焦距的精确测量直接关系到光学仪器的正常使用和技术性能的充分发挥。基于光学离焦成像模型, 结合模糊图像处理快速算法,提出了一种新的实用性强的快速自动测焦方法。根据光学成像原理提出模糊图像条件下测焦原理的数学模型,运用最小二乘法拟合圆的图像处理算法计算模糊图像中两弥散光斑间的距离，利用这个距离值计算出透镜焦距。实验证明该方法能够以较高的精度估计出弥散光斑间的距离值, 从而实现精准且快速的自动测焦。该方法只需一幅模糊图像, 相对于传统的测焦方法, 减少了计算量, 提高了速度和可靠性，降低了系统的复杂度。

The precise measurement of the focal length is directly related to the normal use of optical instruments and give full play to its technical performance. A new practical method based on the model of optical out of focus imaging and blurred image processing of quickly and automatically measuring the focal length is proposed. Based on the principle of optical imagery the mathematical model of focus measurement principle is proposed under the condition of blurred image. The proposed method adopts the least square method for fitting circles and calculates the distance between two diffuse light spots in blurred image. The lens focal length use the calculated distance is calculated. Experiments prove that the proposed method can estimate the distance between diffuse light spots with high accuracy so as to realize the measurement of automatic focus more accurately and quickly. The proposed approach takes only one blurred image, compared with traditional focus measurement method, the amount of calculation is reduced, the speed and reliability is improved, the complexity of system is reduced.