The Complete Lineup of Canon's Phase Detection AF Systems

An illustrated chronological story about how Canon autofocus systems and viewfinders went from a single AF point (1987) to 191 AF points (2020).

Since the introduction of their EOS series of cameras in 1987, Canon has developed 20 phase detection autofocus systems, resulting in 20 different autofocus sensor designs. This article is a completely unique graphical review of all the phase detection autofocus sensors Canon has ever used. An overview like this one has never been done before at this level of detail.

Overview

Scope

Canon had already developed zoom lenses and cameras with autofocus capabilities even years before the first EOS camera had been invented. The Canon Zoom Lens FD 35-70mm 1:4 AF was a lens that had an independent rangefinding system integrated. It was introduced in 1981 and was compatible with all Canon FD mount cameras. Four years later in 1985, Canon introduced their T80 SLR camera. It was Canon's first 35mm film SLR camera that offered an in-body autofocus system. All these systems introduced prior to Canon's EOS series of SLR and DSLR cameras are not in scope of this article. Instead, the following chapters cover 20 different autofocus sensor designs from the introduction of Canon's EOS system (1987) to the last EOS camera using phase detection autofocus (2020).

Autofocus in General

In contrast to manual focus, autofocus allows photographers to focus the camera on a subject automatically. It is one of the most convenient features in photography and it is absolutely crucial for capturing sharp and clear images, especially in dynamic situations. All of Canon's EOS cameras display AF points in their viewfinders. These mark the positions at which the camera is able to focus the lens at a subject automatically.

Phase Detection

This article covers Canon's autofocus (AF) systems that used phase detection (PD) technology in order to determine the correct focusing position of the photographic lens. This technology is also described as through-the-tens (TTL) secondary image registration (SIR) phase detection autofocus. Read more about the underlying principle of phase detection autofocus here.

Phase detection systems use sets of small detector stripes that are arranged on the types of autofocus chips shown in this article. One set of detector lines refers to all physical line detectors on the chip that correspond to one AF point in the camera's viewfinder. Depending on the type of AF detector, one set can be two detector stripes (linear sensor), four detector stripes (cross-type sensor), or eight detector stripes (dual cross-type sensor). Note that multiple adjacent AF points often use the same set of detectors.

The autofocus working range (light intensities at which an AF system can be used) is usually expressed as two exposure values (EV), for example EV 0 - 20. EV units are stops. The low value expresses that the camera can detect autofocus in scenes as dark as EV 0 and as bright as EV 20. Comparing two systems 1) EV 0 - 20 and 2) EV -1 - 21, the second system can still operate in much darker (half as bright) and also much brighter (double as bright) scenes than the first one.

Types of AF Detectors and Detector Orientations

A standard-precision sensor is an autofocus sensor that is capable of focusing within the depth of field of the lens that is currently attached to the camera. Most of the autofocus sensors used are standard-precision sensors. These are designed for use with lenses having a maximum aperture of f/5.6 or faster.
A high-precision sensor is an autofocus sensor that is capable of focusing within 1/3 of the depth of field of the lens that is currently attached to the camera. For that reason, high-precision autofocus detection offers three times the image shift sensitivity compared to standard-precision sensors. These sensors are designed for use with lenses having faster maximum apertures, usually f/2.8 or faster, in order for them to contribute to the autofocus detection.
A linear sensor refers to the physical orientation of the detector lines on the chip. A vertical sensor is sensitive to horizontal contrast lines whereas a horizontal sensor is sensitive to vertical contrast lines, respectively. A horizontal-sensitive point cannot detect vertical lines, and a vertical-sensitive point cannot detect horizontal lines.
A cross-type sensor is an autofocus point that uses two linear detectors that are arranged perpendicularly to each other. This is why a cross-type point is sensitive to both vertical and horizontal contrast lines simultaneously.
A dual cross-type sensor is an autofocus point that uses two cross-type detectors which are arranged at an angle of 45 degrees to each other. This is why a dual cross-type point is sensitive to diagonal contrast lines as well as vertical and horizontal contrast lines. All Canon AF systems use high-precision sensors for the diagonal components of dual cross-type points. For that reason, the diagonal sensors are designed for use with lenses having a maximum aperture of f/2.8 or faster. If a lens slower than f/2.8 is used on a dual cross-type point, this point operates as a (non-dual) cross-type.
It is important to understand that the aperture requirements refer to the maximum value of the relative aperture the attached lens provides, and not the aperture value at which the photo will be shot. The autofocusing measurement is always carried out with the aperture fully open (at the smallest f-number the attached lens provides).

General Observations

Although called AF points, the AF position indicators in the camera's viewfinder are usually small frames – either square or rectangular – and sometimes a pair of square brackets that look like this [ ], or a combination of both. A square indicates that an AF point is a cross-type sensor. A rectangle indicates that an AF point is a linear sensor. The rectangle orientation indicates whether it is a vertical or horizontal detector.
Canon uses their phase detection AF systems across different product ranges, including 35mm film cameras as well as full frame, APS-H, and APS-C digital cameras. The size of the actual autofocus optical systems installed in the camera bodies is often the same, regardless of the film or sensor format used. For that reason, AF coverage is usually larger on APS-C cameras and on APS-H cameras than on full frame or 35mm film cameras.
It is interesting to note that the quality and performance of an AF system is not just depending on the AF sensor but on the extent to which the AF system is integrated into the entire camera electronics. All signals provided by the phase detection system have to be coordinated with the camera's central processing unit (DIGIC), the metering system, the viewfinder's AF point illumination system, as well as the lenses autofocus drive system, in order to provide a perfect autofocusing experience.

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