BS EN 167:2002 pdf download – Personal eye-protection — Optical test methods
1 Scope
This European Standard specifies optical test methods for eye-protectors, the requirements for which are contained in other ENs.
Alternative methods may be used if shown to be equivalent.
Non-optical test methods are given in EN 1 68.
Specifications are given in EN 1 66.
A definition of terms is given in EN 1 65.
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text, and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments).
EN 1 65, Personal eye-protection — Vocabulary .
EN 1 66, Personal eye-protection — Specifications.
EN 1 68, Personal eye-protection — Non-optical test methods.
3 Test for spherical, astigmatic and prismatic refractive powers
NOTE The reference methods for assessment of refractive power are contained in 3.1 and 3.2.
If during measurement using the telescope a doubling or other aberration of the image is observed then the ocular may either be classified as a defective, or subjected to further examination using the method described in annex A.
3.1 Testing unmounted oculars covering one eye
3.1.1 Apparatus Telescope
A telescope with an aperture of nominally 20 mm and a magnification between 1 0 and 30, fitted with an adjustable eyepiece incorporating a reticule. Illuminated target
A target, consisting of a black plate incorporating the cut-out pattern shown in Figure 1 , behind which is located a light source of adjustable luminance with a condenser, if necessary, to focus the magnified image of the light source on the telescope objective. The large annulus of the target has an outer diameter of (23,0 ± 0,1 ) mm with an annular aperture of (0,6 ± 0,1 ) mm. The small annulus has an inner diameter of (1 1 ,0 ± 0,1 ) mm with an annular aperture of (0,6 ± 0,1 ) mm. The central aperture has a diameter of (0,6 ± 0,1 ) mm. The bars are nominally 20 mm long and 2 mm wide with a nominal 2 mm separation. Filter A filter with its maximum transmittance in the green part of the spectrum may be used to reduce chromatic aberrations. Calibration lenses Lenses with positive and negative spherical refractive powers of 0,06 m -1 , 0,1 2 m -1 and 0,25 m -1 (tolerance ± 0,01 m -1 ).
3.1.2 Arrangement and calibration of apparatus The telescope and illuminated target are placed on the same optical axis (4,60 ± 0,02) m apart. The observer focuses the reticule and the target and aligns the telescope to obtain a clear image of the pattern. This setting is regarded as the zero point of the focusing scale of the telescope. The telescope shall be aligned so that the central aperture of the target is imaged on the centre of the cross-line graticule. This setting is regarded as the zero point of the prism scale. The focusing adjustment of the telescope is calibrated with the calibration lenses (3.1 .1 .4) so that a power of 0,01 m -1 may be measured. Any other equivalent calibration method may be used.
3.1.3 Procedure Position the ocular in front of the telescope in the as-worn position, or other position as specified by the manufacturer. If the as-worn position is unknown, or if no position is specified by the manufacturer then the ocular shall be positioned normal to the telescopic axis and the tests conducted at the geometric centre. Spherical refractive power and astigmatic refractive power Oculars without astigmatic refractive power The telescope is adjusted until the image of the target is clearly focussed. The spherical power of the ocular is then read from the scale of the telescope. Oculars with astigmatic refractive power The target, or the ocular, is rotated in order to align the principal meridians of the ocular with the bars of the target. The telescope is focused firstly on one set of bars (measurement D 1 ) and then on the perpendicular bars (measurement D 2 ). The spherical power is the mean, 2 2 1 D D the astigmatic refractive power is the absolute difference, 2 1 D D , of the two measurements. NOTE During this process the best focus shall be used across the whole target for each meridian. Prismatic refractive power The ocular to be tested is placed in front of the telescope, and, if the point of intersection of the lines of the reticule falls outside the image of the large circle, the prismatic power exceeds 0,25 cm/m. If the point of intersection of the lines of the reticule falls inside the image of the small circle of the target, the prismatic power is less than 0,1 2 cm/m.