One of the major challenges of astrophotography is focusing on celestial objects. That’s especially true if you’re using a midrange telescope mounted on a conventional tripod. Turning the focus knob by hand shakes the telescope, which makes it difficult to actually perform the task.
That’s the situation Jason Bowling found himself in with his Celestron 127 SLT telescope. It’s a fairly high-quality computerized telescope, but it still rests on a tripod. That’s stable enough for photos, but when you’re working at astronomical distances it gets jittery as you focus.
To address that, Bowling set up a motorized focusing system that removes the need to touch the telescope at all. The tripod mount on the scope’s body had some extra room on it, so it was the perfect place to put a stepper motor bracket. Under the focusing knob’s rubber grip was a smooth shaft, which made it a snap to add a pulley and a belt going to the stepper motor.
Bowling wanted to be able to focus remotely, so he paired a Raspberry Pi Zero W with an EasyDriver for driving the stepper motor. He then built a simple Flask web app which gives him course, medium, and fine focus control. Combined with a Bahtinov mask and Sharpcap’s Bahtinov aid, that gives him the ability to quickly and easily focus on astronomical bodies.