Fluorite Element
An element made of grown calcium fluoride crystal, which has exceptionally low dispersion and enables near-perfect colour correction.
Measured in
count
In depth
Fluorite outperforms even the best low-dispersion glass and is significantly lighter, which is why it appears in professional supertelephotos where both correction and weight matter. It is expensive to grow, soft, and sensitive to thermal shock, so it is always placed inside the barrel rather than at the front.
Examples in practice
Two fluorite elements let a 600 mm f/4 weigh under 3.1 kg while showing essentially no chromatic aberration.