World’s first and greatest zoom ratio of 15X, covering 28-419mm 35mm-equivalent angle of view
Going back to the basic concept of “one lens covering everything from wide angle to telephoto,” engineers at Tamron took up the difficult task of expanding the zoom range of Tamron’s high power zoom lenses even further. Their unstinting efforts to extend the telephoto end beyond previous limits while retaining the wide-angle end at 18mm has borne fruit as an ultra high power zoom lens that is exclusively designed for DSLR cameras and boasts the greatest zoom range of 15X for the first time in the world.
Tamron’s original VC mechanism for effective shake-free hand-held photography
Tamron’s proprietary VC (Vibration Compensation) mechanism was built in the AF28-300mm F/3.5-6.3 Di VC (Model A20) for the first time. It demonstrated its powerful compensation effect employing a tri-axial system that is designed to let three coils drive a compensator lens electromagnetically via three steel balls. Since the compensator lens is supported on rolling steel balls with very low friction, follow-up performance is also enhanced, resulting in stabilized viewfinder images. Since the mechanism is designed to allow parallel shifting of the compensator lens solely by means of electrical control, the mechanical construction is simpler and more compact, so the lens can be kept as small and light as possible.
Designing a high power, compact zoom lens with VC mechanism: Optical design optimization meets optimum power distribution
In developing the long-range zoom lens, Tamron’s optical designers pursued the optimum distribution of power within the overall optical system based on the optical design know-how Tamron accumulated over 16 years since the introduction of the first compact AF28-200mm in 1992. The resulting optical system uses two LD (Low Dispersion) glass elements and three aspherical elements in order to effectively compensate for various aberrations including astigmatism, yet this design allows the first optical group to be small enough in diameter to realize the overall goal of a compact lens that incorporates a handheld-shake compensation mechanism.
Minimum focusing distance of 19.3” over the entire zoom range for the max. mag. ratio of 1:3.5
The AF18-270mm Di II VC allows close focusing down to 0.49m (19.3 inches) from the subject over the entire zoom range even though it incorporates the VC mechanism. The maximum magnification ratio of 1:3.5(4) at its 270mm telephoto end is the top class capability among high power zoom lenses exclusively designed for digital SLR cameras.
Optical system optimized for digital SLR cameras by taking incident rays of light reaching the image sensor into consideration
In order to effectively compensate for changes in aberrations due to zooming, the zoom lens employs an innovative optical system that is designed to converge the angles of rays of light entering from the center to the periphery of the lens. The light rays thus reach the image sensor within a defined circle that assures high imaging performance and reduces light falloff.
High resolution performance
As a lens exclusively designed for digital SLR cameras, this zoom lens delivers high resolution and contrast performance for outstanding image quality with sufficient flatness of the field under an extremely wide range of photographic conditions.
Thorough countermeasures, including advanced internal surface coatings, prevent ghosting and flare
Tamron employs multi-layer coatings in order to reduce reflections on lens surfaces as well as internal surface coatings (coatings on the cemented surfaces of lens elements) in order to minimize reflections from the sensor itself within the mirror box, a problem inherent to all digital SLR cameras.
The world’s first and greatest zoom power of 15X plus built-in VC mechanism achieved along with a remarkably slim maximum diameter of less than 80mm
Designing a lens with the world’s first and greatest zoom ratio of 15X inevitably entailed a larger travel distance of the components within the optical systems, but Tamron has successfully accommodated the optical system as well as the special VC mechanism in a remarkably compact and slim package by employing mechanical design technology accumulated over many years. The result: A slim design measuring less than 80mm in diameter despite the fact that it is an ultra high power zoom lens that incorporates a VC mechanism. Production engineering this unique zoom lens meant incorporating complex optical/mechanical components, and Tamron’s engineers had to employ innovative manufacturing techniques including methods of further enhancing accuracy, reducing weight, and increasing the strength of many components.
