This is the go-to lens for the sharpest, high quality, close-up photography performance. The red ring is an indicator that this isn't just any Canon lens, but a Canon L-Series lens - guaranteeing it is constructed from the highest available quality dust and moisture resistant materials - and more importantly, contains top notch optics.
The Canon EF 100mm f/2.8L Macro IS USM contains hybrid image stabilisation which ensures two types of camera shake are compensated for - angular and shift. This is most apt for macro photography, because shake has more profound and visible effects on closer shooting. Clever Canon.
Auto focus is performed in the quietest way possible, utilising Ultrasonic Motors (the USM part) - and manual focus is markedly improved by the accuracy afforded by the rubber focusing ring - lauded for its smooth operation. 1:1 image reproduction from this lens results in life-size image reproduction.