White light is a mixture of various successive wavelengths of light (red, green, blue, etc.). Because the refractive index varies according to the wavelength, lenses made with regular glass are not able to focus all the wavelengths on a single point on the image plane and the shifted wavelengths appear as color fringing in resulting images. This color fringing – called chromatic aberration – has long been the Achilles heel of lens performance. As part of ongoing efforts to correct chromatic aberration, Canon successively developed and implemented fluorite, UD, and Super UD lenses. Now, aiming to achieve ideal correction of chromatic aberration, Canon has developed BR (Blue Spectrum Refractive) optics, delivering anomalous dispersion characteristics equal to or surpassing fluorite.
BR optics is based on a new organic optical material, developed by reexamining lens material from its molecular structure. This new lens material features unique anomalous dispersion characteristics that are capable of greatly refracting blue light (short wavelengths spectrum), which has traditionally been difficult to focus on a single point. Incorporation of a BR lens, consisting of BR optics sandwiched between concave and convex glass lenses, makes it possible to control the path of blue light (short wavelength spectrum), producing clear, sharp images by thoroughly reducing chromatic aberration. This makes it possible to achieve excellent rendering performance from large-aperture lenses, traditionally susceptible to chromatic aberration, even when shooting at maximum aperture. BR optics offer new potential for high performance lens design.