| 摘要 |
PURPOSE: An optical system for pin-hole camera is provided, which is applied to a pin-hole camera and realizes a good achromatic state. CONSTITUTION: The first lens(10) consists of a negative magnification lens having a concave surface toward an object side. The second lens(20) consists of a positive magnification lens that has an aspheric surface toward the object side and a convex surface at an image side. The third lens(30) consists of a positive magnification lens having a convex surface toward the object and image side. The fourth lens(40) consists of a negative magnification lens having a concave surface toward the object and image side. fb/fe is equal to or more than 0.81, (Xa-Xb) is less than 0, and T/fe is equal to or less than 2.40. Wherein, fe is a focal distance from an object, fb is a back focal length, T is a distance from the first lens to the fourth lens, Xa is a sag of a reference surface at the aspheric surface of the second lens, and Xo is a sag by the aspheric surface.
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