|Understanding Nikon Multi-CAM 2000 Autofocus
|© Darrell Young|
Back in the good old days of manual focusing cameras you had to turn the lens ring until the subject looked sharp. If you weren't fast enough, well, there was always the next frame.
Nowadays, our cameras are getting smarter and smarter. So many things can be well accomplished by camera automation, including autofocus, that it's now easier than ever to get professional results.
The Multi-CAM 2000 Autofocus (AF) sensor module in the Nikon D2H, D2Hs, F6, and D2x gives us a powerful tool for professional or advanced amateur use. But, it's imperative that the user of these fine cameras take the time to learn about the four modes of operation in Multi-CAM 2000. It can seem complicated when reading the manual, but is not too difficult if you'll spend a little time testing the various modes. Then you'll understand the best settings for your own style of photography.
We'll discuss Multi-CAM 2000 from the standpoint of the Nikon D2x, since this is considered Nikon's top professional model digital camera. There are some slight variances in custom settings found in the other cameras using Multi-CAM 2000. But, these are only minor differences, so it should pose no problem using this article to understand Multi-CAM 2000 in cameras other than the Nikon D2x.
It may be a good idea to have your D2x manual in hand, as well as your camera. We'll refer to both often in this article. Let's proceed!
It's a radically improved version of the famous Multi-CAM 1300 autofocus module found in the Nikon F5 35mm film SLR. Where the Multi-CAM 1300 was limited to only Single Area AF and Dynamic Area AF, the Multi-CAM 2000 adds two more modes and several more AF sensors. The new modes are Group Dynamic AF and Dynamic Area with Closest Subject Priority.
While the Multi-CAM 1300 had five AF sensors, the Multi-CAM 2000 gives us eleven. And, the center nine of the eleven are cross-type sensors which work in either horizontal or vertical camera positions.
Why is it called Multi-CAM 2000? Well, like the older “1300” before it, the number 2000 represents the approximate number of CCD elements in the autofocus system. With so many elements, it will autofocus in very low light levels, and at very high speeds. It's a true world-class AF system, unmatched by any other camera brand.
Let's start our exploration of the Multi-CAM 2000 system by looking at some basic information that many do not fully understand.
One question often asked is, “What does it mean to “lock focus?” That's a great question since it involves how the camera decides when a picture can be taken, and what AF modes you'll find most useful.
If a subject is moving, the camera will use two technologies to track it. We'll talk more about them later. They're called Predictive Focus Tracking® and Focus Tracking with Lock-On®.
Using these technologies, the camera detects that the subject is moving in the few milliseconds that autofocus is in action. According to whether it's in “single-focus” AF-S mode (Single Servo AF) or “constant-focus” AF-C mode (Continuous Servo AF) two distinct events will occur.
Single Servo AF : In this case, the autofocus system sees subject movement and does not “lock” the focus until the subject stops moving. When the subject stops the focus “locks.” Once this lock takes place, the little round green light comes on in the viewfinder, and autofocus activity ceases. You must reactivate autofocus by lifting your finger and reapplying pressure. The focus is truly locked and will not try to follow your subject unless you refocus. To follow a moving subject requires you to tap the shutter button as the subject moves.
Continuous Servo AF : When using this mode the autofocus never “locks” at all. Your camera will capture images with three levels of focus accuracy, according to how you have the AF “priority” set. (Priorities: FPS rate, FPS rate + AF, and Focus) We'll discuss these later in the article.
Many photographers use a method of shooting best called “Focus and Recompose.” A good example of this is photographing a couple of friends who are standing a couple of feet apart. The photographer, using AF-S mode, moves his camera so that the selected AF sensor is pointing at the face of one of the friends. He locks the focus by holding pressure on the shutter button, moves the camera to the composition that looks best, and then snaps the picture.
As long as the photographer holds pressure on the shutter button, the camera will not try to refocus, since the focus is “locked.” When he presses the shutter button the rest of the way, firing the shutter, the camera will not try to refocus on the background between the friends.
How many of us have pictures of a perfectly focused background with two friends blurred and out of focus? I'll never admit it, but I sure do! (huh?) Using AF-S and the “Focus and Recompose method” makes this problem unlikely to happen.
