This is the second part of a post titled. If you navigated to this page directly, please read the first part here: The Only Guide You Need To Master Digital Camera Autofocusing [Part 1]
Autofocus Continuous (AF-C / AI Servo)
The continuous autofocus mode (AF-C), unlike the AF-S mode, is meant for shooting dynamic/moving subjects.
The idea behind AF-C is simple, keep adjusting the focus until perfect focus is achieved.
Let’s continue with the previous example.
We saw that if the subject of the image or the photographer moved in relation to each other before the image is recorded but after the focus is locked, the resulting image may NOT be focused properly with AF-S mode on.
This is because when on the AF-S mode the AF module doesn’t adjust to such changes.
AF-C, on the other hand, keeps on adjusting the focus. If for any reason the camera loses focus, the AF module goes through all the processes we discussed earlier and finds perfect focus again. When on AF-C, the autofocus module continuously looks for improper focus and tries to rectify it.
This mode hence is an absolute godsent for hard to photograph subjects which do not stop for you to get a good focus lock on them. Children, animals, birds are all prime candidates which require the camera to continuously adapt its focus. They simply do not care about your images at all.
Selecting either AF-S or AF-C is easy when you already have an idea about what it is you are about to shoot.
However, when you have no idea about the subject or the conditions, it may be a bit tricky to choose any one of the two modes.
If switching back and forth between AF-S and AF-C doesn’t seem like a good option to you, you may use a technique called Back Button Focusing. It not only helps with this switching conundrum but also gives you a LOT more control of your camera.
I should mention here that not everyone is a fan of the Back Button technique.
I myself use this and I couldn’t recommend this enough. You, on the other hand, have both the option of using and not using this open to you. Give this article a quick read and then you can decide for yourself.
Give it a try that is all I ask. You can always go back if you feel this isn’t for you.
Different manufactures have all different names for the same functions but it essentially about how the camera reacts when the shutter button is fully pressed in relation to the camera autofocus.
Just keep on reading and you will know what I am talking about.
Oh, by the way, all the names I am using below are how they appear in the menu system of my Nikon DSLR. They may not be the same in your camera menu.
Try and understand their functions first and then choose for yourself the one that fits the best with your shooting style.
Your camera also probably has the same functions available but under different names. You would have to hunt for them a little.
The set of three options below are available for AF-S and AF-C individually. You may choose different options depending on the autofocus mode you are on currently.
The release mode effectively tells the camera to take an image every time the shutter button is fully pressed.
What is so surprising about that? Isn’t that what always happens?
Sometimes the default mode of the camera only allows the camera to take an image when it has a sure focus lock on the subject.
To check whether your camera is currently in that mode or not try this:
Try to focus on something really really near the camera. If the subject is closer than the minimum focusing distance of the lens you have on, the camera would not be able to get a focus.
Now see if you can take an image.
If your camera refuses to take the image your currently on a ‘focus check’ mode.
This means that the camera shutter is only allowed to record an image when the focus lock is secured.
This might seem like good insurance to have but it may backfire sometime.
In my photography journey many times I have found that the camera doesn’t recognize tact sharp images as being in focus. Had I had the ‘Focus check’ mode on when taking these images my camera would have simply refused to take those images. This directly means that I would have missed all those shots.
Shooting fast-moving subjects with continuous autofocus sometimes do pose some challenges for our cameras. Especially for the autofocusing department. Keeping the ‘Focus check’ mode on hence may not be your best bet if you ask me.
Just to reiterate, the release mode tells your camera to take an image without checking for focus. With this mode turned on as soon as you press down on the shutter the camera records an image.
The focus mode is what we discussed just a little while earlier.
When on this mode the camera checks for a sure focus lock and only allows recording of an image when it is absolutely sure.
You may use this mode for slow-moving subjects which have a good amount of detail to focus on.
But otherwise, I would rather refrain from using this.
Focus + Release
This is a combination of the two modes above.
It forces the camera to slow down its recording rate (frames per second) to ensure a better focus lock. The idea is to simply give the camera a little more time to focus.
To be honest this isn’t a mode I would ever consider. It isn’t very reliable (at least in my camera) either in ensuring focus nor maintaining a good frame rate per second.
Focus Tracking With Lock On
If you are into Street, Sports or Wildlife Photography, basically any genre with a dynamic subject in a distracting environment you will definitely appreciate this.
This function tells your camera how it should behave when it loses focus. Hang onto that for a second.
Imagine you are standing on one side of the road and want to photograph a person standing on the other side.
You get your camera out, frame the shot and lock focus. But just when you are about to take a shot, a bus honks down the street.
Because the frame was completely blocked for a second or two, your camera is almost sure to have lost focus for that tiny period.
Focus tracking with lock-on determines how the camera behaves when this happens.
There are generally three or four options that you may select from to direct the camera to behave in a certain way. The options themselves denotes the degree of the focus lock.
Let me explain how this works.
Say you choose the option “Short” (shorter duration). This mode instructs the camera’s Af module to immediately search and find a new subject to focus on the second it loses its grip on the previous one.
If this was how our camera was set when the bus passed by, the camera would have immediately tried to focus on the bus the minute it lost track of the man on the other side of the road.
Now let us see how the other end of the spectrum looks.
Let’s assume instead of “Short” you chose “Long”.
Same situation, but this time the camera doesn’t start hunting for a new subject so soon. It holds its ground and keeps the focus locked on to the same distance.
Always remember, you focus for a certain distance from the camera. You may have seen distance markings on the barrel of the lens you use. That’s what they signify.
With the “Long” mode employed the camera delays the focus hunting and keeps the focus locked onto the same distance.
In an environment where there are a few distractions that you cannot control, this is just a way to help your camera focus and lock on to the important subjects better.
Digital Camera Autofocus is really a jungle.
It is hard for a new person with a camera to understand what all the functions and the options actually do and when they should be used.
I hope this post helps you in a small way to better your understanding of the system.
If however you still have some questions, please feel free to post them below in the comments and I will be happy to answer them.
Keep shooting beautiful.