How Autofocus Works
Let's start breaking down the Nikon Autofocus System. I mean that's what today is about, it's about learning the various aspects. We're gonna get right into it here, and my first goal is to help you understand how autofocus works. What is required to get a great photo in focus? So, there are three elements that are required for autofocus. The first one is your subject needs to be lit up. It needs to be in a bright area, or there needs to be enough light in the scene. So light level, let me expand upon that a little bit. Let's say you're outside in the middle of sunny day. Well there's a lot of light, and obviously when there's a lot of light you don't have to worry about the autofocus performance as much because the sensors have no problem capturing that subject. But as the light level drops, as the sun starts to set, and then as the sun goes below the horizon, now we're into the dusk hours, that's when we start having problems with autofocus, when the light levels are low. Just becaus...
e there isn't enough ambient light for the system to focus. Same thing goes for in the studio. Today we're in the studio here at Creative Live, and these lights in here are not actually very light. They're light enough for video work, but maybe not light enough for the autofocus sensors to operate properly in a sports environment or in some other type of environment. So if your sensors are having problems picking up focus, think about light, it's probably a light issue. The next thing that our sensors need is contrast. So the autofocus sensors, as we're gonna discuss in a little bit, inside of the sensor location, in that little box square, you can see it when you look through your camera, you'll see your autofocus sensor. That sensor, inside it needs contrast. So I wore all black today, I didn't wear a shirt that has contrast. And so if I wanna focus on me, if you're the photographer and you're focusing on me, you need to find something on me somewhere that has contrast. So where are those areas? Well my face, there's a lot of contrast here. My eyes, my glasses, that's a great place to focus. I don't know if you're interested in arms you could focus here right, there's a good contrast there between my sleeve and my arm. That's great contrast. So I'm always looking for contrast in the scene. That's actually more important than you might first imagine. I want you to always be thinking about what in my scene has contrast that I can focus on. Maybe it's a rock in the foreground, or maybe it's the edge of the rock in the foreground. Imagine going to the ocean and you're photographing the ocean scene, and it's a hazy day, and you're trying to focus out there and your camera's just hunting back and forth, you can hear it sometimes. (imitating motor sounds) You're like why isn't it focusing? Well the reason why is because it can't find contrast on that hazy day. So I'm looking for something, maybe a crashing wave, there's contrast there, maybe the actual horizon line. The last thing that the autofocus system needs is a distinct line. So if I was to summarize these things, it's a bright, contrasty line. That's what I'm always looking for. Bright, contrasty lines. Some of the autofocus sensors in the Nikon system will only focus on horizontal lines of contrast. So we're talking like a street curb or we're talking like a rugby jersey where there's a horizontal line. Some sensors on Nikon cameras will focus on vertical lines of contrast. Telephone poles, soccer jerseys right, soccer jerseys with a vertical line. So anything with a vertical line. And then, some special sensors on the Nikon cameras will actually focus on what are called cross pattern, or crosses, they'll focus on horizontal lines or vertical lines, those are the best sensors. And as we'll talk as the day goes on, some cameras have a lot of those sensors, for example, the Nikon D500, I've got that over here. The D500 actually has 99 cross pattern sensors. This camera here, this is a D750, and the other one I have over here on my gear table is a D800, those cameras have 15 cross pattern sensors. So the higher end your camera is the more cross pattern sensors and the better the autofocus is going to work. So I'm always looking for distinct lines that are brightly lit. So remember that. Bright, contrasty lines. All of that together equals great autofocus performance in the Nikon system. So this is a little bit of a messy graphic here, and the most important thing I want you to realize with this graphic is where is the autofocus module inside the camera. The way that the autofocus system works is light comes in the lens, and then hits a mirror. So it hits this mirror. Some of the light is actually reflected up to the top. This is called the pentaprism, and this is where you look through, this is why it's called a TTL camera, through the lens. You can actually see through the lens. Well this mirror here is actually a split mirror, some light travels through the mirror, and then bounces down to the bottom to this. This is the autofocus module. This is where the autofocus sensors live. So as you're focusing, the sensors pick up the information down below. It's called the Multi-CAM, the Multi-CAM Autofocus sensor. And every single camera in the Nikon world has a different Multi-CAM sensor. The most sophisticated, and the current one, is on the Nikon D5 and the D500. It has lots and lots of sensor positions and it's the most sophisticated and the fastest so far, versus maybe an older camera like the D800 or the D600, they have a lower end autofocus system, not necessarily lower, they're just older, they don't have as many sensor positions. So, that's the autofocus module.