Achromatic Doublet Lenses from China tell you that chromatic aberration is caused by the difference in dispersion and refractive index of different wavelengths of light in the glass, resulting in different focal points for different wavelengths of light. Achromatic Doublet Lenses from China tells you that using the combination of different materials, such as the combination of crown and flint glass in the converging lens and diverging lens, the dispersion of each glass can be compensated by the other glass, so that the overall chromatic aberration is reduced to lowest.

Achromatic principle. Achromatic Doublet Lenses from China tells you that achromatic lenses are made by bonding convex and concave lenses made of two glasses with different optical properties. Commonly used crown glass with a small refractive index and large dispersion power is used to make convex lenses, and flint glass with a large refractive index and small dispersion power is used to make concave lenses. Achromatic lenses generally can only overlap the image points of the two main colors of light, thereby eliminating the chromatic aberration of the two colors.
Achromatic Doublet Lenses from China tells you that, for example, for vision-aiding optical instruments, considering that it is directly observed with the eyes, the chromatic aberration of the C line (red light with a wavelength of 656.3 nanometers) and the F line (blue light with a wavelength of 486.1 nanometers) can be eliminated; for The photographic lens, considering the photochemistry, can eliminate the chromatic aberration of the D line (yellow light with a wavelength of 589.3 nanometers) and the G line (purple light with a wavelength of 430.8 nanometers). Although there are still residual chromatic aberrations for other color lights, it has little effect on general applications, and it can be considered that the chromatic aberration is basically eliminated.
Through the above introduction and analysis of Achromatic Doublet Lenses from China, hope it helps you.