Manual Focus Lenses
If you are using a manual focus lens it means that you must focus your camera lens by yourself without any automatic assistance from the camera. You generally focus the lens by turning it until you reach a sharp focal point. These cameras are simple to use, and many people prefer a manual focusing system over an automatic one.
Manual focusing gives you complete control over the lens and you can often focus quicker and more accurately this way. It is also better for low light focusing since many automatic systems have difficulty focusing in the dark. Most automatic systems also give you the option of using manual focus and it's a good way to save battery power.
Make sure you never focus the camera manually while it's in the automatic focus mode as it may damage the camera. Manual focus systems should be available on most types of lenses. They range in price from about $50 to several thousand.