Optimizing Autofocus Efficiency in Nikons
The upper-end Nikons DSLRs, such as the D6, D850, and D500 have some pretty confusing jargon for their autofocus configuration. The enthusiast Nikon camera focus jargon is perhaps even worse. Nikon’s menu option descriptions tend to keep people from getting the best performance from their cameras. This article explains how I set up my cameras to optimize autofocus, and why.
Keep in mind that your camera might be waiting around for a cheap/old lens to respond to its focus commands. To properly evaluate the following suggestions, you will need to select a lens that can “keep up” with your camera. Don’t blame your camera for something that your lens can’t do. And for heaven’s sake, do your testing in sufficient light.
In all the tests that follow, I just used the center (cross-type) focus point. My test setup is plenty challenging without introducing off-center focus point comparisons.
AF-ON Button (pro-level Nikons)
First things first: set up your camera to strictly focus using the “AF-ON” button via your thumb for phase-detect photography. If you have stayed with the shutter button half-press to focus, you need to get over it. Pressing a button with your thumb to focus is simply superior. And stick with continuous autofocus (AF-C); single-focus is totally pointless after you configure your AF-ON button. It should take less than 5 minutes to fall in love with the AF-ON button.
Configure your AF-On button
You can configure the “AF-ON” button under the “Custom Settings” (pencil) menu, “Controls”, “Custom control assignment”.
Specialize the AF-ON button
I like to assign both “AF-area mode” and “AF-ON” to my button, and typically assign “D25”. Note in the screen above I have also assigned AF-ON to my depth of field preview (Pv) button with group-area focus. The joystick center button is additionally assigned AF-ON with single-point focus.
Where to combine the AF mode with the AF button
The dynamic-area focus option prioritizes distant subjects, while the group-area focus option prioritizes the nearest subject. I have a total of three buttons assigned focus duty, with three different ways to autofocus.
AF-C Priority Selection
Since it’s settled that you should stick with using the AF-ON button for focus (right??), the next setting is the AF-C priority selection: stick with “release priority”. The camera won’t stop you from taking the shot in release-priority mode. If you set the “focus priority” instead, the camera won’t let you take the shot unless it decides the subject is sharp enough. You want to be making this decision yourself and not the camera. Digital is cheap; you can delete the shot later if it’s really out of focus.
Make sure you make this AF-ON only. Don’t let the shutter button mess with focusing any more.
Focus Tracking with Lock-On
The Nikon “Custom Settings” (pencil) menu is where you configure autofocus “logic”, which they call Focus tracking with Lock-on.
Where to assign the autofocus logic
Block shot response ‘Delayed’, motion ‘Steady’
The first topic here is the option “Blocked shot AF response”. I equate this feature to “attention span”. The settings for this option range from “Quick (1)” to “Delayed (5)”. I always leave mine on “Delayed” or 5. With the “Quick” setting, if your subject escapes outside of your collection of focus points, such as the 25 points in “D25”, then your camera will immediately focus on whatever random subject is presently under the middle focus point. This is nearly always bad.
If you have your camera “blocked shot AF response” set to “Delayed” or 5, then you’re given some grace time to re-locate your subject and get it back inside your focus point collection. If you can successfully re-locate the subject in time, then your subject focus-tracking simply resumes. This is good. This also assumes you’re pressing the “AF-ON” button the whole time.
If you are busy tracking your subject and suddenly notice Bigfoot walking in the background, then all you have to do is briefly stop pressing the AF-ON button and then re-press it after centering your focus sensor over Bigfoot. You have become the master over your attention span, and are no longer at the mercy of your camera. Your camera will now immediately start tracking Bigfoot and forget all about the old subject it was tracking. This is good. I know that people want their focus system to be purely automated, but forcing you to control the “AF-ON” button will get you superior results compared to using the “Quick” blocked-shot response.
The second topic here is the option “Subject motion”. The settings range from “Erratic” to “Steady”, and are just beneath the ‘Blocked shot AF response’. Now, you’d think that “Steady” would mean slow, versus “Erratic” meaning fast or quick. After many tests tracking subjects coming straight at the camera, I have found that “Steady” gives slightly more reliable results, and it seems plenty fast, too. This subject motion option means toward/away from the camera.
I found that the “Erratic” setting tended to exhibit some focus hesitation or hiccups while tracking subjects moving toward me. The “Steady” setting almost never did, until light levels got too low. I couldn’t find meaningful differences in the speed of focus ability between the two modes. Before I ever tested this configuration, I had assumed that “Erratic” would obviously win for focus speed, but the testing results forced me to change my mind.
How I test Focus Tracking
I have done lots of tests with a setup that lets me look at frame-to-frame sharpness and also overall lens focus scale behavior during shooting. My tests let me vary the subject speed and light levels.
My setup includes using a tripod with a reversed center column holding a lens that has a tripod ring. This hardware lets me rotate the camera into any orientation and keep very low to the ground, so that my (short) moving target comes straight at the camera. Rotating with the tripod ring lets me see the lens focus scale (to record video of its motion).
The setup above is testing a Nikon D500 with the Sigma 70-200 f/2.8 Sport lens. This is a very quick-focusing lens, which should be able to keep up with the camera.
I use a second camera to record video at 120fps while being pointed at the Sigma’s lens focus scale. The video camera uses a wired remote to let me easily trigger recording start/stop. The video lets me closely analyze how the lens focus can hesitate and even exhibit forward/reverse/forward hiccups while tracking a moving subject. This focus action is faster than what people can follow, but reviewing the high-speed video after the fact makes it easy to analyze.
Movie mode: assign the shutter release to record movies
To enable my wired remote release to start/stop recording video, I have to assign the shutter release to record video as shown above. This only reassigns the shutter button functionality while in video mode.
