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Interview with Developers: EOS-1D X Mark II (Part 2) – Improved AF Functions

What are the factors that contributed to the high AF precision of the five vertically-arrayed AF points at the centre? What made it possible for all the 61 AF points to support focusing at f/8? We will look into these questions in part two of our developers’ interview to understand the evolution of the EOS-1D X Mark II. (Reported by: Junichi Date)

(From left to right)
Mitsuaki Hattori (Image Communication Products Operations)/ Takeshi Sakaguchi (Image Communication Products Operations)/ Tomoya Masamura (ICP Division 2, Image Communication Products Operations)/ Masato Seita (Image Communication Products Operations)/ Teruyuki Okado (ICP Development Center 2, Image Communication Products Operations)

 

Camera and lens systems expanded—all 61 AF points now support focusing at f/8

Next, I would like to know more about the AF. The AF area is slightly vertically longer than before, but the number of AF points and their layout pattern basically remain unchanged compared to the EOS-1D X, am I right? Recent APS-C size DSLR and mirrorless cameras offer a wide AF area that covers up to the edges of the image. If I could ask for more, I would have liked a larger AF area on the EOS-1D X Mark II.

Is it technically difficult to widen the AF area any further on a full-frame DSLR camera?

The newly-developed AF sensor for the EOS-1D X Mark II. It employs a 61-point reticular AF system, and all of the AF points support focusing at f/8.

Sakaguchi: We made every effort to broaden the sensor surface, and were able to expand the AF area vertically as a result. It would be extremely difficult to widen it any further without increasing the size of the camera.

Left: EOS-1D X Mark II    Right: EOS-1D X

The Intelligent Viewfinder II on the EOS-1D X Mark II allows users to view the shooting information. The area covered by the AF points is vertically longer than that of its predecessors.

Seita: Our team in charge of AF asked us if it was possible to upsize the secondary mirror slightly, but there was no space for us to do so. This was why we tried to broaden the AF area as much as possible by using the light beams from all the way to the edges of the secondary mirror.

- As with the EOS 7D Mark II, a “Large Zone AF” option has been added to the AF area mode on the EOS-1D X Mark II. What I am curious about is the vertically slim AF zone at the centre.

The centre composition, where the main subject is placed in the centre, is often looked down on, but in actual fact, the AF points at the centre boast the highest AF precision and are therefore capable of capturing subjects with vigorous movements accurately. I would think that having a horizontally-wider AF zone would help to ensure that focus is maintained on a moving subject. So why is the centre AF zone arrayed in such a vertically longish shape on the EOS-1D X Mark II? Also, is it possible to group multiple AF points from different zones?

 

Conceptual AF point diagram for the EOS-1D X Mark II

The entire AF area is divided into three blocks, namely left, centre and right. Each of the blocks comes with cross-type sensors with excellent detection and focusing performance. Particularly, the vertical row of five AF points at the centre enable AF in the vertical, horizontal and diagonal directions for superb AF precision.

 

Sakaguchi: We tried to optimise the shape of the eyeglass lens and the layout of the AF sensors to achieve higher accuracy, and this resulted in a design that separated the centre block from the left and right blocks.

As to whether we can group multiple AF points from different blocks, the left and right blocks that are adjacent to the centre block contain only line AF points. When we take the ability to capture and track subjects into consideration, it’s probably not very desirable to combine them with cross-type AF points.

Large Zone AF

A Large Zone AF option, which had not been available on the EOS-1D X, has been added to the EOS-1D X Mark II, and comes in handy in cases where the conventional Zone AF feature is unable to handle subjects with vigorous movements. The centre block has been made slightly longer.

- The number of AF points is 61, the same as that on the EOS-1D X, but it is impressive that all 61 AF points support AF at f/8. When the EOS-1D X was first launched, it was not compatible with AF at the maximum aperture of f/8. It was after the release of a new firmware update that the centre AF point as well as the four AF points (top, bottom, left and right) in the expanded AF area were able to support focusing at f/8.

What were the key reasons that enable all the 61 AF points on the EOS-1D X Mark II to support AF at the maximum aperture of f/8?

Sakaguchi: Many of our customers requested for compatibility with AF at f/8, but what we could offer on the EOS-1D X was limited. This was why we have been working on this point since the day we embarked on the development of the EOS-1D X Mark II.

By expanding the camera and lens systems to allow light at f/8 to be utilised to the fullest, we were able to achieve AF at f/8 with a sufficient level of focusing accuracy.

Extender EF 1.4xIII. Attaching it to an EF lens lengthens the focal length of the lens by 1.4 times.

However, as lenses have different characteristics, there may be some lens pairings that don’t support the use of AF points in the outermost circumference, or where not all 61 AF points are usable.

