Bahtinov Style Mask
In 2005, Russian astronomer Pavel Bahtinov started a thread on his message board proposing a new type of focusing mask which uses a diffraction spike pattern to aid in focusing. A very active discussion followed which led to several designs of masks which allow precise focusing using a diffraction spike pattern. In 2008, a message thread was started on CloudyNights.com which alerted the Cloudy Nights community to this style of mask. Several members suggested that someone needed to make a commercial version of the mask and Jerry Hailey and John Wunderlin answered the call. Jerry made some modifications to the basic design and the result is the Spike-a mask.