Macro Photography

Macro photography is arguably one of the more difficult forms of photography to master, it is certainly more technical than some others and it is important to understand the effects of depth of field. In many ways, depth of field is one of the biggest hurdles a macro photographer has to overcome, either by using a narrow aperture or to embrace the narrow depth of field in such a way that it becomes a form of creativity. At wider apertures, the depth of field can be measured in millimetres. Almost without exception, manual focus should be used because of the narrow depth of field, even at f/16.
True macro is considered to be 1:1 or life size (or larger). Many zoom lenses are marketed as macro lenses, but typically, they are around 1/3 or 1/4 life size and they certainly don't have the sharpness associated with true macro prime lenses. The choice of lens is dependent on what sort of subjects interest you as a photographer and what backgrounds you want to include. At their closest focusing distance, all macro lenses will blur the background to an equal degree for any given aperture, although the focal length will determine how close it focuses. For example, a 100mm lens will have a closer focusing distance than a 180mm lens, but if both are 1:1, they will both blur the background to the same degree. However, the 180mm lens will include less of the background, making a pleasing background easier to achieve, as it will potentially have less distracting background elements (such as bright objects). For best results a tripod (or monopod/bean bag) should always be used, although sometimes it simply isn't possible.
Shorter macro lenses are good all-round lenses (50-60mm range), useful for a range of macro (and non-macro) subjects, although trying to get close enough to insects would be a challenge, so they are best used for still life or where there is limited space. The medium sized macro lenses (90-105mm) become more useful for insect macro photographs, so are perhaps even more useful as all-rounders, although in confined spaces, it may be difficult to fit larger subjects in the frame (i.e. non-macro images). If insects are likely to be your main interest, then the longer (150-200mm) lenses are going to be the most useful, although they do come at a price and they tend to be less sharp than the medium focal length lenses, also some sort of support is essential. Luckily, because you're further away from the subject, it is much easer to set a tripod up, without disturbing the subject and sending it flying away. Another advantage with the longer macro lenses, they are compatible with teleconverters (extenders in Canon land) and not just extension tubes. Teleconverters and extension tubes both increase the magnification (and converters also increase focal length of course), but the 2x converters can reduce image quality quite a bit and extension tubes prevent infinity focus. Most (but not all) of the shorter macro lenses are unable to make use of teleconverters, although they can make use of extension tubes. Short of getting specialist macro lenses (like Canon's MPE-65 5x macro lens or microscope attachment), this is the greatest magnification you can achieve.
There isn't really a bad macro lens in terms of image quality and they all have a high reputation interms of image quality. In the two most poular mounts (Canon and Nikon), Nikkor, Canon, Sigma and Tamron all make excellent lenses, with Sigma offering the greatest range of focal lengths. Sigma and Tamron also make lenses in the other popular mounts, along with other options from the camera manufacturers. It may also be possible to get adaptors to use other lenses, such as Zeiss, Leica and M42 mounts.