Magnification Ratios and Working Distances of "Head and Attachment Magnifiers" Made by Eschenbach

ISSN： 1388-235X

Source： Visual Impairment Research, Vol.9, Iss.2-3, 2007-05, pp. : 51-57

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Abstract

Purpose: Because magnification ratios (MRs) indicated (IMRs) in catalogues of "Head and Attachment Magnifiers" made by Eschenbach are not common values, we examined the IMRs in relation to the working distances (WDs) indicated (IWDs) in the catalogues and then calculated the corrected WDs. Methods: From information about loupes given in the catalogues and measurements made with a lensometer, we determined (1) the power of each magnifier and (2) the accommodation needed; we then (3) calculated the MR and (4) established the corrected WD. Results: When used within the IWD, monocular loupe had an MR that was the same as the IMR. However, for binocular loupes, the MR was lower than the IMR. When the loupes were used at the revised WD recommended by the engineer of Eschenbach, binocular loupes had an IMR of "-1," meaning that a WD shorter than the revised WD was needed to attain the IMR. Conclusion: With Eschenbach head and attachment magnifiers, the IMR is only attained when viewed at a shorter WD than that indicated in the catalogue (IWD) and with adequate accommodation.