Why does ProtoStar use the 180º arch design?
There are many secondary support configurations that meet the “180-degree rule”, and thus, symmetrically spread diffraction. The 180º arch design yields the highest ratio of rigidity (a mechanical design consideration) to obstruction ratio (an optical design consideration). Another way of saying this is that for a given amount of edge-on obstruction, a 180º arch is the most stable of the curved designs. In theory, the 180º single-arch design can be scaled up for any size Newtonian. However, other less-obvious factors may steer you towards one design over another. For example, a typical truss-style upper cage does not have anchoring points for our 180º arch at the necessary locations (see question 5). If you wanted to use a curved mount on a truss-style scope, a 4-vane curved mount would work better, even at the expense of more total diffraction. (If the upper cage had only three strut pipes, then a 3-vane curved mount would be the natural choice.) In short, choosing the right curved mo
