ISO 8980-1:2004 pdf download – phthalmic optics-Uncut finishedspectacle lenses – Part 1: Specifications for single-vision and multifocal lenses.
6 Test methods
6.1 General
A lens measured with a focarieter calibrated to the mercury e-Iine reference wavelength may show a difference in power when compared to the same lens measured at the same point using a focimeter calibrated to the helium d-line.
Alternative measurement methods are acceptable if shown to perform equivalently to the reference test methods in this section.
6.2 Measurement method for the focal power of single-vision lenses and the distance portion of multifocal lenses
Lenses shall be measUred with the intended back surface against the focimeter support. The lens shall be centered at the distance reference point. The focal power shall be verified according to Table 1.
6.3 Measurement method for cylinder axis
6.3.1 Single-vIsion lenses
Cyirder axis is only applicable to single-vision lenses with a predetermined onentation, e.g. prism base
selting
6.3.2 Multifocal lenses
Measure the tolerances, it applicable, in relation to the horizontal ri one of the following ways:
a) for round segment multifocal lenses, by the segment position prescribed on the lens order:
b) for non-circul segment multifocal lenses, by the orientation of the segment.
6.4 Centration and prismatic power
Lenses shall be measured with the intended back surface against the focimeler support. The lens shall be centred at the distance reference poönt. The centratlon and pflsmnatlc power shall be verified according to Table 4. A pnsm-compensating devce corresponding to the prismatic power and opposite base setting may be used.
6.5 Addition power measurement
6.5.1 Specification of measurement method
There are two addition power measurement methods: front surface and back surface measurement. Unless otherwise stated by the manufacturer, the surface chosen for measurement shall be the segment side.
NOTE 1 In the case of an asphenc lens, the distance reference point should be specified by the manufacturer. NOTE 2 D,fterenoes may occur between front surface and back surface measurements
NOTE 3 Differences may occur between measurements made with IOA and FOA focimelers (see Clae 3) at points on a lens where prism is not zero. This is because 01 the different obôquity of the ray paths ttwouph the lens caijsed by the prismatic effect at those points.
6.5.2 Front surface method for addition power m.asur.m.nt
Establish pout D, which is the symmetrical point of N willi respect to B (see Figure 3). If the position of point N is not specified, choose a point 5 mm below the top of the segment as point N.
Place the lens so that the front surface Is against the foclmeter lens support. centrabze the lens at point N. and measure the near power.
Keeping the front surface against the focimeter support, centralize the lens at D (see Figure 3) and measure the distance power
Calculate the addition power as the difference between the near power and the distance power. Near and distance power may be either the power measured using the nearer to vertical lines of the target or the spherical equivalent power.
6.5.3 Back surface method for addition power measurement
Establish pomt D, which is the symmetrical point of N with respect to B (see Figure 3). If the position of point N is not specified, choose a point 5mm below the top of the segment as point N.
Place the lens so that the back surface is against the focimeter lens support, central.ze the lens at point N, and measure the near power.
Keeping the back surface against the focimneter support, centralize the lens at D (see Figure 3) and measure the distance power.
Calculate the addition power as the difference between the near power and the distance power. Near and distance power may be either the power measured using the nearer to vertical lines of the target or the spherical equivalent power.