My moving target
My moving target with a better focus target on its face
To track focus, I get my helper to pull the toy straight at the camera at different speeds and in different light levels. I start the video recording (of the lens focus scale) and then start high-speed shooting (10 fps) as the target gets pulled toward my camera. The flat target on the toy’s face makes it easy for the camera to track the subject. I don’t want to use an ambiguous target distance that will just muddy the results.
Before you snicker too much about using this toy target, read on. There’s method to my madness.
With this rig, I get to monitor the resolution of each frame to evaluate the quality of focus. I know the exact distances involved, to calculate just how fast the subject is moving (using 10 frames per second shooting), and the video of the focus scale lets me review the smoothness of the lens focus tracking action.
Lenses have to work much harder to focus at close distances, because they have to move their glass over larger distances inside the lens. My little tracking rig really stresses the camera focus capabilities, compared to distant subjects. Focus errors are much more obvious at close distances, too.
My tests started at about 14 feet from the subject and finished at 4 feet (the minimum focus distance for this lens). The focus system has to work very hard in this scenario, due to moving the internal lens elements so far and also because of the percent distance change to the subject. Because of this, the target doesn’t have to move at blinding speeds (it was moving typically at about 6 feet per second). The depth of focus (135mm f/2.8) at 14 feet is 0.53 feet and it narrows down to just 0.04 feet (12mm) at the 4-foot-away finishing distance.
Performing autofocus tests at long distances isn’t nearly as stressful for a camera or the lens. Depth of focus is relatively huge and the internal lens elements have to be moved much less to track the subject. For distance testing, your subject has to move at very high speeds to be as challenging as doing close-up testing.
Shooting with this D500 at light levels down to EV 5.9 I didn’t see any slowdown in focus tracking, compared to bright light levels. The “Erratic” subject motion setting had more focus failures than the “Steady” setting did, although it generally recovered focus within 1/10 second (I didn’t get 2 frames in a row out of focus at 10 fps). The differences I noted between Erratic/Steady are subtle.
To be honest, I would be hard-pressed to guess at which “Subject motion” setting was being used by conducting these tests. There just wasn’t that much of a difference; both settings generally produced excellent responses that went well beyond my initial expectations. I’d be wary of reviewers claiming obvious differences between the “Subject motion” settings without knowing just how controlled their focus-tracking tests were.
For Nikons like the D610 and the D7000-series (and the current Z cameras), the focus tracking configuration options decrease. You can still assign a button (AE-L AF-L) to give you “AF-ON”, which should be your first priority. Again, stick with AF-C focus.
Focus configuration Nikon D610
To adjust the camera’s response to a moving subject, you need to select the “Focus tracking with lock-on” option.
Quick subject distance change response is ‘Short’ (1)
There isn’t a pair of configuration options like the pro-level Nikons provide. Instead, the options are reduced to a single selection. The Nikon explanation isn’t entirely helpful.
Nikon’s focus help
The explanation above indicates that you would like to set it to “Short” to quickly react to something coming toward you or away from you. So far, so good.
You need to select “Long” to prevent re-focus if you briefly have your subject get outside of your focus point collection (the same as ‘blocked’).
The “help” also indicates you need to turn this option off altogether if you are switching between subjects at different distances. (Remember my discussion above about assigning “AF-ON” to a button so that you can handle this task?)
These two Nikon explanations are at odds with each other. You really want both quick response to subject distance changes and slow response to re-focus if you briefly lose the subject from your focus point collection (side-to-side motion).
Since you can’t have both, I feel the best compromise is the “1 Short” choice. You want the camera to react quickly if your subject suddenly comes towards you or away from you. This choice is a higher priority than having the camera give you a longer grace period to re-acquire your subject. You’re now faced with the added pressure to never let your subject get outside of your focus point collection. You can, of course, change to a larger dynamic area (number of focus points in your collection) to lessen the chance of having the subject escape outside of the focus point box.
Now you can see why the ‘pro’ cameras give you a pair of choices for the autofocus logic.
After lots of tests using a D610, I am more convinced than ever that it should be relegated to landscape photography. It was woefully inadequate at tracking focus in my tests, unless the target was moving fairly slowly. It didn’t matter which “Focus tracking with lock-on” values I chose; it seemed equally inept at any setting. The contrast to tests done with the D850/D500 was stark, and really makes me appreciate the pro-level autofocus that those cameras possess. My D7100 consistently seems more adept at autofocus than the D610, even though the two cameras are supposed to be roughly equal at autofocus, and they both sport the Expeed 3 processor. My little focus test toy was just too much for the D610 to cope with.
I realize I’m overreacting to the D610 results. I just remember the high percentage of lost shots of moving animals and how frustrating that was. My D500 and D850 are so far above its focus capabilities, it’s hard to believe they were all made by the same manufacturer.
People have very strong opinions when it comes to autofocus. Rather than taking my suggestions at face value, I’d suggest you try some tests on your own. While pressing the AF-ON, try panning your camera off and then back on a static subject to get a feel for the focus “attention span” duration. As you may have inferred, it’s much trickier to evaluate near/far focus behavior.
I always try to show how you test something, and not just give you "results" or opinions or regurgitate marketing literature. There are so many elements that go into autofocus results (including practice). To me, this is the most complicated aspect of mastering a camera. The camera models that let you assign different autofocus modes to different buttons are golden, but you still have to train yourself to use them
I can’t stress enough that you need to get comfortable with using the AF-ON button (or an assigned button for this purpose). Use your thumb to control when to focus on a different subject; don’t get trapped into the notion that you have to wait for your camera to decide when to refocus on a new target.