BS EN ISO 10938:2016 pdf download – Ophthalmic optics — Chart displays for visual acuity measurement — Printed, projected and electronic 4.1.3 Contrast of optotypes Optotypes shall be specified by the background luminance in cd/m 2 and by the luminance of the optotype as a percentage of the background luminance. The luminance of the optotype shall be not more than 15 % of the luminance of the background upon which the optotype is located. Optypes in a series shall not differ noticeably in contrast. 4.1.4 Quality of presentation Optotypes as presented shall appear with sharply defined contours to an observer with a binocular visual acuity of 1,0 to 1,25 at an observation distance of 1/3 of the distance at which the optotypes are designed to be used. Similar optotypes in a size series shall not differ noticeably in shape or edge sharpness. For electronic displays, if anti-aliasing (i.e. modifying the brightness of pixels at the borders of optotypes) is used to smooth the naturally occurring jagged edge formed by pixels at curved edges, it shall not cause a change in the perceived size of the optotype outside of the 5 % variability in optotype size allowed by ISO 8596. Furthermore, there shall be no performance difference between the electronically displayed optotype and a printed display of standard optotypes that meets the requirements of ISO 8596. NOTE Anti-aliasing may add or subtract from the width of the detail and may change the calibration. Optotypes presented in displays for which the design prevents viewing at 1/3 the normal distance shall be observed with a magnification of 3× in order to verify the quality of presentation. 4.1.5 Resolution For optically projected charts, the minimum resolved spatial frequency on the screen shall be at least 2 cycles per minute of arc measured from the minimum test distance specified by the manufacturer. For electronically generated charts, the pixel size shall be sufficiently small that there is no performance difference between the electronically displayed optotype and an optotype that meets the requirements of 4.1.4. Ideally, the pixel size should be not larger than 0,25 min of arc measured from the minimum test distance specified by the manufacturer 4.2? Requirements? specific? to? optically? projected? displays 4.2.1 Focus range For projector charts, the minimum focus range shall be 2,9 m to 6,1 m. 4.2.2 Projector screens If the projector requires the use of specific screens, the specification of...
Download Address
Download