| 摘要 |
An achromatic lens system includes a negative single lens element, a positive single lens element, and a negative single lens element, in this order from the object, and satisfies the following condition:whereinthetapt designates the partial dispersion ratio at the t-line, defined by (nC-nt)/(nF-nC) with respect to the positive single lens element;thetant designates the average of the partial dispersion ratios at the t-line, defined by (nC-nt)/(nF-nC) with respect to the negative single lens elements;nC designates the refractive index at the C-line;nt designates the refractive index at the t-line; andnF designates the refractive index at the F-line.
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