Achromatic Objective: This is a common objective, and there is often a "ACH" word on the casing. This type of objective lens can only correct the position color difference (red, blue 2 color) and the ball difference (yellow-green light) and the elimination of near-axis points. The color difference and ball difference of other color light cannot be corrected, and the field song is large. The earliest chromogenic mirror is made by Zeiss.
