When we say a Barlow lens is achromatic, we mean that it is made up of two lenses joined together to form one. It is usually made up of convex and concave lenses. Overall performance is improved by efficiently minimizing chromatic aberration or splitting colors and lights in different directions. An achromatic lens for a Barlow is made up of at least two lenses. An apochromatic Barlow usually has three or more lenses. Meanwhile, achromatic coatings on a Barlow lens indicate that the coating aids in the elimination of internal reflection within the glass. As a result, the image is crisper and clearer.