1:1 reproduction ratio Ultrasonic Motor Focus distance limiter For those looking to specialise in macro photography the Canon EF 100mm f/2.8 Macro USM is an excellent prospect, and is equally capable of portrait and action images. The affordable price and versatile focal length mean it is suited to an advanced APS-C DSLR such as the EOS 50D. The predecessor lens misses out on the quick, quiet USM focus motor whereas the more recent version adds L series weatherproofing and image stabilization, which are useful if being used on long shutter speeds or outdoors. The main benefit of this lens is the ability to highlight fine detail, thanks to the 1:1 reproduction ratio which means images are captured life size on the camera sensor. Being able to focus within 31cm of the subject makes this process all the easier. And when shooting objects at a greater distance the focus limiter prevents the autofocus from hunting throughout the range.