基于朗奇-泰伯效应及莫尔条纹技术,利用发散光和不等周期光栅的焦距测量方法被用于小口径长焦透镜的焦距测量。将一块曲率半径存在加工误差的平凹长焦透镜作为待测透镜进行焦距测量。在未知透镜真实曲率半径的情况下,首先计算待测透镜曲率半径误差对焦距检测精度的影响,并确定透镜在整个检测系统中的位置,然后进行透镜焦距实际测量,分别计算多组测量焦距值。通过对比发现,在未知待测透镜曲率半径的情况下,检测焦距的重复性、稳定性均一致,所测焦距均为33200~33270 mm,且重复性精度高于±0.055%,测量精度优于焦深的1/5。结果充分说明,所提方法对小口径长焦透镜的焦距检测是可靠、有效的。

Based on the Ronchi-Talbot effect and moire fringe technique, the focal length measurement method using divergent light and unequal-period grating is used for the measurement of the focal length of lens with a small aperture and long focal length. The long focal length of a plano-concave lens as a lens to be measured with a processing error in the curvature radius is measured. When the true curvature radius of the lens is unknown, first, the influence of the curvature radius error (of the lens to be measured) on the focal length detection accuracy is analyzed, and the position of the lens in the whole detection system is determined. Then, the focal length of the lens is measured, and multiple groups of measured focal length values are calculated separately. By comparison, it can be found that when the curvature radius remains unknown, the repeatability and stability of the focal length measurement are consistent. The measured focal lengths are in the range of 33200--33270 mm. The repeatability precision is greater than 0.055%, and measurement accuracy is better than one-fifth of the focal depth. These results prove that the proposed method is reliable and efficient in the focal length measurement of small-aperture lenses with long focal length.