BS EN ISO 8624:2020 pdf – Ophthalmic optics – Spectacle frames – Measuring system and vocabulary

BS EN ISO 8624:2020 pdf – Ophthalmic optics – Spectacle frames – Measuring system and vocabulary.
1 Scope This document specifies a measuring system for spectacle frames and related vocabulary. It is applicable to spectacle frames with fronts that are intended to be symmetrical. 2 Normative references There are no normative references in this document. 3? Terms? and? definitions For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at http://www.iso.org/obp — IEC Electropedia: available at http://www.electropedia.org/ 3.1 Principal terms of the boxed lens system 1) 3.1.1 boxed lens system system of measurement and definitions of spectacle frames based on rectangular boxes that circumscribe the lens shapes and that are used for the determination of the dimensions of the spectacle front and in which the upper tangent is both common to the right and left lens shapes and regarded as being horizontal Note 1 to entry: In the case of spectacle frames having a significant face form angle, the line touching the uppermost edges of the right and left lens shapes shall be regarded as horizontal. Note 2 to entry: For measurement of a lens aperture, the measurements should be taken as if projected onto the base of the rectangular box which is regarded as being tangential to the plane of the lens shape at its boxed centre. This plane is close to that formed by the upper and lower tangents to the lens shape. For frame measurements, the aperture is taken to be the size of the hypothetical lens that fits the frame. Measurements to the apex of the groove or equivalent can give slightly different values. Note 3 to entry: Since the tangent common to the right and left lens shapes is regarded as being horizontal, the lines at right angles to it, e.g. the two sides of the box either side of the lens shape, are called “vertical”.
3.1.5 boxed centre distance c horizontal distance between the boxed centres (3.1.2) Note 1 to entry: See Figure 1. Note 2 to entry: For spectacle frames having a significant face form angle, the boxed centre distance shall be measured between the vertical centrelines passing through the groove of the frame aperture. See Figure 4. 3.1.6 distance between lenses d horizontal distance between the nasal vertical sides of the rectangular boxes that circumscribe the right and left lens shapes (3.2.10) Note 1 to entry: See Figure 1. 3.1.7 overall length of side l length from the intersection of the dowel screw’s axis with the median plane of the joint to the end of the side and parallel to the centreline of it, the drop having been straightened Note 1 to entry: See Figure 2. Note 2 to entry: For sides without a joint, the side should be held open at (90 5 0 − )° to the front or to that part of the side (the lug) that is intended to be attached to the front, and the length measurement is from the end of the side to the back surface of the lug less 10 mm. See Figure 3.