Focuser Class

Master Interfaces Reference

These green boxes in each interface member each have a link to the corresponding member definition in Master IFocuserV4 Interface (external). The information in this Alpyca document is provided for your convenience. If there is any question, the info in ASCOM Master Interface Definitions (external) is the official specification.

class alpaca.focuser.Focuser(address: str, device_number: int, protocol: str = 'http')

Bases: Device

ASCOM Standard IFocuserV3 Interface

Attention

It is possible to command the focuser to a position exceeding its limits (see notes for MaxStep) without receiving an exception. This is by design.

Initialize Focuser object.

Parameters:

  • address (str) – IP address and port of the device (x.x.x.x:pppp)

  • device_number (int) – The index of the device (usually 0)

  • protocol (str, optional) – Only if device needs https. Defaults to “http”.

Action(ActionName: str, *Parameters) → str

Invoke the specified device-specific custom action

Common to all devices

Parameters:

  • ActionName – A name from SupportedActions that represents the action to be carried out.

  • *Parameters – List of required parameters or [] if none are required.

Returns:

String result of the action.

Raises:

Note

  • This method, combined with SupportedActions, is the supported mechanic for adding non-standard functionality.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for Action(), find this specific device’s specification, and see Action() there.

CommandBlind(Command: str, Raw: bool) → None

Transmit an arbitrary string to the device and does not wait for a response.

Common to all devices

Parameters:

  • Command – The literal command string to be transmitted.

  • Raw – If true, command is transmitted ‘as-is’. If false, then protocol framing characters may be added prior to transmission.

Raises:

Attention

Deprecated, will most likely result in NotImplementedException

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for CommandBlind(), find this specific device’s specification, and see CommandBlind() there.

CommandBool(Command: str, Raw: bool) → bool

Transmit an arbitrary string to the device and wait for a boolean response.

Common to all devices

Returns:

The True/False response from the command

Parameters:

  • Command – The literal command string to be transmitted.

  • Raw – If true, command is transmitted ‘as-is’. If false, then protocol framing characters may be added prior to transmission.

Raises:

Attention

Deprecated, will most likely result in NotImplementedException

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for CommandBlind(), find this specific device’s specification, and see CommandBlind() there.

CommandString(Command: str, Raw: bool) → str

Transmit an arbitrary string to the device and wait for a string response.

Common to all devices

Returns:

The string response from the command

Parameters:

  • Command – The literal command string to be transmitted.

  • Raw – If true, command is transmitted ‘as-is’. If false, then protocol framing characters may be added prior to transmission.

Raises:

Attention

Deprecated, will most likely result in NotImplementedException

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for CommandString(), find this specific device’s specification, and see CommandString() there.

Connect() → None

Connect to the device asynchronously.

Common to all devices

Returns:

Nothing

Raises:

DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • Non-Blocking Use Connecting to indicate completion.

  • Natively present only in Platform 7 (2024) devices, but this library emulates Connect()/Disconnect()/Connecting mechanic for older devices.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for Connect(), find this specific device’s specification, and see Connect() there.

Disconnect() → None

Disconnect from the device asynchronously.

Common to all devices

Returns:

Nothing

Raises:

DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • Non-Blocking Use Connecting to indicate completion.

  • Natively present only in Platform 7 (2024) devices, but this library emulates Connect()/Disconnect()/Connecting mechanic for older devices.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for Disconnect(), find this specific device’s specification, and see Disconnect() there.

Halt() → None

Immediately stop any focuser motion due to a previous Move() call.

Raises:

Note

  • You should try to call this method aftr initialization to see if halting is supported by your device. You can use this info to possibly disable a Halt button in your user interface.

Master Interfaces Reference

Focuser.Halt() (external)

Move(Position: int) → None

Starts moving the focuser to a new position

Non-blocking: Returns immediately after successfully starting the focus change with IsMoving = True. See Notes, and How can I tell if my asynchronous request failed after being started?

See Notes for details on absolute versus relative focusers

Parameters:

Position – Step distance or absolute position, depending on the value of the Absolute property.

