the calibration stars and determination of the quadrants

- Reductions either manual plots or automatic

- Measure of the internal dispersions

- Generation of importable log for other software

The program and its documentation are distributed freely on simple demand.