1. Field of the Invention
The present invention relates to a refractive characteristics measuring apparatus for measuring the refractive characteristics of a lens to determine the distribution of refractive power in the lens and, more particularly, to a refractive characteristics measuring apparatus for determining the respective positions of the far viewing section and near viewing section of a progressive multifocal lens through the measurement and observation of the distribution of refractive power in the progressive multifocal lens.
2. Description of Related Art
The refractive power of a progressive multifocal lens, which has become prevalent in recent years, varies continuously from a far viewing section through a progressively varying focus area to a near viewing section. The progressive multifocal lens is similar in appearance to a single-focus lens and it is impossible to discriminate between the far viewing section and near viewing section of the progressive multifocal lens from the appearance of the same.
Therefore, the far viewing section and near viewing section of a progressive multifocal lens as manufactured, such as a progressive multifocal lens as shipped from the lens maker, are indicated by marks and dimensions of the respective positions of the far viewing section and the near viewing section, which differ between progressive multifocal lenses of different types. The respective positions of the far viewing section and the near viewing section are determined by measuring the progressive multifocal lens with reference to concealed marks indicating reference points and additive diopter or by placing the progressive multifocal lens on a layout chart showing the far viewing section and the near viewing section and printed on a sheet of paper. The respective refractive powers of the far viewing section and the near viewing section are measured individually by a lens meter.
However, it is difficult and requires much time to determine the respective positions of the far viewing section and near viewing section of the progressive multifocal lens by measuring the progressive multifocal lens after the progressive multifocal lens has been shaped and framed. Furthermore, there have been no effective optical measures for detecting errors in the specified positions of the far viewing section and the near viewing section and it is possible that the respective positions of the far viewing section and near viewing section are determined erroneously by measurement.