Not available nor applicable with SkyGuide

SkyGuard allows to define different relative roundness (RRDN) calibrated values for each filter.

That should not be confused with the filter offset values used by the imaging software for keeping the imaging camera at best focus from one filter to the next. As a matter of fact such offsets are changing the guider FOV astigmatism and related roundness values, which in term requires this filter calibration for SkyGuard.

This is very useful when the filters that are mounted in the filter wheel are not parfocal.

To define the relative roundness per filter, click on the  button.

Current filter displays the name of the filter currently selected in the filter wheel

RRDN offset allows to define the same offset to all filters.

This is very useful when the camera and its filter wheel are mounted to another setup. It allows to compensate the difference between the two setups without having to set a new RRDN to each filters.

Filter settings displays the list of all available filters mounted in the filter wheel. Beside each filter, the specific RRDN is displayed if it has been defined. If o value is displayed this means that the related RRDN offset is zero indeed.

Usually one does not need any filter offset calibration for the filter used for the initial focuser calibration (likely the broadest band one).

To define a reference RRDN for each filters of your filter wheel, please follow the procedure below:

 The focuser must be calibrated before!

 This is an important step that should be done with as much care as possible, take your time. We also suggest to use a bright (yet below clipping) single star, near the zenith. More than one star in the guider FOV is not recommended for SKG calibration.

1. Start exposing

2. If focusing is running then stop focusing to avoid focuser move while defining filter RRDN

3. Move the filter wheel to one filter mounted in the filter wheel (e.g. the red one)

4. Imaging camera should be at best focus (use your usual focusing procedure to set the imaging camera to its best focus).

5. Define the averaging constant to at least 12 frames

6. Check the show average roundness check box.

7. Wait at least 25 frames and click on  button to set the relative roundness displayed in the HUD to the current filter (i.e. +4.75% will be set to the red filter)

8. Redo the same procedure for each filters mounted in the filter wheel.

To clear the RRDN value for the selected filter just click on the  button.

In case that all your filters are parfocal, the RRDN value defined for the current filter can be applied to all filters. To do that, just click on the button.