1. Introduction : The purpose of the image sharpening process is to estimate and compensate for the optical aberrations seen on the focal plane of the Near Infrared camera NIRC2. Most of these aberrations are not seen by the wavefront sensor which lies on a different lightpath; they represent the non-comon path aberrations. The nature of these aberrations will also depend on the NIRC2 camera and filter settings. The software used for image sharpening was developed by Scott Acton and the application was further developed by Marcos van Dam. The program is written in IDL and is used from a Graphical User Interface. It has now been completely automated and works at the touch of a button. The key is to press the right button! The program estimates the phase using a modified version of the Gerchberg-Saxton phase retrieval algorithm. It requires one or more images with different amounts of focus error (phase diversity) to compute the phase. Two images are adequate and having a third image improves the accuracy of the algorithm. Since the algorithm estimates the phase, using a narrowband filter improves the quality of the reconstruction. Once the phase is estimated, it gets converted to a wavefront and then this is used to drive the SFP Z-position and the DM actuators to cancel the measured wavefront. This process is performed iteratively, three times by default. The final phase on the DM gets saved using the WYKO interferometer, and the position of the SFP must be manually saved with the SC GUI. A document to calibrate the Image Sharpening Algorithm is available. 2. Procedure: The following steps are needed to run the image sharpening algorithm.
You are now ready to do the WFS (and LBWFS) calibration. Below is a picture of the GUI.
![]()
|