Masamura: For the latest lenses such as the EF600mm f/4L IS II USM, EF500mm f/4L IS II USM and EF100-400mm f/4.5-5.6L IS II USM, all 61 AF points are usable, even when you pair them with an extender, which results in a maximum aperture of f/8. However, you will have to use an extender from Series III.

- This is also true for the EOS 80D, which has 45 AF points in total, out of which 27 points can focus at f/8 with the exception of those in the outermost circumference. When you use it with the EF100-400mm f/4.5-5.6L IS II USM combined with the Extender EF 1.4xIII, AF is possible at areas other than the centre, and users are able to enjoy a stress-free super telephoto shooting experience.

Frankly speaking, as a user of the EOS 7D Mark II, I am truly envious of this. In the case of the EOS 7D Mark II, is it difficult to update the firmware to allow some, if not all, of the AF points outside the centre area to support focusing at f/8? Previously, the performance of the EOS 7D was enhanced significantly with the release of the version 2.0 firmware. I was hoping that a revolutionary firmware update would be released for the EOS 7D Mark II as well. Will this ever happen?

Sakaguchi: As I have mentioned earlier, all the 61 AF points are able to focus at f/8 on the EOS-1D X Mark II due to the camera and lens systems. It would be rather challenging to increase the number of AF points compatible with f/8 by updating the firmware.

- The AF point at the centre supports a low light limit of up to EV-3. What about that for the peripheral AF points?

Sakaguchi: The low light limit of EV-3 is applicable to the centre AF point when the camera is used with a bright lens that is at least f/2.8. Comparatively, the low light limit of the peripheral AF points would have a low light limit that is approximately 1 to 2.5 stops higher.

The EOS-1D X Mark II offers a low light limit of up to EV -3, which enables the use of AF for darker scenes.

 

- What is the reason for the improvement in the low light sensitivity performance of the camera? Is it because of the enhanced sensitivity of the new-generation AF sensor?

Sakaguchi: Yes, one of the reasons is the enhanced sensitivity of the AF sensor. Besides that, the key factor that affects AF under a low light condition is noise, so we came out with a new AF sensor that is capable of reducing noise by a large extent.

- The latest version of AI Servo AF is “III+”. What does the “+” sign mean?

Sakaguchi: AI Servo AF III performed extremely well when tracking subjects that are moving constantly toward or away from the camera. However, tracking may slow down in some cases when the moving subject changes its speed or direction suddenly.

To address such sudden changes in speed and direction of the subject, we have boosted the subject tracking performance during predictive AF with AI Servo AF III+. For example, the predictive AF algorithm has been improved to enable a speedier response to abrupt changes in the speed and direction in a scene such as motor sports cornering, where a fast-moving subject approaches a corner, changes its direction of movement and moves away from the camera at a high speed.

 

Auto Selection of Initial AF Point for Al Servo AF

- In the past, when automatic AF point selection is chosen for AI Servo AF, we would need to establish focus on the subject using the initial AF point selected by the user, and then half-press the shutter button to start AI Servo AF.

I believe it was from the EOS 7D Mark II that an “Auto” option has been added to the initial AF point for AI Servo AF. What is the order of priority when the camera determines the main subject in this Auto mode?

Sakaguchi: When the starting AF point for AI Servo AF is set to “Auto”, the camera basically behaves in the same way as One-Shot AF, which selects an AF point by regarding the subject that is closest to the camera as the main subject.

However, when “EOS iTR AF (Face priority)” is set and a human face is detected in the image by the 360,000-pixel RGB+IR sensor, the camera will choose an AF point to ensure that focus is established on the face. This makes it easier to achieve focus on the human face even though other objects may be located closer to the camera in the composition.

EOS iTR AF on the EOS-1D X Mark II is able to detect and maintain AF on human faces, even if they are very small in size.

If your composition is almost fixed and you know where in the image the subject you want to establish focus on will appear, the best way is to manually select the AF point to start focusing. In contrast, if the subject is moving randomly and hard to capture, selecting the “Auto” mode enables the camera to establish focus with priority placed, as far as this is possible, on the subject that is closest to the camera.

Seita: For the face detection function of EOS iTR AF, the metering sensor resolution of 360,000 pixels is comparable to that of digital cameras in the dawning era. It is able to detect human faces even if they occupy only a small area in the image, and establishes focus automatically on the face even if the human subject is located far away from the camera.

- Indeed, I am amazed that the camera is able to automatically select the AF point that overlaps with the human face even if the size of the face is almost the same as that of the AF point, and even switch to another AF point according to the movement of the subject.

Sakaguchi: While the EOS-1D X was only capable of tracking the subject with an AF point, we revised the tracking algorithm of EOS iTR AF starting from the EOS 7D Mark II to enable tracking within an entire area. With the new improved algorithm, the camera is able to switch to another AF point by tracking distinctive colours that are found in the subject.

