Modulation Transfer Function Tester, Automatic Focusing Technology

Manual focusing requires that the operators have professional expertise and do cumbersome operation. It always brings errors with eyeballing of the human eyes. With the development of automation and intellectualization of the digital image processing, whether we can do automatic focusing, collect and analyse the images at the focus quickly and efficiently is becoming more and more important.The thesis is mainly based on the research of the automatic focusing system of modulation transfer function (MTF) testing device with point-light source. The testing device is used for lens testing. It determines the image quality and eliminates substandard lens. The automatic focusing system in the testing device plays an important role because whether the testing device can collect exact images on focus is related to the precision of the MTF value. And the MTF value is an important parameter of the lens.The thesis introduces the basic principles of automatic focusing and analyses several focusing criterion functions, especially the focusing criterion function using the frequency domain method. It chooses the Fourier transform to calculate MTF for the focusing criterion function and devises a practical algorithm for automatic focusing.The thesis rebuilds the hardware part of the original equipment of the automatic focusing system with a million-pixel CCD camera to obtain better images. The pulse generator of the step motor has also been changed so the step motor can be easily controlled by ordinary personal computers, not only the industrial control computers.The thesis also designs a friendly software interface for the automatic focusing system of the MTF testing device. The system can be controlled by the computer and be operated easily. It has greatly improves the efficiency and accuracy of the testing.At last, the thesis sums up the project and puts forward the shortcoming of the automatic focusing system and gives the development tendency of the future work.