Apochromats
Apochromatic systems combine targeted material selection with optimized correction of chromatic and monochromatic aberrations.
DGE development examples include doublet and triplet apochromats using ED glasses or calcium fluoride (CaF₂). In addition to theoretical image quality, tolerancing, mount design, thermal behavior and manufacturability are considered.
Doublet Apochromats
Two-element systems with a low element count and demanding material and tolerance requirements.
Triplet Apochromats
Three-element systems providing additional degrees of freedom for aberration correction.
Reference: Uwe Laux, Astrooptik. Optik-Systeme für die Astronomie, 3rd revised and expanded edition, 2017.