LanguagesLenses: Black or white lenses?
Most EF lenses have black barrels, but a few are white (actually a light grey or beige). The white lenses are all large super-telephotos. There is a good reason for this.
Lenses contain glass elements. These expand with heat. This is not usually a problem with compact lenses − the amount of expansion is small. But large lenses contain large elements and here expansion can bring a lens close to the limits of its design tolerances. A white surface reflects sunlight, helping to keep the lens cooler.
Incidentally, you will find that the manual focusing action of some black lenses allows focusing past its infinity setting (sometimes called over-focusing). This is also to allow for expansion. If the lens is used in hot conditions, infinity focusing will be closer to the end of the travel.
The EF200mm f/1.8L USM lens has large glass elements susceptible to heat expansion. The white lens barrel reflects the rays of the sun and helps to keep the elements cool. The smaller elements of the EF200mm f/2.8L USM lens are less affected by heat, so a black lens barrel is suitable.
