How does focus tracking with lock on work?
The Nikon D800 and its later sibblings D810 and D850 have a very powerful autofocus system with features not seen on earlier Nikon D-SLR's. This short guide, an excerpt from the NikoniansPress book Mastering the Nikon D800 by Darrell Young, shows how the focus tracking with lock-on works on these cameras.
The Focus Tracking with Lock-On (Custom Setting a3, Users manual page 283)
Focus tracking with lock-on allows you to select the length of time your camera will ignore an intruding object that blocks your subject.
In other words, let’s say you are focused on a bird flying past you. As you pan the camera with the bird’s movement, the autofocus system tracks it and keeps it in good focus. As the bird flies by, a road sign briefly interrupts the focus tracking as the bird moves behind it and then reemerges. How would you feel if the bright, high-contrast road sign grabbed the camera’s attention and you lost tracking on the bird? That would be quite aggravating, wouldn’t it?
The D800 provides Focus tracking with lock-on to prevent this from happening. The “lock-on” portion of this function helps your camera keep its focus on your subject, even if something briefly comes between the camera and subject. The camera locks on to your subject doggedly if this function is enabled.
Without Focus tracking with lock-on, any bright object that gets between you and your subject may draw the camera’s attention and cause you to lose focus on the subject.
The camera provides a variable time-out period for the lock-on functionality. Lock-on time-out allows an object that stays between the camera and your subject for a predetermined length of time to attract the camera’s attention. You can adjust this time-out according to the delay time period that works best for you. Plan to experiment a bit so that you can determine what is best for your style of shooting. The factory default is Normal, which I’ve determined from my own testing seems to be about a 1-second delay.
Here are the screens and steps to configure Focus tracking with lock-on (figure 4.4 above):
1. Select a Autofocus from the Custom Setting Menu and scroll to the right (figure 4.4, screen 1).
2. Highlight a3 Focus tracking with lock-on and scroll to the right (figure 4.4, screen 2).
3. Choose one of the six choices from the menu. Figure 4.4, screen 3, shows 3 (Normal), the factory default of about 1 second. The longest period, 5 (long), seems to provide only about 2 seconds of delay in my experience. Time each of these for yourself and see what you think.
4. Press the OK button to select the time-out period.
This function allows you to fine-tune how you want Focus tracking with lock-on to work. The camera can ignore an intruding subject for a second or two.
With Single Point AF, the camera will start the lock-on time-out as soon as the single AF point is unable to detect the subject.
With Dynamic-area AF or Auto-area AF and Focus tracking with lock-on enabled, I was amused at how adamant the camera was about staying with the current subject. I'd focus on a map on the wall and then cover most of the focusing points with the user’s manual. As long as I allowed at least one or two AF points to remain uncovered so the camera could see the map, the focus did not switch to the manual. I could just hear the D800 muttering, "Hah, you can't fool me, I can still see a little edge of that map there, so I'm not changing focus!"
Only when I stuck the D800 manual completely in front of the lens, covering all the AF points, did the camera decide to start timing the Focus tracking with lock-on time-out. After a second or two, the camera would give up on the map and focus on the manual instead.
Try this yourself! It's quite fun and will teach you something about the power of your camera's AF system.
Does Lock-On Cause Autofocus to Slow Down?
Some misunderstanding surrounds this technology. Because it is designed to cause the autofocus to hesitate for a variable time period before seeking a new subject, it may make the camera seem sluggish to some users.
But, this "sluggishness" is really a feature designed to keep you from losing your subject's tracked focus. Once the camera locks on to a subject's area of focus, it tries its best to stay with that subject even if it briefly loses the subject. This keeps the lens from racking in and out and searching for a new subject as soon as the previous subject is no longer under an AF point.
It also causes the camera to ignore other higher-contrast or closer subjects while it follows your original subject. You will have to judge the usefulness of this technology for yourself. I suggest that you go to some event or down to the lake and track moving objects with and without lock-on enabled. Your style of photography has a strong bearing on how you'll use—or whether you'll use—Focus tracking with lock-on.
Focus tracking with lock-on has little to do with how well the camera focuses. Instead, it is concerned with what it is focused on. Here are some good reasons to leave Focus tracking with lock-on enabled in your camera.
If Focus tracking with lock-on is set to Off, Dynamic-area AF and Auto-area AF will instantly react to something coming between your subject and the camera. When Focus tracking with lock-on is enabled, the camera will ignore anything that briefly gets between you and your subject. If you turn it off, your camera will happily switch focus to a closer subject even if it only appears in the frame for a moment. A good example of this is when you are tracking a moving subject and just as you are about to snap the picture, a closer or brighter object enters the edge of the frame and is picked up by an outside sensor. The camera may instantly switch focus to the intruding subject.
If you turn off Focus tracking with lock-on, you'll have a camera that doesn't know how to keep its attention on the subject you are trying to photograph if something interferes. When using Dynamic-area AF or Auto-area AF mode, I call turning off Focus tracking with lock-on "focus roulette!"
Configuring Custom setting a3 is not difficult. However, you'll need to decide just how long you want your camera to stay locked on to a subject’s area before it decides that the subject is no longer available when something intrudes.
Settings Recommendation: I leave Focus tracking with lock-on enabled at all times. When I’m tracking a moving subject I don’t want my camera to be distracted by every bright object that gets in between me and the subject. In fact the camera defaults to 3 (normal) from the factory. Nikon gives us variable focus lock time-outs so we can change how long the camera will keep seeking the old subject when we switch to a new one. I suggest you play around with this function until you fully understand how it works. Watch how long the camera stays locked on one subject’s area before an intruding object grabs its attention. The time-out period seems shorter on the D800 than on previous Nikons I’ve worked with. Even the Long setting seems to give me only about 2 seconds of lock-on delay. You will have to decide which delay period is best for you. I choose 5 (Long).
This is one of those functions that people either love or hate. Personally, I find it quite useful for my type of photography. Try it and see what it does for you.
More on Autofocus tracking
Autofocus tracking with cluttered backgrounds
Photographing birds in flight and other fast subjects
Using the AF back-button for newbies
All Nikonians articles that discuss focusing
Nikonians wiki on phase-detect AF and contrast-detect AF
Want more info on the Nikon D800's series?
More on the Autofocus system of the Nikon DXX series
Forums: More Nikon D850/D810 & D800 reading and discussion in the Forums.
Articles where the Nikon D800 is reviewed or being used
Articles relating to the Nikon D850
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Originally written on December 31, 2020
Last updated on January 27, 2021
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David Summers (dm1dave) on June 26, 2021
Great article explaining an often misunderstood feature.