Focusing on moving objects - options.

Four different ways of focusing on a moving object.  Center, Active, 3D and eye tracking.

Stationary subjects are relatively easy to achieve critical focus on.  The task becomes much more complicated when the subject is moving.  Cameras typically have many ways to obtain a sharp focus.  Wide-angle lenses with small apertures typically require little extra help in this area, but when you are shooting with long lenses using wide-open apertures, the task is exponentially more difficult.  There are a few different ways to handle this.

You generally want to use continuous focusing when photographing a moving subject as the focal plane to subject distance is constantly changing.  The exception to this would involve using center-point focusing (Box 1) where you would lock focus, reframe, and shoot.  It is far easier if reframing is not necessary and you could shoot the subject in the center of the field.  This works in some circumstance, but would not be advisable in the situation above.

Using active focusing (Box 2), you can pick the place where you want the subject to be in the frame.  This has the advantage of not having to reframe, this means you can use continuous focusing instead of locking focus in place.  The downside is that older cameras may not have very many focus zones to choose from.  If this is your case, stick with the first option.  Also, erratic subjects will likely flit outside the selected focus area and your focus will reset, possibly wasting time.

This brings us to 3-D focus tracking (Box 3).  I use this often with my higher-end cameras, but in earlier models, the number of focus zones and the speed of the processor limit its functionality.  You won't know until you try it.  Keep in mind that not all cameras come with the option, and if yours does, you will have to know how to access it.  Continuous focusing has to be selected, it has to be enabled through the menu if, that option exists, and then you choose it through the where-to-focus selection controls.

Of the four methods shown, eye tracking (Box 4) is the best as it makes sure the focus point is on the head of whatever you are shooting.  However, it is even more processor-intensive than 3-D tracking and requires the ability to track a single eye for birds and certain mammals rather than a pair of eyes for humans facing forward.  Some cameras come with a particular option for birds; these will he higher-end cameras, fairly new, and have extremely fast microprocessors.  Watching these work though is a thing of beauty.  3-D tracking tends to be wildly sporadic, with the active sensor bouncing all over the place.  It could lock onto a wing or some other body part, rendering the head out of focus.  The eye-focusing tracking method is superb if you have the right equipment.

Any of the last 3 systems require fast, internal focus lenses with minimum apertures less than f/8.  My 500 mm PF Nikkor prime works well with 3-D tracking but fails completely if I put a 1.4x teleconvertor on (it brings the minimum aperture up to f/8 - which for my D500 camera is too little).  The exact limit will depend on your camera, the lens, and any multipliers used.  Before making a purchase, make sure it all works the way you want it to.

Thanks for reading.

Eric Svendsen     www.ericspix.com