Phase2 UI: Sequence Builder

Although sequences can be constructed from scratch using this tool, for the majority of observations you are better to use the wizard templates. Even for more complicated sequences it is usually easier to create the template sequence first to get the basic structure correct, submit it and then edit the details. A worked example illustrating this is available in the Sequence Builder Tutorial.

Telescope Functions


Select target, field orientation and tracking rates. This command moves the telescope to the new target and starts open-loop tracking. The target is placed on the mechanical centre of the telescope focal plane, so you normally want to be refine this using the "FOCAL PLANE" command to place the target on a specific instrument.

Focal Plane

A slew places the target on the mechanical centre of the telescope focal plane. This would be within the field of view of most instruments, but not necessarily the centre. A "FOCAL PLANE" command offsets the telescope by a predetermined amount to place the target in the centre of the nominated instrument. This is still "blind pointing" of the telescope and depends on the telescope's current pointing model.

Fine Tune

Invoke an iterative process of short exposures, automatically offsetting the telescope after each to place the target on a specified pixel in the camera. This is a closed loop process and no longer dependent on the telescope's blind pointing model. The only common use of this is to fine tune the blind pointing and place a target precisely on the FRODOSpec IFU fibre array. To do this, select "Acquire using IO:O" and "Science Instrument FRODO" which instructs the system to iteratively use IO:O to fine tune the pointing to be correct for FRODO. For more detailed description of acquisition modes see the FRODOSpec webpages.

Position Offset

Offset telescope in RA,Dec. Non-cumulative offsets are with respect to the latest target so successive offsets with the same values would all leave the telescope at the same position. Cumulative offsets are with respect to telescope's current position and successive offsets with the same values would walk the telescope off in a straight line.


Select rotator mode and field orientation. This is included in a SLEW so you only use this function is you want to change field orientation during the sequence. There are two options, CARDINAL and MANUAL:

  • CARDINAL orients the cassegrain derotator so the image will be aligned on the nominated instrument on one of the cardinal sky orientations N, E, S or W though you cannot control which one. The telescope automatically chooses the field orientation best placed at the time of the observation in order to give the longest available observation duration without encountering the axis limits.
  • MANUAL allows you to explicitly set the field orientation you want. This may be defined either as a sky position angle on a nominated instrument or as the mechanical mount angle of the cassegrain derotator. In most cases we advise leaving this on cardinal unless your sequence is longer than a couple of hours in duration. For detailed discussion, please read Cassegrain Rotator.


Use of the autoguider may be "Off", "Yes" or "On if available". When set to "On if available", guiding will be attempted, but if it fails for any reason the group will continue without it. If set to "Yes" then failure to lock the autoguider is an error and the entire group would be aborted. Other points to remember when using the autoguider:

  • The autoguider is not robust to offsets so you should only insert the AUTOGUIDE command after you have finished all stages of your acquisition. When dithering or mosaicing you must switch off the autoguider before any position offset and switch it back on afterwards. This is not done automatically.
  • When using the autoguider with FrodoSpec you should only engage the guide loop after switching instrument from the acquisition camera to FrodoSpec. See "Phase2UI User Instructions: FrodoSpec" for full details and examples of how to do this.
  • The autoguider is not compatible with non-sidereal tracking.

Instrument Functions

Instrument Config

This only needs to be sent when you want to change the configuration, not before every exposure. You must send an INSTRUMENT CONFIG before the first science exposure in your group simply in order to define which instrument should be used. Subsequent exposures within the sequence will continue to use the same instrument and configuration until a new INSTRUMENT CONFIG command is sent.


Defocus the telescope. The system automatically applies all offsets required to keep the instruments and filters in focus. Only explicitly apply DEFOCUS when you want your data to be defocused. Non-cumulative offsets are with respect to correct focus, so successive offsets with the same values would all leave the focus unchanged. Cumulative offsets are with respect to the current position. We recommend using +ve DEFOCUS values because of better compatibility with the autoguider, but -ve values are legal and perfectly fine if you are not guiding.


Instructs the most recently configured instrument to obtain one or more integrations with the same integration time. The current instrument configuration, whatever was last set, is used. Though you do not need to precede every exposure with a configuration command, it is required that at least one instrument config command has been issued in the sequence before any exposures are made. This is required in order to identify which instrument is to be used. For most instruments, EXPOSE is simply a run of integrations all with identical instrument and telescope configuration. For example 3x1200sec would give 1 hour of integration split into three twenty-minute exposures.


Obtain bias, dark and arc frames. The recommended calibrators required for each instrument are discussed in detail on the instruments' own individual web pages.

Control Flow


Create a block which will be repeated a specified number of times. Might be used in conjunction with offsets to create a dither pattern or to cycle through a sequence of filters multiple times such as this BrizrizrizB filter sequence.


Split the control flow so that two tasks are executed in parallel. This is typically used only for FRODOSpec in order to allow simultaneous exposures on both arms. Control will not flow on past the branch until both tasks are completed. Apart from this there is no control of synchronization between the two branches and each will simply execute its list of tasks in direct sequence. You cannot for example ensure that the shutters on the two cameras will open precisely together, however if both arms simply contain an instrument config and possibly an arc frame before the exposure command, they are going to be synchronized to within a few seconds. See the FRODOSpec-specific phase2UI guide for considerably more detail on this topic.



To modify an existing item, click on it to select it in the sequence tree and then press "Edit". The currently configured parameters will appear in the upper panel where they can be changed before clicking "Replace" to overwrite the previous values.


To remove an existing item, click on it to select it in the sequence tree and then press "Delete".


To reorder the command sequence, click on any item in the sequence tree and use the "Up" and "Down" buttons to move it.


It is very important to validate your sequence at the end of any editing session. This will provide feedback on any illegal options you have selected and also provide warnings for any particularly unusual configurations. The telescope will accept and attempt sequences which yield warnings, but it is likely that what is specified is not what you really wanted.