What's New in the EOS 1D Mark IV: Advanced Auto Focus System

March 30, 2011

What's New in the EOS 1D Mark IV: Advanced Auto Focus System
With the new 1D Mark IV AI Servo II AF algorithm, stability, reliability, and AF precision have all been improved without a sacrifice in responsiveness.

The new EOS-1D Mark IV Digital SLR camera features Canon’s most advanced Autofocus system to date. It is equipped with a newly developed 45-point AF sensor featuring 39 high-precision cross-type AF points, and an all new AI Servo II AF mode that gives still photographers the power and performance to track and focus a fast-moving subject at speeds up to 10 frames per second. With more than twice as many cross-type focusing points as the EOS-1D Mark III and a new AF sensor construction that improves performance in dark and bright light, and with low contrast subjects, the EOS-1D Mark IV has greater subject detection capabilities than any previous EOS model.

To complete the range of AF improvements, Canon has developed a new AI Servo II AF predictive focusing algorithm that significantly improves responsiveness and stability by making better decisions on focus tracking in a variety of shooting conditions.

New AF Sensor

The AF sensor's basic configuration and focusing optics are similar to those of the EOS-1D Mark III. However, there are now 39 cross-type AF points available for manual AF point selection, compared to 19 for the EOS-1D Mark III and only 7 for the EOS-1D Mark II/II N. (Note that these 39 points work as cross-type points only during manual AF point selection. During automatic AF point selection, the same 19 AF points as on the EOS-1D Mark III will work as cross-type points; for more details, see 'AF Point Selection' later in this article). This change was made possible by the high-speed, vertical line-sensitive f/2.8 sensor components whose reading position is now switchable. The new reading method improves both AF precision and the subject tracking success rate. The precision of the focusing optics has also been improved with stricter AF adjustment standards and improvements in the manufacturing process to improve the stability of AF performance.

New AI Servo II AF algorithm

To go along with the hardware and manufacturing process improvements, Canon also completely revamped the firmware used to calculate predictive focus. As a result, a significantly improved AI Servo AF algorithm now called AI Servo II AF eliminates focusing errors, maintains tracking and improves response. In the past, Canon AF system development concentrated on achieving fast response. Highly responsive AF systems offer accurate predictive AF (they focus quickly on subjects in the AF frame), but they have difficulty stabilizing focus if the subject leaves the AF frame during AI Servo AF continuous shooting.

The 1D Mark III, highly responsive by design, consequently has a lower probability of accurately focusing on fast-moving subjects that are hard to keep within the AF frame. With the new 1D Mark IV AI Servo II AF algorithm, stability, reliability, and AF precision have all been improved without a sacrifice in responsiveness. Predictive AF is more intelligent and avoids over-response, and difficult lighting – both low contrast and very bright conditions -- is handled better. Canon has conducted numerous field tests with professional photographers both in the US and abroad, and the resulting feedback has helped to make the algorithm precisely suited to the shooting needs of pro users.

During predictive focus with the revised AI Servo II AF algorithm, if a continuous focusing result is not obtained, the focusing result for the missing moments is ignored.  Stable lens driving is executed based on the next obtainable continuous focusing result.  Also with AI Servo II AF, even if an obstacle is detected or if the AF point loses the subject, the subject tracking continues with predictive control based on the focusing result immediately before the obstacle was detected or before the subject was lost. If there is a sudden abnormal measurement, it is disregarded. Instead, focusing is based, on the most recent successful measurement. To enable instantaneous response to the subject's movement, the camera can now start predictive control with the measurements taken immediately after the subject starts to move.  In sum, the success rates for focusing moving subjects and for subjects whose distance keeps changing, as is often the case in hand-held close-up shooting, are substantially improved.

AI Servo AF operation characteristics and AF point expansion have also been improved to work effectively with the new Spot AF and orientation-linked AF point selection features.

As an example, with an EF300mm f/2.8L IS USM lens, the EOS-1D Mark IV can track a subject approaching at 50 kph/31 mph up to about 8 meters/26.2 feet away. This is the same specification as the EOS-1D Mark III. However, with the 39 cross-type AF points, the Mark IV's subject detection and tracking performance have improved substantially over the EOS-1D Mark III's. This combination of hardware and software (AI Servo II AF algorithm) improvements enables a more stable AI Servo AF control.

