Early cameras relied on manual focusing, adjusting the lens group so that the subject would form a sharp image in the focal plane (where the film was). Autofocus cameras have been popular since the late 1970s, and the camera uses technologies such as phase difference, ultrasound or infrared to control the lens to precisely focus on the selected part of the photographer, so as to obtain a clear focus photo. Autofocus reduces the photographer's labor intensity and provides convenience for those with poor vision. There are many ways to automatically focus, such as the eye-controlled focus mode in Canon EOS series cameras, where the camera chooses the focus according to the photographer's eye movement and fixation orientation. There are many ways to focus, but all of them are targeted according to the specific area chosen by the photographer, with as few as 4-5 constituencies and as many as 10 constituencies. The selected area is displayed through a box or small highlight in the frame, and the photographer can select the focus point by flipping the knob as needed when focusing. That is to say, when using an autofocus camera, it is not necessary to do no operation and completely have the camera "automatic" processing, in fact, it is still necessary for the photographer to carefully determine the focus, but the process of manually rotating the focus ring is changed to the camera automatic completion. The key to the operation of an autofocus camera is to ensure the consistency of focus during exposure and focus. If you need to re-compose after the focus is completed, the camera may re-autofocus during the movement, so half-press the shutter or hold down the "AF/AE" lock button on the fuselage, and then adjust the composition to complete the shooting. In the foreground, there are objects with similar appearance such as railings and glass interference, and the automatic focusing system of the camera may fail. If necessary, manual focusing should be used to complete the focus. In addition, when shooting still life, in order to arrange the focus more finely, manual focus can also be used to accomplish.