One of an important observation target of solar telescope is high resolution imaging observation of the sun.Solar telescope often have serious defocus problem because the temperature change of the solar telescope is big.In order to make the telescope work in the best state and get the better observation data,we must focus the telescope in very high precision. The most common focusing method is the image processing technology method that find the focus position by the sharpness of the image.Ground-Based large solar telescope is seriously effected by atmospheric turbulence and atmospheric turbulence can also lead to telescope image blur.It is difficult to distinguish which make image blur,so it can't accurately determine the focus of the solar telescope by the sharpness of the image.Although the wavefront detecting technology can overcome the atmosphere turbulence problem and detect the focus in high precision，it need special detecting equipment and optical system.Solar telescope’s observation target is extended object,so the way of the full width at half maximum of average short exposure PSF that is commonly used by night astronomy telescope is not suitable to solar telescope.There are so many different for Ground-Based large solar telescope’s focus detection,so we put forward a new and special focus detecting method.the method base on the high-resolution statistical techniques.the method can eliminate the target information and the effect of atmospheric turbulence. Firstly,we simply analysis the main reason of defocus of the NVST.We find the problem and effect of defocus is serious,so it is necessary to focus to NVST.Then we introduce some common focus method.Finally,we discuss how and why we put forward the method that base on the statistical high-resolution reconstruction technology and introduce the basic principle of the method.we have done the simulation experiment and actual measurement experiment of the method.The experiment results prove that the method is feasible and effective.
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