High-precision, cross-type sensors

As was the case with the EOS-1D Mark III, the center AF point of the EOS-1D Mark IV has a cross-type sensor which is vertical line-sensitive up to a maximum aperture of f/4 and horizontal line-sensitive to a maximum aperture of f/8. Therefore, with a lens (or lens-plus-extender combo) whose maximum effective aperture is f/4 or faster, high-precision, cross-type focusing is possible. With lenses or lens/extender combinations whose maximum aperture is between f/4 and f/8, AF is possible at the center point with horizontal-line detection. The center row of cross-type AF points, including the center AF point, have a thin line sensor for vertical line detection with f/2.8 or faster EF lenses. This allows autofocus with lower contrast subjects and improves detection precision. Also, the center AF point uses a new double line design that enables it to detect the subject even when it is grossly defocused. This reduces the lens' search driving operation to detect the subject, making AF control faster and easier.

Low noise AF sensors

Low noise is just as important for AF sensors as it is for imaging sensors. AF sensor noise contaminates the signal-to-noise ratio and makes accurate focusing in difficult light problematic. Phase difference detection, the judging of the focusing error, becomes difficult. The low-noise CMOS AF unit in the EOS-1D Mark IV, designed and manufactured by Canon, improves detection accuracy and provides greater stability in dark, super-bright and low-contrast conditions.

As with the EOS-1D Mark III, the sensitivity range of AF extends from EV -1 to EV 18 (at 23°C/73°F, ISO 100). The configuration of AF points as seen in the viewfinder is also the same as the EOS-1D Mark III's, but the functionality of the EOS-1D Mark IV's AF system is greatly enhanced compared to the EOS-1D Mark III.

Automatic point-of-focus compensation for spectral source variation

The EOS-1D Mark IV can automatically correct the slight error in the point of focus caused by differing spectral characteristics of light sources, resulting in a more consistent AF. This correction feature is especially effective under artificial light sources, such as fluorescent tubes and mercury vapor lamps. It is achieved with a dedicated light source detection sensor on the back of the pentaprism.

AF Point Selection

During manual AF point selection, 38 (or 18 during automatic AF point selection) cross-type AF points (excluding the center AF point) will work as cross-type sensors sensitive to vertical lines at f/2.8 and sensitive to horizontal lines at f/5.6. If the lens' maximum aperture is f/2.8 or faster, high-precision cross-type focusing points are enabled.  Also, if the lens' maximum aperture is f/5.6 or faster, AF is possible with horizontal-line sensitive focusing points.

The following current EF lenses are compatible with f/2.8-sensitive cross-type sensors (discontinued EF lenses with maximum apertures of f/2.8 and larger are also compatible with the 39 cross-type focusing points):

  • EF 16-35 f/2.8L II
  • EF 28 f/1.8
  • EF 100 f/2
  • EF 24-70 f/2.8L
  • EF 28 f/2.8
  • EF 135 f/2L
  • EF 70-200 f/2.8L
  • EF 35 f/1.4 L
  • EF 135 f/2.8
  • EF 70-200 f/2.8L IS
  • EF 35 f/2
  • EF 200 f/2.8L II
  • EF 15 f/2.8 Fish Eye
  • EF 50 f/1.2L
  • EF 200 f/2L IS
  • EF 14 f/2.8L II
  • EF 50 f/1.4
  • EF 300 f/2.8L IS
  • EF 20 f/2.8
  • EF 50 f/1.8 II
  • EF 400 f/2.8L IS
  • EF 24 f/1.4L II
  • EF 85 f/1.2L II
  • EF 24 f/2.8
  • EF 85 f/1.8

Note that although the maximum aperture of the following lenses or combinations is f/4, cross-type focusing with 39 AF points is now possible with these lenses:

  • EF 17-40mm f/4L USM
  • EF 24-105mm f/4L IS USM
  • EF 70-200mm f/2.8L IS USM + Extender EF1.4x II
  • EF 200mm f/2L IS USM + Extender EF2x II
  • EF 300mm f/2.8L IS USM + Extender EF1.4x II
  • EF 400mm f/2.8L IS USM + Extender EF1.4x II


