Macro Photography is defined as the process whereby a subject is captured on the camera sensor at life-size or more, otherwise, it would just be a close-up. In my early days of digital shooting, I did attend a Macro Masterclass, where close-up imagery was considered Macro. Nowadays I would contest that position.
For true macro shots, I have two lenses, the first is a 100mm Macro lens which is capable of capturing very crisp images at that macro-defining magnification of one-2-one on the sensor. This lens is fairly versatile and can be used in the same way as any other, auto-focusing, prime lens. But it has the additional capability to focus so close to a subject that you get into the realms of macro images.
The second lens is called a Canon MP-E65, this lens is totally unique in that it has no focusing ring it only has a zoom ring that increases the magnification of the lens. The concept is that at any magnification, the lens has a single point of focus and you have to move the camera back and forth until that focal point is on your subject. At minimal magnification, that focal point is so close to the subject that the required one-2-one scaling is achieved. Using the zoom ring increases the magnification up to 5 times life-size on the sensor which generates an incredible look into a whole new world of detail. At these high levels of macro shooting, the depth of focus is minute, and is often impossible to get the whole of your subject in focus. To obtain a photograph of the requires a technique called focus stacking. The photographer must take many shots of the same subject with the focal point adjust microscopically at each press of the shutter. Image processing software then takes the "In-focus" portion of each shot and builds a composite image of the entire subject. This truly is a labour of love, but it is well worth the time and effort.
The image of the vole skull used a focus stack of 85 images, which gives you a flavour of the effort required to capture this kind of shot.