| 摘要 |
PURPOSE: To provide an optical system for copying machine having high contrast and the brightness of F8 and capable of reducing the cost by using the glass of a low unit price by comprising the system of plural lens groups composed of single lenses, respectively, and satisfying a specified condition. CONSTITUTION: This system is composed of a first lens group composing of a single lens having a positive refractive power, a second lens group composed of a single lens having a negative refractive power and a third lens group composed of a single lens having a positive refractive power successively arranged from the object side. The respective conditions: 0.37f<f1 <1.6f, -0.31f<f2 <0.19f, 1.55<n1 <1.65, 2.3<(ν1 +ν3 )/ν2 <3.3 are satisfied, where, f: the composite focal distance of a whole system for (d) line, f1 , f2 : focal distances of the first lens group and the second lens group for (d) line, respectively, n1 : the refractive index of the first lens group for (d) line andν1 -ν3 : the Abbe numbers of the first to the third lens groups 1-3, respectively.
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