The 90mm Di lens offers a medium telephoto focal length making it particularly useful as a portrait macro lens when used with a film camera. When the lens is mounted on a digital camera (with an APS-C sized image sensor) it provides a focal length equivalent to that of 140mm, so it can be used conveniently as a telephoto macro lens for digital photography.
Tamron’s Technical Terms
Di (Digitally Integrated)
Is the designation Tamron puts on lenses featuring optical systems designed to meet the performance characteristics of digital SLR cameras as well as film cameras. These lenses may be used on cameras with full format (FF) or APS-C sensors (with a crop factor relative to the camera).
SP (Super Performance)
Professional class lens; currently the best lenses made by Tamron for the consumer market.
Macro photography is the reproduction of small objects from a magnification ratio of approx. 1:4 up to about 5:1 (at which point microphotography begins).