Hot crimping structure and method for fixing a lens to a lens frame, and hot crimping tool therefor

A hot crimping method of fixing at least one lens element to a lens frame made of synthetic resin, a lens holder opening for accommodating said lens element being formed on said lens frame, an inward stepped portion which is engaged with that portion of one side surface of said lens element adjacent to a rim of said lens element being formed on said lens frame in said lens holder opening, a portion of said lens frame being crimped by heat to serve as a crimped edge which lies on the portion of the other side surface of said lens element adjacent to said rim of said lens element,

• wherein said hot crimping method comprises:
• forming an outward expansion surface on an inner peripheral surface of said lens frame so that said outward expansion surface extends outwards from a close vicinity of said rim of said lens element;
• preparing a hot crimping tool including an annular crimping edge having an acute angle in cross section, an outer diameter of said annular crimping edge being greater than a diameter of said lens holder opening;
• and
• bringing said hot crimping tool into contact with said outward expansion surface to form a recess on said outward expansion surface by heat of said hot crimping tool to thereby produce said crimped edge by movement of melting synthetic resin which is melted due to the formation of said recess.