Achromatic systems are the most common type of optical systems. At present, the selection of the designed wavelength band of the achromatic systems is mainly determined by the reception range of the human eyes or the detectors, or by previous experience. In this paper, a more accurate method to determine the designed waveband range of achromatic system is proposed. Firstly, the characteristics of the longitudinal chromatic aberration curve of the achromatic system is analyzed. Secondly, establishing the depth of focus(DOF) and wavelength relationship. The DOF is proportional to the wavelength and the square of working F#. Then, a working position is selected and the defocus amount between the working position and the focal position of each wavelength is calculated. Finally, the maximum allowable waveband range is determined by comparing the defocus amount of each wavelength at the working position with 2 times DOF. The method can be used to analyze the design waveband range of achromatic system, which is valuable for designing and testing of optical systems.
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