When you buy a digital SLR camera your often only buying the camera body, meaning you don't get a lens. The only time you get a lens is when you buy your digital SLR in a bundle style package. Whenever your buying your own lens your thinking of price, size and weight. Lenses are priced based on how large the aperture is, the larger the aperture the heavier the lens and also the larger the price tag.

All kinds of companies make lenses but the two stand outs are Canon and Nikon. Both companies are manufacturers of cameras so they have credentials in the camera industry. All companies make lenses that are specific for there cameras and even some just meant for one certain model.