|Most lenses have an automatic diaphragm: the lens focuses wide open, but can shut down to a prearranged setting when the shutter release is pressed. This feature is absolutely essential when using a flash.
For taking close-up pictures, the most satisfactory lens is probably the micro, also called macro, lens. This lens can focus from infinity to close up, and you need not approach your subject closer than about 10'. Nor does it require changing lenses, adapter rings, and extension tubes. There are 3 standard sizes from which you can choose: 55mm, 90mm, and 105mm. Consider both the size of the subject you want to photograph and how close you will be able to approach without causing it to fly away. At a distance of 10', a 55mm lens will not produce a large enough image of most butterflies, and if you get closer you may lose your subject. The lens is good, however, for subjects that are stationary or do not move quickly, such as a chrysalis or slow-moving bug, or for photographing very tiny things, such as butterfly eggs.
Although they cannot focus as closely as the 55mm lens, the 90mm and 105mm lenses are both excellent for obtaining a large image. You can keep a greater distance between you and the butterfly and still photograph relatively small subjects. Telephoto/macro lenses and zoom lenses are also available for some cameras. They enable you to take close-up pictures from a distance of 4-5'. However, these lenses are not necessary for photographing most butterflies.