The Nikon D2X AF System Revisited - Editors note
This in-depth review by seasoned Nikonian Ed Erkes, shares with you his findings about the multiple autofocus options available with the D2X. He provides further understanding on how these combined options work, adding to the excellent work on the subject by Digital Darrell: Understanding the Nikon Multi-CAM 2000 AF Module.
If you are the proud owner of a Nikon D2X, D2Xs, D2H, D2Hs, or Nikon F6, and getting tired of spending endless long nights trying to decrypt the manual, this article is for you. It serves as another complementary addition to our "in-the-field" proven group of custom settings to suit your shooting needs, fully illustrated with example images.
Nikon D2X AF System Revisited
The Nikon D2X contains Nikon's most advanced and complicated autofocus system. It offers an unprecedented number of focusing system options that can be accessed through a series of buttons, levers, and custom menu settings, to cater to all amateurs and professionals specific shooting situations and personal styles.
The various combinations of choices can create a confusing number of AF possibilities. Unfortunately, Nikon's instruction manual is not particularly well written and (in my opinion) makes things even more confusing. I also found Thom Hogan's D2X eBook confusing in its description of focus modes — although it does explain very well some aspects of the AF system that are not discussed in the instruction manual.
The best source to learn about this AF system by far is Digital Darrell's article: "Understanding Nikon Multi-CAM 2000 Autofocus Module," previously published here in the Nikon articles of the Resources. His article is a "Must Read" for anyone wanting to better understand the Nikon D2X AF capabilities (or those of the D2H, D2Hs, F6 and now the D2Xs).
This review is my attempt to organize the different AF options in an understandable manner (for me). It initially began as a simple outline with notes, but in the spirit of sharing with others, has been expanded. By carefully considering the various options, how they interact, and one's own shooting style, one can eliminate many of the combinations and narrow down the options for specific shooting situations. I'll discuss the various options as well as the rationale for my own preferences.
To better understand my personal choices, it would probably be useful to discuss my photography style.
I've been a serious amateur photographer since 1982. I do not specialize in sports or weddings and events photography, preferring to concentrate on scenic and nature photography. For the last seven years, photographing birds with telephoto lenses has been my favorite activity. I have been using an autofocus telephoto lens (the 200-400mm f/4G ED IF AF-S VR Zoom Nikkor) for a little over a year. Some of my images can be seen here.
The Nikon D2X/D2Xs autofocus options include: two AF activation methods, three Focus Modes (two autofocus and one manual), four AF Area Modes and control over the Lock-On Predictive Focusing. Your choices from these numerous options combine to determine how the camera's autofocus system functions.
The Nikon D2X has eleven AF sensors. Nine of the sensors are sensitive to both horizontal and vertical detail. The three sensors in the center row are crosshatched. The upper and lower rows consist of sensors that are T- shaped and inverted T-shaped, respectively.
The far right and left sensors are narrow lines that are sensitive to detail in the cross-axis direction only. It is important to note that the actual sensor shape does not correspond to that depicted by the viewfinder focus brackets. The sensors are narrower and longer than the viewfinder AF areas brackets (see figure below). For reliable accurate AF, it is best if the subject covers at least half of the sensor area.
Many Options, one at a time
I. Two Autofocus Activation Methods
These are controlled via Custom Settings Menu (CSM) a5, AF Activation.
a) "On Shutter/AF-ON" (Shutter Button/AF-On Button) is the default setting. Autofocus is initiated by either depressing the shutter button halfway or by pressing the AF-On button.
b) Selecting "OFF AF-On only", separates the focusing action from the shutter release. Autofocus can then only be initiated by pressing the AF-On button. Depressing the shutter button has no effect on autofocus action. However, the focus status can have a definite effect on shutter release. If camera Focus Mode (AF-S or AF-C) is in Focus priority, then the shutter will only release if the area in front of an active AF sensor is in focus.
*My personal preference is to set CSM a5 to "OFF AF-On only", to separate AF action from the shutter release button. I use the AF-On button exclusively for auto focusing.
II. Three Focus Modes
These modes are selected via a lever on the front of the camera, next to the lens mount:
|S||(AF-S)||Single-servo AF (Camera focuses, then locks focus)|
|C||(AF-C)||Continuous-servo AF (Camera continually adjusts focus, does not lock)|
The first two AF focus modes can be modified through custom functions CSM a1 and a2—allowing two types of shutter-release priorities to be set: Focus priority or Release priority. The Manual focus option won't be discussed here, to concentrate on autofocus issues, although it is a powerful option in the hands of an experienced photographer.
