Summary

This document describes the use of the ifuFocusComp widget, a tool used by the observer or the OA to adjust the telescope and guider focus to work with the ESI IFU.

Background

The ESI Integral Field Unit is an “image slicer” which allows the observer to obtain a spectrum over a much wider contiguous area than is possible with the standard ESI echellette slits. However, the IFU slicer array is not in the same plane as the standard echellette and low-D slit plates; thus, when the IFU is in use the telescope focus must be adjusted to move the telescope focal plane to coincide with the slicer array.

The ESI guider must also be adjusted, and since the reflective entrance aperture for the IFU is not in the same plane as the ESI guider pickoff mirror, the required adjustment to the guider focus depends on whether the guide star will be on the IFU mirror or on the pickoff mirror. These various constraints can make it difficult to keep track of which adjustments to the telescope and guider focus are required when switching between IFU and normal modes on ESI. As described below, the ifuFocusComp tool make this a pushbutton operation.

Invocation

Observers can launch the ifuFocusComp tool from the background menu under

	ESI Utilities > IFU Focus Comp Tool

OAs can launch the tool off the DCS GUI.

Usage

This section described how to use the widget in operation.

Mode Selection

The widget allows you to switch between 3 modes:

• IFU off. This is the normal (non-IFU) ESI operational mode. In this mode, the telescope and guider focus are at their nominal positions. The values of Delta TELFOC and Delta TVFOC for this mode are zero.
• IFU on (Slit guiding). This is the mode to select when using the IFU and guiding on the mirror on the IFU (on the bottom half of the guider display). Both the telescope and guider focus values change in this mode, with the amount of change given by the Delta TELFOC and Delta TVFOC.
• IFU on (Pickoff guiding). This is the mode to select when using the IFU and guiding on the normal ESI pickoff mirror (on the top half of the guider display). The telescope focus in this mode is the same as for the IFU on (Slit guiding) mode, but the guider focus (Delta TVFOC) is very different.

Offsets

Each of the three modes has an associated Delta TELFOC and Delta TVFOC which indicate how much to adjust the telescope or guider focus, respectively, when in that mode. Default values are built into the source code, but these values can be changed on the fly as needed simply by typing new values into the corresponding box. For example, if one determined (by, for example, running AUTOFOC in both the normal and IFU modes) that the value of Delta TELFOC should be different than the default, the new value can simply be entered into the appropriate box on the widget. Please note that such values are not stored, and would need to be re-entered if the widget were killed and restarted.

Quit

The Quit button will simply kill the GUI without making any changed to the telescope or guider focus.

Initialization

When launched, the tool will attempt to determine which of the three modes the guider and telescope are in, based on whether the guider is at the nominal focus or not. It will then make that the currently selected mode. If you find that it is not selecting the correct mode, the recommended action is to:

• Quit the widget
• Reset the telescope focus to the nominal (non-IFU) value
• Reset the guider focus to the nominal value for that particular filter (by, for example, invoking the correponding Named Setup file from the ESI dashboard GUI)
• Restart the widget

Logging

A helpful transcript of the session is logged in the file ~/ifu_focus_comp.log in the account's HQ home directory. This may be useful for debugging purposes. Here's a typical snippet: