To many of the people reading this, you don’t even know what focus modes are. It’s enough for you to just TRY and get the composition right without having to worry about different, more complicated settings! However, while initially confusing, these different modes will not only make it easier for you to understand your camera, but will also dramatically increase your own ability to take wonderfully focused inmages. So what are focus modes?
Without going into the nitty gritty of camera mechanics, when you tell your camera to focus on an object, you are asking your lens to shift in such a way that it is making the image at a particular DISTANCE sharp. So, if I lock the focus on a person three feet from me and then take a step backwards, my image will be out of focus because my camera’s focus is locked for a three foot distance and the subject, who is now 3.5 feet away, will be out of focus.
Make sure this foundational principle makes sense before moving on. But assuming you understand that, I will continue. Now that you know what focusing actually is, let’s talk about the different modes DSLRs have and why each exists. There are three modes I will discuss. The trio are simply different settings that affect the way your camera changes focus.
1. Single-Servo AF [AF-S] or One Shot AF
Here, the simplest of the three, once the camera finds the thing it’s supposed to focus on, it stops looking and holds it right there until you take your shot. When you place the focus point and hold the shutter button halfway down, the focus fixates and doesn’t change even if the subject moves. Obviously, this is best for subjects that don’t plan on moving anywhere, like in posed portraiture or still nature shots. However, as I’m about to explain, you should almost NEVER use this mode for shooting high speed moments unless you are going for some kind of blur affect in your images. [As examples, I’ll be using images from a recent engagement shoot between two friends I mine, Ben and Geneva. If you’d like to see more of their images, you can find them here]
2. [AF-C] or Ai Servo
The problem with Single-Servo Mode comes whenever you subject is moving. Imagine you are at a sports event photographing your child playing peewee soccer. You stand behind the goal he’s running towards to get a shot of him rushing to score his first goal, and you lock your focus and… CLICK! You are so proud of yourself because you KNOW you got the composition right. The next day you put your images on your computer and notice something… All the images of your child when he/she is running are INCREDIBLY out of focus… Why is this? As explained previously, once you lock your focus on AF, if your subject moves, the camera doesn’t adjust to the new distance. So, in steps AF-C! This is the exact opposite of the Single-Servo setting. Instead of locking in and holding a focus, this mode changes as a given focus point moves. This is most useful when trying to hold a focus onto a subject that is moving. Remember, focus is determined the lens shifting to accommodate for the distance you are from your subject. So, if something is running away or towards you, the camera has to be continuously adjusting its focus to keep up.
3. AF-A or AI Focus AF
A hybrid between the two, this mode detects if a subject is moving or stationary and chooses either continuous or single servo depending on the circumstance. Though it sounds a little sketchy, this setting has proven to be fairly reliable. However, it doesn’t appear on most higher end cameras, as it is mainly to help beginners.
4. Full-Time Servo [AF-F]
Use in videography, this mode is constantly tracking its subject in an attempt to create seamless, constantly focused footage. I’ve heard that this setting isn’t very effective however with fast-moving targets.
So there it is! The very basic guide to the three different shooter modes. As usual, don’t hesitate to shoot me an email at “firstname.lastname@example.org” with any further questions you may have. And if you’d like to see the full day from Ben and Geneva’s engagement, you can check it out here.
If while playing with your depth of field and trying to get the focus correct, you may notice that you just simply can’t get it right! You’ll focus on someone’s face and the camera focuses on the nose but the eyes are out of focus! This is extremely frustrating. The question then becomes, “How do I make my depth of field larger?” Simple answer: make your aperture smaller by increasing your F-Stop. Now, if that doesn’t make sense to you, check out my introductory guide to Manual Mode [here]. It’s not hard to understand but takes a little bit of space to explain.
As always I hope this helps! But remember, you can learn this. How do I know? Because I did.