| 摘要 |
<p>An fθlens containing a first lens group having an object-side convex positive lens, a second lens group having an object-side concave negative lens, a third lens group having a positive refractive power, the third lens group being a single positive lens, an assembly of a positive lens and a negative lens or another assembly of a positive lens and another positive lens. The lens components satisfy the conditions (a) to (c); (a) <DF>-2.2</=f2/f</=-0.3 </DF> (b) <DF>0.4</=f3/f</=0.9 </DF> (c) <DF>1.8</=d/f</=2.4. </DF> where f2 is the focal length of the second lens group, f3 is the focal length of the third lens group, f is the focal length of the whole lens system and d is the distance from the front focus to the image plane. The material of the lens is zinc selenide (ZnSe) or germanium (Ge). Adoption of an aspherical lens facilitates the design of the fθlens.</p> |