Let's take these lever settings one at a time.
S (AF-S): Single-servo helps if you want the camera to focus on a stationary subject, and then lock that focus.
If the subject moves before the photo is taken, it will be out of focus unless you release the focus button and then re-press to reacquire focus. If the subject was moving when the focus button was initially pressed, then the camera will predictively track focus until subject stops. Once the subject stops moving, focus locks as noted above.
You can adjust CSM a2 options for your AF-S single servo:
AF-S with Focus Priority is the Default setting. The camera shutter will not fire unless the subject in front of active AF sensor is in focus. If you choose AF-S with Release Priority the camera shutter can be fired even if the subject in front of active sensor is out of focus.
Nikon recommends AF-S for use with relatively static subjects. AF-S is often used with the "Focus, then Compose" technique--generally with the D2X in AF-S and its default CSM a2 and a5 settings (Focus priority setting and shutter button activating AF). The selected AF sensor is positioned over the subject and focus is locked by pressing halfway on the shutter release. The camera is then shifted to place the subject in the desired composition within frame and photo is taken. In Single Frame (S) Advance mode, only one photo with this composition can be taken at a time, since the shutter button must be released before a second photo can be taken. Unfortunately, releasing the shutter button unlocks focus and, when then pressed again, the camera will refocus on the area now in front of active sensor (and original subject will then be out of focus).
There are several methods available to work around this problem and allow the taking of multiple photos without having to repeat the "Focus, then Compose" technique for each shot (with D2X in AF-S, Focus priority, and shutter button activating AF).
One can press the AF-On button to lock focus (essentially it acts the same as keeping the shutter button partially depressed). With the AF-On button depressed, the focus remains locked as you release pressure off the shutter button.
The AE-L/AF-L button can be depressed to lock focus and allow multiple photos to be taken without having to repeat "Focus, then Compose."
Note: There is no AE-L/AF-L button near the vertical shutter release; however the vertical AF-On button can be programmed via CSM a8 to function as an AE-L/AE-L button.
If you switch from Single Frame Advance to a Continuous Frame Advance mode (CL or CH) you will not have to release the shutter button to take a second shot. You can easily take multiple photos as long as shutter button is kept partially depressed.
*I seldom use AF-S mode any longer, except in dim lighting and/or low contrast conditions—situations where the capabilities of any AF system are challenged. If the AF action slow downs with more hunting and searching, I want the camera to lock focus once achieved. Obviously this works only with relatively stationary subjects.
C (AF-C): Continuous-servo AF
If you flip the focus mode lever to C, autofocus never locks on subject. As long as the focus button is pressed, the camera continually tracks a moving subject and constantly adjusts focus. AF-C can be set to Focus or Release Priority through CSM a1 settings.
Continuous Servo also has options (CSM a1):
AF-C with Focus Priority: The camera continually focuses but the shutter will only release when the subject in front of the active sensor is in focus. Since the camera will not fire until in-focus confirmation is received, there is the possibility of a shutter delay between pressing the shutter button and the shutter release. With fast action, this delay may not be desirable.
AF-C with Release Priority (actually termed FPS Rate): (This is the Default setting). Photos can be taken whenever the shutter release button is pressed, even if the subject is out of focus. The rationale is that continuing focus action may achieve focus during the time period that the mirror lifts and shutter opens. Another possibility is that there may be adequate depth of field to cover desired area of focus.
CSM a1 also offers a third option termed FPS Rate + AF which is basically Release Priority with some emphasis on focus. When in CL or CH advance modes, the frame advance rate may slow, if needed, to allow for improved focus accuracy if subject is dark or low in contrast.
*I use AF-C almost exclusively, presently using FPS Rate (Release priority)
When I first started using the D2X, I primarily used AF-S Focus mode in CL or CH frame advance. I used the shutter button for activating AF and often used the "Focus, then Compose" technique. By using a continuous frame advance mode (CL or CH) I could easily take multiple photos after composing as long as I kept the shutter button partially depressed.
When I was photographing action—for example, birds in flight—I would switch to AF-C Focus mode in CL or CH. I would continue to use the shutter button to initiate autofocus.
These AF methods worked well most of the time. However, there were times when I missed potentially exceptional images because I was in AF-S mode and could not reach for the switch and go to AF-C quickly enough when interesting action occurred, for example, an egret or heron that would suddenly take flight.
