What is an achromatic objective lens
This is the most widely used type of microscope objective, often with the words "Ach" on the housing. It corrects the chromatic aberration (red and blue dichroism), spherical aberration (yellow-green light) and sinusoidal aberration of the point on the axis, and maintains the Qiming condition. The astigmatism of off-axis points does not exceed the allowable value (-4 belongs to luminosity), and the secondary spectrum is not corrected.
The low magnification achromatic objective lens with a numerical aperture of 0.1~0.15 is generally composed of a double-gel objective lens with two lenses glued together. Achromatic objectives with numerical apertures up to 0.2 are composed of two sets of doublet lenses. When the numerical aperture increases to 0.3, a plano-convex lens is added, which determines the focal length of the objective lens, while other lenses compensate for the aberration produced by its plane and spherical surfaces. The plane aberration of the high magnification objective lens can be eliminated by dipping. High-magnification achromatic objectives are generally immersion-type, consisting of four parts: front lens, crescent lens and two double-gel lens groups.
