Having some back focus in AF-C

[fjrabon]

Hmm, I've never had a particularly tough time with my D7000 in AF-C for football with the 80-200 f/2.8, which isn't even a focusing speed demon because it's a big lens and uses the D7000's fairly small focus motor.

 

[bribrius]

Hmm, I've never had a particularly tough time with my D7000 in AF-C for football with the 80-200 f/2.8, which isn't even a focusing speed demon because it's a big lens and uses the D7000's fairly small focus motor.

probably a better lens in better light. Try it with a 70-300 in crappy light.

 

[Derrel]

Autofocus Guide Everything D7100 D7000

As we read here, using the 21 point AF option is NOT suggested for slow targets moving in a predictable manner, but the 9-point AF I suggested earlier is suggested for predictable movement on slowish subjects. The 9-point system uses only neighboring points...the 21-point pattern is, to put it simply, "scanning for" outlying points as well, and is probably sensing the child's moving arms, and at times, at the right distances, might even be reading areas off to the sides of her body, since the 21 points with a 50mm can cover a reasonably large area of real estate.

I'd suggest taking a look at this instruction guide to D7100 autofocus, and going through it, and reviewing some of the basics of how the system has been engineered to operate. If you cannot get even ONE frame out of 60 on something as slow as a toddler, but the system absolutely NAILS wide-aperture, close-range shots, in backlighting, I'm gonna guess that the problem is not the hardware, but the way the hardware is being set-up, and how it is being used.

AF systems have become complicated. The D7100 has three AF mode types, and four AF area modes, plus Custom Settings. Shoot in Continuous advance mode AND keep your finger on the trigger.

Again...3-D tracking depends on the USER being able to correctly configure the camera, and then actually manually starting the sequence, every sequence, with a focus acquisition starting point.

A good way to check if it is you, the user, or the hardware, might be to slap the camera into Auto Area AF mode, and let the camera determine the best focusing approach, based on the computer tracking the subject's speed, direction, and using the SRS or scene recognition system, which can measure luminance values, distances, and measure RedGreenBlue coloring of objects. You have nothing to lose if you've set the camera up and your idea netted you 0 out of 60 shots on a toddler, but as soon as she stops, the system NAILS focus. MY bet is that in Auto Area AF, the camera can out-perform you in this situation.

 

[Derrel]

Hmm, I've never had a particularly tough time with my D7000 in AF-C for football with the 80-200 f/2.8, which isn't even a focusing speed demon because it's a big lens and uses the D7000's fairly small focus motor.

But you also know (as in know-know) how Nikon's sophisticated AF area and AF modes work too...you're actually a very studied, studious, dedicated gearhead and shooter...

 

[fjrabon]

Hmm, I've never had a particularly tough time with my D7000 in AF-C for football with the 80-200 f/2.8, which isn't even a focusing speed demon because it's a big lens and uses the D7000's fairly small focus motor.

But you also know (as in know-know) how Nikon's sophisticated AF area and AF modes work too...you're actually a very studied, studious, dedicated gearhead and shooter...

right, it's a weird system to get the hang of. That's what I was kind of suggesting, is that the problem is likely in the modes being employed, as opposed to any issue with the camera, which is totally understandable because Nikon designs things weirdly at times and names them even more counterintuitively (can't they just hire somebody whose first language is dang english, so they stop having all these weird translation based names). I kind of hate the AF system from a user experience design standpoint, but I like the results and I'm used to it now.

For my animals I typically used the 3D focus tracking setting, which is probably the closest to the OP's situation. For sports I tend to use the d9 setting or the 3D setting, depending on where I'm starting and if I'm picking up and dropping subjects. Most commonly I use d9 with back button focusing for sports.

 

[Derrel]

Nikon's naming of "lock-on" is killing the AF performance for at least half of Nikon users, I suspect.

What Nikon calls "Lock-on" should be named something like, "How fast do you want the camera to drop an already acquired focus subject being tracked, and go zipping off to focus on some new, momentarily-appearing thing in the frame?" What Nikon calls lock-on should in American English be named something like "All-New AF Target Searching: Slow 1-2-3-4-5 Fast"

People setting "lock-on" to the fastest setting wonder why the danged camera drops focuses for no apparent reason, or drops a target when the camera is swung past an object that suddenly appears momentarily in the foreground.

AF systems have become VERY complicated, very configurable, very much multi-mode systems. In on-line forums there are multiple schools of thought, ranging from adamant advocacy of ALWAYS using just one,single central AF point, all the way to learning exactly what each option was designed to do, and how to best configure the camera for multiple types of photography, as well as somewhere in the middle, allowing the Auto AF Area to use the computer to handle decision using 3-D color matrix, face recognition, and all the associated technologies like auto-vignette correction and Active D-Lighting, and maybe even a bit of TTL-FP-BL flash. So, on one hand, we have right here on TPF a number of one-af square, center-ONLY advocates who want to turn a 2015 Nikon into a 1969 Nikkormat, and we have people who use multiple approaches, and even use those new-fangled AF-On buttons and such.

As to the OP's initial photo problem, which was in my opinion, slight back focus at f/3.2 at 1/800 second at ISO 250...I can see an easy and immediate elimination of the problem, feasible with just a few slight exposure tweaks, and the ages-old advice "Stop down a bit." The exposure parameters are closer to the bleeding, cutting edge of failure than of what the Speed Graphic manual calls a "Safe Zone"...the OP was shooting at settings that do not leverage his modern camera, and are biased the wrong way, toward low ISO and toward only marginally safe DOF. The 1/800 speed is a good decision, but the other two parameters are not good decisions.

In daylight, try AUTO ISO set to f/5.6 at 1/800 and watch the back-focus magically disappear. If the child is running toward the camera, even 1/800 is a bit faster than needed. Background defocus with a 50mm at those close ranges is going to be almost imperceptibly different than f/3.2 at such frame-filling distances as seen on the two examples. Again...f/3.2,a moving subject in flat backlighting...at close distance; the old safe zone concept assigns priority #1 to adequate DOF to cover real-world contingencies. I call this my safety margin, and I never go 0 for 60 with a 50mm lens. Ever.