Comparative analysis of focusing methods for long-focus objectives

Advanced methods for focusing the long-focus objectives are considered. Accuracy estimation is carried out for focal plane arrangement while using coherent and non-coherent radiation. Coherent methods allowing to register wave defocusing down to 1/360 of the radiation wave length that is significantly less than for non-coherent methods, are investigated in details. So, the objective can be controlled with the beam diameter of 1/36 of its focal length, and with the focal plane arrangement error that does not exceed error of the most sensitive non-coherent method.