I am looking to buy a macro lens and I notice Sigma offer different types. How do I choose between them?

Each of the Sigma prime macro lenses offer up to 1:1 (Life-size) reproduction images, but at different working distances. For example, the 50mm lens provides the shortest working distance and the 180mm lens the longest working distance. Therefore, if you are looking to do copy or reproduction work, the 50mm is likely to be your best choice. If however you photograph small insects, the 150mm or 180mm may be better suited as these allow you to stand a little further away from the subject whilst still giving you the same image. This may prevent disturbing the insect. All provide excellent optical performance, and are fully compatible with current 35mm AF and digital SLR cameras.