Autofocuser 3 FAQ

While testing our units, we carefully write down every issue that arises and solution to it - from basic connectivity, firmware upgrade to more complex problems like focuser slip and play. In result, this section composed from development and testing experiance, gathered from countless nights through years of astrophotography in field. Should you have additional questions not listed here, please let us know!

What kind of power adapter can I use?

We recommend 12V DC power adapter, as the units are fine tuned to this specific voltage. However, autofocuser will work up to 14V. Socket specification: tip positive, 5.5mm x 2.1mm. Should you not have 12V adapter at hand, the units also work in range from 12V-14V without issues. Current output of the power adapter should be 1A minimum, but can be more (it will not damage the autofocuser).

When I connect the autofocuser to computer, Windows does not recognize it. What can I do?

pre 2020 (mini USB port version): You probably need to install the CH340 driver for Arduino compatible boards to provide USB connectivity. You can download it here or from authors website.

2020 update (micro USB port version): if you are using Windows 10, the driver will self install. If you are using Windows 7, please install 32 or 64 bit driver. Should you experience any problems with detection, try:
  • different USB cable
  • direct connection (without USB hub)
  • using USB 2.0 port (instead of 3.0)

How can I upgrade focuser firmware?

Please refer to the firmware upgrade instructions.

How can I use the autofocuser on Linux/Mac OS/BSD

You can connect with AF3 INDI driver in KStars. IMPORTANT: you have to change the baud rate from 9600 to 115200 in order to connect successfully!

Focuser is recognized by Windows and virtual COM port is created. What now?

Next step is installation of ASCOM driver, so you can use the focuser with any of the automation programes, like SGPro. You can download the ASCOM driver here. You also need to install ASCOM platform.

I successfully installed new version of ASCOM driver, but now focuser will not connect. How can I fix it?

First check if you chose the correct COM port. If that does not work - ASCOM driver is developed for specific version of autofocuser firmware (specified in the readme file). We recommend you to always use latest firmware and latest ASCOM driver.

Can you explain the ASCOM driver settings?

General settings

  • COM port - virtual COM port, assigned to your focuser.
  • Reverse direction - reverses motor direction.
  • Temperature compensation - enables ASCOM temperature compensation mode. (WARNING: enabling this option disables manual control of the autofocuser as per ASCOM documentation requirements)
  • Trace on - ASCOM driver trace log. If you experiance autofocuser issues, turn this setting on and send us the log files. They are located in "C:\Users\username\ASCOM" (Windows).


  • Step size - supports step sizes from 1 to 1/256. For most applications, step size of 1/2 or 1/4 should suffice.
  • Speed mode - speed of the motor, available options: Very slow, Slow, Medium, Fast and Very fast. Defaults to Slow.
  • Settle buffer - if your focuser has any play, this can affect the autofocuser performance. SGPro for example goes aways from current position and than starts traversing back. When it changes focus direction (traverse back), focuser play can cause FOV to jiggle just a bit, which causes enlongated stars on the next exposure. Settle buffer option returns IsMoving as TRUE for specified time after focuser reaches target position, letting it to settle a bit. This only works well from SGPro version 3.0.0 beta and later.
  • Max. position - maximum position of focuser (in steps).
  • Max. movement - maximum position change in a single movement (in steps).

On next connect

  • Reset settings - if you experiance weird focuser behavior or for example hit 0 or max focuser position, you can reset the settings to the defaults with next connect.
  • Set position - change absolute (software!) position of focuser to the entered position on next connect. This does not cause the actual movement of the motor.

Coils control

  • Move current multiplier (%) - % of the maximum motor current used during the movement
  • Hold current multiplier (%) - % of the move motor current, used when motor is not moving (Used equation: I_hold = Hold_current_multi_% * I_move * 0.8)


  • Reboot AF3 - reboot the unit.
  • Firmware version - message box with current firmware of the connected unit.

I have changed the ASCOM settings but they have no effect, what can I do?

That happens if you change the settings while connected to the focuser. In order for ASCOM settings to have effect, you have to first disconnect from the autofocuser, change the settings and connect again.

How can I use the focuser in combination with the rest of my equipment (camera, guiding, mount...)?

Mounting of focuser is up to the customer, as stated in IMPORTANT section of autofocuser page. We recommend you mounting via timing belt, because it is less invasive to the focuser than shaft to shaft coupling. That is why every focuser comes with MXL pulley and free option of timing belt with various lengths. We also separately sell 3D printed mounting adapters for a few focusers. You can check more in autofocuser mounting adapter section.

Can I control the focuser manually?

AF3 comes with multiple ways of manual control, so you can focus with bahtinov mask or use it for visual observation without touching the focuser with your hands.

AF3 Control Panel

AF3 Control panel can be used for firmware upgrade or as manual control application. Once connected, you can move the motor in a variety of ways: fixed number of steps, 90/180 degrees, specific absolute position, continuous motion,...

Hand Controller

  • Connection - connect it to audio jack port on the autofocuser unit.
  • Interface - 2 buttons, + and -.
  • Single press - with a single press, the motor moves for a 100 steps in either direction. The amount of movement depends on the current step mode (read below)
  • Continuous movement - you can move the motor continuously by pressing and holding + or - button.
  • Step mode - by clicking both buttons at the same time, you can decrease step size & speed. If you want to reset to full speed, press and hold both buttons for 2s.

What about temperature compensation?

AF3 comes with an option of temperature sensor. You can connect it to the audio jack port. Once connected, AF3 provides ASCOM/INDI with the temperature reading neccessary for the temperature compensation mode.

SGPro temperature compensation tutorial

  • In ASCOM settings, check "Temperature compensation" checkbox
  • Once connected to the AF3, you will be able to configure how often SGPro autofocuses in relation to the temperature change
  • After every finished frame, SGPro will check if refocus is neccessary. For example autofocus will be triggered, once the current frame is finished in this example (temperature differance from last autofocus is larger than 0.5 degree):
  • After autofocus procedure is finished, timestamp and temperature of last autofocus are updated.

Timing belt is too loose/tight. What can I do?

L bracket has slotted holes. Try undoing the 4 bolts that connect the motor to the L bracket and moving it up/down.

When focuser is turning, it causes vibration. What can I do about it?

Some amount of vibration is normal with stepper motors, included in our focusers. If you are using full step or half step mode, try to change it to 1/4 or 1/8 in ASCOM driver properties and increasing number of steps per change in SGP.

SGPro autofocus graph spike on right is causing smart focus to move away from in-focus position instead of towards. How can I fix this?

This can happen if you have any play in the focuser drawtube. Please check Settle buffer in ASCOM settings section.