Starting the Focus GUI

To start the software from the observing computer, select it from the observer dropdown menu, or type the command nickelfocus in a terminal on nandor.

The left side of the Slew tab shows the telescope's Current coordinates; these are updated once a second. To acquire a target with known coordinates, enter a sexagesimal RA and Dec under Target coordinates (e.g., 05:30:00 and +20:15:00) and press Move to Target. The status line on the Log tab reports when the telescope arrives or why the move could not be made. You must enable movement and tracking (using POCO) to control the telescope via the GUI.

The right side allows you to quickly find a target near the telescope's current position, and the target coordinates will be updated for you. Typically, you will use the Focusing * button, which finds the nearest focus star. You can also use Pointing * to find the nearest pointing star. These stars are selected from a catalog of stars that comes with the software. You can also search your own starlist instead: Enter the file location under Starlist (or use Browse…), optionally enter part of an object name under Target pattern, and press Object. The name and coordinates of the target found are shown in the status line; check them, then press Move to Target.

The Grid, Auto, and Single tabs all take new exposures. Each one provides the same exposure settings on its left side: Exposure time (s), readout Speed (Slow or Fast), and Binning (1,1, 2,2, or 4,4). We recommend you always use the Fast mode for focusing.

There are two ways to take a focus sequence:

• Grid takes exposures at evenly spaced focus values: a Start focus, a Step size, and a Number of steps (at least 3).
• Auto searches for the best focus. It starts at Start focus, moves by Step size, decides from the first few exposures which direction improves the image, and keeps stepping until it has passed through the best focus. It stops after taking 3 exposures beyond the exposure that yielded the minimum FWHM, or when it hits the maximum number of focus steps (set by Max steps), whichever comes first. Because it follows the curve, the focus values may not be taken in order.

The Replay tab analyzes a focus sequence that is already on disk, without using the telescope or camera. Assuming you save the focus images (they are saved by default), you can use this tab to reanalyze the focus sequence. Enter the Data directory (or use Browse…), the file name Prefix and Suffix (by default n and .fits; you will likely not need to change these), and Obsnum, the observation number of the first exposure in the sequence. Then enter the Start focus, Step size, and Number of steps the sequence was taken with (you will need to note these in the observing log; they are not kept in the file headers), and press Load. The exposures are expected to be numbered consecutively, starting at Obsnum; this "Replay" option may fail when reanalyzing data taken with the "Auto" sequence. The results are displayed exactly as for a live sequence, and the m key can be used to measure a different star. (The "Replay" tab was used to construct Figure 4.)

The Options tab has one setting, Remember settings between sessions; this will likely be removed in future versions such that settings will always be saved. When it is checked, the Slew tab's starlist and target pattern, the settings on the Single, Grid, Auto, and Replay tabs (except the Single tab's focus value), and the image stretch are saved when the GUI is closed and restored the next time it starts. Unchecking it erases any saved settings when the GUI is closed.

Every error is reported in the status line on the Log tab and added to the log history below it; unexpected errors also include the full Python traceback. When you encounter a problem, please provide the full Python traceback to help developers determine the issue.