It is total different about structure of segment in stitching paraboloidal mirror and stitching spherical mirror or flat. Because of cuvature of the spherical mirror or flat is identical, even if in different points and different directions, so its surface appearance and external dimensions of all segments are identical too. But in paraboloidal mirror, its curvature radius is lengthening gradually, when the point deviates from apex to outer zone, even if in same point, its curvature is also different in different directions. When stitching all segments to an entire paraboloidal mirror, in order to make each edge curves of neighbouring segments keeping coincidence, all off-axis segments aren’t regular hexagon, its external dimensions have slight variations.

According to Dr. H. Martin’s stitching pattern1, if the maximum dimension of subsegment is 0.9M, the curvature radius of apex of paraboloid is 2.88M (the focal ratio of the entire paraboloidal mirror is near F/0.6), the author calculates the external dimensions of off-axis segment, its nearest optimum paraboloid, its nearest optimum sphere. On the other hand, the author analyzes the advantages and disadvantages about selecting which axis as rotative axis of off-axis segment under removal proceeding, for example selecting its normal line of center point of segment or its perpendicular bisector of segment in meridional plane. According to these analyses and calculations, this paper gives some suggestions and several sets of data about structure of off-axis segments. All these are just a base for further research in stitching paraboloidal mirror.