Taking photographs, in the olden days, was truly an art form. Taking photographs, for classic photographers such as Ansel Adams or Henri Cartier-Bresson, required dexterity and excellent vision. Many photographers today cannot fathom using a camera that sees the image slightly different from what is in the viewfinder. Or, most importantly, using a camera that can only be focused manually. Luckily, technology has eased the task of making images by automating some of the tasks that used to require the photographers’ attention. One these tasks is focusing.
With the introduction of modern technology, the problem of focusing – which back then required accuracy and good vision- has been all but eliminated. Morden camera are equipped with a system that evaluates the scene and set the focus automatically to achieve a sharp image. But as with most technology advances, simple task become complicated and a source of headaches. Autofocusing is no exception.
Nikon cameras offers different amount of focusing points from 51 point to a single point. The image above, courtesy of Nikon USA, shows the focus points within the frame.
Autofocus, indeed, is a wonderful thing, even a lifesaver, but it has become so complicated so much so that novice photographers are perplexed by the many modes of autofocusing available to them. When and how to use which mode of focusing has left a lot of photographers to simply rely on only one mode of focusing (automatic focusing) ignoring all other modes available to them.
If you are struggling with the many modes of focusing, today we demystify and simplify the many modes focusing. To decipher the many modes of autofocusing let us start with the old focusing method - manual focusing
This is the original focusing system. As the name implies getting the image into focus is not done automatically rather the photographer is tasked with the job of getting a sharp image by physically moving the focusing ring on the camera or changing the distance between the subject and the camera, in order to get a sharp in-focus image. As you can imagine this method though it can and has produced sharp images, increases the chances of getting images that are out of focus. Think of photographers with poor vision. It is a challenging to objectively access how in or out of focus the subject when your own eyes are out of focus (this is one of the problems that has been address in modern camera as they will indicate if you have achieved focus even in manual mode). To address the shortfall of manual focusing camera manufactures, introduce automatic focusing.
Automatic focusing, as the name implies, automatically focus the lens to get an image that is in focus. The task of focusing is taken from the hands of the photographer and tasked to the camera. To achieves focus, the camera uses a build in sensor which evaluates the points (the little squares you see in your viewfinder) to find the point with the most contrast. Once it finds this point, together with the distance of the point from the camera, a signal is sent to the motor in the lens to move the lens elements to a position them to put the point in focus (hence the moving sound you hear when the camera is focusing). In this mode unlike in manual focusing mode, all the photographer does is to compose the image click the shutter halfway, wait for the camera to focus and then click the shutter all the way to take the image.
Nothing is without its own shortfalls. The effectiveness of autofocus depends on the number of points within the image area that manufacture has set, the nature of the subject whether is stationary or moving as well as how the camera is reading the tonal variance in the image. Hence the introduction of two additional autofocus modes – continuous focus and single area focus.
I-Continuous Focus Mode
Depend on your camera manufacturer the name of this mode will be different. For example, Canon calls this mode "AI Servo" while Nikon calls it "Continuous/AF-C” regardless of the name how this works is the same.
In this mode the camera does not lock focus rather it keeps on focusing anytime the subject or the photographer moves. In other words, focusing jumps from on point to another depend on the point with the most contrast and distance from the camera. Simply put the camera tracks the subject.
II-Single Area Focus Mode
As with continuous focus mode, the name of this mode depends on the camera manufacturer although they operate in the same way. Nikon cameras label this mode as "AF-S" while on Canon cameras it is called "One Shot AF" other camera manufacturers use their own unique names as well. But no matter what it is referred to as it works by locking in focus.
Once you set a point for the camera to focus on and the camera has successfully focused on the point, focus is locked in. What this means is that if your subject moves the camera will not track to find another focus point but rather keep the original focus point sharp.
How to use what mode?
No one mode is superior to the other. Every mode is useful in one scenario and useless in the other. The best solution here is to access your needs and choose the appropriate mode. As a rule of thumb, single mode focusing is ideal for stationary subjects. For example, when taking landscape image, you pick a point -hyperfocal point- focus on that to get sharp landscapes from front to back. Posed portraits is another scenario where single point focus will be ideal. Since eyes in portraits are supposed to be sharp and the subject is stationary you focus on the eyes and fire away.
But, when you are taking images of moving objects single point will fail. In this case you need continuous focusing, so the camera can take track the subject to keep it in focus. Action photographer or when taking images of toddlers and children continuous focus is ideal to keep track of these moving subjects.
Tip: Back button focusing combines both single areas focus and continuous focus mode into one button. With back button focusing you switch between the two modes on the fly by removing focusing form the shutter button and assigning it to the AFL lock button. In this case, when you press and let go the AFL-lock button focusing is locked on the point you have focused (single point focus mode). If on the other hand, you continuously hold the button the camera will continue to focus until when you take the picture or let the button the go (continuous focus mode). To us back button focusing, check your camera manual or simply google it!
Manual focus, as cumbersome as it is, becomes ideal when you are in low light situations. Most DSLRs have a light to help illuminate the subject but the effectiveness of this light is limited.
This is the case that calls for manual focusing to achieve ideal focus. The same applies to microphotography where you need to fine-tune your focusing to get at point you want to be in focus.
As is with all artistic endeavors the mode you chose will depend on your artistic vision. Happy shooting!