tracer treating the ray as if it refracts directly from one element into the next. Cemented groups may assist to decrease the physical length of the optical system. Provides superior control for minimising spherochromatism and other aberrations, allowing the creation of more advanced optical systems using fewer elements. Disadvantages Cementing elements requires a high precision to ensure correct centering of the cemented components. This difficulty greatly increases on groups of more than two elements. Precision cementing is high in manufacturing cost. It is often cheaper to AR-coat two air-spaced elements. See also Achromatic lens Triplet lens References Lenses 2 (number)