I have been shooting Nikon cameras for a long time. I am confused when reading in the manuals, about the focus system. For those who are not confused stop here.

For those who are new to high performance cameras or have never really understood the system, maybe this will help.

There are two types of Focus Options that must be selected: (1) Focus Mode (2) Focus Point Selection Mode
Note that I used the word mode in both cases.

(1) Focus Mode. There are 2 focus modes. Single and Continuous.
Single focus mode will focus then stop when the object is in focus. It will not refocus on it’s own.

Continuous focus mode runs continuously while the shutter or other button is engaged. If you or the subject move the system will refocus, as long as the button is pressed. Stop pressing the focus system stops. They call it lock but it doesn’t truly lock focus, it just stops leaving the lens sitting at the same focus point. If you release the button and move the subject will Go out of focus. (If you hold the button and move the system will refocus.)

(2) Focus Point Selection Mode. There are many focus point modes to choose from.
The focus point selection mode establishes how the focus point will be selected. There are x number of focus points. You can select groups of them, or one. You can can choose to do the focus point selection or you can let the camera select the focus point. You can tell the camera to track objects as they move toward or away from the camera, (tracking) or as they move Across the frame (3-d tracking).

The simplest way to start is select the the single focus point Mode. You move the focus point where you want it and the camera will focus there. I use that 90% of the time. Select the single focus point mode then try enabling different groups of focus points and note what happens.

If you want to learn more about the dynamic system, sit down with he camera and manual. Pick a mode. Select some object and focus on it. Get up and walk slowly toward it while keeping the focus system running (continuous focus). Stop the focus. Observe what happens. Re start it. Walk sideways, observe what happens. This is how you can learn about the camera focus system.

Most of all, have fun.

Hope that helps.

Feel free to add comments or corrections.

Depending on your camera model, manual focus accuracy can be enhanced by reprogramming appropriate buttons to magnify the live view image. For example, on my Nikon D7200, under the Custom Settings Menu => f Controls => f1 OK button => Live View => Zoom on/off, I have 3 options to set the Zoom in/out magnification ratios, viz 50%, 100%, 200%. I usually set mine to 100%.

So when I am displaying a scene through Live View all I have to do is press the OK button and the image will be magnified to whatever Zoom level I have chosen earlier. Pressing the OK button again toggles the magnification off and the live view image reverts to that seen when first entering Live View.

This method gives very accurate focusing when focusing manually. No other aids are really needed. Obviously it works best on static subjects.