Precision glass moulding lens design it should be considered that the lens has to be mountable in measurement systems. The shape of the preform or "blank" needs to be chosen according to the geometry of the finished optical element. Possible preforms are spherical (ball), near spherical (gob), plano-plano, plano-convex, plano-concave, biconvex and biconcave blanks. Ball and gob-blanks do not have to be premachined whereas other preforms require grinding and polishing. The following section describes basic traits of preform choice: “Used specifically for lenses with positive power: biconvex, plano-convex, and meniscus where the convex side is stronger than the concave side, this only works
Parallel projection Parallel projection A parallel projection is a projection of an object in three-dimensional space onto a fixed plane, known as the "projection plane" or "image plane", where the "rays", known as "lines of sight" or "projection lines", are parallel to each other. It is a basic tool in descriptive geometry. The projection is called "orthographic" if the rays are perpendicular (orthogonal) to the image plane, and "oblique" or "skew" if they are not. A parallel projection is a particular case of "projection" in mathematics and "graphical projection" in technical drawing. Parallel projections can be seen as the limit of a