One of the best additions I have made to my astrophotography equipment list is undoubtedly autofocusing. This device is a digital stepper motor that attaches to the focus shaft of a telescope (using appropriate adapters for the specific telescope in question) to enable adjustment of focus through the computer interface. This brings a number of advantages.

Probably the most important advantage is that the autofocuser can make incredibly small movements that are repeatable, which enables very precise adjustment that can be controlled based on measurements from captured images.

Another advantage is that the focus can be adjusted without having to touch the telescope. Any physical interaction introduces vibrations, and also brings the possibility of inadvertently knocking it off from its polar alignment position.

Thirdly, focus adjustment being made automatically allows me to remain indoors in the warmth, relying on the remote connection of my laptop computer to the mini computer that is attached to the telescope to control everything. No one wants to be outside in the freezing cold if it's not necessary.

You can read more about this device on the ZWO website.