So, remember this. Once autofocus “locks” it stops working until you release pressure from the shutter button. This is perfect for non-moving subjects, or even slowly moving subjects. If your subject never stops moving, is moving erratically, or only stops briefly, AF-S is probably not the best mode to use. Then AF-C is better, since it never locks focus and you can better follow movement. So, “locking focus” simply means that the autofocus system is finished doing its job, and is waiting for you to finish by taking the picture. This only applies to Single Servo AF (AF-S) mode.
First, let's consider a couple of custom settings that cause more users to get slightly out-of-focus images than might be believed. They're Custom Settings “a1” and “a2,” which sets the camera to either FOCUS PRIORITY or RELEASE PRIORITY. These apply to AF-C or Continuous Servo AF and AF-S or Single Servo AF. AF-C uses custom setting a1, while AF-S uses a2.
FOCUS PRIORITY simply means that your camera will refuse to take a picture until it can reasonably focus on something. RELEASE PRIORITY means that the camera will take a picture when you decide to take it, WHETHER ANYTHING IS IN FOCUS OR NOT! (Read the last paragraph again, until it sinks in)
Now, you might ask yourself “why is there such a setting as Release Priority?” Well, many photographers are shooting high-speed events at high-frame rates, taking hundreds of images, and are using depth-of-field (or experience and luck) to compensate for less than accurate focus. They are in complete control of their camera's systems, having a huge amount of practice in getting just what they want from their cameras.
And, for many pro photographers, the camera's choice of focus points are not what the photographer wants the camera to focus on, so they override the focus using various means.
Here is a quote from a professional D2x user on why he rarely uses Focus Priority: “ I want what I want in focus and not what the camera wants in focus. Let me give you a few examples. Many times, the part of an open wheel race car which has the most ‘edges' for the camera's brain to focus on, is the nose and front wing with all of the decals and sponsor's names and suspension parts. Many times, what I want in focus is the helmet. A lot of times, if you are in “focus priority mode” the camera will not fire when it is focused on the helmet… I do not want the camera to tell me I can't take a picture when what I want to be in focus is in focus, even though it may not be what the camera thinks should be in focus. I want to be able to take when I want to take, and I want what I WANT to be in focus. ” (John Cote)
So, clearly there are very valid reasons for photographers to not use Focus Priority. But, most of those same photographers do not let the shutter release button start the autofocus either, since the focus would change every time the shutter button is pressed. These photographers usually set Custom Setting a5 so that the autofocus does not even activate until the AF-ON button is pressed. (see D2x manual page 185)
You need to ask yourself, “What type of a photographer am I?” If you are a pro shooting fast race cars, focus priority may not be for you. But, for the average photographer imaging his kids running around the yard, deer jumping a fence, flying birds, or a bride tossing a bouquet, Release Priority may not be the best choice. For many it is better to have the camera refuse to take the picture unless it is able to focus on your subject. For most, Focus Priority is the best setting.
From my own testing with the D2x I find that Focus Priority almost always gives me well-focused pictures. When shooting quickly it may skip a series of out-of-focus ones, but I don't want those anyway. Focus Priority will impair your camera's frame rate, so that it will not reach the maximum 5 fps or 8 fps. But, I have to ask, what is the point of 10 out-of-focus images and 5 in-focus images? Why waste the card space, and then have to weed through the slightly out-of-focus images?
In Figure 1 are pictures of the series of menu screens used to set Release vs. Focus Priority.
For AF-C Mode using Custom Setting a1:
In AF-C mode and Custom Setting a1, “ FPS rate ” and “ FPS rate + AF ” are both forms of Release Priority, with “ FPS rate + AF ” giving “improved” autofocus while still allowing the image to be taken no matter what. For reliably sharp focus in AF-C mode, use Focus Priority. On this menu, it's the bottom selection.
Now, let's turn our attention to AF-S mode and Custom Setting a2. We need to verify whether Focus or Release Priority is set. Examine Figure 2 for the correct sequence of menu items.
For AF-S Mode using Custom Setting a2:
In figure 2, your choices are “ Focus” and “ Release .” Since the factory default is Focus Priority, it may already be set to “Focus.” If not, then select Focus.
Congratulations! Now your D2x is set up to take an image ONLY if it can focus on your subject.
There is some confusion about the differences between Predictive Focus Tracking (manual page 73) and Focus Tracking with Lock-On (manual page 185). In fact, these are not the same technologies, but do work together to help you get well focused images.
Predictive Focus Tracking…
… is a technology designed to help in instances when your subject is moving as you press the shutter button to actually take the picture. There's a delay in the shutter actuation time of only a few milliseconds. This delay, though small, could tend to cause fast moving subjects to go out of focus by the time the shutter actually fires.
