Background

Although the Xfocus widget makes it easy to analyze pinhole-mask focus data to derive a best overall focus, additional information can be recovered from LRIS focus images. For example, it is possible to generate contour maps of the focus as a function of position on the detector. This document describes the procedure for doing so.

Requirements

A set of full-frame pinhole focus images.

Procedure

Phase 1: Run Xfocus

Log into an HQ computer as user lriseng.
Launch xfocus from the command line, specifying both the side you wish to analyze (red or blue) and the number of pinholes to be found. As of 2009, the appropriate commands are:
- Blue: ~lris/widgets/released/xfocus/xfocus -vm blue 374
- Red: ~lris/widgets/released/xfocus/xfocus -vm red 357
Use the File > Open menu on Xfocus to select images to analyze.
Xfocus should generate an image and save data to disk. Note the name of the output file, which is given in the last line of the IDL transcript:
```
% WRITE_LOGFILE: saved results to /home/lris/data/xfocus/focus.LRISBLUE.G.2009-06-04_8.fits
```

Phase 2: Generate Map

Log into an HQ computer as user lriseng.
Navigate to a directory in which you want to store resulting files from analysis.
Launch IDL via command start.idl70.

Execute the analysis program on the FITS file generated by Xfocus:

lris_analyze_xfocus_data, '/home/lris/data/xfocus/focus.LRIS.R.2009-06-04_8.fits'

This will generate several PostScript files in the current directory:
- focus.*.xy.ps: Shows variation in best focus as a function of row and column on detector.
- focus.*.focus-contour.ps: Shows contour map of best focus across detector.
- focus.*.bestsize-contour.ps: Shows contour map of best size at each point across detector.
- focus.*.size-contour.ps: Shows contour map of pinholes sizes for the image which was acquired closest to the Xfocus best focus position.