Setting the strut length when building one
of my kits is pretty easy. Here's is a simple procedure:
A -- Set the focuser travel to
one-half the distance (if the focuser draw-tube travels 2", set
it at 1").
B -- Measure the distance from the center of the diagonal to the
top of the draw-tube.
C -- Measure the distance from the underside of the front ring
to the center of the focuser.
D -- Calculate the distance between the secondary and the front
of the mirror (see below).
E -- Measure the distance from the front of the primary mirror
to the front surface of the mirror board.
C+D+E -- Add these numbers for the strut length