Raises:

Note

  • Asynchronous (non-blocking): The method returns as soon as the focus change operation has been successfully started, with the IsMoving property True. After the requested position is successfully reached and motion stops, the IsMoving property becomes False. See How can I tell if my asynchronous request failed after being started?

  • If the Absolute property is True, then this is an absolute positioning focuser. The Move() method tells the focuser to move to an exact step position, and the Position parameter of the Move() method is an integer between 0 and MaxStep.

  • If the Absolute property is False, then this is a relative positioning focuser. The Move() method tells the focuser to move in a relative direction. The Position parameter of the Move() method is actually a step distance and is an integer between minus MaxIncrement and plus MaxIncrement.

Master Interfaces Reference

Focuser.Move() (external)

property Absolute: bool

The focuser does absolute positioning. See Move().

Raises:

  • NotConnectedException – If the device is not connected

  • DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

True means the focuser is capable of absolute position; that is, being commanded to a specific step location. False means this is a relative positioning focuser.

Master Interfaces Reference

Focuser.Absolute (external)

property Connected: bool

(Read/Write) Retrieve or set the connected state of the device.

Common to all devices

Set True to connect to the device hardware. Set False to disconnect from the device hardware. You can also read the property to check whether it is connected. This reports the current hardware state. See Notes below.

Raises:

DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • The Connected property sets and reports the state of connection to the device hardware. For a hub this means that Connected will be True when the first driver connects and will only be set to False when all drivers have disconnected. A second driver may find that Connected is already True and setting Connected to False does not report Connected as False. This is not an error because the physical state is that the hardware connection is still True.

  • Multiple calls setting Connected to True or false will not cause an error.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for Connected, find this specific device’s specification, and see Connected there.

property Connecting: bool

Returns True while the device is undertaking an asynchronous Connect() or Disconnect() operation.

Common to all devices

Raises:

DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • Use this property to determine when an (async) Connect() or Disconnect() has completed, at which time it will transition from True to False.

  • Natively present only in Platform 7 (2024) devices, but this library emulates Connect()/Disconnect()/Connecting mechanic for older devices.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for Connecting, find this specific device’s specification, and see Connecting there.

property Description: str

Description of the device such as manufacturer and model number.

Common to all devices

Raises:

  • NotConnectedException – If the device status is unavailable

  • DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • This describes the device, not the driver. See the DriverInfo property for information on the ASCOM driver.

  • The description length will be a maximum of 64 characters so that it can be used in FITS image headers, which are limited to 80 characters including the header name.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for Description, find this specific device’s specification, and see Description there.

property DeviceState: List[dict]

List of key-value pairs representing the operational properties of the device

Common to all devices

Raises:

DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for DeviceState, find this specific device’s specification, and see DeviceState there.

property DriverInfo: List[str]

Descriptive and version information about the ASCOM driver

Common to all devices

Returns:

Python list of strings (see Notes)

Raises:

DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • This describes the driver not the device. See the Description property for information on the device itself

  • The return is a Python list of strings, the total length of which may be hundreds to thousands of characters long. It is intended to display detailed information on the ASCOM (COM or Alpaca) driver, including version and copyright data. . To get the driver version in a parse-able string, use the DriverVersion property.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for DriverInfo, find this specific device’s specification, and see DriverInfo there.

property DriverVersion: str

String containing only the major and minor version of the driver.

Common to all devices

Raises:

DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • This must be in the form “n.n”. It should not to be confused with the InterfaceVersion property, which is the version of this specification supported by the driver. Note: on systems with a comma as the decimal point you may need to make accommodations to parse the value.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for DriverVersion, find this specific device’s specification, and see DriverVersion there.

property InterfaceVersion: int

ASCOM Device interface definition version that this device supports.

Common to all devices

Raises:

DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • This is a single integer indicating the version of this specific ASCOM universal interface definition. For example, for ICameraV3, this will be 3. It should not to be confused with the DriverVersion property, which is the major.minor version of the driver for this device.

