Most low-end pocket digital cameras do all the focus work for you. These are literally "point and shoot" cameras. Furthermore even if you wanted to manually focus using such cameras it would have been practically impossible since they do not include a real optical viewfinder. Using the LCD to check for focus is useless as the LCD is not good enough to truly let you know if an object is perfectly focused or not.

Digital SLR cameras on the other hand have an optical viewfinder that allows you to truly see the photo through the camera's lens. With digital SLR cameras you can see how well the objects in the photo are focused and correct the focus as needed.

Manual focus: In this mode the camera does not automatically focus on the objects in the photo. You will have to manually set the focus as desired. This is accomplished by either pushing some buttons that in turn change the focus or more commonly by rotating a focus ring on the lens clockwise or counterclockwise as needed. You can see the results of changing the focus by looking through the viewfinder. When you are happy with the focus you can press the shutter button to take the photo.

Single auto focus: In this mode the camera automatically focuses on the objects in the photo. The camera automatically focuses when you press the shutter button either all the way down to shoot a photo or half way down to lock the focus. In this mode the automatic focus process is carried out only once as soon as the shutter button is pressed. Once the focus is achieved it is locked and it is not changed until the next time the shutter button is pressed. If you keep the shutter button pressed half way down and then the camera moves or the object moves the focus might be lost. This mode is useful when shooting static objects. In most cases you will press the shutter button and hold it half way down. The camera will run the auto focus process. It will let you know when focus is achieved by displaying a green icon and by playing a short beep.

Continuous auto focus: In this mode the camera continuously focuses on the objects in the photo. Once the shutter button is pressed and as long as it is held half way down the camera continuously focuses on the objects in the photo. In this mode the camera continuously corrects the focus as the objects distance from the camera changes. This mode is useful when you shoot photos of moving objects such as a race car during a race or airplanes during an air show. You can hold the shutter button half way down and continuously move the camera to follow the object. The camera will continuously keep the object in focus. When you are ready to shoot the photo simply press the shutter button all the way down. One drawback of this mode is high power consumption as the camera continuously corrects the focus it uses the power hungry motors in the lens in order to move the optical components.

Like any other feature automatic and manual focus modes have their pros and cons. The first step to using them to your advantage is to understand how they work and what they were designed for. The next step is to experiment shoot photos using different focus modes and different types of objects and see how the camera behaves. Once you have done that you will be ready to instinctively use the best focus mode for each photo situation.

Ziv Haparnas writes about practical technology issues. Find more on photo printing and photography is on printrates.com - a place about digital photo printing.