When you press the shutter button for autofocus the camera's computer asks, “Is this subject moving?” Here's what happens next:
Predictive Focus Tracking cannot be disabled by changing Custom Setting “a4” to off. That custom setting disables “Focus tracking with Lock-On,” a completely different technology. According to Nikon, Predictive Focus Tracking cannot be disabled...period.
Lens movement, especially with long lenses, can be interpreted by the camera as subject movement. Predictive Focus Tracking, in that case, is tracking your camera movement while simultaneously trying to track your subject. Attempting to handhold a long lens will drive your camera NUTS, as it will you, when you later view the shaky pictures. Use a vibration reduction (VR) lens or a tripod for best results with Predictive Focus Tracking.
Nikon says that there are special algorithms in Predictive Focus Tracking that notice sideways movement, realize that you are panning, and shut down Predictive Focus tracking.
In fact, page 73 of the D2x manual says, "If the subject is moving toward or away from the camera, the camera will track focus while attempting to predict where the subject will be when the shutter is released." (italics mine)
Notice it says “toward or away,” which means Predictive Focus Tracking is not the best technology for sideways movement or panning.
Focus tracking with Lock-On® (custom setting a4) …
… is a technology designed with a completely different purpose in mind. It's a focus algorithm that allows your D2x to lock focus on a subject and IGNORE ANYTHING THAT COMES BETWEEN THE CAMERA AND THE SUBJECT, while tracking where that subject is on the array of focus sensors. It's best to use more than one sensor when using Focus Tracking with Lock-On. Dynamic Area AF will give you more accurate tracking of moving subjects. When you switch to AF-C mode, also get in the habit of switching to one of the Dynamic Area or Group Dynamic focusing modes.
Should I turn off custom setting a4, which disables the “Lock-On” functionality? Some have claimed that this will improve the autofocus on the D2x. But, in my opinion this may not be entirely true! Custom setting a4 has little to do with HOW WELL the D2x focuses. Instead it is concerned with WHAT it is focused on. We will discuss some of the controversial issues surrounding a4 towards the end of this article. In the meantime, here are some good reasons to leave Custom Setting a4, “or Lock-On, enabled in your D2x.
As we will consider below Dynamic Area AF with Closest Subject Priority, with Lock-On disabled, will instantly react to something coming between your subject and the camera. By enabling custom setting a4, the camera will ignore anything that briefly gets between you and your subjects. If you turn a4 off and use Closest Subject Priority, your camera will happily switch focus to a closer subject, even if it only appears in the frame for a moment.
A good example of this is when you are tracking a moving subject, and just as you are about to snap the picture a closer object enters the edge of the frame and is picked up by an outside sensor. The camera will instantly switch focus to the intruding closer subject. If you turn off Custom Setting a4, that's exactly what you'll get; a camera that doesn't know how to keep its attention on the subject you are trying to photograph. I call turning off custom setting a4, “focus roulette!”
Spend a little time testing each of these AF modes, and in no time, you'll feel comfortable with each of them. Then, at a moment's notice, you‘ll know just which mode will best serve your purpose.
It is important that custom setting a4 is turned on with this mode since, otherwise, any intruding subjects might get the camera's attention. Remember, setting a4 controls Focus Tracking with Lock-On . If you were focused on a squirrel walking along the ground, and a big bird landed behind him, the D2x might just decide it likes the bird better and switch focus. Lock-On (a4) prevents that from happening by forcing the D2x to track the subject you first focused on.
Since Dynamic Area AF is truly dynamic, it sees any high-contrast subject in any of the 11 focus areas as fair game for autofocusing upon, even though you have a different sensor selected with the thumb switch. It doesn't matter if the new subject is in front of or behind the old subject. If it has more contrast, or is larger and brighter, the D2x will eagerly seek to change to that new subject. By leaving custom setting a4 set to ON, the D2x is much smarter and tracks your real subject until it leaves the frame, or you take the picture.
Many sports photographers use this mode for sports shooting. It allows an area around the primary focus point to stay active, which helps track a moving person, but not all AF sensors are in use which might tend to pull the autofocus to another unintended person moving nearby.
