Focus
A camera's auto-focus system intelligently adjusts the camera lens to obtain focus on the subject, and can mean the difference between a sharp photo and a missed opportunity. It is a seemingly simple goal to try and achieve image sharpness at the focus point, but the inner workings of how a camera acquires a focus are unfortunately not straightforward. This lesson aims to improve your photos by introducing how auto-focus works, thereby allowing you to make the most of the power and avoid the shortcomings.
Improving Quality
The key to improving manual focusing quality is to decrease the DOF thereby decreasing the range of variation in the depth of the image that appears sharp. In very basic cameras, there is not much control over depth of field.
Point and Shoot Cameras
Most new cameras have a little light that will blink in the viewfinder around the point on which you have selected to focus. However, that doesn't mean the camera has selected the right point to focus on. With point and shoot cameras, the preferred focus point is directly in the middle of the image. If your preferred focus point is not in the centre of the frame, you can trick the camera into focusing on your preferred point. Simply centre your preferred point in the frame and press the shutter release button half-way down to lock focus and exposure. Then move the camera and recompose your image without releasing the button. Once you have the image set the way you want it, press the shutter release button the rest of the way down to activate the exposure. Please remember that if your camera does not have a TTL (through the lens) viewfinder, what you see in the viewfinder will not be exactly the same as the image you take.
DSLRs
Most SLR cameras allow you a lot of options when focusing on a subject. Some allow you to switch between manual focus and automatic focus. Some allow you to select how the camera chooses its focal point. Like point and shoots, a small light will blink on the point on which the camera is focusing. If that is not the point you prefer you can do one of the following:
- Use the manual focus selector switch to rotate through the points of focus in your cameras viewfinder
- Use the same method of recomposing as a point and shoot camera
- Switch to manual focus
- Override the focus selection point
The exact method you choose will depend on your camera's capabilities as outlined in the manual that came with the camera.
Auto Focusing Problems
Auto-focus systems can make mistakes, beware of the following circumstances:
- The key auto-focus sensor is in the centre of the viewfinder image, so any off-centre subjects may not be correctly focused. To correct this, hold the shutter button half way down, and focus on your subject with it in the centre of the viewfinder/lcd display. Now don't let go of the shutter release button and recompose your image the way you want in the viewfinder/lcd and press the shutter realease button the rest of the way down.
- When photographing through glass, reflections from the glass may confuse the infrared sensor.
- Extremely bright objects in the focusing region - sparkling reflections on polished metal, for example, could overload the sensor and harm accuracy.
- Photographing beyond objects that are close to the lens, for example, through a bush or between the gaps in the fence, can confuse the autofocus system.
- With very fast moving subjects, it may be better to focus on a set distance and then wait for the subject to reach that point before shooting.
Across the bottom is the status line that shows: (8) auto-focus status, (9) metering mode, (10) AE lock, (11) shutter speed, (12) aperture setting, (13) exposure mode, (14) flash compensation, (15) EV comp, (16) ISO sensitivity, (17) # of pictures remaining, (18) Flash-ready, (19) Flash value lock, (20) Flashsync, (21) Aperture stop, (22) electronic analog exposure display, (23) Auto sensitivity, (24) "K" appears when memory remains for over 1000 exposures.
Manual Focus
Most compact cameras do not allow for manual focus however, DSLR's do. On the side of the lens there is a toggle switch that switches between auto-focus (A) and manual focus (M). Put the lens in M mode and look through the viewfinder. The little red or green square will come on when that spot is in focus. Turn the focusing ring on the lens (see the instruction booklet that came with the camera) left and right (slowly). Your camera may beep as well to indicate that you are set.
The Advantages of Manual Focusing
- Best accuracy and control
- Does not change if something passes between camera and subject
- Best for wide-angle
- Excellent for a static subject
The Disadvantages of Manual Focusing
- Manual focusing is slow and may shake or move if the camera is moved
- May be less accurate than auto-focus with very long lenses
- Less accurate in low-light unless using optical rangefinder is used
What Went Wrong?
There are numerous factors that can cause blurry photos. To explore the top 10 mistakes visit this article.