Why you should switch to manual mode
There are various ways to focus a macro shot. The obvious choice is autofocus (AF), but there are several disadvantages to using this for macro work.
The main one is that it’s important to have full control over the exact point of focus, and at such close range AF lacks this control and has a tendency to hunt to acquire focus, especially in low-contrast, low-light situations.
For this reason it’s best to switch to manual focus (MF). For even greater precision, use MF in conjunction with Live View (see page 64), as this allows you to magnify the subject on screen up to x10.
An alternative is to pre-focus the lens at a set distance using manual focus and then gradually move the camera forwards, with your eye to the viewfinder, until the subject comes into focus.