Zoom lenses are very convenient. The equivalent of two or more fixed focal length lenses in one unit. The maximum aperture of some zoom lenses changes as you alter the focal length, but through-the-lens (TTL) metering takes this into account to give correct exposure.
Developed to succeed the EF75-300mm f/4-5.6 II this compact, lightweight high-magnification telephoto zoom lens covers medium telephoto 75 mm to super telephoto 300mm.
Like the EF75-300mm f/4-5.6 III USM, it has a metal ring at the front of the zoom ring to give it an upscale image. It uses a DC motor as AF drive actuator. The optical system and controls are the same as those of the EF75-300mm f/4-5.6 III USM. For environmental protection, only lead-free glass lens elements are used.