Promaster Disc. AF 28-200mm F/3.8-5.6 XR Aspherical (IF) Super Zoom Lens with Silver Finish and hood for Canon EOS - USA with 6 Year USA Warranty

The world's smallest, most lightweight 28-200mm high magnification zoom lens. With a minimum focal distance over the entire zoom area of 49cm, and a maximum magnification of 1:4 (at 200mm), this remarkable lens achieves high magnification zoom performance with the compact size of a standard zoom lens. Through XR (Extra Refractive Index) glass and efficient use of aspherical lenses, Tamron has achieved a 25% reduction in size and a 27% reduction in weight over the previous model (Model 371D), along with a decrease in filter diameter by two-steps °72mm- °62mm) without compromising the superior image quality characteristic of Tamron 28-200 lenses.

The first most important reason that the lens is so compact is the use of high refractive index glass. That is, XR Glass. High refractive index glass bends light more than normal or lower refractive index glasses. Normally, glass material having a refractive index of more than 1.69 is called high refractive index glass. In the A03 optical system, glass material having a refractive index of more than 1.69 is used in the first group. In addition, refractive index of the whole optical system is enhanced. By using high refractive index glass in the first group, we could make the elements in the first group thinner, and reduce one element in the second group. This made the overall length of the whole optical system shorter. Now, with a shorter optical system, the distance from the diaphragm to the front surface of the objective lens becomes shorter, which enabled us to make the clear aperture (the front element diameter) of the front element smaller by two full filter sizes. This allowed us to also incorporate 3 Aspherical elements to further correct for any aberrations. Also, LD glass is not used in this lens since any chromatic aberration is very well compensated for with the optical system that uses a combination of XR and Aspheric elements. Also, multi-coated surfaces are used in abundance.

A mechanism reduced to fit a more compact barrel. The moving triple cam is key to the perfection of the lens was development of a mechanism to achieve rock-solid stability during the radical barrel movement between the retracted 28mm position to the extended 200mm position: the moving triple cam. This remarkable mechanism transforms the conventional fixed triple cam into a moving unit that slides in conjunction with the zooming action. In order to fit such a complex mechanism into the compact barrel, the mechanical design was enhanced to incorporate parts and mechanisms of greater precision and performance with less weight and volume. The dramatic compact, lightweight design combined with uncompromising performance and durability were the result.