1. Note: The etalon weight is 19.5 kg, not including the mounting plate.
2. If the MMTF etalon is not attached to its mounting plate, attach it. The orientation of the etalon is important. In the left figure below, the CS-100 cable ports are in the correct rotational orientation (at the bottom of the picture) with respect to the mounting plate flanges. In the right figure below, the ports are such that the etalon is right-side up.

   A top view of the MMTF, attached to its mounting plate. Note the correct orientation of the CS-100 cable ports (at bottom) with respect to the mounting flanges. (Click for a larger image.)

   A side view of the MMTF, attached to its mounting plate. Note the correct orientation of the CS-100 cable ports, ensuring that the etalon is right-side up. (Click for a larger image.)
3. Ensure that the two clear, protective covers covering the etalon aperture are in place.
4. Secure the etalon in the disperser wheel using the same procedure as for other IMACS gratings. In the disperser wheel service position, the MMTF cable sockets will be pointing out and down, as shown in the image below (in the "5 o'clock" position as viewed from the rear of the instrument, looking toward the telescope).

   A view of the MMTF when mounted in the disperser wheel, with CS-100 cables connected. (Click for a larger image.)
5. Plug into the MMTF the 5 cables connecting the etalon to the CS-100 controller. Be sure that the X, Y, and Z cables are matched properly with their respective sockets.
6. Remove the two covers protecting either side of the etalon aperture.

1. Install the intermediate-band blocking filters specified by the observer.

2. If charge-shuffling has been specified by the observer, insert MMTF slit mask "A".

3. Find and install an IMACS slit mask that has 5-10 guide star holes (square apertures) dispersed somewhat evenly over the central half of the field-of-view. This mask will be used for checking the position of the optical axis.

The CS-100 is the electronic brain of MMTF. It is located in the IMACS electronics rack. For a more detailed description than that provided here, read the CS-100 manual.

Features

• Mode Knob. In Balance mode, changes to the etalon controls balance out the capacitance bridges in the feedback loop, but do not move the etalon plates. In Operate mode, changes to the controls affect the position of the etalon plates.
• X_coarse, X_fine, X_quad, Y_coarse, Y_fine, Y_quad (X and Y coarse, fine, and "quadrature balance" knobs). The X and Y settings control the degree to which the etalon plates are parallel by tilting one of the plates around two axes parallel to the plate surface. The coarse and fine knobs control the actual tilts, while the quad knobs fine-tune the electronic balances.
• Z_coarse, Z_fine, Z_quad (Z coarse, fine, and "quadrature balance" knobs). The Z settings control the spacing between the plates ("piston" motion).
• LED indicators. There are 4 indicators in the center of the panel. (1) The green Operate light indicates that the etalon feedback loop is on and working properly. (2) The orange Balance light indicates that Balance mode is enabled. (3) A red Out of Range light when the etalon is in Operate mode signifies that the etalon is not properly balanced. (4) The red Disabled light illuminates when control of the CSS-100 is taken over by the IMACS computer. (The CS-100 front panel controls do not work when the computer has control.)
• Meters. The three meters show how far away the X, Y, and Z feedback loops are from being balanced. The center position ("0") indicates balance.
• Meter Display Knob. In the Offset position, the meters respond to changes in X_fine, Y_fine, and Z_fine. In the Quadrature Error position, the meters respond to changes in X_quad, Y_quad, and Z_quad.
• Response Time Knob. This knob controls how quickly the etalon responds to requested changes in X, Y, and Z. It should be set to 2.0 ms.

Initial Configuration

1. Ensure that the Mode knob is in the Balance setting. Power on the CS-100.
2. Ensure that the CS-100 Meter Display knob is set to Offset. Using the knobs on the left side of the CS-100, dial in the following numbers to balance the capacitance feedback loop and parallelize the etalon. Replace ? with the Z_coarse specified by the observer.

       coarse fine  quad
   X   -1     7.11  4.20
   Y    0     6.80  3.78
   Z    ?     4.10  4.34
   

3. Turn the Mode knob to Operate. After a few seconds, the Operate light should illuminate, indicating the feedback loop is now in active operation and functioning properly. If instead the Out of Range light illuminates, the etalon must be re-balanced; follow the balancing instructions.

Changing Zcoarse

Follow this procedure.

Once the CS-100 in the rack is powered on, you are ready to initialize the IMACS software for MMTF use and perform set-up calibrations.

Procedure when starting MMTF at the beginning of a run:

1. If the IMACS software is already loaded, exit the software.
2. Run the IMACS Setup Tool (command % imacs setuptool, which must be run from the imacs account) to input the CS-100 settings that presently appear on the front panel dials . The settings are those originally dialed in, plus any changes made to tweak the balance.
3. Enable access to MMTF observing scripts by typing

   % touch .imacs_use_script

   in the imacs user's home directory (/Users/imacs/). If this step is performed once the IMACS GUIs have already been loaded, simply exit and restart the f/2 CamGUI.
4. Start up the IMACS software (% imacs).
5. Run standard IMACS initialization procedures.
6. Open the HardHat GUI to enable changes to X_fine and Y_fine.
7. Parallelize the etalon. [procedure]
8. Check the position of the optical axis. [procedure]
9. Take a reference ring and sausage cube in each filter the observer will use. Be sure to first optimize the parallelism in each filter. [procedure]

Procedure if MMTF has already been set up, and you are simply changing the value of Z_coarse in the middle of a run:

