Sequencer

Role

The Sequencer module orchestrates automatic acquisition for an astrophotography session. It executes a list of sequence lines, each defining the filter, exposure duration, and number of images to acquire. Frame type, gain and offset are shared by the whole sequence rather than set per line. FITS files are saved automatically into a folder tree organised by object and filter, and the module can request camera cooling, autofocus, and guiding around each line as needed.

Required devices

Device	Role
Camera	Image acquisition, and cooling if enabled
Filter wheel	Optional — the sequence runs without one; positioning and per-filter focus profiles are simply skipped

Sequence structure

A sequence is made up of several lines. Each line defines:

Column	Description
Filter	Filter selected from the filter wheel
Exposure	Exposure duration in seconds
Count	Number of images to acquire for this line

Lines are executed in order, from first to last. Frame type, gain and offset apply to every line (see Sequence parameters below).

Parameters

Settings are split across three groups, so sequence, guiding and focus behavior don’t get mixed together.

Object

Parameter	Description
Name	Name of the imaged object — used to name the save folder
RA	Right ascension of the object
DEC	Declination of the object

Slave modules

The sequencer interacts with other modules for focusing and guiding.

Parameter	Description
Focus module instance	Name of the Focuser module instance to use (e.g. `focus`)
Guider module instance	Name of the Guider module instance to use (e.g. `guider`)

Sequence parameters

Parameter	Description
Enable camera cooling	Requests cooling to the target temperature before starting the sequence, and waits until it is reached
Target temperature (°C)	Sensor target temperature
Frame type	Light (L), Bias (B), Dark (D), or Flat (F) — applies to every line
Gain	Camera gain — applies to every line
Offset	Camera offset — applies to every line

Guide parameters

Parameter	Description
Use guiding	Enables guider integration (dithering, settle, RMS monitoring, focus suspension). The guider must already be guiding, or be started by the sequencer as needed.
Resume guiding settle time (s)	Wait time in seconds after guiding resumes, before continuing acquisitions
Dither every N shots (0=disabled)	Requests a dither every N captured frames
RMS recalibration threshold (0=disabled)	Aborts the current exposure and triggers a guider recalibration when the peak RMS during that exposure exceeds this value

Focus parameters

Parameter	Description
Auto-focus on filter change	Triggers a focus run whenever the filter changes — this also covers the very first line of a sequence, since no focus has happened yet in this module session. Re-running the same sequence skips a redundant focus if the last one already matches the current filter.
Suspend guiding during focus	Pauses guiding before the focus run and resumes it afterwards
HFR refocus threshold (0=disabled)	Triggers an extra focus run mid-line when the measured HFR exceeds this value
Focus profile to load	Profile to load on the focus module before requesting autofocus; leave empty to keep whatever profile is currently loaded there

Focus profile per filter

A dedicated grid lets you override the focus profile for specific filters — useful when narrowband filters need different focus settings than LRGB, for instance.

Column	Description
Filter	Filter this row applies to
Focus profile	Profile to load when focusing on this filter

If the current filter has a row in this grid, its profile is used. Otherwise, the sequencer falls back to Focus profile to load above. If that is also empty, the focus module keeps whatever profile it currently has loaded.

Algorithm

Sequence start

Connect to the camera and reset the frame
If Enable camera cooling is on, request the target temperature and wait until reached (skipped immediately if disabled or the camera is not configured)
Start the first line

Line execution

For each line of the sequence:

Select the filter on the filter wheel (skipped if no filter wheel is configured)
If Auto-focus on filter change is enabled and the filter differs from the one used for the last focus run this session: trigger auto-focus (loading a profile first — per-filter override, then the general fallback — and suspending/resuming guiding if configured)
Start or confirm guiding if Use guiding is enabled
Dither if the configured shot interval is reached
Acquire the defined number of images one by one, refocusing mid-line if the HFR threshold is exceeded

File saving

FITS files are saved in the following folder tree (the object and filter segments are omitted when not set, instead of leaving stray separators):

<object>/
  LIGHT/
    <filter>/   ← Light frames
  FLAT/
    <filter>/   ← Flat frames
  BIAS/         ← Bias frames
  DARK/         ← Dark frames

Each file name includes the object name, frame type, filter, and a timestamp.

Integration with the Focus module

When an auto-focus is requested:

If a profile applies (per-filter override, or the general fallback), the sequencer asks the Focuser module to load it
The sequencer sends the autofocus action to the designated Focuser module
It pauses acquisitions and waits for the focus run to complete
If Suspend guiding is enabled, it sends abortguider to the Guider module before focusing, then guide afterwards
If a settle time is configured, it waits that delay before resuming

Integration with the Guider module

Guiding is started (or confirmed already running) before exposures begin, when Use guiding is enabled
Dithering is requested every N shots, then the sequencer waits for the configured settle time
If the peak RMS during an exposure exceeds the configured threshold, the exposure is aborted and the guider is recalibrated before resuming

Progress

Progress is tracked both live (updated during acquisition) and as running averages/durations kept since the module was loaded.

Indicator	Description
Sequence (shots)	Number of shots completed out of the total across the whole sequence
Sequence (time)	Elapsed exposure time out of the total estimated exposure time, updated live during the current exposure
Current exposure	Progress of the current exposure (0 to 100 %)
Theoretical total duration	Sum of count × exposure over every line, recalculated whenever the grid is edited — even before the sequence starts
Theoretical remaining duration	Theoretical total minus the time already accounted for
Real elapsed duration	Wall-clock stopwatch, reset to zero each time the sequence starts
Average focus duration	Running average of time spent waiting for autofocus, since the module was loaded
Average guide-start duration	Running average of time spent waiting for the guider to start, since the module was loaded

Actions

Action	Description
Start sequence	Starts executing the sequence from the first line
Abort	Immediately stops the current sequence, and also propagates an abort request to the Guider and the Focuser instances configured in Slave modules, so guiding and any in-progress focus run are stopped too