I recently received an email asking me which focus modes and focus points I use. I started to answer the email and decided I would share it on my blog instead. It is important to remember that I shoot primarily with Canon gear and I use the shutter button to focus. This information may be pretty basic for some of you but remember we all have to start somewhere and since I teach a lot of folks that are just moving into bird photography, all of this may be helpful to them.
Autofocus points aka AF points are what the camera uses to focus on a subject. When you are set on automatic AF selection, you’ll know where the camera is focusing by which AF points light up when your shutter button is pressed halfway down. When you select all of your focus points you are asking the camera to decide where to focus. I prefer to use Single-point AF as this is where you work with only one AF point, and that point can be moved manually anywhere within the AF array of available focus points. This gives the photographer complete control over what the focus point area should be.
So why not decide for yourself all the time?
Well, there are times when the camera can do a great job in making a focusing decision for you. If you have a solid colored background like a clear blue sky and you have a bird fly into that background; the job of the camera is easy and you will most likely get your shot. However, if the background is busy or there is low contrast than it has been my experience that the camera cannot pick up the subject from the background as easily and that is where single point focus comes in handy as you are able to decide quickly and force the camera to focus where you want it. Recently, I have been experimenting with Expand AF and Surround AF but I never use Zone AF or Auto Selection AF.
Below is a video tutorial by Rudy Winston from Canon that goes over each of the AF Area Options for those of you that may want to go through them all:
Ok, now onto Focus Modes…
Auto focus works in one of two ways with Canon, either in “One-Shot” mode or “AI Servo” (AI stands for Artificial Intelligence). There is a third focus mode called “AI Focus” which is basically where you let the camera decide which of these two it should use. For example if you are shooting a still subject and it starts to move the camera should switch automatically to “AI Servo”. However, I have been told by some experts that “AI Focus” is not reliable and was initially designed for beginners. I have also heard some pros refer to it as the focus mode that you use when you don’t care if you acquire focus–LOL. I never use it.
The difference between these two modes is this:
“One Shot” is best suited for still subjects because once you have acquired focus on a subject, provided you keep your shutter button pressed half way down, the focus won’t shift. This allows you to re-frame your subject. However if your subject is walking towards (when the focusing distance changes) you will have trouble keeping focus on your subject.
“AI Servo” is better suited for moving subjects when the focusing distance keeps changing, like birds in flight. So while you hold down the shutter button halfway (*if you are not using Rear Focus), the subject will be focused continuously—that is, until you move the focus point off the subject, then the focus will try to adjust.
* I don’t like using Rear Focus, especially for flight photography. In my opinion it makes you work twice as hard.
Photo of me, courtesy of Jim Fennessy.