The LRIS blue shutter is prone to getting stuck, preventing observers from acquiring images in the normal way. Fixing the stuck shutter is a major repair requiring removal of the entire LRIS blue dewar; hence, this repair will probably not be made until the conclusion of the current LRIS run. Fortunately, if the blue shutter fails during a run it is possible to operate the blue side in a shutter-less mode and still obtain usable data as long as certain procedures are followed. This document describes the required hardware modifications and observing procedures to carry out observing in shutter-less mode.

Hardware Changes

In the event that the blue side shutter is stuck, the following hardware changes must be made to operate the LRIS trapdoor as a shutter for the blue side.

Observing strategies

Below are observing strategies to assist observers in acquiring data. There are many work arounds for a failed shutter and the observers will have to choose which observing procedures to follow. Below are some recommendations.

Useful Scripts

The following scripts may be used to acquire the arc lamp data, flats and science data using the trapdoor as a shutter.


Acquires a single Hg arc lamp exposure using only the blue side. The exposure length is hard coded, and could be a variable to acomodate different slit widths. The script does the following:


Acquires a single Cd+Zn arc lamp exposure using only the blue side. The exposure length is hard-coded (but the script could be modified to make this variable to accommodate different slit widths and grisms). Prior to running the script the observers must allow the lamps to warm up for 5 min. The script does the following:

cal_trap_flat_blue exptime

Acquires a single Halogen lamp flat using only the blue side. The variable exptime is a required variable defining the exposure time [in seconds] for the internal Halogen flat field lamp. The script does the following:

goitrapb [-both]

Acquires images on the blue side, operating the trapdoor as a shutter for the blue side detector. The optional keyword "-both" will acquire a single image on the red and blue sides simultaneously. The script will check to ensure that the red side exposure time is 3 seconds less than the exposure time on the blue side. The script will do the following:

To focus the LRIS BLUE side CCD

The procedure is similar to the standard focusing procedure, except that the acquisition of the blue-side images required running a special script. Follow these steps to acquire the images: Once the images have been acquired, you can analyze them as usual using the XFOCUS blue IDL widget accessible from the desktop menu.