ABSTRACT
Longer exposures and higher magnifications demand better focus. In astrophotography, precise focus is essential; all puns aside, stellar images ruthlessly expose poor technique, as one instinctively knows what stars should look like. Poor focus increases star sizes in general and makes them more diffuse. There are some wonderfully inventive methods to use optical effects to enhance the eye’s ability to find the focus point. The focus mask technique is inexpensive, effective and portable. A motorized focuser imparts little vibration into the imaging system, and unlike manual focus adjustments, the motorized focuser is ready to make an immediate assessment without waiting for the image to stabilize. Indirect focus methods are great but ultimately, if the stars are as small as they can be, everything else is good. Computers, however, are adept at measuring star diameters at different focus positions and automatically finding the precise position at which the stars are at their smallest diameter, i.e. in focus.