I soon realized that in order to be continually ready for action photography, I needed to keep the camera in AF-C mode. However I also wanted to be able to use the "Focus, then Compose" technique. My solution was to use the AF-On button for autofocusing (setting CSM a5 to AF-On Only), and AF-C mode in Release priority (setting CSM a1 to FPS Rate). The "Focus, then Compose" technique could easily be performed by placing the active AF sensor on subject and then pressing AF-ON button to acquire focus. The AF-On button was then released, the camera shifted for proper composition, and the photo taken.
**See next pages for an alternative method to use "Focus, then Compose" in AF-C focus mode.
The advantages of AF-On with AF-C in Release priority
You're always ready for action photography.
The "Focus, then Compose" technique can still be easily used.
Switching to manual focus with telephoto lenses is easily accomplished at any time by simply releasing the AF-On button and manually turning the focusing ring.
Note: To use the "Focus, then Compose" process with AF-On Only and AF-C focus mode, Release Priority (FPS Rate) must be used. If the AF-C focus mode is set to Focus Priority, then the shutter will not fire once the camera is shifted for desired composition (since the area now in front of active AF sensor would be out of focus).
Admittedly, it does take some time to get adjusted to using the AF-On button. Initially there will be some fumbling at times to locate the AF-On button with your thumb. This problem is compounded by the fact that the vertical release AF-On button is in a different (more vertical) position compared to the horizontal release AF-ON button. With practice, however, it will soon become second nature.
**Alternative Solution: One can also use the "Focus, then Compose" process in AF-C mode with Shutter Button activating AF (CSM a5 in default setting). Simply press the AE-L/AF-L button to lock AF and then recompose. To do the same when using the vertical shutter release, you must use CSM a8 to reprogram the vertical AF-On button to function as an AE-L/AF-L button. This method works, but I prefer to completely separate AF from shutter release by setting CSM a5 to AF-On only.
Some photographers question the accuracy of AF-C for routine photography since they find that the camera often continually adjusts focus on a "stationary" subject. They consider this a sign that the camera is "hunting" for the correct focus. In actuality the camera is simply doing what it is supposed to be doing—continually adjusting focus after subject or camera movement. Often it is the camera that is moving—slightly shifting the active sensor position horizontally and/or vertically across a three-dimensional subject. You can check this out easily for yourself by focusing on a two-dimensional, high contrast subject (such as a brick wall) with camera locked in position on a tripod. The camera will focus quickly and accurately, without hunting, whether in AF-S or AF-C mode.
Note: In low light with low contrast subjects, the D2X can be slow in acquiring focus. The focus indicator oscillations that are occurring in this situation may actually be due to "hunting" for correct focus rather than adjusting to subject/camera movement. The result may be out of focus images. In these situations, it may be best to use AF-S, which locks focus once acquired, or to manually focus.
Other photographers complain of a problem using the AF-On button for AF acquisition when using telephoto lenses with VR. Since the AF-On button does not activate vibration reduction, they feel that VR "kicking in" as the shutter button is depressed can blur images. I have not noticed this problem, but I tend to partially depress the shutter button as I get ready to take a photo, allowing VR to activate before fully depressing the shutter button.
III. Four AF Area Modes
The AF Area Modes determine which sensor(s) are active in initial focus acquisition and predictive focus tracking. The active sensor(s) can either be user-selected or camera-selected (in Closest Subject Priority).
Single Area AF: Only one of the AF sensors is used for AF. The sensor is user-selected. To allow predictive focus tracking to operate with moving subjects, the sensor must be kept positioned over the subject. If the sensor drops off the subject, the camera AF mechanism will start focusing on the area now positioned in front of the sensor. The camera may try to focus on areas in the foreground or background and in low contrast situations may hunt and search. The Nikon instruction manual recommends Single Area AF for relatively static subjects or with moving subjects that can be easily kept within active focus sensor.
Dynamic Area AF: Focusing begins with the user-selected AF sensor but the camera will switch focus to other sensors to follow a moving subject. If the subject moves onto an adjacent sensor, predictive focus will track its movement and AF activity will be transferred to sensor positioned over the subject. Nikon recommends Dynamic Area AF for erratically or rapid moving subjects—situations where it may be difficult to keep a single active sensor positioned on the subject.
Group Dynamic AF: Group Dynamic AF is the most complex of the AF Area Modes. Instead of selecting a single initial focusing sensor, the user selects a group of sensors. CSM a3 determines the number/shape of sensors in the group (the pattern) and how initial focus acquisition is achieved (center sensor or closest subject). Nikon recommends Group Dynamic AF for erratically or rapid moving subjects — in situations when one knows the general area within frame where the action will occur.
