Nikon D2x - Custom Setting a4 “Lock-On®”- Does it work?
© Darrell Young
Nikon Digital Camera Series

There's some misinformation floating around the Internet about the Nikon D2x's Custom Setting a4, and how turning it off will somehow mysteriously make the D2x focus better than before. If you read comments proclaiming that it's best to turn off a4, and they offer nothing more than a mystery as to why, think before you act! In fact, turning off a4 will “dumb down” your otherwise smart D2x, and actually cause some of the problems people are trying to prevent by turning it off.

But, I must add that many people have written me with experiences that seem to indicate that they have personally had better results with a4 turned off. I have thought about this a lot, and have come to some conclusions (opinions) why this might be true for them, or you. Read my opinions, test for yourself, and you decide.

One D2x user wrote : “When shooting macros there's little chance of anything getting between you and your subject. Removing the slight delay that appears to be present with A4 on, when your subject can abruptly change direction (for example a bee in flight at a flower), seems to reduce the chance of the camera not responding at the crucial moment because the focus isn't quite on the subject. It also depends on how you've set Custom Setting A1.” (Alan Clifton)

Does a4 slow down the camera? Well, in a certain way of thinking, it does! It makes the camera “think” harder and not react to subject area changes so quickly as it is tracking your subject. I've noticed that having a4 on tends to make the camera less quick to jump to other subjects besides the one it is tracking. Really, that's how Nikon designed it work. Once it has focused on a subject, then lost it, it will stay focused on the "area" where the subject was last seen for at least a couple or three seconds. Then it will search for a new subject.

So, Custom Setting a4 tends to make the D2x stay with the "subject area" it is tracking. This is what Nikon technicians indicated to me when I asked them about this subject. And it's what I've found personally by testing. But, that lack of willingness to easily give up on an area, and switch to a new one, may seem like slowness to some people. Remember, though, that's what a4 is designed to do--make your camera lock onto a subject's area and stay with it. You'll have to judge for yourself whether that "speed decrease" affects YOUR photography. If it does, turn a4 off.

Dynamic Area and Group Area AF are designed to use multiple sensors to track the subject that is "moving erratically." ALL SENSORS ARE ACTIVELY SEEKING A SUBJECT AT THE SAME TIME, but only ONE is doing the tracking. (see manual page 73)

But, why does the D2x sometimes seem to have problems staying with certain small, rapidly moving subjects? Since we have Predictive Focus Tracking, and Tracking with Lock-On the D2x will tend to stay with the subject, unless it's having problems due to the subject blending in with the background. That is one important problem! If the subject is rather low-contrast, enters a dark area, etc. it is entirely possible that the D2x will switch focus points to a higher contrast area. I think that this has been well borne out by many actual users who are trying to photograph birds flying in front of a confusing background, such as trees. And the problem is compounded, I'm afraid, by the big size of the AF sensors in the D2x. They exceed the edges of the AF sensor points in the viewfinder significantly. These wider sensors can cause a problem. If you are focusing on a rapidly moving bird, and it is only covering part of a sensor, it is going to be VERY difficult or impossible for the D2x to track it well. The sensor is so wide that it is confused about where the subject ends and the background begins.

I think that the good results some are having in tracking a bird against an open sky, and less accurate tracking against trees and such, shows that NO autofocus system can be as accurate as the human eye. The camera's autofocus system is contrast based, and if contrast gets weak, or everything is of similar contrast, autofocus does not work well. Especially is this true if a long zoom lens is in use!

If we shoot birds flying against a blue sky, then, OF COURSE there will be a better response from the camera if a4 (Lock-On) is turned OFF. With a4 off, the camera is simply not concerned with staying locked-on to a particular subject or subject area; and since you are giving it an easy to follow subject, with high contrast, the camera will react faster. Less processing is involved!

But, put that same subject in a low contrast environment, like a bird flying in front of trees, and whooeeee the processing requirements just exploded. In this case, a4 (Lock-On) may do better, since it's smarter at staying with the subject. The reason is that, if the D2x loses the subject briefly, it will then try to stay focused on the subject's last known area for a couple of seconds, hoping to pick the subject back up again. Bottom line... if the contrast between the subject and background is too low, even a4 won't help!

My advice to those who are having problems with autofocus is this. Examine your subject. If it is colored like the background, or is far enough away that it doesn't cover a sensor fully, your camera is going to have problems following it no matter what mode you put your autofocus in. That's why they left a MANUAL switch on the D2x.

Listen...the D2x and cousins have some of the best autofocus technology in the world. They've added all sorts of little improvements like Predictive Tracking and Lock-On, but they all have SERIOUS limitations in low-contrast environments, or with long zoom lenses and small subjects that don't cover a sensor.

YOU know this, but it's great fun to complain and whine and feel sorry for ourselves. (I'm including myself in this!) Maybe the D3x or D5x will have enough processing power to track a bird by the contrast between its eyeball and beak. In the meantime, we may have to help our cameras focus. (GASP!) It's a partnership. If you spent $10,000 for your camera, it still would not focus and track low-contrast subjects very well. I think Nikon is to be commended for providing powerful technology that works MOST of the time. No one else is doing it better for the money.

Use the technology when it works well, and when it doesn't...turn it off and use your eye. How did we all survive without autofocus for so many years?

Keep on capturing time...

This article is a small part of the much larger article, "Understanding Multi-CAM 2000 Autofocus."
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Copyright © 2005 by Darrell Young, a.k.a. Digital Darrell, All Rights Reserved