  • During manual AF point selection, the six AF points (or 26 AF points during automatic AF point selection) other than the 39 cross-type AF points will work as horizontal line-sensitive sensors at maximum apertures up to f/5.6.
  • They have the same detection performance as the EOS-1D Mark III's assist points working at maximum apertures up to f/5.6. The two AF points at the immediate top and bottom of the center AF point have improved detection performance and precision due to the doubling of the number of lines (to two) for the f/5.6 sensor.
  • The 45 AF points can be selected automatically, or any one of them can be selected manually. (With the EOS-1D Mark III, only 19 AF points could be selected manually.) To select an AF point, press the AF point selection button; then use the Multi-controller, Main Dial, or Quick Control Dial. Pressing the Multi-controller straight in selects the center AF point. With the center AF point selected, pressing the Multi-controller again will set automatic AF point selection. Pushing the Multi-controller up, down or to the side  selects the AF point in the respective direction. Turning the Main Dial selects a horizontal AF point, while the Quick Control Dial selects a vertical AF point. While the 45 AF points are selectable, if you use the Multi-controller or Main/Quick Control Dial to select a vertical AF point, the AF point selection will switch as follows: Single AF point -> Two AF points -> Single AF point. (This is the same as with the EOS-1D Mark II N.) If AF is executed while two AF points are selected, automatic AF point selection with the two AF points will take effect.

Enhanced AF Customization

Release/Tracking priority

[C.Fn III -3: AI Servo 1st/2nd image priority] has had the [3: Release/Tracking priority] setting added. Shutter-release priority (rather than focus priority) is given to the first shot. During continuous shooting (from the second shot onward), stable focus-tracking of the subject is given priority. This new setting, which was the only option for AI Servo AF release/tracking priority with the original EOS-1D, EOS-1D Mark II and EOS-1D Mark II N, was conspicuously absent on the EOS-1D Mark III. Now, EOS-1D Mark IV users will have the best of both worlds together with the new improvements to AF hardware and software.

Spot AF

The new AF system allows for considerable customization, particularly because new controls have been added to the complement of Custom Functions. For example, when C.Fn III-6-7 is set and you press the AF Stop button on a super telephoto lens that has AF Stop buttons, the focusing line sensor's usable area becomes narrower; the focusing field of view is reduced by about half. The AF system can then focus on a smaller area, reducing detection errors caused, for example, when a sensor sees a bit of extraneous background. The following lenses have this feature:

  • EF 200mm f/2L IS USM
  • EF 300mm f/2.8L IS USM
  • EF 400mm f/2.8L IS USM
  • EF 400mm f/4 DO IS USM
  • EF 500mm f/4L IS USM
  • EF 600mm f/4L IS USM
  • EF 800mm f/5.6L IS USM

Some examples of situations in which Spot AF will be effective include staying focused on the eye of a helmeted driver in an open-cockpit racing car, capturing an athlete on a distant victory stand without using a telephoto lens and being confident the cropped photo will be clear enough, capturing baseball players through the backstop and photographing wild animals through trees in a forest.

Spot AF works regardless of the AF mode and AF point selection method. It is especially effective for manual AF point selection. However, since the decrease in size may make it difficult to keep the AF point centered on a moving subject, focusing might be difficult. When starting with a scene entirely out of focus, Spot AF focusing may be slow. As a reminder that Spot AF has been set, the AF point display in the viewfinder will flash brighter than normal.

AF point expansion

With C.Fn III -8 and a manually-selected AF point, AF can be expanded by using the AF points adjacent to the selected AF point. If the manually-selected AF point cannot achieve focus, focus can be achieved with one of the adjacent (expanded) AF points. The range of expandable AF points is shown in the diagram given here:

These settings can be effective for shooting a moving subject that is difficult to track with just one AF point. The [1: Left/right AF point] and [2:Surrounding AF points] options are the same as the EOS-1D Mark III. The [3: All 45 points area] setting is a very powerful option that’s new to the 1D series. It effectively allows the photographer to manually select the starting point for focus detection while gaining the ability to track the subject anywhere it moves within the 45-point Area AF ellipse indicated on the focusing screen. (By comparison, when automatic focusing point selection is combined with AI Servo AF, the subject must be initially detected with the center AF point.) Moreover, C.Fn III-8-3 allows the camera to display the active focusing point in the viewfinder as it follows the subject during a burst shooting sequence.