1. Release computer control of the CS-100 with the Etalon button in the HardHat GUI. [procedure]
2. At the CS-100 front panel, switch to Balance mode. Turn the Z_coarse dial by one unit in the direction of the desired Z_coarse. Switch back to Operate mode. If the Operate light illuminates, repeat this procedure until the desired Z_coarse is reached. If instead the Out of Range light illuminates, follow these steps.
3. Run the IMACS Setup Tool (% imacs setuptool) to input the new Z_coarse setting, plus any changes made to tweak the balance.
4. Re-acquire computer control of the CS-100 with the Etalon button in the HardHat GUI. [procedure]
5. Parallelize the etalon at the new value of Z_coarse. [procedure]
6. Take a reference ring and sausage cube in each filter the observer will use. Be sure to first optimize the parallelism in each filter. [procedure]

When MMTF is properly initialized by touching the .imacs_use_script file in the observer's directory, a new version of the f/2 CamGUI is enabled:

The additional Script section of CamGUI allows the following tasks:

• Exec: Run an etalon script (opens a confirmation dialog box).
• Create: Create an etalon script for observing, sausage cube calibrations, or parallelism calibrations (opens a dialog box).

There is also a new ExpType: MMTF-Shuffle, for the charge shuffling / freqency straddle observing mode. Selecting this opens a dialog box.

Part of the HardHat GUI is specifically devoted to MMTF:

This additional area enables the following:

• Control of the CS-100 is released from / acquired by the IMACS observing computer with the Etalon button. Control of the CS-100 should be returned to the instrument front panel if, e.g., the etalon goes Out of Balance, Z_coarse needs to be changed, or the CS-100 is being turned off. On pressing the Etalon button, the user will be prompted to release the etalon. Once it is released, the button will alternately flash red and black and the Disabled LED on the CS-100 will turn off. When the button is pressed again, computer control is re-acquired, the Etalon button stops flashing, and the Disabled LED illuminates.
• X_fine and Y_fine are adjusted only through the dialogue boxes in the HardHat GUI. Z_fine can be changed either here, or in the MechGUI.
• The front panel settings, as specified in the IMACS Setup Tool, are displayed here. (I.e., if they were entered incorrectly into the Setup Tool, they'll be wrong here, as well as in the FITS headers.)

NOTE: The X, Y, and Z fine computer units uniquely specify the absolute plate spacing only in reference to the CS-100 front panel dials. When the front panel dials are set and control of the CS-100 is acquired by the IMACS computer, the computer X, Y and Z fine values are set to a reference value of 2048. Changes in X, Y, and Z fine are then defined such that 2048 computer units = 1.00 front panel units, or 1/10 of a full dial turn. (However, the values initially displayed in the HardHat GUI when IMACS is started may not always be the reference values.)

When the etalon needs to be dismounted from the IMACS disperser wheel, the CS-100 needs to first be turned off and unplugged from the etalon. Use the following procedure:

1. Release computer control of the CS-100 with the Etalon button in the HardHat GUI.
2. At the CS-100 front panel: Turn the Mode knob to Balance. Once the Balance light illuminates, turn the CS-100 off using the Power switch.
3. At the IMACS disperser wheel: Attach a clear fiberglass cover to side of the MMTF aperture. Remove the MMTF cables from their sockets.
4. Dismount MMTF!

The etalon will sometimes fail to operate when the Mode knob is first turned to Operate, as indicated by the Out of Range light. (This occurs most often at very low or high values of Z_coarse.) Alternatively, the CS-100 will operate only briefly, or go Out of Range when changes are made to X, Y, or Z at the computer. If computer control is enabled, this failure state should be accompanied by a message from the IMACS observing software, but will also manifest itself as an absence of coherent Fabry-Perot rings in images.

If the etalon goes Out of Range while at the IMACS computer, first release computer control of the CS-100.

At the CS-100 panel, turn the Mode knob from Operate to Balance and back again. If the etalon is still Out of Range, use the following procedure, which involves adjusting the quadrature balances at a Z_coarse value near the one at which you are working.

1. Raise or lower Z_coarse by 1 unit (while in Balance Mode).
2. Turn the Mode knob to Operate and the Meter Display knob to Quadrature Error.
3. You may find that the meter voltages in X, Y, and/or Z deviates significantly from zero. Re-null the proper channel(s) using the quadrature balance knob(s) while in Operate mode.
4. Switch to Balance, move Z_coarse back to the desired value, and switch back to Operate.
5. If the etalon operates without going out of range, you're done. Write down the new values of X, Y, and Z_quad from the quadrature balance knobs, and enter them into the computer with the IMACS Setup Tool before (re-)aquiring computer control.

We include here for completeness the procedure for re-balancing the etalon from scratch. However, this should not be needed under practical circumstances.

1. Ensure that the Mode knob is set to Balance and the Meter Display knob set to Offset.
2. Adjust the X, Y, and Z coarse and fine dials so that the three meters are nulled (the needles should point to 0, or straight up).
3. Switch the Meter Display knob to Quadrature Error.
4. Adjust the X, Y, and Z quadrature balance dials so that the three meters are nulled.
5. Repeat steps 1-4.
6. Switch the Mode knob to Operate. If the Operate light illuminates, the feedbak loop is in operation and functioning properly. If instead the Out of Range light illuminates, the feedback loop is not properly balanced. Repeat the above procedure.