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球面反射镜是简单而且有用的光学部件。因为它是一个反射镜,所以它成的象是没有色差的。因此,它可以用于紫外(UV)到红外(IR)整个频谱范围中,而不改变聚焦的位置。这和折射的光学部件比较起来,球差很小。例如,对于无限远处的物体,球面反射镜的球差比具有同样焦距、同样孔径和具有最佳性能形状的单透镜的球差约小8.5倍。而且,当用球面反射镜得到1:1的放大倍率时,球差可减少到零。然而,球面反射镜不是没有缺点的。因为象聚焦在入射辐射的同侧,所以,接收元件必定遮住部份入射光。如果“离轴”使用反射镜来避免遮拦,则会引起另一个问题,即反射镜倾斜使物点发出的光线沿主光线成象在不同的位置(图1)。这正是已知的象散现象,此象散为孔径光阑位置、反射镜倾斜度、物距和反射镜曲率的函数。
Spherical mirrors are simple and useful optics. Because it is a mirror, it does not appear as a color difference. Therefore, it can be used in the entire spectral range of ultraviolet (UV) to infrared (IR) without changing the focus position. This is a small difference in spherical aberration compared to refracting optics. For example, for infinity objects, the spherical mirror has a spherical aberration that has about the same spherical aberration, and the same aperture and spherical aberration of a single lens with the best performance shape are about 8.5 times smaller. Also, when you get a 1: 1 magnification with a spherical mirror, the spherical aberration can be reduced to zero. However, spherical mirrors are not without their drawbacks. Because the image is focused on the same side as the incident radiation, the receiving element must cover part of the incident light. Another problem that arises if “off-axis” mirrors are used to avoid obscuration is that the mirrors tilt the light emitted by the object point at different positions along the principal ray (Figure 1). This is the known phenomenon of astigmatism as a function of aperture stop position, mirror tilt, object distance and mirror curvature.