Background

The lspecfocus task is used for focusing LRIS in spectral mode. With some tweaking, it can also be used to investigate variations in spectral focus along the dispersion. See the instructions below.

Requirements

A set of spectral focus images, acquired with either a longslit or multislit mask.

Procedure

Launch IRAF on any HQ machine (preferable a fast one).
Load the keck and lris packages.
Run the lspecfocus task, being sure to set the following parameters:
- logfile: set to the name of a logfile to save
- ndisp: set to the number of dispersion subsamples to generate. Reasonable values are 3-5.
Mark 1 or 2 desired slit regions to perform analysis.
After analyzing a region, specfocus will plot the variation in focus along the dispersion. At this point, use the following keystrokes in the graphics window to access different plots:
- b to display the best focus plot (the starting plot)
- p to plot spectral profiles within each dispersion subset
- s to plot spectra within each dispersion subset
- w to display spectral widths within each dispersion subset
When done analyzing results, type q in the graphics window to exit specfocus.
If you selected a second slit region to analyze, repeat the previous 2 steps for the additional region.
When done, results are saved to the specified logfile for reference.