Focusing Your Camera

When shooting landscapes, architecture, or other stationary subjects, the speed of focus may not be critical.  But, when shooting moving objects or people, time spent waiting for your camera to focus can make the difference between getting the shot you want or not.  When testing your next camera, you may want to pay attention to the speed of focus.

Autofocus systems depend upon being able to see edges of objects so that they can  properly gauge distance.  Low light situations reduce contrast, which reduces the camera's ability to discern edges and achieve photo sharpness.  Better cameras focus more effectively with less light.  And, some cameras (e.g. Nikon D300 and others) use an autofocus assist lamp that lights nearby subjects momentarily until focus is obtained.

An off-center subject often helps your composition, but simple autofocus cameras use a single autofocus point at the center of the image.  They require you to focus with the subject in the center of the view-finder. 

There is a common workaround.

If your subject is off-center, you first center the camera on the subject and then depress the shutter release half-way to lock focus on the subject.  That done, you continue to hold the shutter release half-way down as you recompose your image with the subject where you want it.  Then, you take the picture.

The movable focus point (red box) allows you to compose your picture and focus on an off-center subject at the same time.

This is an effective method for attaining photo sharpness, but more advanced cameras provide multiple focus points to make this easier and faster.  With the thumb pad control on the back of these cameras, you can move the focus point left, right, up, and down so that it aligns with your subject while the image is properly composed.

The focus mode selector on the Nikon D300 lets you select between (C) continuous-servo, (S) single-servo, and (M) manual focus.

What if you are photographing moving objects - perhaps at a soccer game or your child on a ride at an amusement park.  As the subject moves toward you, or away, the camera's focus setting needs to change. 
In a single-servo focus system, once you have locked focus, you are stuck at that setting unless you release the shutter button and start over.  This reduces the odds of your getting an in-focus result.

More advanced cameras address this with a continuous-servo focus mode.  As long as your finger is on the shutter release button, the camera will adjust focus as the subject moves.  For this to work, of course, you need to be able to focus on off-center subjects (as well as centered), as described above.

Face recognition takes even more work out of your photo sharpness challenge.  In many newer cameras, a face detection mode tells the autofocus system to identify faces and focus on the nearest one.

What if you don't want to use the shutter release button to focus?  For example, you may need to set focus on a subject that doesn't align with a  focus point, requiring you to focus then recompose your image.  It would be helpful to focus on the subject, then let go of the shutter release as you recompose the image. 

Advanced cameras provide two ways to do this. 

• The first is a partial solution - the camera may provide a focus lock or focus/exposure lock button.  This is useful because it also locks exposure, but it still requires pressing and holding a button.
  
  

• The AE-L/AF-L button at left locks exposure and focus, allowing you to recompose your image once these settings are correct.  The AF-ON button at right is an alternative to using the shutter release as a focus button. (Controls on Nikon D300).

  The other method is to use a separate button to activate autofocus, and remove the focus function from the shutter release.  When your camera is in focus, let go of the button.  The camera stays set on the focus distance and will not change until you use the button again. 
  
  After years of using the shutter release to focus, this may method sound strange to you.  But, it doesn't take long to get comfortable with this method.  Surprisingly, it provides a new sense of freedom when using your camera, akin to the days of only manual focus (you're starting to get old if can you remember those days).

Complex scenes

You may be shooting a complex scene and want to use shallow depth of field to isolate the main subject.  If it is difficult to select the right point on the subject, then manual focus may be your best bet for photo sharpness.

Landscapes

In a landscape, you want photo sharpness from foreground to background.  For this, you will use a small aperture for maximum depth of field.  Still, you may not find an ideal point on which to autofocus that will assure the background and foreground will both be in focus.  Manual focus makes it easier to take advantage of maximum depth of field.

Portraits

Precise manual focus on Tom's left eye leaves the right side of his face out of focus.

In portraits, you usually want the eyes in precise focus.  Manual focus is often easier to use than trying to align a focus point on the eyes.

Macro Photography

With macro lenses or, for fixed lens cameras, in a macro mode, the depth of field is very limited.  This means that you need to be very precise in selecting the point of best photo sharpness.  It helps if you can move your camera or the subject into approximate position, then fine tune the focus manually.

Low Light or Small Maximum Aperture

When the autofocus mechanism does not receive enough light, it struggles to find a focus point - you'll hear the focus motor "hunting" as it tries to find the ideal spot for photo sharpness.  Nighttime photography or shooting into deep shadows can cause this problem.  Also, as the maximum aperture of lens gets smaller, the photo sharpness challenge gets worse, since the small aperture further limits light reaching the sensor.

Some cameras project a bright light that illuminates the subject for the brief period of time needed to reach focus.  But, this system supports only a short distance - maybe up to ten feet.

Manual focus overcomes the limitations of these circumstances.

The Late-Arriving Subject

The most obvious example of a late-arriving subject is that of a self-portrait.  You may use your camera's self-timer to give you time to move into the picture.  Then, you want to focus the camera on the spot where you expect your eyes to be when you move from behind the camera to your pose.

Another example may be in sports.  If you don't have a camera whose focus can follow a moving object, as described above, then you want to focus on a spot where you expect the moving subject to be when you  take the picture. 

A good example would be a sprinter crossing the finish line.  Manually focus on the finish tape and snap the shutter as the runner touches it.

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