CSM a3 Options are Pattern 1/Center Sensor, Pattern 1/Closest Subject, Pattern 2/Center Sensor, and Pattern 2/Closest Subject
Pattern: Either a diamond/triangular pattern of four/five sensors (Pattern 1) or a row/triangular pattern of three/four sensors (Pattern 2) can be selected (see figures below).
Initial Focus Acquisition: Center Sensor or Closest Subject.
With Center Sensor selected by CSM a3, initial focus acquisition will be performed with the center sensor of the user-selected group but can automatically switch to other sensors in the group if the subject moves. Using center sensor does limit initial focus acquisition to only five of the eleven AF sensors (the center sensor of each group). Dynamic Area AF, on the other hand, allows any one of the eleven sensors to be selected for initial focus acquisition.
In Closest Subject Priority, the camera will analyze contrast and distance information in front of each sensor of the selected group and will attempt to focus on the closest subject. When one presses the focus button the selected group of sensors will light up in red briefly. In AF-S mode, the sensor that acquires focus will blink in red briefly once AF is achieved. In AF-C mode, the sensor used to set focus will blink in red briefly after photo is taken.
Dynamic Area AF with Closest Subject Priority
All eleven AF sensors are active and the camera always attempts to focus on the closest subject. There is no user input at all on the sensor selected. The camera analyzes contrast and distance information in front of all AF sensors and will try to focus on the closest subject.
In AF-S mode, the sensor that acquires focus will light up in red briefly once focus is achieved. In AF-C mode, the focus sensor that set the focus will light up briefly immediately after the photo is taken. According to the Nikon D2X manual (p.77), "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". Nikon recommends this mode for erratically or rapid moving subjects when you know that the subject will be the closest object to camera.
In my tests, Dynamic Area AF with Closest Subject sometimes focused on a more distant object if it was higher in contrast. This was true whether the lens was wide angle or telephoto and it was especially true in low light situations. Group Dynamic AF (in Closest Subject Priority) would usually focus on a near lower-contrast object more reliably than Dynamic Area AF with Closest Subject. It is logical that Group Dynamic AF with Closest Subject priority would focus faster and more accurately than Dynamic Area AF with Closest Subject priority. Fewer sensors are active in Group Dynamic AF so less distance/contrast data has to be analyzed. Theoretically, using the same logic, Pattern 2 should be more responsive than Pattern 1, since fewer sensors are active.
Also in my tests, initial AF acquisition was generally faster with a user-selected AF sensor than when the camera was in Closest Subject priority. With a user-selected sensor, the camera knows which sensor to use for initial focusing; it does not have to analyze data from multiple sensors (as in Closest Subject modes) before beginning initial focusing action.
Deciding which AF Area Mode works best for particular situations requires testing under different conditions. I honestly haven't worked with the different modes enough to make definitive conclusions, but I'll share my opinions.
When speed of initial focus acquisition is the prime consideration, the camera's AF responsiveness will be faster with a user-selected sensor than a camera-selected Closest Subject sensor. So the reason to use the Closest Subject modes would be for situations with erratic action in which the camera would probably pick up the closest subject quicker than the photographer can find and center the subject on a selected sensor. One caveat, of course, is that Closest Subject priority can only be used when the subject of interest will be the closest object within the field of active sensors. Of the Closest Subject modes, Dynamic Area AF with Closest Subject would be the slowest since the camera has to analyze data from all eleven sensors before initiating AF. Group Dynamic AF with Closest Subject should be faster since fewer sensors are active, and as mentioned above, Pattern 2 should theoretically be faster than Pattern 1.
The logic gets more complicated with the user-selected modes. Is Single Area AF mode faster than Dynamic Area AF? If it isn't, why even have a Single Area AF mode—since a single initial sensor is also selected with Dynamic Area AF (and you have the added advantage of the camera predictively tracking the subject to other sensors)? If Dynamic Area AF is slower, then it must be because the other ten sensors are involved in the AF algorithms. Following the same logic, one would assume that Group Dynamic AF with Center Sensor selection is faster than Dynamic Area AF, since fewer total sensors would be involved in the AF algorithms, and that Pattern 2 would be more responsive than Pattern 1. At the present I'm not sure how much of this discussion actually involves practical vs. just theoretical differences.
*Presently I'm using Dynamic Area AF most of the time. I've compared it to Single Area AF in the field several times and can't really tell any significant difference in initial focus acquisition. With subjects moving directly toward me, I sometimes use Group Dynamic Area AF (with center sensor selection). I have been experimenting with Group Dynamic AF (with Closest Subject Priority) and Dynamic AF with Closest Subject Priority on flight shots with birds.
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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