Calibration

Calibration

You can view the calibration coefficients (Ks and Kc) in the FocusLock Tab of the settings panel. Note that these values are a starting point for the system. They can vary significantly from calibration to calibration. FocusLock constantly updates and adjusts these values internally to find the true system coefficients using the thousands of data points generated by the auto-focus method. See the theory section for more details.

FocusLock offers two methods of calibration. The first is manual calibration. This involves manually moving the focuser, causing changes in the roundness of the guide star. The second method is automatic calibration. Both methods, assuming proper use, will generate valid and useful preliminary calibration coefficients for the Lock.

Calibration Checklist, for manual calibration:

• 1. Calibration should be done in relatively good seeing conditions when possible.
• 2. Consider an averaging constant of at least 12 frames or more, especially if the seeing is less than optimal.
• 3. Calibration requires moving the focuser for increasing the average absolute roundness (AARDN) by at least 15%.
• 4. Calibration requires at least 15 guider camera frames to insure good AARDN estimations. Take your time.
• 5. Use a bright star near the zenith.
• 6. If you use a filter wheel select the wider band filter, such as luminance.
• 7. Center the star on the imaging and guiding camera chips.
• 8. Imaging and guiding cameras should be at best focus.
• 9. Adjust the guider camera exposure time for good SNR, yet stay below the chip saturation level.
• 10. Wait several guider frames and check that the AARDN is at least below 7%, we recommend below 3%.
• 11. Hit the Manual Calibrate option.
• 12. Then move the focuser ~15 microns using your favorite focuser control program, you can use the Optec ASCOM Server to share the driver.
• 13. Wait several guider frames and watch the average AARDN values. If the AARDN does not change by much increase the step size.
• 14. If the AARDN decreases, then reverse focuser motion (very important)!
• 15. Continue by successive focuser moves in the direction of increasing AARDN.
• 16. Wait several frames after each move to allow for a good AARDN and angle estimations.
• 17. When the AARDN is at least 15% higher than its initial value, click on the "Manual Calibration" option again.

Calibration Checklist, for automatic calibration:

• 1. Calibration should be done in relatively good seeing conditions when possible.
• 2. Consider an averaging constant of at least 12 frames or more, especially if the seeing is less than optimal.
• 3. Calibration requires moving the focuser for increasing the average absolute roundness (AARDN) by at least 15%.
• 4. Calibration requires at least 15 guider camera frames to insure good AARDN estimations. Take your time.
• 5. Use a bright star near the zenith.
• 6. If you use a filter wheel select the wider band filter, such as luminance.
• 7. Center the star on the imaging and guiding camera chips.
• 8. Imaging and guiding cameras should be at best focus.
• 9. Adjust the guider camera exposure time for good SNR, yet stay below the chip saturation level.
• 10. Wait several guider frames and check that the AARDN is at least below 7%, we recommend below 3%.
• 11. Adjust the settings in the Calibration Tab in the settings window as per the instructions.
• 12. Click on the AutoCalibrate option under tools.
• 13. Click on the View Plots Option
• 14. Adjust the settings in the Calibration Tab in the settings window as needed.
• 15. When the system has enough data it will activate a pop up. You can abort by hitting the AutoCalibrate option again. If it had enough data on abort it will ask if you wish to save the data.

Calibration steps based on the calibration section from Innovations Foresight's SharpLock Documentation.