====== Focusing A Camera ======

| **Field** | Photography |
| **Went Obsolete** | Not yet obsolete, but no longer common |
| **Made Obsolete By** | Automatic Focus |
| **Knowledge Assumed** | Good vision, lens operation, understanding depth of field |
| **When useful** | When using a manual camera or when automatic focus fails to focus on the actual subject |

For much of the history of photography, the only way to get a sharp image of the subject was to focus the lens manually. Focus is a function of distance, aperture size, and the size of the light sensitive medium. There are several methods used.

==== Rangefinder cameras ====

Rangefinder cameras use a split image in the viewfinder produced by an offset viewing window and a movable mirror. The control for the mirror is attached to the lens focusing mechanism. Focusing involves lining up the two images in the viewfinder. When they are aligned, the object that was used as a focusing reference is in focus. Rangefinders were once common in medium and small format film cameras. There are a few digital rangefinder cameras today, but they are not common.

==== Lens based focusing ====

The most common type of focusing involves adjusting the lens. On some lenses, the entire barrel can be turned. On most, there is a focusing ring. Turing the ring changes the focal distance. Most lenses of this type today have a switch either on the lens or the camera body that allows the user to turn automatic focus on or off, giving the photographer complete control when needed.

==== Body based focusing ====

Some medium format cameras and all large format cameras use body based focusing. The body of the camera itself is moved. These cameras, along with tilt-shift lenses for other cameras, often allow for selective focus of different objects at the same distance.

==== Fixed focus cameras ====

Some cameras are fixed focus, requiring no manual or automatic focus. This is common on disposable or otherwise low end cameras. Fixed focus is achieved by using a very small aperture. This requires the user to increase the sensitivity of the film if the camera is to be used in low light.

Manual focus is still commonly used today. Lenses, even some made for modern digital SLR cameras, are still made with manual focus only. For the majority of people who simply want to capture a memory, AKA snapshot photographers, autofocus is good enough. These photographers will likely never use manual focus. More advanced photographers use manual focus frequently to get the photograph they have in mind or because the camera has no automatic focus.

Many low-end digital SLR cameras (such as the Nikon D40) lack a built-in auto focus motor, requiring the motor to be built into the lens. In that case, using older lenses requires focusing manually.