Deep Sky Dad AF3 Autofocuser Settings

With the SpaceCat build all wired up for bench testing, I'm starting to go through each of the component systems to evaluate their functionality. Part of this process involves installing the latest drivers and software, updating firmware, and configuring settings. For the most part, it's been pretty straightforward. Although, settings for the Deep Sky Dad AF3 Autofocuser have been somewhat less intuitive, and as a result, a bit more challenging to configure. 

TL;DR: Set the zero position of the focuser, and then find the max position using a step size that yields a position value greater than or equal to 10,000 at full extension

Deep Sky Dad provides instruction for the AF3 Autofocuser in the form of an FAQ page. The goal of this article is to provide further guidance and insight into configuring ASCOM driver settings for the DSD AF3 Autofocuser, and the DSD AF3 Control Panel software.

Identifying the COM Port 

First and foremost, the ASCOM driver and Control Panel software both task the user with identifying the COM port assigned to the AF3 Autofocuser. This is done by selecting one of the available ports listed in the dropdown menu for the COM Port setting. In some cases, there may only be one COM port listed. However, if there are multiple devices connected to the computer (such as a mount, filter wheel, field rotator, flap panel, etc.), there will likely be more than one COM port available to choose from.

There are a number of ways to identify which COM port is assigned to a device. Aside from just selecting one at random and hoping for the best, the easiest way of identifying which COM port the AF3 is assigned to is probably to use the Firmware Version button found in the ASCOM driver under Advanced settings. This will display device and firmware information for any DSD device using the selected COM port.

Using this method, identifying which COM port is assigned to the AF3 is simply a matter of checking the firmware version for each COM port listed until the AF3 device is found.

Accessing Driver Settings

To access the ASCOM Deep Sky Dad AF3 driver settings window, first open ASCOM Diagnostics.

Then select Choose Device > Choose and Connect to Device from the menu bar to open the Device Connection Tester window.

From the Device Connection Tester window, select Focuser from the dropdown menu under Select Device Type, and select Choose to open the ASCOM Focuser Chooser.

Next, select one of the ASCOM Deep Sky Dad AF3 options from the dropdown, and select Properties... to open the ASCOM Deep Sky Dad AF3 driver settings window.

With the driver settings window open, select Advanced >> to show additional settings and options. Then select Firmware Version to view device and firmware information for the selected COM port.

Setting the Zero Position

While the ASCOM DSD AF3 driver settings window is still open, this would be a good time to reset the AF3 Autofocuser position value to zero. Being that there is no option to specify a minimum position value in settings, resetting the position value to zero appears to be the only method for setting the minimum focuser position. If the AF3 Autofocuser position value is greater than zero when the focuser draw tube is fully retracted, it's probably best to reset the zero position.

Before doing so, first make sure that the focuser draw tube is fully retracted. This can be done manually while the AF3 Autofocuser is powered off. Once powered on though, current is applied to the stepper motor that prevents the focuser from shifting under load. With the AF3 powered on, the focuser position can be adjusted through software using the AF3 Control Panel, or any ASCOM compatible telescope control software package (such as SharpCap or NINA), or by using the DSD hand controller.

With the focuser draw tube fully retracted, enable the Set position option under the section titled On next connect, and set its value to zero.

The AF3 Autofocuser position value will then be reset to zero the next time the ASCOM driver is used to connect to the device.

Back That Glass Up

Using the AF3 Control Panel, make an attempt to extend the focuser by increasing the AF3 Autofocuser position value. This can be done by selecting the plus (+) button under Move - releative in the Control tab, or increasing the value under Move - absolute and select GO.

If the focuser draw tube retracts instead of extends when the position value increases, enable the Reverse direction option found under the Settings tab.

Also enable the Reverse direction option in the ASCOM driver as well if needed.

Finding the Maximum Position Value

This part can be a bit tricky. The maximum position value can be determined by finding the position at which the focuser reaches full extention. There's a limitation, though: the maximum position value must be greater than or equal to 10,000 steps.

This presents a challenge when the focuser is able to reach full extension with a position value less than 10,000 steps. In my case for instance, the William Optics SpaceCat 51 reaches full extension in only 1,350 steps when using a 1/2 step size. While searching for a solution, I found one other user on Cloudy Nights who encountered the same issue when using an AF3 with their Samyang 135mm f/2 lens.

The step size is key to understanding and solving this problem. Step sizes are listed under settings as inverse powers of two, and can be treated as inversely proportional to the maximum position value. With this understanding, these values can be scaled by powers of two to achieve a maximum position value that exceeds 10,000 steps.

In the following examples, the maximum position value is calculated using the lowest power of two that produces a value greater than or equal to 10,000 when multiplied by the position value at full extension. The inverse of that power of two in turn can be used to determine the step size.

Maximum position example,

  1,350 steps *  2^3 1,350 steps *  8  = 10,800 steps

Step size example,

  1/2 step *  1/2^3 1/2 step /  8  = 1/16 step

Having established a maximum position value greater than or equal to 10,000, the Step size and Maximum position values can be updated under the Settings tab of the AF3 Control Panel.

The same values should be applied to the ASCOM driver as well.

Troubleshooting Tips

Note that the AF3 Autofocuser can only accept one serial connection at a time. If the AF3 Control Panel is connected to the device, the Control Panel software will need to be disconnected before the ASCOM driver can connect to the device using the same COM port, and vice versa. The ASCOM platform serves as a virtual device hub, though. So once the ASCOM driver is connected to the device and configured, any software that supports ASCOM can then be connected to the device through the ASCOM driver.

If unable to identify the COM port assigned to the AF3 Autofocuser, double check power and USB connections. Keep in mind that before the AF3 can be assigned a COM port, it must first be connected to the computer via USB, and powered on using an adequate power supply (12V, 1A minimum) with a DC 5521 connector.

Additionally, try inspecting the Windows Device Manager for any COM ports that might be listed under the Ports (COM & LPT) category. The AF3 Autofocuser will appear connected as a USB Serial Device. 

When inspecting property details of the AF3 Autofocuser, the Bus reported device description will list Arduino Nano Every as its value. As of this writing, Deep Sky Dad products typically report this value as the device description since they are built using the Arduino platform.

Further inspection can be done using USBView to browse all USB controllers and connected USB devices. As with the Device Manager, the AF3 Autofocuser will appear connected as a USB Serial Device in the device tree, and will list Arduino Nano Every as the iProduct value.