The Focus Detecting Of NVST

One of an important observation target of solar telescope is high resolution imagingobservation of the sun.Solar telescope often have serious defocus problem because thetemperature change of the solar telescope is big.In order to make the telescope work in the beststate 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 findthe focus position by the sharpness of the image.Ground-Based large solar telescope is seriouslyeffected by atmospheric turbulence and atmospheric turbulence can also lead to telescopeimage blur.It is difficult to distinguish which make image blur,so it can’t accurately determine thefocus of the solar telescope by the sharpness of the image.Although the wavefront detectingtechnology can overcome the atmosphere turbulence problem and detect the focus in highprecision，it need special detecting equipment and optical system.Solar telescope’s observationtarget is extended object,so the way of the full width at half maximum of average shortexposure PSF that is commonly used by night astronomy telescope is not suitable to solartelescope.There are so many different for Ground-Based large solar telescope’s focusdetection,so we put forward a new and special focus detecting method.the method base on thehigh-resolution statistical techniques.the method can eliminate the target information and theeffect of atmospheric turbulence.Firstly,we simply analysis the main reason of defocus of the NVST.We find the problem andeffect of defocus is serious,so it is necessary to focus to NVST.Then we introduce some commonfocus method.Finally,we discuss how and why we put forward the method that base on thestatistical high-resolution reconstruction technology and introduce the basic principle of themethod.we have done the simulation experiment and actual measurement experiment of themethod.The experiment results prove that the method is feasible and effective.