Join Ben Long for an in-depth discussion in this video Autofocus, Area mode, and focus points, part of Shooting with the Nikon D5100.
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When you look at a scene, you usually take it for granted that out of the whole vast view that you can perceive, you automatically choose one place to focus on. Your camera's autofocus mechanism has to do the same thing. It needs to focus at one particular distance in your scene; ideally, you want that distance to be on your subject. Your camera includes a number of focus points spread around its field of view. By default, it automatically tries to identify which one of those points is sitting on the subject of your scene, but there will be times when you'll need to override that automatic mechanism because it will have chosen the wrong point, and so you'll need to manually choose the focus point yourself to force the camera to focus to a particular place.
If you don't understand all this focus point stuff, check out Foundations of Photography: Exposure. By default, your camera has an autofocus area mode that is set to auto-area autofocus. That's what this icon means right here. In this mode, the camera will automatically try to figure out what the subject of your image is and select the appropriate focus point, but you have some other options here. If I pop open this menu, I see that I have four different options. These middle two have to do with shooting on a moving subject.
Let's come back to those and go down here and look at this one, single-point autofocus. If I pick this, then when I come back out here, my Focus Point display has now changed. I just see a single focus point and I can move it around. I can pick which focus point I want of eleven different focus points, and I will see this same display superimposed over my viewfinder when I'm using the optical viewfinder. So what this lets me do is just pick one point that I know the camera is going to analyze. So, for example, maybe I'm set on a tripod and I'm shooting a landscape scene and there is something in the left part of the frame that I want to be in focus.
I can go pick that focus point and make sure that it's sitting on my subject. Or maybe I prefer to just not have to worry about which focus point is going to be used. I might want to choose just the center one. And now, I always know that the camera is going to autofocus on the dead center of the frame. I can then focus there and reframe accordingly as I want different things in focus in different parts of my frame. If I'm shooting moving subjects then I may want to consider one of these two focus modes. If I choose dynamic-area autofocus, then when I come out here in dynamic-area autofocus, I can pick a point and the camera will focus on the thing underneath that point, but it will also pay attention to some of the surrounding points.
So, if my subject leaves that point and goes into another one, it will still be able to keep it in focus. This is a great mode for things that are moving erratically, that might suddenly change position and then go back to where they originally were. For something that's moving a little more predictably or a little more fluidly then I might want to go to 3D-tracking. It says 11 points. It's going to use all the eleven points, but I'm going to pick one and it's going to focus on whatever is in that spot, and as it moves, it's going to keep it in focus--or it's going to try to keep it in focus.
If the subject leaves the viewfinder entirely, you need to take your finger off the button and refocus on it so that it can, again, lock onto that subject and try to track it. So let's review here. I've got these four different modes. In single-point auto-focus, I can just pick the focus point that I want the camera to use. In dynamic-area auto-focus, I pick a point and it watches what's there, and if it moves a little bit into one of the surrounding auto-focus points it will be able to keep it in focus. And then finally I have 3D-tracking, wherein I select a point, the camera starts focusing on that, and tracks it throughout my frame.
Most of the time though, you're probably going to be okay just leaving things on the auto-area autofocus.
- What is an SLR?
- Attaching a lens to a camera
- Deciding how many batteries and media cards are needed
- Setting Auto mode
- Changing ISO
- Changing image format and size
- Manually selecting a focus point
- Correcting exposure while shooting
- Controlling white balance
- Using a driver and self-timer
- Auto exposure bracketing
- Selecting a picture style
- Using Live View
- Shooting video
- Using custom functions, such as ISO expansion and mirror lockup
- Cleaning the camera and sensor
Skill Level Beginner
Foundations of Photography: Exposurewith Ben Long3h 24m Appropriate for all
1. Getting to Know Your Nikon Digital SLR
2. Shooting in Auto Mode
3. Shooting in Program Mode
4. Controlling Autofocus
5. Controlling White Balance
6. Understanding Release Modes
7. Understanding Exposure Control Options
8. Learning More Playback Options
9. Shooting with Scene Modes
10. Shooting with Flash
11. Shooting with Picture Controls
12. Using Live View
13. Shooting Video
14. Customizing Menus and Settings
15. Retouching Images
16. Taking Care of Your Camera
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