To achieve a high loop frequency, the shutter of the CCD camera has to stay open and the camera is operated in a kind of frame transfer mode (see section Imaging modes). As the exposure is slightly different in the shutter modes like Movie and in the 'frame transfer modes' one has to take images with Store Corrected before starting the final Tip-tilt ON for unlimited correction.
Store Corrected reads out a limited number of frames that has to be specified in Frames to store. The >> indicates that by clicking on the text Frames to store a popup menu gives a selection of numbers that can be chosen. Once Store Corrected is started it cannot be stopped.
Be careful not to choose 1 second exposure time and 4096 frames: that keeps the system busy for more than an hour. Then, the only cure is resetting the VxWorks system.
One should aim at using a Loop frequency of at least 50 Hz, and to have an exposure time of at least the readout time. This can be checked by roughly estimating the cycle time as the reciprocal of the Loop frequency, and compare it to the Exposure time. At 50-70Hz, the exposure time is usually larger than the readout time.
As all images are stored when using Store Corrected the images are displayed at the end of the sequence. The display style is defined by AstroCam. They call it tile image because the images are displayed like tiles on the wall. Use the mouse to check whether the number of counts is alright and the stars look nice, i.e. round. As the tip-tilt correction is on in this mode the star should be spread out equally over the four central pixels. If you have counts between 2000 and 50000, with the background being set to 1000, things are fine. If the counts are too high, choosing a lower binning factor reduces the flux per pixel.
At the end of the Store Corrected sequence, two graphs with two curves each pop up. The first shows the centroid positions (in CCD pixel units) that should all be around zero, the second shows the piezo commanded positions that have to be between 0 and 4095. If the latter curve is a straight line at 0 or 4000 that means that the piezo has reached the limit of its throw. The star has to be repositioned in its subarray, by using the middle mouse button in Movie mode. One exits from this display by moving the mouse into the xterm window that was opened with the graphs and hitting the return key.