Using a macro lens makes it possible to achieve a high image ratio. The reproduction ratio describes the relationship between the actual size of an object with the depicted size on the photo sensor. With a ratio of 1:2, for instance, the photographed object is twice as large as it is depicted on the sensor. Just as with the human eye, there is a minimum distance required between the object and the lens in order to produce a sharp picture. In order to achieve a bigger reproduction ratio, the distance between the lens and the sensor is increased. With macro lenses, the minimum focusing distance is decreased, which enables the camera to get closer to the object being photographed.
Normal lenses are optimised for taking pictures of objects from a distance and taking an extremely close-up photo of an object is not possible with such lenses. Macro lenses, on the other hand, are designed specifically for taking high quality pictures of objects from an extremely close distance. In order to achieve this, many macro lenses are built with additional close-up lenses or a reversing ring. Due to their complex construction, macro lenses are usually larger and heavier than normal lenses with comparable focal lengths.
Macro lenses are available in various focal lengths, usually between 40 and 100mm. In order to shoot objects with a macro lens from a larger distance, there are also macro lenses with a focal length of 200mm. A drawback of using such a lens is the operating speed of the autofocus. Due to the large adjustment range, the autofocus operates significantly slower than when using a normal lens with the same focal length.
In order to decide what focal length your macro lens should have, you need to consider what you would mainly like to photograph. Macro lenses are usually made with a fixed focal length; there are very few good quality macro lenses with an adjustable focal length.
Macro lenses with a focal length of 60mm are relatively cheap and light. Due to their smaller focal length, however, you have to get very close to the object you want to photograph. When photographing plants or insects, this is usually not problematic. When photographing certain animals, however, they might run away if you get too close to them. Something else to consider is that unwanted shadows might appear in your photo due to the close proximity to the object you’re photographing.
Focal lengths from 100mm make it possible to photograph the object from a further distance and thus solve the problem of unwanted shadows appearing in your photo. These macro lenses are, however, comparatively heavier and more expensive.
If you want to photograph animals that are shy and have a tendency to run away when people get too close to them, a macro lens with a focal length of 180mm is most suitable. These, however, are extremely heavy and come at a very high price. These lenses also make your images very susceptible to camera shake. When using such a lens, it’s almost mandatory to use a tripod.