IV. Predictive Focus Tracking with Lock-On: Set via CSM a4
This prevents sudden large changes in focus distance from causing the camera to restart focus acquisition. It is designed to prevent errors in focus due to either the photographer failing to keep sensor on subject or another object briefly passing between subject and sensor. Lock-on is enabled by default. Previous Nikon cameras, such as the F5 and the D1X, had "Lock-on" built into the AF algorithms. The Nikon D2x has added the capability to turn it off, if desired.
*I usually leave Lock-On enabled in my photography. When I'm photographing flying birds, I try to keep the active sensor on the head and/or neck of the bird. However, this is not always easy to do with a fast-moving subject. Lock-On prevents abrupt loss of focus due to the sensor dropping off the bird and onto the background. It also prevents loss of focus due to a foreground object passing in front of subject. With flight shots, the foreground object that passes in front of the sensor can sometimes be the near wing of the bird as it flaps up and down. If I disable Lock-On, I find that I more easily lose focus on flying birds, especially if I'm using teleconverters on my telephoto lens (especially with a 2X converter, where initial focus acquisition is much slower).
Nikon D2X. 200-400AF f/4.0G VR lens with TC20EII teleconverter. Dynamic Area AF with center sensor selected.
I spent the better part of three days photographing a pair of juvenile red-tailed hawks that allowed a closer approach than any other hawks I've tried to photograph.
I later learned that they had been born and raised in captivity and just recently released to the wild.
I had been photographing this hawk perched on a branch when he suddenly swooped down to catch a small mammal.
Because I was in AF-C mode and prefocused on the perched bird, all three flight images were sharp—even though I was using a 2X teleconverter.
Lower photo with Nikon D2X, 200-400 f/4.0G VR lens, this time with TC14EII. Group Dynamic AF Pattern 1 / Center Sensor (Center group selected).
The wildlife rehabilitator was still providing supplemental feedings to the released hawks. He let me photograph during one feeding. The bird dropped more than anticipated when he left the branch, but predictive focus tracking continued to function as the bird moved from the center sensor onto the lower sensor. He was halfway off the bottom of frame by the next shot and I totally lost him on the following one. By cropping to more of a panoramic format, I was still able to make a print with a nice composition.
Nikon D2X. 200-400 VR lens with TC20EII. Dynamic Area AF with center sensor selected.
Top two images were cropped for more pleasing composition. With no foreground objects closer than the tundra swans, one of the focus modes with Closest Subject priority could have been used.
In the lower photo, there is the risk that, as the swan dropped further, a Closest Subject mode may have transferred focus to foreground grasses (especially if a Pattern 1 group was selected).
I didn't use a Closest Subject Priority mode in any of these because AF acquisition is slow with a 2X converter on the 200-400 and I get better results with Dynamic Area AF and a user-selected sensor.
Nikon D2X, 200-400 VR lens with TC14EII. Group Dynamic AF, Pattern 2 / Closest Subject with Center 1 group selected.
You may click on any image for larger view.
As mentioned at the start, by carefully considering the various options, how they interact, and one's own shooting style, one can select from the many combinations and narrow down the options for our own specific shooting situations and personal style.
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