摘要：

The invention relates to a preform (1) for producing plastic containers in a two-stage stretch blow-moulding process, wherein the preform has an elongated preform body (2), the one longitudinal end of which is closed by a bottom (3), while the other longitudinal end adjoins a neck section (4) having threaded sections (5) or similar positive protrusions. The preform (1) is produced from a plastic material suited for the stretch blow-moulding process, said material having a refractive index of 1.3 to 1.6 at a temperature of 100°C to 120°C. The preform bottom (3) is designed such that the outer wall (18) thereof and the inner wall (17) thereof delimit a flat divergent lens. The outer wall (18) and the inner wall (17) of the preform bottom (3) designed as a divergent lens have radii of curvature (c, b) which are greater at least by a factor of 1.4 than the radii of curvature (s, r) of the associated outer wall (8) or inner wall (7) in the region of the preform body.

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