The examples a,b,c,and d show achromatic combinations of x 2.5, x10, x40 and x100 objectives respectively. At e is shown an example of an apochromat x 100, where it can be seen to be exceedingly complex in structure, with a total of 10 elements, a proportion of which will be fluorite. The difficulty in working this mineral together with the work and expertise required to fashion and accurately align 20 optical surfaces of glass of very small size accounts for the intrinsically high cost of this type, which can exceed $ 3-4000 (2013).