There is another custom setting in the D2x that applies directly to this mode. Custom Setting a3 modifies how your Group Dynamic AF works. This setting allows you to be very precise in using individual groups of AF sensors by using selectable “sensor patterns.” In figure 10, we see a series of pictures of the menu screens used to set a3:
In figure 11 let's examine Custom Setting a3's patterns. First notice Pattern 1 and let's discuss how it works:
In figure 11, pattern 1 on the left has a cross-shaped arrangement. The center AF sensor is providing primary initial focus (sensor in red), while the surrounding sensors (see + signs) are active and awaiting the subject's movement. If the subject moves out from under the center sensor, the surrounding sensors will track the focus. You'll not be able to see which sensor is actually tracking the focus when your subject leaves the sensor you first started using. It would be nice if Nikon turned the sensor red as a new sensor starts detecting focus, but that's not the way it works in this camera. This is the factory default setting for the D2x in Group Dynamic AF mode.
The second pattern, on the right in Figure 11, shows the Closest Subject focus arrangement. It is exactly the same as in Center Focus, except that ALL the sensors in red are used together. You will not be able to select or determine which sensor is initially providing focus, or which is tracking focus. The camera focuses on the closest subject with enough contrast to provide a good focus.
Now, let's look at figure 12 and Pattern 2 of Group Dynamic Custom Setting a3:
In figure 12, Pattern 2, you will see a smaller pattern than the cross-arrangement in Pattern 1. Instead of a cross shape, the camera provides either a vertical or horizontal line pattern. I have only included the horizontal view in my illustration above. (See page 184 of your D2x manual for a view of both horizontal and vertical patterns.)
Pattern 2 works exactly like Pattern 1 except there are fewer sensors involved. (see + signs). This pattern allows you very fine control of the tracking of moving subjects in a horizontal or vertical direction. Remember, you can move these patterns around with the multi-selector thumb rocker switch.
How many of us have beautiful pictures of the background, while the two people we wanted to take a picture of are completely out of focus? When you focused your camera, YOU were looking at the people, but the camera sees the gap between them, and a nice bright something in the background. Voila, ruined picture!
Close Focus Priority pretty much eliminates that problem, since the subjects are closer than the background. But, what happens when someone walks between you and your subjects? Do you want the camera to focus on the new closer subject? Not usually! So, it is also important that custom setting a4 is left ON with this AF mode. Focus Tracking with Lock-On prevents anything that might move in front of our “locked on” subject from interfering with our focus.
One important note, the D2x manual on page 77 states the following: “Camera may be unable to select focus area containing closest subject when telephoto lens is used or subject is poorly lit. Single-area AF is recommended in these cases.”
So, all you birders, wildlife shooters, and sports photographers out there take heed. It may not be a good idea to use Closest Focus Priority with your big telephoto lenses, unless the subject has very high contrast. Be forewarned! Why not try regular Dynamic Area AF instead.
Custom Setting a4 “Lock-On®” – Does it work?
There's some misinformation floating around the Internet about 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, just re-read the above reasons for not turning it off. 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's 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.
But, why does the D2x sometimes seem to have problems staying with certain small, rapidly moving subjects? 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) 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?
For static subjects like nature shots, family, and slow moving wildlife try these settings:
For moving subjects like a flying bird, a race car or cycle, or even a bride and groom walking up the aisle, I'll use the following:
For sports shooting where my human subject is moving around in a group of other humans:
For macro shooting of static subjects like flowers, trees, rocks, and such try these settings:
For fun shooting like a party where I don't want to think about my camera's settings, but want great pictures:
These cover my styles of shooting, and will probably cover most of yours.
The D2x is a very flexible DSLR camera, with four fairly easy to learn AF modes. Don't stay stuck in Single Area AF mode, when there is so much more intelligence available in your D2x. Let it assist you by dynamically tracking your subject, keeping the focus locked on a subject, or taking over completely so you can have some fun.
Personally, after researching this article, I am going to make much more use of the Dynamic Area AF mode of my camera, since it lets me controls the AF sensor in use, but also allows my camera to react if my subject decides to start moving.
There's enough good information in this article to at least start your experimentation with all the aspects of the Multi-CAM 2000 autofocus system. While this is fresh on your mind, go out and shoot a few hundred frames. Play with this flexible AF system, and you'll find yourself really enjoying your mastery of it. At the very least, make your OWN intelligent decision on how to set Custom Setting a4, and other important custom settings.
Nikon has given us a real powerhouse of an image maker. Use it to the full by learning to use all the AF modes.
Keep on capturing time…