| 摘要 |
PURPOSE:To use laser light with multi-mode wavelengths, by constituting the lens in such a way that the lens can satisfy specific conditions, and performing achromatization. CONSTITUTION:This lens is composed of a 1st group whose concave surface is on the light source side and having a negative refracting power, a 2nd group of a positive meniscus lens having its convex surface on the image side, a 3rd group composed of two positive lenses and one negative lens and having a positive refracting power as a whole, and a 4th group composed of two plane-convex lenses from the light source side, and satisfies conditions of Formulae I-VII. The f, fI, fIII, dIII IV, and fIV of the formulae respectively represent the focal distance of the whole system, focal distance of the 1st group, focal distance of the 3rd group, interval between the 3rd and 4th groups, and focal distance of the 4th group. Moreover, the nuII, nuIII p1, nuIII p2, nuIII N, and fII III respectively represent the Abbe's number of the 2nd group, Abbe's number of the positive lens on the light source side of the 3rd group, Abbe's number of the image side positive lens of the 3rd group, Abbe's number of the negative lens of the 3rd group, and resultant focal distance of the 2nd and 3rd groups. Therefore, chromatic aberration is corrected so that laser light with multi-mode oscillation can be used.
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