I have built a few electronic focusers for various telescopes. Here are some of the focusers built with stepper motors, stepper drivers, and an Arduino Uno microcontroller. These focusers work with astronomy software such as the Nighttime Imaging N Astronomy (NINA). When the autofocus command is called, NINA takes a series of photos at various focus distances and then measures the diameter of stars for star fields (or the highest contrast for moon and planets). It then calculates the proper distance travel for best focus, and then moves the focuser to that position. An automatic focuser ensures that stars remain focused during unattended imaging runs while you are away from the telescope.
This DIY electronic focuser attached to a standard Crayford focuser. The controller keeps track of the draw tube’s current position and saves this information even when the focuser is powered off.
Here is an electronic focuser for a Vixen R114 reflector for automated and precise focusing.
DIY microfocuser for a telephoto lens using a Vixen’s alt-az mount azimuth lock mechanism
DIY electronic focuser for an 8 inch SCT using a motor drive from a Vixen Super Polaris mount
DIY Autofocuser for Celestron C8 using the Pentax Screw Drive focusing system. To view how I used a Pentax kit lens to add autofocus capabilities to my telescope, click here.
Electronic focusers can be quite useful especially in unattended automatic focusing. There are instances, however, when I would still prefer a mechanical non-electronic focusing, since electronic focusers tend to be slow, and it requires power. In all these DIY focusers, I have always included a clutch mechanism, to disengage the electronic focuser and still allow manual focusing.
Related link: DIY DSLR-based Autofocuser for Celestron 8 inch SCT
Night Sky in Focus © Anthony Urbano | Bacoor, Philippines
Night Sky in Focus 
That’s very clever and must have been a lot cheaper than buying an ‘off the shelf’ focuser.
It is also a lot of fun learning how to build one :)