The Tamron 28-75mm f/2.8 SP AF XR Di LD Asph. (IF) BIM Lens is a ground-breaking high-speed mid-range zoom is prized by pros and serious shooters for its fast F/2.8 constant aperture, evenness of illumination, and its outstanding imaging performance, and by all photographers for its compact size and reasonable weight that make it feel like an ordinary standard zoom. These admirable characteristics have been achieved by the use of special XR and LD glass, the efficient use of aspherical elements, and non-rotating internal-focus (IF) design. This remarkable zoom lens also focuses down to 0.33m(13") (1:3.9 magnification) at all focal lengths for satisfying close-up performance and is compatible with APS-C and full-frame-format SLRs. Not surprisingly it is widely acclaimed as a classic.
This is the magnifying factor of a lens. Macro lenses will often be described by their “magnification factor”. A lens with a 1:1 magnification factor produces a projected image on the sensor which is the same as the subject.
The individual pieces of glass that form the overall optical construction. Most lenses have between four and eleven elements to bend the light rays to ensure a perfectly formed image appears on the light sensitive surface, such as a film or CCD. The elements are arranged in groups and may be seen in specification sheets as, for example, 6 elements in 4 groups. That configuration may have two single elements and the other four grouped in pairs.
A lens with a 1:1 magnification factor produces a projected image on the sensor which is the same as the subject. A 1:1 magnification factor is usually considered the minimum for a lens to be described as a “macro” lens. Specialist macro lenses are often 1:3 or even 1:10 magnification factors, meaning that 1mm across the subject becomes 3mm or 10mm when projected onto the sensor, thus 3 or 10 times magnification.