By Don Selle
In Part 1 of this article, I described several techniques you could use to manually focus your smartphone or your DSLR used either stand alone or attached to your telescope. Adding an inexpensive Bhatinov mask to the front of your telescope or DSLR lens (yes you can get them that size) makes achieving critical focus using the camera’s live view focusing very doable. This technique can also be used for a dedicated astro-imaging camera on your telescope if you view the focus images as they are downloaded to the computer controlling the camera.
The Bhatinov mask works great, but let’s face it, manual focusing can be a tedious and time-consuming task. When I first started astro-imaging, manual focusing was the norm for me and others like me starting out because the motorized focusers were few, and they were rather expensive. In addition, there was not much software to automate the focusing process and there were no real interface standards to allow computer control of the telescope focuser. So, we learned to focus by hand and by eye.