Fluorite lenses were first developed and designed by Canon Company of Japan. However, due to the high cost of fluorite lens, Canon later developed another substitute, which is made of optical glass mixed with patented oxide and named UD- super dispersion lens and super UD lens. Generally speaking, two ultra-low dispersion lenses are equivalent to a fluorite lens, and a super UD lens can provide the same performance as a fluorite lens. The lenses made of these two kinds of lenses have strong anti-dispersion ability and minimal chromatic aberration, which can significantly improve the image definition, especially when used in telephoto lenses.