Here’s how it works: When C.Fn III-8-3 is combined with AI Servo AF, up to 18 AF points adjacent to the manually-selected AF point will become active. Each time the subject moves to another AF point, the expanded AF points will also shift to surround the AF point covering the subject. In response to the subject's movement, the AF point lit in red also shifts continuously. Since the clump of active focusing points can shift automatically according to subject movement, all 45 focusing points are effectively available for burst mode shooting.

As long as the subject is within the Area AF frame, autofocusing of the subject will continue. This is the same logic as with automatic AF point selection. However, since the focusing is concentrated over a smaller area than during automatic AF point selection, focusing a particular subject is easier. Also, if the main AF point loses the subject by a considerable amount during automatic AF point selection, all 45 AF points are used to search for the subject.

With C.Fn III-8-3, the 18 expanded AF points are instead used to search for the subject. For example, even if there is an object closer than the main subject, the camera can still quickly and securely track the main subject.

If One-Shot AF is set and focus cannot be achieved with the manually-selected AF point, focus is executed with an expanded area of up to 44 AF points. Subject detection is done in three instant steps, with 6, 18, then 44 AF points. Because the manually-selected AF point is where the subject is supposed to be, focusing is easier with the AF points closer to the main AF point. Better yet, DPP 3.7.3 and higher can display the active focusing point for each image when C.Fn III-8-3 is used together with manual focusing point selection, even when the active focusing point differs from the manually selected focusing point.

C.Fn III-8-1, III-8-2, or III-8-3 must be on for C.Fn III-4 [AI Servo AF tracking method] to become fully effective. The exception occurs when using Automatic Focusing Point Selection, in which case both settings for C.Fn III-4 are effective.

Regardless of which C.Fn III-4 setting is used, the C.Fn III-2 setting [AI Servo tracking sensitivity] generally takes priority. However, if a subject blocks the main subject when the C.Fn III-4 setting is 0, the camera refocuses on the new subject regardless of the C.Fn III-2 setting.

Use of Multi-controller

While exposure metering is active, the new C.Fn III-9 enables/disables the Multi-controller’s ability to select an AF point. This setting was included in the EOS-1D Mark III's [C.Fn III-9: Selectable AF point]. It is now a separate Custom Function.

Selectable AF points

With C.Fn III-10, one can control the number of manually-selectable AF points. At the default setting (III-10-0), all 45 points are manually selectable. Other options include 19 points, 9 inner points, or 9 outer points (the same options as the EOS-1D Mark III). During automatic AF point selection, AF will be executed with 45 AF points regardless of the C.Fn III -10 setting.

Switch to registered AF point

For [C.Fn III-11: Switch to registered AF point], the [2: Only while '*' (the AE Lock Button) is pressed] setting has been added. The setting name for 1 has been changed to [1: Switch with Multicontroller]. This Custom Function is very useful when the photographer wants to alternate quickly between two manually selected focusing points without changing the camera's orientation.

AF-assist beam firing

[C.Fn III-15: AF-assist beam firing] has had the [2: IR AF assist beam only] setting added. Set this to disable the series of small flashes fired as the AF-assist beam, as with Speedlite 270EX.

Orientation linked AF point

With C.Fn III-16-1, one can set the AF point for the vertical orientations separately from the AF point for the horizontal orientation.

During shooting, the camera detects the change in the camera's orientation and instantly switches to the corresponding AF point that was set.

With C.Fn III -16-1, one can also select the AF point to be used in three different camera orientations: horizontal, vertical (grip on top), and vertical (grip on bottom). Automatic AF point selection is also selectable in any orientation as the corresponding AF point. When one changes the camera orientation, the AF point will also change automatically. If one clears the camera settings to their defaults, the selected AF points for the respective orientations will all be reset to the center AF point.

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