What is the difference between achromats and close-up lenses. It appears as if both let you focus to very small distances. Achromats are more expensive. What do you get for the extra cost? Thanks.
A closeup lens is also called a singlet, typically has blurry outer edges and color fringing.
An achromats (aka doublet) correct some of the color fringing by aligned two colors on the same plane and the edges are a little sharper than a singlet...
An apochromat (aka triplet aligns three colors) does the best job, but you don't usually find them for use these purposes.
