确定透镜焦距f有两种方法:一种是绝对确定法,另一种是成象测定法。绝对确定法常在设计与制造透镜时使用,它是根据几何光学中理想成象的基本原理,求出球面折射各基点(面)与焦距值,然后再求出由两个球面折射所粗成的单透镜以至于由任意个单透镜形成的透镜组的焦距及其各基点(面)。由于此法用到的只是在设制时就能准确确定的一些量,例如透镜材料的折射率,球面的半径及诸球面间的间隔大小等,因而是确定焦距最准的方法。然而由于计算过于复杂,另一方面对于现成的透镜,往往又很难甚至于无法准确地知道以上各量,所以,此法一般并不常用;而且即使对设制 There are two ways to determine the focal length f of a lens: one is the absolute determination and the other is the imaging assay. Absolutely determine the law often used in the design and manufacture of the lens, which is based on the principle of geometric optics in the ideal imaging, find the spherical refraction of the base point (surface) and the focal length value, and then find out by the two spherical refractive index Of the single lens so that the focal length of the lens group formed by any one of the single lenses and its respective base points (planes). Since this method uses only those quantities that can be accurately determined at the time of fabrication, such as the refractive index of the lens material, the radius of the spherical surface and the spacing between the spherical surfaces, etc., it is the most accurate method of determining the focal length. However, due to the calculation is too complicated, on the other hand for the ready-made lens, it is often difficult and even impossible to accurately know the above quantities, so this method is not commonly used; and even for the system