For the purpose of achromatic aberration and focal depth extension

an achromatic method in visible band is presented for the optical imaging objective with long focal depth in this works

which is based on the refractive-diffractive hybrid objective. By analyzing the formation of the logarithmic phase

the dispersion of the element with long focal depth is discussed. According to the refractive-diffractive hybrid achromatic principle

the phase distributive of the refractive and diffractive elements was restructured. In the novel objective system

the diffractive elements were employed for the focal depth extension and the achromatic focal power. Compared with traditional objective system

Simulation results showed that the on-axis intensity distribution of the achromatic hybrid refractive-diffractive objective based on novel phase relationship is unaltered in central wavelength λd(587nm)

and they are the coincidence in achromatic wavelength λF(486nm)

λc(656nm).