Auto-focus lenses are one of the great advances of photography in recent years. There are fast, quiet and usually very accurate. The new Canon Eye Control lenses are quite astonishing in their ability to focus on what your eye is looking at. However, there are one or two limitations and drawbacks and it is wise to be aware of them.

Firstly, just like oils ain't oils, autofocus ain't necessarily autofocus. When you focus manually, the photographer can select a theoretically infinite number of focus points from the closest focusing distance to infinity. With auto-focus the camera/lens manufacturer sets the number of points you can focus on. With very cheap cameras, this may be as few as three, five or seven points. With very expensive cameras it may be as high as 45, but it is limited to those points. 

{The remedy is to use FOCUS LOCK! Point your focus box or cross hair at the subject you want to be sharp. Depress the shutter half way until the 'radar' locks on. You will get a visual and/or an audio signal that focus is locked. Then reframe the photo and fully depress the shutter. Sounds difficult? Very easy with a little practice. And super sharp shots every time.} 

Thirdly, in order to focus, most auto-focus lenses require contrast in the subject. If the camera is pointed at a dimly lit subject mostly of the one shade, the lens 'hunts' for the focus but cannot zero in on the subject, because, from the camera's viewpoint, there isn't a subject. 

Five Tips for Getting Sharper Portraits

  Focus on the eyes

  Use a tripod

  Use faster film

  Use fastest shutter speed you can

  Use electronic flash (large source)