Focus Servo Modes
Let's get into now some of the nitty gritty. So focus sensors, we talked about that, now how do we use those focus sensors? How are those sensors providing information for the camera to operate? Well one of the first things we need to think through is the servo mode, autofocus single servo, versus autofocus continuous servo, versus autofocus automatic servo, versus autofocus full time servo. So in the Nikon camera world, your camera might have anywhere from two servos to four different servos, and I'll try to parse that out as we discuss this over the next couple minutes. Let's start with AFS, the way that we actually make that change, I'm gonna grab my D500 here, the way that we make that change in the higher end cameras is there's a button here on the front of the camera right there. So we push that button in, and then on the top of the camera, I'll turn it this way, on the top of the camera, we rotate our thumb and we go between AFC and AFS, that's the little, tiny information down ...
below, AFC versus AFS. By the way, you can also see it on the back of the camera by pushing the info button. I'm gonna now push in my focus selector, and I rotate the switch here with my thumb, AFS and AFC, you see that down there in the lower left. Okay, so this camera that I'm doin' this on is the D500, and it only has two servos, but the truth is, that's all you really need. Other cameras, let's say maybe like the Nikon D610, or maybe the Nikon D7200, those cameras actually have three servos, they have AFS, AFC, and then another one called AFA, and I'll talk about AFA in just a minute. So now you've seen how to adjust the servo, let's talk about what that servo means. Let's start with AFS. AFS stands for autofocus single servo. So single servo works like this, let's say you're taking a photo of a person, it's a portrait image, and that person is sitting on a stool. So you focus on that person's eye, you hold your shutter release finger down, and now the focus is locked. That's called single servo. So you focus, you hold it down, now it's locked, and now as long as my finger is held down, I can recompose and take the shot, okay? AFS is for focusing and recomposing, focusing and recomposing. Where else do we use AFS? Well, we use AFS in landscape photography, so you wanna focus on the rocks or the flowers in the foreground, so you focus, and then you recompose to get the mountain. Maybe we use AFS for flower photography and macro, where you focus on the middle of the flower and then you move a little bit so the flower's on the left or the right. So you can see, AFS is really for stationary objects, it's for things that aren't moving. Well the next servo is AFC, so autofocus continuous, and AFC is really where we live for wildlife, we live for sports, action, movement, anything that's moving towards you or away from you that you wanna track, you want to be in AFC mode. So how does that work? Well let's say I'm photographing a basketball player and that basketball player is running towards me, well I need to push my autofocus button here, and then rotate the back to get to AFC, and now I can track the movement, and as long as I keep my finger pressed down on my autofocus button, either my shutter release button or my AF on button, as long as I press either one of those, the system will actually track the movement of the subject as they're coming in closer or moving away, but I gotta keep that sensor on the subject, otherwise I misfocus right? So keep the focus sensor on the subject, keep pressing down, subject's moving in and out. So AFC and AFS. Most of the time you'll be in either one of these two servo modes. Let's talk about the other two servo modes. These modes you're really not going to use very much. So this one here is AFA, you'll find AFA on what I would call prosumer cameras like the D7000, like the D610, maybe the D5300, the D3300, those types of Nikon cameras. So AFA stands for autofocus automatic servo, AFA. Autofocus automatic servo. Well all that means is that Nikon is going to try and figure out for you whether or not your subject is moving. So let's say I'm photographing a bird and the bird's coming towards me, I bring the camera up, and I start tracking the bird, if I'm in AFA mode, the camera hopefully will choose AFC, does that make sense? So I was in AFA, I start tracking the bird, and now hopefully the camera figures out that that bird is moving and it automatically switches to AFC mode. On the other hand, let's say I'm shooting a portrait, I'm in AFA mode, I start the portrait, I focus, and I hold down the shutter release button, the camera should very quickly figure out that the subject is not moving, and therefore switch to AFS mode. So the real question is, does AFA work? Ah, you know I'm gonna say ish, 'cause sometimes it chooses wrong. Sometimes it chooses continuous when I'm shooting a portrait, and sometimes it uses single when I'm shooting a bird. So I generally shy away from AFA. I know, 'cause I'm the photographer, I'm in control here, I know what I'm shooting and I know what servo I need to accomplish my goals. So I recommend you not using AFA. If you wanna get better at your autofocus, don't use AFA, pick or choose AFS or AFC. The last one I have for you doesn't really pertain to still photo, or still photography. This really pertains to video work. A lot of the newer Nikon cameras allow you to shoot video, and they do a great job of shooting video. In fact, the new ones allow you to shoot 4K video, which is great. In that video mode, we have a new series of focus servos, one of them being AFF, and you can see AFF at the top of the screen, right here, AFF, the way you choose it, the way you select it is the same way you do all the other ones. You push the autofocus button, and then you'll just rotate your main command dial, and you'll see here at the top of the screen, it'll go AFF versus AFS, as in AF single. Well AFF stands for full time autofocus, and its goal, its purpose in life is to track the movement of whatever you start the focus on. So in this example, let's say I had these radio controlled cars here, I focus there, as the car moves, AFF its purpose in life, its goal is to actually track that wheel as that wheel moves around the screen. Should you use it? No, don't use AFF. Video, DSLR video is its own special world, and very few people actually use autofocus when they're recording video on these cameras. You'll see people they have video rigs, and they have follow focus rigs that actually manually focus, that's the best way to use focus in the video environment. So don't use AFF, rather, when you're shooting video, flip your switch down here to M, just flip it to M, in other words, manual focus. So in video mode, I always recommend manually focus your lenses, that's the way the pros do it. There's a few cameras that actually work well in autofocus, but not DSLRs. DSLRs just haven't really done well in that world yet. So there are your servos, in general AFS and AFC.