- For tiny subjects that are moving irregularly and quickly, such as wild birds, it is difficult to maintain focus on the subject with the same AF point that has been selected. There are also many instances where the subject suddenly moves out of the composition the moment we get distracted.

Of course, if the subject moves away from the AF point, the camera would start an AF search to locate the subject. This causes focus to shift to a location where the focusing distance is totally different from that of the subject. For a super telephoto lens with a shallow depth of field and narrow angle of view, it would be difficult to capture the subject again within the same composition.

If the AF point loses track of the subject in this case and the camera is unable to locate the subject after running an AF search, will the lens stop at the closest focusing distance or at infinity?

Sakaguchi: The camera searches for the subject nearby, after which it returns to infinity and stops there.

- While this may vary depending on the type of subject, I believe there are cases where it is easier to locate the subject again through the viewfinder if the camera returns the focus to the focusing distance right before it lost track of the subject. What do you think?

Sakaguchi: You can also configure the camera to stop focus search in the “Lens drive when AF impossible” menu.

- In order to achieve a continuous shooting speed of approximately 14 fps, were there any other important design considerations besides those for mirror drive and the AF system?

Seita: The image sensor and image processor would heat up more easily taking into account the camera’s compatibility with the 4K/60p resolution and the higher continuous shooting speed, so we introduced thorough measures to discharge heat efficiently.

As illustrated in our product catalogue, we installed a heat pipe on the board to which the image processor is mounted so that heat is discharged to the aluminium alloy at the roof of the battery compartment. In addition to the heat pipe, we also included lead wires for heat from inside the metallic body to escape. Such thoroughgoing measures to prevent heating are not found on the EOS-1D X.

A: Heat Pipe
B: Roof of Aluminium Alloy Battery Compartment

 

 

Heat pipe for heat dissipation

We have positioned the image processor right behind the image sensor to achieve a high readout speed. As both these components contribute to heating, we installed a heat pipe to form a structure that enables heat to be discharged efficiently from different parts of the body.

- That’s very similar to the structure around a high-spec PC motherboard or graphics card. By the way, there is a question which I missed out at the beginning of the interview: how did you arrive at a resolution of approximately 20.2 megapixels for the EOS-1D X Mark II?

Okado: We took into consideration the balance among the pixel count (resolution), ISO speed and frame rate. Raising the pixel count excessively makes it difficult to increase the frame rate as the signal readout speed would slow down as a result. The pixel size would also be smaller, which also makes it more difficult to enhance the ISO speed.

- The resolution of the EOS-1D X was approximately 18.0 megapixels. To me, the increase to 20.2 megapixels on the EOS-1D X Mark II is very small.

Masamura: There may be some who feel that we might as well keep the pixel count unchanged, but there are also users who wanted a higher pixel count. In order to satisfy the needs of as many users as possible as a flagship model, we believe there is significance in enhancing the resolution, no matter how small the increment might be.

- Was compatibility with 4K/60p movies a consideration? In other words, was 20.2 megapixels the optimal pixel count for processing 4K/60p movies?

Okado: No, the resolution has nothing to do with 4K movies.

- In the past, whenever a new-generation image sensor or image processor is introduced, the maximum ISO speed for normal use would be raised at least by about one stop even when there is an increase in the pixel count. It was therefore surprising to find that the maximum ISO speed of the EOS-1D X Mark II remained unchanged at ISO 51200 compared to its predecessor.

Hattori: A higher pixel count would, in principle, cause more noise. To address the noise issue, we tried to make improvements to the sensor’s structure and employed the latest image processor for sophisticated image processing to ensure that ISO 51200 remains usable as the maximum normal ISO speed.

Indeed, it would be ideal if we could raise the ISO speed to one stop higher, but we were still unable to achieve that level. However, if you take a test shot at the same ISO speed using both the EOS-1D X and EOS-1D X Mark II, you would find that chromatic noise is less noticeable on the EOS-1D X Mark II at a high ISO speed setting.

Photo taken using the EOS-1D X Mark II at ISO 51200. Chromatic noise is less noticeable compared to the EOS-1D X, and image quality is also higher.

 

- I had reservations about using ISO 25600 on the EOS-1D X, but there is little uneven colour and banding noise at the same ISO speed on the EOS-1D X Mark II. I think ISO 25600 on the EOS-1D X Mark II will certainly come in handy for some scenes.

 


EOS-1D X Mark II

 

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Junichi Date

Born in Hiroshima in 1962. Graduated from the Department of Image Science, Faculty of Engineering, Chiba University. Besides his career as a photographer such as for magazines, Date is also involved actively in writing using his expertise.

 

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