  • This value is cached internally after first retrieval since it is repeatedly used if emulating Connect/Disconnect semantics on older (pre - Platform 7) devioces.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for InterfaceVersion, find this specific device’s specification, and see InterfaceVersion there.

property IsMoving: bool

The focuser is currently moving to a new position

Raises:

  • NotConnectedException – If the device is not connected

  • DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • This is the correct property to use to determine successful completion of a (non-blocking) Move() request. IsMoving will be True immediately upon returning from a Move() call, and will remain True until successful completion, at which time IsMoving will become False.

Master Interfaces Reference

Focuser.IsMoving (external)

property MaxIncrement: int

Maximum number of steps allowed in one Move() operation.

Raises:

  • NotConnectedException – If the device is not connected

  • DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • For most focusers this is the same as the MaxStep property. This is normally used to limit the increment display in the host software.

Master Interfaces Reference

Focuser.MaxIncrement (external)

property MaxStep: int

Maximum step position permitted.

Raises:

  • NotConnectedException – If the device is not connected

  • DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • The focuser can step between 0 and MaxStep. If an attempt is made to move the focuser beyond these limits, it will automatically stop at the limit.

Master Interfaces Reference

Focuser.MaxStep (external)

property Name: str

The short name of the driver, for display purposes.

Common to all devices

Raises:

DriverException – If the driver cannot successfully complete the request. This exception may be encountered on any call to the device.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for Name, find this specific device’s specification, and see Name there.

property Position: int

Current focuser position, in steps.

Raises:

Note

  • Do not use this as a way to determine if a (non-blocking) Move() has completed. The Position may transit through the requested position before finally settling. Use the IsMoving property.

Master Interfaces Reference

Focuser.Position (external)

property StepSize: float

Step size (microns) for the focuser.

Raises:

  • NotImplementedException – If the device does not intrinsically know what the step size is.

  • NotConnectedException – If the device is not connected

  • DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Master Interfaces Reference

Focuser.StepSize (external)

property SupportedActions: List[str]

The list of custom action names supported by this driver

Common to all devices

Returns:

Python list of strings (see Notes)

Raises:

DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • This method, combined with Action(), is the supported mechanic for adding non-standard functionality.

  • SupportedActions is a “discovery” mechanism that enables clients to know which Actions a device supports without having to exercise the Actions themselves. This mechanism is necessary because there could be people / equipment safety issues if actions are called unexpectedly or out of a defined process sequence. It follows from this that SupportedActions must return names that match the spelling of Action() names exactly, without additional descriptive text. However, returned names may use any casing because the ActionName parameter of Action() is case insensitive.

Master Interfaces Reference

Alpyca uses a common Device class but this is not available in the ASCOM Master Interface Definitions (external). To see the reference info for SupportedActions, find this specific device’s specification, and see SupportedActions there.

property TempComp: bool

(read/write) Set or indicate the state of the focuser’s temp compensation.

Raises:

  • NotImplementedException – On writing to TempComp, if TempCompAvailable is False, indicating that this focuser does not have temperature compensation. In that case reading TempComp will always return False.

  • NotConnectedException – If the device is not connected

  • DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • Setting TempComp to True puts the focuser into temperature tracking mode; setting it to False will turn off temperature tracking.

  • If TempCompAvailable is False this property will always return False.

Master Interfaces Reference

Focuser.TempComp (external)

property TempCompAvailable: bool

If focuser has temperature compensation available.

Raises:

  • NotConnectedException – If the device is not connected

  • DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Master Interfaces Reference

Focuser.TempCompAvailable (external)

property Temperature: float

Current ambient temperature (deg. C).

Raises:

  • NotImplementedException – The temperature is not available for this device.

  • NotConnectedException – If the device is not connected

  • DriverException – An error occurred that is not described by one of the more specific ASCOM exceptions. The device did not successfully complete the request.

Note

  • Historically (prior to 2019) no units were specified for this property. You should assume this this is in degrees Celsius but old devices may supply temperature in other units. By now (2022) however devices should be providing degrees celsius.

Master Interfaces Reference

Focuser.Temperature (external)